text
stringlengths 640
1.02k
|
|---|
oupings of lights may generate confusion distract from obstacles including those that they may be intended to illuminate and potentially cause accidents clutter is particularly noticeable on roads where the street lights are badly designed or where brightly lit advertising surrounds the roadways depending on the motives of the person or organisation who installed the lights their placement and design may even be intended to distract drivers and can contribute to accidents overillumination overillumination is the excess use of unnecessary light specifically within the united states estimations claim that overillumination is responsible for approximately two million barrels of oil per day in energy wastage overillumination stems from several factors not using timers occupancy sensors or other controls to extinguish lighting when not needed improper design especially of workplace spaces by specifying higher levels of light than needed for a given task incorrect choice of fixtures or globes which do not direct li |
ght into areas as needed improper selection of hardware to utilize more energy than needed to accomplish the lighting task incomplete training of building managers and occupants to use lighting systems efficiently inadequate lighting maintenance resulting in increased stray light and energy costs most of these issues can be readily corrected with available inexpensive technology however there is considerable inertia in the field of lighting design and with landlord tenant practices that create barriers to rapid correction of these matters most importantly public awareness needs to improve dramatically for industrialized countries to realize the enormous payoff in reducing overillumination sky glow los angeles at night with a brightly illuminated sky sky glow refers to the glow effect that can be seen over populated areas it is the combination of light reflected from what it has illuminated and from all of the badly directed light in that area being refracted in the surrounding atmosphere this refraction is st |
rongly related to the wavelength of the light rayleigh scattering which makes the sky appear blue in the daytime also affects light that comes from the earth into the sky and is then redirected to become sky glow seen from the ground as a result blue light contributes significantly more to sky glow than an equal amount of yellow light sky glow is of particular irritation to astronomers because it reduces contrast in the night sky to the extent where it may even become impossible to see the brightest stars astronomers have begun to use the bortle dark sky scale to quantify sky glow since it was published in sky the problem with light pollution one nine nine six estimating the level of sky glow due to cities one nine nine six this whiteout zone can stretch many tens of kilometers this hurts amateur astronomers and it has been suggested that it also diminishes public understanding of space astronomy and science in general the british house of commons first special report two zero zero three natural bridges natio |
nal monument utah has the least light pollution and the darkest skies in the continental united states according to a recent study by backpacker magazine america s last wild places two zero zero four effects on human health and psychology in particular common levels of office fluorescent lighting in offices is sufficient to elevate blood pressure by about eight points there is some evidence that lengthy daily exposure to moderately high lighting leads to diminished sexual performance there is clear evidence that levels of light in most office environments in the u s lead to increased stress as well as increased worker errors dilouie two zero zero six bain one nine nine seven medical research on the effects of excessive light on the human body is extensive and there is clear evidence that many different adverse health effects are caused by light pollution or excessive light exposure numerous studies have been conducted to show the adverse effects of overillumination and improper frequency spectrum of artificia |
l light these effects include loss of visual acuity fatigue stress decreased worker performance and adverse social behavior cambridge two zero zero one two studies have been published that suggest a link between exposure to light at night and risk of breast cancer due to suppression of the normal nocturnal production of melatonin davis et al two zero zero one schernhammer et al two zero zero one le scienze italian translation of scientifican american online two two december two zero zero five confirms these evidences by laboratory studies on rats several studies have shown adverse health effects of overillumination in workplaces including increased headaches stress fatigue and decreased worker performance philips two zero zero zero studies of classroom learning have shown that student performance and test scores are degraded when artiifcial rather than natural light is emphasized other health effects are noted bain one nine nine seven state of the art lighting design textbooks use human health as an explicit |
criterion for proper interior lighting steffy two zero zero one myopia and ambient lighting at night nature vol three nine nine one three may one nine nine nine affective disorders neuropsychopharmacology one nine nine nine vol two one no three disruption of ecosystems life evolved with natural patterns of light and dark so disruption of those patterns influences many aspects of animal behavior longcore and rich two zero zero four light pollution can confuse animal navigation alter competitive interactions change predator prey relations and influence animal physiology studies suggest that light pollution around lakes prevents zooplankton such as daphnia from eating surface algae helping cause algal blooms that can kill off the lakes plants and lower water quality moore et al two zero zero zero light pollution may also affect ecosystems in other ways for example lepidopterists and entomologists have documented that night time light may interfere with the ability of moths and other nocturnal insects to navigate |
frank one nine eight eight night blooming flowers that depend on moths for pollination may be affected by night lighting as there is no replacement pollinator that would not be affected by the artificial light this can lead to species decline of plants that are unable to reproduce and change an area s longterm ecology migrating birds can be disoriented by lights on tall structures estimates by the u s fish and wildlife service of the number of birds killed after being attracted to tall towers range from four five million per year to an order of magnitude higher malakoff two zero zero one the fatal light awareness program works with building owners in toronto canada and other cities to reduce mortality of birds by turning out lights during migration periods other well known casualties of light pollution are sea turtle hatchlings emerging from nests on beaches it is a common misconception that hatchling sea turtles are attracted to the moon they are not rather they find the ocean by moving away from the dark s |
ilhouette of dunes and their vegetation a behavior with which artificial lights interfere salmon two zero zero three juvenile seabirds may also be disoriented by lights as they leave their nests and fly out to sea nocturnal frogs and salamanders are also affected by light pollution since they are nocturnal they wake up when there is no light light pollution may cause salamanders to emerge from concealment later giving them less time to mate and reproduce loss of safety it is generally agreed that many people require light to feel safe at night but campaigners for the reduction of light pollution often claim that badly or inappropriately installed lighting can lead to a reduction in safety and that at the very least it is wrong to assume that simply increasing light at night will lead to improved safety for example the international dark sky association claims there are no good scientific studies that convincingly show a relationship between lighting and crime furthermore the association claims that badly inst |
alled artificial lights can create a deeper contrast of shadows in which criminals might hide the new england light pollution advisory group claims that some light emitted by some fixtures can be a significant hazard to motorists pedestrians and bicyclists due to their scattering of light and glare the specific effects of outdoor lighting on safety are still a topic of debate and formal research in the area is not well established reducing light pollution reducing light pollution implies many things such as reducing sky glow reducing glare reducing light trespass and reducing clutter the method for best reducing light pollution therefore depends on exactly what the problem is in any given instance possible solutions include utilizing light sources of minimum intensity necessary to accomplish the light s purpose turning lights off by timer or manually when not needed improving lighting fixtures so that they direct their light more accurately towards where it is needed and with less side effects adjusting the t |
ype of lights used so that the light waves emitted are those that are less likely to cause severe light pollution problems evaluating existing lighting plans and re designing some or all of the plans depending on whether existing light is actually needed improving lighting fixtures a flat lens cobra luminaire which is a full cutoff fixture is preferable for reducing light pollution it ensures that light is only directed below the horizontal which means less light is wasted through directing it outwards and upwards this drop lens cobra luminaire allows light to escape sideways and upwards where it may cause problems most campaigners for the reduction of light pollution advocate the use of full cutoff lighting fixtures as much as possible it is also commonly recommended that lights be spaced appropriately for maximum efficiency and that lamps within the fixtures not be overpowered a full cutoff fixture when correctly installed reduces the chance for light to escape above the plane of the horizontal light releas |
ed above the horizontal may sometimes be lighting an intended target but often serves no purpose when it enters into the atmosphere light contributes to sky glow some governments and organisations are now considering or have already implemented full cutoff fixtures in street lamps and stadium lighting by preventing light from escaping unnecessarily the use of full cutoff fixtures may help to reduce sky glow effects of glare may also be reduced since by their nature full cutoff fixtures usually prevent luminaries from being directly visible it is also commonly argued by campaigners that full cutoff fixtures are more efficient than other fixtures since light that would otherwise have escaped into the atmosphere is instead directed towards the ground the use of full cutoff fixtures may allow for lower powered bulbs to be used in the fixture with the same or sometimes better effect due to being more carefully controlled in every lighting system some sky glow also results from light reflected from the ground this |
reflection can be reduced however by being careful to avoid overpowering the lamp within the fixtures and setting spacing between lights appropriately nyserda planners two zero zero two a common criticism of full cutoff lighting fixtures is that they are sometimes not as aesthetically pleasing to look at this is most likely because historically there has not been a large market specifically for full cutoff fixtures due to the specificity with their direction of light full cutoff fixtures sometimes also require expertise to install for maximum effect another criticism of full cutoff lighting particularly in the usa is that luminaires with full cutoff distributions typically have to be closer together than other light distributions used to meet the same roadway lighting requirements specified by the illuminating engineering society of north america of light level uniformity and glare keith journal of the illuminating engineering society two zero zero zero two zero zero two and two zero zero three this means tha |
t using full cutoff luminaires corresponds to increased initial costs maintenance costs operating costs energy use energy pollution and possibly light pollution compared to using other distributions to meet the same roadway lighting requirements adjusting types of light sources several different types of light sources exist each consisting of different properties that determine their appropriateness for certain tasks as well as their efficiency it is often the case that inappropriate light sources have been selected for a task either due to ignorance or because more sophisticated light sources were unavailable at the time of installation therefore badly chosen light sources often contribute to light pollution unnecessarily by re assessing and changing the light sources used it is often possible to reduce pollutive effects some types of light sources in order of energy efficiency are many astronomers prefer their neighbouring societies to use low pressure sodium lights as much as possible because the single wa |
velength involved is comparably easy to filter the low cost of operating sodium lights is another feature in one nine eight zero for example san jose california replaced all street lamps with low pressure sodium lamps whose light is easier for nearby lick observatory to filter out similar programs are now in place in arizona and hawaii disadvantages of low pressure sodium lighting are that fixtures must usually be larger than competing fixtures colour cannot be distinguished due to its emitting only a single wavelength of light see security lighting and conflicts with yellow traffic lights due to the substantial size of the light emitting part of the lamp the arc tube control of light emissions from low pressure sodium luminaires is very difficult resulting in higher amounts of light pollution from luminaires running these lamps than any other light source except fluorescent tubes this has led many authorities to instead adopt more controllable high pressure sodium lighting for their street lights re designin |
g lighting plans in some cases evaluation of existing plans has determined that more efficient lighting plans are possible for instance light pollution can be reduced by turning off unneeded outdoor lights and only lighting stadiums when there are people inside timers are especially valuable for this purpose one example of a lighting plan assessment can be seen in a report commissioned by the office of the deputy prime minister in the united kingdom towards better practice two zero zero five the report details a plan to be implemented throughout the uk for designing lighting schemes in the countryside with a particular focus on preserving the environment in another example the city of calgary has recently replaced most residential street lights with models that are comparably energy efficient the motivation is primarily operation cost and environmental conservation the costs of installation are expected to be regained through energy savings within six to seven years organisations the international dark sky as |
sociation ida campaigns for reduced light pollution mostly in the usa but with a world wide reach the campaign for dark skies cfds is part of the british astronomical association and campaigns for reduced light pollution in the united kingdom ida uai cielobuio italian joint organization by local ida representative unione astrofili italiani cielobuio volunteer people see also history of street lighting in the united states lighting national dark sky week scuse me while i miss the sky an episode of the television series the simpsons dedicated to light pollution references light pollution responses and remedies by bob mizon isbn one eight five two three three four nine seven five springer two zero zero one america s last wild places backpacker magazine page five six october two zero zero four bain a the hindenburg disaster a compelling theory of probable cause and effect procs natl hydr assn eight th ann hydrogen meeting alexandria va march one one one three pp one two five one two eight one nine nine seven camb |
ridge handbook of psychology health and medicine edited by andrew baum robert west john weinman stanton newman chris mcmanus cambridge university press one nine nine seven isbn zero five two one four three six eight six nine craig dilouie advanced lighting controls energy savings productivity technology and applications the fairmont press inc two zero zero six isbn zero eight eight one seven three five one zero eight gary steffy architectural lighting design john wiley and sons two zero zero one isbn zero four seven one three eight six three eight three estimating the level of sky glow due to cities september one nine nine six information sheet one one international dark sky association federal aviation administration one nine may two zero zero five miscellaneous changes to commercial space transportation regulations proposed rule national archives and records administration federal register seven zero nine six two nine one six three two nine one six eight pdf first special report government response to the c |
ommittee s seventh report session two zero zero two zero three light pollution and astronomy december two zero zero three british house of commons papers two zero zero three zero four one two seven isbn zero two one five zero one four five five three available online html pdf hard copy purchase reproduced on line in part by the international dark sky association pdf nyserda planners nyserda how to guide to effective energy efficient street lighting for planners and engineers october two zero zero two new york state energy research and development authority also available online available in december two zero zero five pdf the problem with light pollution june one nine nine six information sheet one international dark sky association office of the deputy prime minister united kingdom external links campaign groups international dark sky association links and web resources austria verein kuffner sternwarte how many stars in german campaign for dark skies uk new england light pollution advisory group selene new |
york citizens for responsible lighting based around a distributed discussion group virginia outdoor lighting taskforce italian site of ida uai cielobuio research about light pollution the discover article relating light pollution to insects birds and breast cancer requires paid registration ecology of the night symposium two zero zero three conference ecological consequences of artificial night lighting two zero zero two conference by the urban wildlands group light pollution and the protection of the night environment unesco ida regional meeting three six zero pages two zero zero two english italian proceedings are available as a downloadable pdf collections of links related to light pollution lightlynx list open directory project light pollution miscellaneous how many stars a star counting experiment for comparing populated areas the night sky in the world satellite monitoring of artificial light light pollution awareness site usa santa clara valley lighting the largest uncensored and most active forum on l |
ight pollution darksky list forum email discussion group and resource library reduction in light pollution achieved near the observatories in chile observational astronomy ecology lighting leo tolstoy pictured late in life count lev nikolayevich tolstoy russian commonly referred to in english as leo tolstoy september nine one eight two eight november two zero one nine one zero n s august two eight one eight two eight november seven one nine one zero o s was a russian novelist social reformer pacifist christian anarchist vegetarian moral thinker and an influential member of the tolstoy family tolstoy is widely regarded as one of the greatest of all novelists particularly noted for his masterpieces war and peace and anna karenina in their scope breadth and realistic depiction of russian life the two books stand at the peak of realistic fiction as a moral philosopher he was notable for his ideas on nonviolent resistance through his work the kingdom of god is within you which in turn influenced such twentieth cen |
tury figures as mahatma gandhi and martin luther king early life tolstoy was born at yasnaya polyana the family estate situated in the region of tula russia he was the fourth of five children in his family his parents died when he was young so he was brought up by relatives tolstoy studied law and oriental languages at kazan university in one eight four four until he eventually left the university teachers described him as both unable and unwilling to learn he returned in the middle of his studies to yasnaya polyana and spent much of his time in moscow and st petersburg after contracting heavy gambling debts tolstoy accompanied his elder brother to the caucasus in one eight five one and joined the russian army tolstoy began writing literature around this time in one eight six two he married sofia andreevna bers who was one six years his junior and together they had thirteen children the marriage with sofia andreevna bers was marked from the outset by tolstoy on the eve of their marriage giving his diaries to |
his fianc e these detailed tolstoy s sexual relations with his serfs despite so their early marriage life was comparatively blissful and idyllic and allowed tolstoy much freedom to compose the literary masterpieces war and peace and anna karenina his late marriage life has been described by a n wilson as one of the unhappiest in literary history his relationship with his wife deteriorated as his beliefs became increasingly radical novels and fictional works tolstoy was one of the giants of one nine th century russian literature his most famous works include the novels war and peace and anna karenina and many shorter works including the novellas the death of ivan ilyich and hadji murad his contemporaries paid him lofty tributes dostoevsky thought him the greatest of all living novelists while gustave flaubert gushed what an artist and what a psychologist anton chekhov who often visited tolstoy at his country estate wrote when literature possesses a tolstoy it is easy and pleasant to be a writer even when you k |
now you have achieved nothing yourself and are still achieving nothing this is not as terrible as it might otherwise be because tolstoy achieves for everyone what he does serves to justify all the hopes and aspirations invested in literature later critics and novelists continue to bear testaments to his art virginia woolf went on to declare him greatest of all novelists and thomas mann wrote of his seemingly guileless artistry seldom did art work so much like nature sentiments shared in part by many others including marcel proust vladimir nabokov and william faulkner his autobiographical novels childhood boyhood and youth one eight five two one eight five six his first publications tell of a rich landowner s son and his slow realization of the differences between him and his peasant playmates although in later life tolstoy rejected these books as sentimental a great deal of his own life is revealed and the books still have relevance for their telling of the universal story of growing up tolstoy served as a se |
cond lieutenant in an artillery regiment during the crimean war recounted in his sevastapol sketches his experiences in battle helped develop his pacifism and gave him material for realistic depiction of the horrors of war in his later work his fiction consistently attempts to convey realistically the russian society in which he lived the cossacks one eight six three describes the cossack life and people through a story of a russian aristocrat in love with a cossack girl anna karenina one eight seven seven tells parallel stories of an adulterous woman trapped by the conventions and falsities of society and of a philosophical landowner much like tolstoy who works alongside the peasants in the fields and seeks to reform their lives tolstoy not only drew from his experience of life but created characters in his own image such as pierre bezukhov and prince andrei in war and peace levin in anna karenina and to some extent prince nekhlyudov in resurrection war and peace is generally thought to be one of the greates |
t novels ever written remarkable for its breadth and unity its vast canvas includes five eight zero characters many historical others fictional the story moves from family life to the headquarters of napoleon from the court of alexander i of russia to the battlefields of austerlitz and borodino it was written with the purpose of exploring tolstoy s theory of history and in particular the insignificance of individuals such as napoleon and alexander somewhat surprisingly tolstoy did not consider war and peace to be a novel nor did he consider many of the great russian fictions written at that time to be novels this view becomes less surprising if one considers that tolstoy was a novelist of the realist school who considered the novel to be a framework for the examination of social and political issues in nineteenth century life war and peace which is to tolstoy really an epic in prose therefore did not qualify tolstoy thought that anna karenina was his first true novel and it is indeed one of the greatest of al |
l realist novels after anna karenina tolstoy concentrated on christian themes and his later novels such as the death of ivan ilyich one eight eight six and what then must we do develop a radical anarcho pacifist christian philosophy which led to his excommunication from the orthodox church in one nine zero one religious and political beliefs portrait of leo tolstoy one eight eight seven by ilya yefimovich repin tolstoy s christian beliefs were based on the sermon on the mount and particularly on the phrase about turn the other cheek which he saw as a justification for pacifism nonviolence and nonresistance tolstoy believed being a christian made him a pacifist and due to the military force used by his government being a pacifist made him an anarchist he felt very isolated in these beliefs suffering on occasion with depression so severe that whenever he saw a rope he thought of hanging himself and he hid his guns to stop himself from committing suicide tolstoy believed that a christian should look inside his o |
r her own heart to find inner happiness rather than looking outward toward the church or state his belief in nonviolence when facing oppression is another distinct attribute of his philosophy by directly influencing mahatma gandhi with this idea through his work the kingdom of god is within you full text of english translation can be found here tolstoy has had a huge influence on the nonviolent resistance movement to this day he believed that the aristocracy were a burden on the poor and that the only solution to how we live together is through anarchy he also opposed private property and the institution of marriage and valued the ideals of chastity and sexual abstinence discussed in father sergius and his preface to the kreutzer sonata tolstoy s later work is often criticised as being overly didactic and patchily written but derives a passion and verve from the depth of his austere moral views the sequence of the temptation of sergius in father sergius for example is among his later triumphs gorky relates ho |
w tolstoy once read this passage before himself and chekhov and that tolstoy was moved to tears by the end of the reading other later passages of rare power include the crises of self faced by the protagonists of the death of ivan ilyich and master and man where the main character in ilyich or the reader in master and man is made aware of the foolishness of the protagonists lives tolstoy had a profound influence on the development of anarchist thought prince peter kropotkin wrote of him in the article on anarchism in the one nine one one encyclop dia britannica without naming himself an anarchist leo tolstoy like his predecessors in the popular religious movements of the fifteenth and sixteenth centuries chojecki denk and many others took the anarchist position as regards the state and property rights deducing his conclusions from the general spirit of the teachings of jesus and from the necessary dictates of reason with all the might of his talent he made especially in the kingdom of god is within you a powe |
rful criticism of the church the state and law altogether and especially of the present property laws he describes the state as the domination of the wicked ones supported by brutal force robbers he says are far less dangerous than a well organized government he makes a searching criticism of the prejudices which are current now concerning the benefits conferred upon men by the church the state and the existing distribution of property and from the teachings of jesus he deduces the rule of non resistance and the absolute condemnation of all wars his religious arguments are however so well combined with arguments borrowed from a dispassionate observation of the present evils that the anarchist portions of his works appeal to the religious and the non religious reader alike a letter tolstoy wrote to an indian newspaper entitled letter to a hindu resulted in a long running correspondence with mohandas gandhi who was in south africa at the time and was beginning to become an activist the correspondence with tolst |
oy strongly influenced gandhi towards the concept of nonviolent resistance a central part of tolstoy s view of christianity along with his growing idealism he also became a major supporter of the esperanto movement tolstoy was impressed by the pacifist beliefs of the doukhobors and brought their persecution to the attention of the international community after they burned their weapons in peaceful protest in one eight nine five he aided the doukhobors in migrating to canada in one nine zero four during the russo japanese war tolstoy condemned the war and wrote to the japanese buddhist priest soyen shaku in a failed attempt to make a joint pacifist statement tolstoy was an extremely wealthy member of the russian nobility he came to believe that he was undeserving of his inherited wealth and was renowned among the peasantry for his generosity he would frequently return to his country estate with vagrants whom he felt needed a helping hand and would often dispense large sums of money to street beggars while on t |
rips to the city much to his wife s chagrin he died of pneumonia at astapovo station in one nine one zero after leaving home in the middle of winter at the age of eight two his death came only days after gathering the nerve to abandon his family and wealth and take up the path of a wandering ascetic a path that he had agonized over pursuing for decades thousands of peasants lined the streets at his funeral bibliography ivan mozzhukhin in the one nine one seven screen version of father sergius childhood detstvo one eight five two the raid one eight five two boyhood otrochestvo one eight five four youth yunost one eight five six sevastopol stories sevastolpolskye rasskazi one eight five five five six family happiness one eight five nine the cossacks kazaki one eight six three ivan the fool a lost opportunity one eight six three polikushka one eight six three war and peace voyna i mir one eight six five six nine a prisoner in the caucasus one eight seven two father sergius one eight seven three anna karenina one |
eight seven five seven seven a confession one eight eight two strider the story of a horse one eight six four one eight eight six what i believe tolstoy also call my religion one eight eight four the death of ivan ilyich smert ivana ilyicha one eight eight six how much land does a man need one eight eight six the power of darkness vlast t my one eight eight six drama the fruits of culture play one eight eight nine the kreutzer sonata and other stories kreutzerova sonata one eight eight nine the kingdom of god is within you available at wikisource one eight nine four master and man and other stories one eight nine five the gospel in brief one eight nine six what is art one eight nine seven resurrection voskresenie one eight nine nine the living corpse zhivoi trup published one nine one one drama hadji murad written in one eight nine six one nine zero four published one nine one two see also christian anarchism mahatma gandhi one nine two nine the story of my experiments with truth available at tolstoy family |
tolstoyan vladimir chertkov alexandra lvovna tolstoy s daughter who established the tolstoy foundation in america external links leo tolstoy a comprehensive site with pictures e texts biography genealogy etc leo tolstoy s life tolstoy s personal professional and world event timeline from masterpiece theatre synopsis of leo tolstoy s life from masterpiece theatre recording of tolstoy s voice searchable works and quotes of leo tolstoy tolstoy on life death tragedy of tolstoy tolstoy s legacy for mankind a manifesto for nonviolence part one tolstoy s legacy for mankind a manifesto for nonviolence part two read leo tolstoy s works online in an easy to read html format alexander ii and his times a narrative history of russia in the age of alexander ii tolstoy and dostoevsky one eight two eight births one nine one zero deaths leo tolstoy anarchists russian essayists russian novelists russian short story writers autodidacts vegetarians anti war people the lagrangian points ipa also lagrange point l point or libratio |
n point are the five positions in interplanetary space where a small object affected only by gravity can theoretically be stationary relative to two larger objects such as a satellite with respect to the earth and moon they are analogous to geosynchronous orbits in that they allow an object to be in a fixed position in space rather than an orbit in which its relative position changes continuously a more precise but technical definition is that the lagrangian points are the stationary solutions of the circular restricted three body problem for example given two massive bodies in circular orbits around their common center of mass there are five positions in space where a third body of comparatively negligible mass could be placed which would then maintain its position relative to the two massive bodies as seen in a frame of reference which rotates with the same period as the two co orbiting bodies the gravitational fields of two massive bodies combined with the centrifugal force are in balance at the lagrangian |
points allowing the third body to be stationary with respect to the first two bodies history and concepts in one seven seven two the famed italian french mathematician joseph louis lagrange was working on the infamous three body problem when he discovered an interesting quirk in the results originally he had set out to discover a way to easily calculate the gravitational interaction between arbitrary numbers of bodies in a system because newtonian mechanics conclude that such a system results in the bodies orbiting chaotically until there is a collision or a body is thrown out of the system so that equilibrium can be achieved the logic behind this conclusion is that a system with one body is trivial as it is merely static relative to itself a system with two bodies is very simple to solve for as the bodies orbit around their common center of gravity however once more than two bodies are introduced the mathematical calculations become very complicated a situation arises where you would have to calculate every |
gravitational interaction between every object at every point along its trajectory lagrange however wanted to make this simpler he did so with a simple conclusion the trajectory of an object is determined by finding a path that minimizes the action over time this is found by subtracting the potential energy from the kinetic energy with this way of thinking lagrange re formulated the classical newtonian mechanics to give rise to lagrangian mechanics with his new system of calculations lagrange s work led him to hypothesize how a third body of negligible mass would orbit around two larger bodies which were already orbiting one another which at specific points in its orbit would become stationary relative to one of its host bodies planets these points were named lagrangian points in lagrange s honor in the more general case of elliptical orbits there are no longer stationary points in the same sense it becomes more of a lagrangian area the lagrangian points constructed at each point in time as in the circular c |
ase form stationary elliptical orbits which are similar to the orbits of the massive bodies this is due to newton s second law d mathbf dt mathbf where p mv p the momentum m the mass and v the velocity is invariant if force and position are scaled by the same factor a body at a lagrangian point orbits with the same period as the two massive bodies in the circular case implying that it has the same ratio of gravitational force to radial distance as they do this fact is independent of the circularity of the orbits and it implies that the elliptical orbits traced by the lagrangian points are solutions of the equation of motion of the third body a diagram showing the five lagrangian points in a two body system e g the sun and the earth the lagrangian points the five lagrangian points are labeled and defined as follows l one the l one point lies on the line defined by the two large masses m one and m two and between them example an object which orbits the sun more closely than the earth would normally have a short |
er orbital period than the earth but that ignores the effect of the earth s own gravitational pull if the object is directly between the earth and the sun then the effect of the earth s gravity is to weaken the force pulling the object towards the sun and therefore increase the orbital period of the object the closer to earth the object is the greater this effect is at the l one point the orbital period of the object becomes exactly equal to the earth s orbital period the sun earth l one is ideal for making observations of the sun objects here are never shadowed by the earth or the moon the solar and heliospheric observatory soho is stationed in a halo orbit at the l one and the advanced composition explorer ace is in a lissajous orbit also at the l one point the earth moon l one allows easy access to lunar and earth orbits with minimal delta v and would be ideal for a half way manned space station intended to help transport cargo and personnel to the moon and back l two the l two point lies on the line defin |
ed by the two large masses beyond the smaller of the two example on the side of the earth away from the sun the orbital period of an object would normally be greater than that of the earth the extra pull of the earth s gravity decreases the orbital period of the object and at the l two point that orbital period becomes equal to the earth s sun earth l two is a good spot for space based observatories because an object around l two will maintain the same orientation with respect to the sun and earth shielding and calibration are much simpler the wilkinson microwave anisotropy probe is already in orbit around the sun earth l two the future herschel space observatory as well as the proposed james webb space telescope will be placed at the sun earth l two earth moon l two would be a good location for a communications satellite covering the moon s far side if m two is much smaller than m one then l one and l two are at approximately equal distances r from m two equal to the radius of the hill sphere given by r appr |
ox r sqrt three where r is the distance between the two bodies this distance can be described as being such that the orbital period corresponding to a circular orbit with this distance as radius around m two in the absence of m one is that of m two around m one divided by sqrt approx one seven three examples sun and earth one five zero zero zero zero zero km from the earth earth and moon six one five zero zero km from the moon l three the l three point lies on the line defined by the two large masses beyond the larger of the two example l three in the sun earth system exists on the opposite side of the sun a little further away from the sun than the earth is where the combined pull of the earth and sun again causes the object to orbit with the same period as the earth the sun earth l three point was a popular place to put a counter earth in pulp science fiction and comic books l four and l five the l four and l five points lie at the third point of an equilateral triangle with the base of the line defined by |
the two masses such that the point is ahead of or behind the smaller mass in its orbit around the larger mass l four and l five are sometimes called triangular lagrange points or trojan points examples the sun earth l four and l five points lie six zero ahead of and six zero behind the earth in its orbit around the sun they contain interplanetary dust the sun jupiter l four and l five points are occupied by the trojan asteroids the giant impact hypothesis suggests that an object named theia formed at l five and crashed into the earth after its orbit destabilized forming the moon stability the first three lagrangian points are technically stable only in the plane perpendicular to the line between the two bodies this can be seen most easily by considering the l one point a test mass displaced perpendicularly from the central line would feel a force pulling it back towards the equilibrium point this is because the lateral components of the two masses gravity would add to produce this force whereas the components |
along the axis between them would balance out however if an object located at the l one point drifted closer to one of the masses the gravitational attraction it felt from that mass would be greater and it would be pulled closer the pattern is very similar to that of tidal forces although the l one l two and l three points are nominally unstable it turns out that it is possible to find stable periodic orbits around these points at least in the restricted three body problem these perfectly periodic orbits referred to as halo orbits do not exist in a full n body dynamical system such as the solar system however quasi periodic i e bounded but not precisely repeating lissajous orbits do exist in the n body system these quasi periodic orbits are what all libration point missions to date have used although they are not perfectly stable a relatively modest effort at station keeping can allow a spacecraft to stay in a desired lissajous orbit for an extended period of time it also turns out that at least in the case |
of sun earth l one missions it is actually preferable to place the spacecraft in a large amplitude one zero zero zero zero zero two zero zero zero zero zero km lissajous orbit instead of having it sit at the libration point since this keeps the spacecraft off of the direct sun earth line and thereby reduces the impacts of solar interference on the earth spacecraft communications links another interesting and useful property of the collinear libration points and their associated lissajous orbits is that they serve as gateways to control the chaotic trajectories of the interplanetary transport network in contrast to the collinear libration points the triangular points l four and l five are stable equilibria cf attractor provided the ratio of the masses m one m two is two four nine six this is the case for the sun earth and earth moon systems though by a smaller margin in the latter when a body at these points is perturbed it moves away from the point but the coriolis effect then acts and bends the object s path |
into a stable kidney bean shaped orbit around the point as seen in the rotating frame of reference libration point missions the libration point orbits have unique characteristics that have made them a good choice for performing some kinds of missions nasa has operated a number of spacecraft at the sun earth l one and l two points including the l five society is a precursor of the national space society and promoted the possibility of establishing a colony and manufacturing facility in orbit around the l four and or l five points in the earth moon system see space colonisation natural examples in the sun jupiter system several thousand asteroids collectively referred to as trojan asteroids are in orbits around the sun jupiter l four and l five points other bodies can be found in the sun saturn sun mars jupiter jovian satellite and saturn saturnian satellite systems there are no known large bodies in the sun earth system s trojan points but clouds of dust surrounding the l four and l five points were discovere |
d in the one nine five zero s clouds of dust called kordylewski clouds even fainter than the notoriously weak gegenschein are also present in the l four and l five of the earth moon system the saturnian moon tethys has two smaller moons in its l four and l five points telesto and calypso the saturnian moon dione also has two lagrangian co orbitals helene at its l four point and polydeuces at l five the moons wander azimuthally about the lagrangian points with polydeuces describing the largest deviations moving up to three two degrees away from the saturn dione l five point tethys and dione are hundreds of times more massive than their escorts see the moons articles for exact diameter figures masses are not known in several cases and saturn is far more massive still which makes the overall system stable other co orbitals the earth s companion object three seven five three cruithne is in a somewhat trojan like orbit around the earth but not in the same manner as a true trojan rather it occupies one of two regul |
ar solar orbits periodically alternating between the two due to close encounters with earth when the asteroid approaches earth it takes orbital energy from earth and moves into a larger higher energy orbit some time later the earth catches up with the asteroid which is in a larger and slower orbit at which time earth takes the energy back and so the asteroid falls into a smaller faster orbit and eventually catches earth to begin the cycle anew this has no noticeable impact on the length of the year since earth s mass is over two zero billion times more than three seven five three cruithne epimetheus and janus satellites of saturn have a similar relationship though they are of similar masses and so actually exchange orbits with each other periodically janus is roughly four times more massive but still light enough for its orbit to be altered another similar configuration is known as orbital resonance in which orbiting bodies tend to have periods of a simple integer ratio due to their interaction see also list |
of objects at lagrangian points interplanetary transport network hill sphere kordylewski clouds lunar space elevator big splash home on lagrange the l five song external links explanation of lagrange points by prof neil j cornish explanation of lagrange points by prof john baez home on lagrange filksong elementary derivation of the l one point l two is analogous elementary derivation of the l four point l five is analogous celestial mechanics earth orbits lucid dreaming is the conscious perception of one s state while dreaming enabling a more cogent lucid control over the content and quality of the experience the complete experience from start to finish is a lucid dream stephen laberge a popular author and experimenter on the subject has defined it as dreaming while knowing that you are dreaming there are many unanswered questions about lucid dreaming and about dreaming itself laberge and his associates have called people who purposely explore the possibilities of lucid dreaming oneironauts literally from the |
greek meaning dream explorers the topic attracts the attention of a diverse and eclectic group namely psychologists self help authors new age groups mystics occultists and artists this list is by no means exhaustive nor does interest in lucid dreaming apply necessarily to each group clear and consistent knowledge about lucid dreaming is difficult to find amongst the many interpretations of the experience especially considering its highly subjective nature it may be classified as a protoscience pending an increase in scientific knowledge about the subject researchers such as allan hobson with his neurophysiological approach to dreaming have helped to push the understanding of lucid dreaming into a less speculative realm lucid dreamers regularly describe their dreams as exciting colourful and fantastic many compare it to a spiritual experience and say that it changed their lives or their perception of the world some have even reported lucid dreams that take on a hyperreality seemingly more real than real where |
all the elements of reality are amplified lucid dreams are prodigiously more memorable than other kinds of dreaming even nightmares which may be why they are often prescribed as a means of ridding one s self of troubling dreams achieving and recognizing lucid dreams the most important aspect in lucid dreaming is to recognize that one is dreaming any time that a person recognizes a dream sign or anything that is out of the ordinary they should perform a reality test as stated below many people report having experienced a lucid dream during their lives often in childhood however even with training achieving lucid dreams on a regular basis can be difficult and is uncommon despite this difficulty techniques have been developed to achieve a lucid dreaming state intentionally a number of universities notably stanford conduct continued research into these techniques and the effects of lucid dreaming as do some independent agencies such as laberge s the lucidity institute at present there are no known cases where lu |
cid dreaming has caused damage on either a psychological or physiological level however it would be very hard to determine whether some form of lucid dreaming might prevent one from receiving a benefit from normal dreaming jungian psychology seems to indicate that non lucid or partly lucid dreaming is a way to achieve self understanding dream recall the ability to remember one s dreams is very important to lucid dreamers because it is usually desired that the lucid dreamer be able to remember lucid dreams improvement of dream recall is usually the first step people take to learn to have lucid dreams a common practice used to increase dream recall is to keep a dream journal or a notebook of dreams the dream journal should be kept right next to the bed so that dreams can be written down as soon as a person wakes up this is important because waiting until later in the day to write dreams down will usually cause one to forget most of their content after waking up it is often helpful to keep your eyes closed while |
trying to remember a dream ability the ability to experience lucid dreams depends on many factors some naturals have lucid dreams more often and more easily than others meditation and involvement in consciousness focusing activities can strengthen the ability to experience lucid dreams induction techniques see below can help much in becoming lucid common techniques reality testing reality testing is a common method that people use to determine whether or not they are dreaming this method involves performing an action with results that are difficult to re create in a dream an example of a reality test is to read some text look away and read it again or to look at your watch and remember the time then look away and look back observers have found that in a dream the text or time will often have changed in the real world the text will not change and the time will not change by more than one minute other tests include flipping a light switch or looking into a mirror light switches rarely work in dreams and reflec |
tions from a mirror often appear to be blurred or distorted another form of reality testing involves identifying one s dream signs clues that one is dreaming these can be anything such as a pink elephant on parade or a talking dog dream signs are often categorized as follows action the dreamer another dream character or a thing does something unusual or impossible in waking life such as photos in a magazine or newspaper becoming three dimensional with full movement context the place or situation in the dream is strange form the dreamer another character or a thing changes shape or is oddly formed or transforms this may include the presence of unusual clothing or hair or a third person view of the dreamer awareness a peculiar thought a strong emotion an unusual sensation or altered perceptions in some cases when moving one s head from side to side one may notice a strange stuttering or strobing of the image though occurrences like these may seem out of place in waking life they may seem perfectly normal to a d |
reaming mind and learning to pick up on these dream signs will help in recognizing that one is dreaming experienced lucid dreamers will often use more advanced techniques such as those described below to induce lucid dreams at will mnemonic induction of lucid dreaming mnemonic induction of lucid dreaming mild is a common technique used by lucid dreamers to induce a lucid dream at will this method involves setting an intention to recognize dream signs while falling asleep wake back to bed induction technique wbtb wake back to bed is often the easiest way to induce a lucid dream the method involves going to sleep tired and waking up five hours later then focusing all thoughts on lucid dreaming staying awake for an hour and going back to sleep the odds of having a lucid dream are then much higher this is because the rem cycles get longer as the night goes on and this technique takes advantage of the best rem cycle of the night also lucid dreams are usually longer and more vivid at this time waking induction of l |
ucid dreaming waking induction of lucid dreaming wild is one of the most common induction techniques used by lucid dreamers in this particular technique a person goes directly from being awake into a lucid dream the key to this technique is recognizing the hypnagogic stage this stage is within the border of being awake and being asleep if a person is successful in staying aware while this stage occurs they will eventually enter the dream state while being fully aware that it is a dream proponents recommend three steps to induce lucid dreaming relax stay aware and enter your dream there are key times at which this technique is best used while success at night after being awake for a long time is very difficult it is relatively easy after being awake for one five or so minutes and in the afternoon during a nap users of this technique often count envision themselves climbing or descending stairs chanting to themselves or any various form of concentration to keep their mind awake while still being calm enough to |
let their body sleep during the actual transition into the dreamstate one is likely to experience sleep paralysis including rapid vibrations and the old hag syndrome aural focusing technique the aural focusing technique is not fully understood but seems to work very well in amateur or casual lucid dreaming this involves a very simple setup one must stay awake until sleep is highly desirable while watching a television or listening to a radio radio use seems to yield drastically lessened instances of successful lucid dreaming and then lowering the volume to a point where the sound is just above the noise that is currently occupying the surroundings the subject then lies down and focuses all attention on the sound while imagining climbing infinite stairs under this method the user will sometimes find themselves in a room extensively similar to the room in which they fell asleep in but upon leaving this room something will be radically different an interesting effect of this method is full auditory awareness usu |
ally the subject will hear the television program that is on but upon inspection of the television screen in the dream state the subject will find mostly static images and sometimes scrolling text with mostly garbage characters and one or two repeating words which change when the television is left and returned to planning a lucid dream a lucid dream can be planned ahead the scenario of the dream can be memorized and rehearsed when awake and the score can be performed when lucidity is achieved an example i will recite my street address and phone number during my next lucid dream then i will break the first glass object i encounter this will most probably be remembered upon entering lucidity and the actions will work out as planned other phenomena associated with lucid dreaming false awakenings in a false awakening one suddenly dreams of having awakened if the person was lucid he she often believes that he she is no longer dreaming and may start exiting their room etc since the person is actually still dreamin |
g this is called a false awakening this is often a nemesis in the art of lucid dreaming because it usually causes people to give up their awareness of being in a dream but it can also cause someone to become lucid if the person does a reality check whenever he she awakens people who keep a dream journal and write down their dreams upon awakening sometimes report having to write down the same dream multiple times because of this false awakening phenomenon upon waking a second time the dreamer realizes that the first entry in the journal was actually done in a dream and must be rewritten a second or even third time when the dreamer is actually awake rapid eye movement rem and communication during sleep during dreaming sleep the eyes move rapidly scientific research in the one nine five zero s found that these eye movements correspond to the direction in which the dreamer is looking in his her dreamscape extraordinarily this apparently enabled trained lucid dreamers to communicate the content of their dreams as |
they were happening to researchers by using eye movement signals this research produced various results such as that events in dreams take place in real time rather than going by in a flash sleep paralysis during rem sleep the body is paralyzed by a mechanism in the brain because otherwise the movements which occur in the dream would actually cause the body to move however it is possible for this mechanism to be triggered before during or after normal sleep while the brain awakens this can lead to a state where a person is lying in his or her bed and he or she feels frozen hallucinations may occur in this state especially auditory ones people also generally report feeling a crushing sensation on their chest possibly because they try to consciously control their breathing people trying to lucid dream sometimes try to trigger this state or accidentally trigger this state while using a waking induction of lucid dreaming wild technique to enter a lucid dream directly when falling asleep things to do in a lucid dr |
eam flying one of the more common and pleasurable activities of lucid dreamers is flying lucid dreamers realizing they are dreaming then go on to realize that normal limitations like gravity or solidity no longer apply many lucid dreamers report they are able to float fly and transport themselves anywhere in the dreamworld at will with practice so called impossible feats such as flying at supersonic speeds zipping around like ufo s without inertia or flying through objects are possible some dream flyers claim their flights might in some cases be out of body experiences transformations some people believe that after some practice one can transform one s dream self into real or fictional animals or any number of other forms some also claim to have tried sensory experiences not normally achievable while awake such as three six zero degree stereo vision sonar bat vision etc spiritual practice some religions claim that lucid dream states give the dreamer a special kind of access to the spiritual world by practicin |
g prayer and meditation during a lucid dream the dreamer can gain access to mystical states of awareness that would not be accessible from the waking state such practices are sometimes classified as dream yoga history of lucid dreaming research even though it has only come to the attention of the general public in the last few decades lucid dreaming is not a modern discovery in the old testament in the song of solomon five two there is some debate as to whether lucid dreaming is mentioned the new living translation of this verse reads as follows one night as i was sleeping my heart awakened in a dream i heard the voice of my lover he was knocking at my bedroom door other translations are less clear the revised standard version of the same passage states only that i slept but my heart was awake it is in the fifth century that we have one of the earliest written examples of a lucid dream in a letter written by st augustine of hippo in four one five a d and even as early as the eighth century the tibetan buddhis |
ts were practising a form of yoga supposed to maintain full waking consciousness while in the dream state an early recorded lucid dreamer was the philosopher and physician sir thomas browne one six zero five one six eight two browne was fascinated by the world of dreams and stated of his own ability to lucid dream in his religio medici yet in one dream i can compose a whole comedy behold the action apprehend the jests and laugh my self awake at the conceits thereof r m part two one one the marquis d hervey de saint denys was probably the first person to argue that it is possible for anyone to learn to dream consciously in one eight six seven he published his book dreams and how to guide them in which he documented more than twenty years of his own research into dreams the term lucid dreaming was coined by dutch author and psychiatrist frederik van eeden in his one nine one three book a study of dreams originally published in the proceedings of the society for psychical research vol two six one nine one three |
this book was highly anecdotal and not embraced by the scientific community the term itself is considered by some to be a misnomer because it means much more than just clear or vivid dreaming a better term might have been conscious dreaming the senoi hunter gatherers of malaysia have been reported to make use of lucid dreaming extensively to ensure mental health the one nine five zero s research in which lucid dreamers apparently communicated the content of their dreams in real time using eye movements prompted philosopher norman malcolm s one nine five nine text dreaming which argued against the possibility of checking the accuracy of dream reports in this way the first book on lucid dreams to recognise their uniqueness and scientific potential was celia green s one nine six eight study lucid dreams reviewing the past literature as well as new data from subjects of her own green analysed the main characteristics of such dreams and concluded that they were a category of experience quite distinct from ordinary |
dreams she predicted that they would turn out to be associated with rem sleep a prediction which was subsequently confirmed by keith hearne in the uk and stephen laberge in the us independently of each other green was also the first to link lucid dreams to the phenomenon of false awakenings the enthusiastic endorsement of lucid dreaming during the one nine seven zero s by new age proponents such as carlos castaneda did little to enhance its scientific credibility however during the one nine eight zero s further scientific evidence to confirm the existence of lucid dreaming was produced and lucid dreamers were able to demonstrate to researchers that they were consciously aware of being in a dream state usually again by using eye movement signals additionally techniques were developed which have been experimentally proven to enhance the likelihood of achieving this state one outstanding question on the neurophysiological nature of lucid dreaming concerns the electrical activity in the frontal cortex which is g |
enerally suppressed during normal sleep the behavior of the frontal cortex has not at present been crucially analyzed with respect to lucid dreaming there is a substantial cottage industry based around the technique of lucid dreaming with an array of induction devices usually based around flickering light arrays commercially available to allegedly allow induction of lucid dreams their proponents also sometimes claim that these devices help achieve a higher level of spiritual consciousness and associate it with other new age concepts such as astral travelling or dream sharing regardless of these claims validity lucid dreaming as a scientifically verified phenomenon is well established some proponents of the technique claim they can use symbolic methods to research program and modify their nervous system itself memory management creative solution generation accelerated healing autoinduced priapism and ecstatic envelopment of one s body are among the various claimed techniques there are thought to be some insigh |
ts into the workings of the brain that can be found by lucid dreaming in particular in surveying the experiences of lucid dreams many have noticed that the brain at least while in dreaming has the feature whereby it is possible for a single individual thought memory definition belief etc to be incorrect while the rest of the mind appears to be working normally an example would be where the lucid dreamer was walking around the dream world knowing he was dreaming retaining his full sense of identity and waking memories yet believing for some reason a locked door can only be opened with a fish and not a key many lucid dream reports contain this kind of phenomenon this is contrary to normal experience of brain malfunctions which are usually more general such as wholesale memory loss or broad emotional imbalance it is helpful to propose a construct of consciousness that is more on a continuum and that certain functions such as reflective awareness might be selectively activated this is a fluid process moment to mo |
ment in the context of the lucid dream and it is experienced as discontinuities popular culture the movies abre los ojos open your eyes vanilla sky and waking life are partly about lucid dreaming while the nightmare on elm street series directly involves lucid dreams as a plot device by which the villain threatens the heroes the movie mulholland drive can be interpreted as a study of lucid dreaming and dream interpretation the matrix while not about lucid dreaming has the hero in the similar position of living in a simulated world complete with its own distinctive dream signs such as a subtle overall green hue and the slightly inaccurate mechanics and being able to control it by simply being aware that it isn t real the song silent lucidity by queensr che a top five hit in one nine nine zero was about the benefits of lucid dreaming the video clip for everlong by the foo fighters features lucid dreaming in which a man uses lucid dreams to save his girlfriend from a nightmare the book only you can save mankind |
by terry pratchett is mostly set in a videogame world accessed by lucid dreaming books lucid dreaming one nine eight five isbn zero eight seven four seven seven three four two three by stephen laberge lucid dreams one nine six eight isbn zero nine zero zero zero seven six zero zero three by celia green lucid dreaming the paradox of consciousness during sleep one nine nine four isbn zero four one five one one two three nine seven by celia green and charles mccreery exploring the world of lucid dreaming one nine nine one isbn zero three four five three seven four one zero x by stephen laberge creative dreaming one nine seven four isbn zero six seven one two one nine zero three zero by patricia l garfield dreams and how to guide them one eight six seven one nine eight two isbn zero seven one five six one five eight four x by hervey de saint denys the lucid dreamer one nine nine four isbn zero six seven one eight seven two four eight six by malcom godwin tibetan yogas of dream and sleep one nine nine eight isbn o |
ne five five nine three nine one zero one four by tenzin wangyal rinpoche see also astral projection dreams false awakening macropsia micropsia out of body experience senoi sleep paralysis waking life external links about com lucid dreaming changing a lucid dream through the practice of dream yoga brilliant dreams dream enhancement supplement claimed to aid lucid dreaming the lucidity institute inc dreamviews information on lucid dreaming lucid dreaming faq dream know it control conscious dreams join a team of lucid dreamers dreaming lyric may refer to lyric poem is a form of poetry that expresses a subjective personal point of view lyric from the greek language a song sung with a lyre lyrics the composition in verse which is sung to a melody to constitute a song lyric is a classification of the human voice in classical singing the adjective describes a quality and range at the upper end of the given voice part e g lyric soprano see vocal weight lyric fm a radio telef s ireann radio station lyric an r known f |
or the song hot and tipsy three leds of different colors a light emitting diode led is a semiconductor device that emits incoherent narrow spectrum light when electrically biased in the forward direction this effect is a form of electroluminescence the color of the emitted light depends on the chemical composition of the semiconducting material used and can be near ultraviolet visible or infrared rubin braunstein born one nine two two of the radio corporation of america first reported on infrared emission from gaas and other semiconductor alloys in one nine five five nick holonyak jr born one nine two eight of the general electric company developed the first practical visible spectrum led in one nine six two led technology physical function an led is a special type of semiconductor diode like a normal diode it consists of a chip of semiconducting material impregnated or doped with impurities to create a structure called a p n junction as in other diodes current flows easily from the p side or anode to the n s |
ide or cathode but not in the reverse direction charge carriers electrons and holes flow into the junction from electrodes with different voltages when an electron meets a hole it falls into a lower energy level and releases energy in the form of a photon as it does so the wavelength of the light emitted and therefore its color depends on the bandgap energy of the materials forming the p n junction in silicon or germanium diodes the electrons and holes recombine by a non radiative transition which produces no optical emission because these are indirect bandgap materials the materials used for an led have a direct bandgap with energies corresponding to near infrared visible or near ultraviolet light led development began with infrared and red devices made with gallium arsenide advances in materials science have made possible the production of devices with ever shorter wavelengths producing light in a variety of colors conventional leds are made from a variety of inorganic semiconductor materials producing the |
following colors aluminium gallium arsenide algaas red and infrared aluminium gallium phosphide algap green aluminium gallium indium phosphide algainp high brightness orange red orange yellow and green gallium arsenide phosphide gaasp red orange red orange and yellow gallium phosphide gap red yellow and green gallium nitride gan green pure green or emerald green and blue indium gallium nitride ingan near ultraviolet bluish green and blue silicon carbide sic as substrate blue silicon si as substrate blue under development sapphire al two o three as substrate blue zinc selenide znse blue diamond c ultraviolet aluminium nitride aln aluminium gallium nitride algan near to far ultraviolet blue and white leds an ultraviolet gan led commercially viable blue leds based on the wide bandgap semiconductor gallium nitride and indium gallium nitride were invented by shuji nakamura while working in japan at nichia corporation in one nine nine three and became widely available in the late one nine nine zero s they can be ad |
ded to existing red and green leds to produce white light though white leds today rarely use this principle most white leds in production today use a four five zero nm four seven zero nm blue gan gallium nitride led covered by a yellowish phosphor coating usually made of cerium doped yttrium aluminium garnet ce three yag crystals which have been powdered and bound in a type of viscous adhesive the led chip emits blue light part of which is efficiently converted to a broad spectrum centered at about five eight zero nm yellow by the ce three yag the single crystal form of ce three yag is actually considered a scintillator rather than a phosphor since yellow light stimulates the red and green receptors of the eye the resulting mix of blue and yellow light gives the appearance of white the resulting shade often called lunar white this approach was developed by nichia and was used by them from one nine nine six for manufacturing of white leds the pale yellow emission of the ce three yag can be tuned by substitutin |
g the cerium with other rare earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminium in the yag with gallium due to the spectral characteristics of the diode the red and green colors of objects in its blue yellow light are not as vivid as in broad spectrum light manufacturing variations make the leds produce light with different color temperatures from warm yellowish to cold bluish the leds have to be sorted during manufacture by their actual characteristics white leds can also be made by coating near ultraviolet nuv emitting leds with a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminium doped zinc sulfide zns cu al this is a method analogous to the way fluorescent lamps work however the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in led packaging causing manufacturing challenges and shorter lifetimes this method is less efficient th |
an the blue led with yag ce phosphor as the stokes shift is larger and more energy is therefore converted to heat but yields light with better spectral characteristics which renders colors better due to the higher radiative output of the ultraviolet leds than of the blue ones both approaches offer comparable brightness the newest method used to produce white light leds uses no phosphors at all and is based on grown zinc selenide znse on a znse substrate which simultaneously emits blue light from its active region and yellow light from the substrate a new technique just developed by michael bowers a graduate student at vanderbilt university in nashville involves coating a blue led with quantum dots that glow white in response to the blue light from the led this technique produces a warm yellowish white light similar to that produced by incandescent bulbs other colors recent color developments include pink and purple they consist of one or two phosphor layers over a blue led chip the first phosphor layer of a p |
ink led is a yellow glowing one and the second phosphor layer is either red or orange glowing purple leds are blue leds with an orange glowing phosphor over the chip some pink leds have run into issues for example some are blue leds painted with fluorescent paint or fingernail polish that can wear off and some are white leds with a pink phosphor or dye that unfortunately fades after a short time ultraviolet blue pure green white pink and purple leds are relatively expensive compared to the more common reds oranges greens yellows and infrareds and are thus less commonly used in commercial applications the semiconducting chip is encased in a solid plastic lens which is much tougher than the glass envelope of a traditional light bulb or tube the plastic may be colored but this is only for cosmetic reasons or to improve the contrast ratio the color of the packaging does not substantially affect the color of the light emitted organic light emitting diodes oleds combined spectral curves for blue yellow green and hi |
gh brightness red solid state semiconductor leds fwhm spectral bandwidth is approximately two four two seven nanometres for all three colors if the emissive layer material of an led is an organic compound it is known as an organic light emitting diode oled to function as a semiconductor the organic emissive material must have conjugated pi bonds the emissive material can be a small organic molecule in a crystalline phase or a polymer polymer materials can be flexible such leds are known as pleds or fleds compared with regular leds oleds are lighter and polymer leds can have the added benefit of being flexible some possible future applications of oleds could be inexpensive flexible displays light sources wall decorations luminous cloth operational parameters and efficiency most typical leds are designed to operate with no more than three zero six zero milliwatts of electrical power around one nine nine nine commercial leds capable of continuous use at one watt of input power were introduced these leds used muc |
h larger semiconductor die sizes to handle the large power input as well the semiconductor dies were mounted to metal slugs to allow for heat removal from the led die in two zero zero two five watt leds were available with efficiencies of one eight two two lumens per watt it is projected that by two zero zero five one zero watt units will be available with efficiencies of six zero lumens per watt these devices will produce about as much light as a common five zero watt incandescent bulb and will facilitate use of leds for general illumination needs in september two zero zero three a new type of blue led was demonstrated by the company cree inc to have three five efficiency at two zero ma this produced a commercially packaged white light having six five lumens per watt at two zero ma becoming the brightest white led commercially available at the time in two zero zero five they have demonstrated a prototype with a record white led efficiency of seven zero lumens per watt at three five zero ma today oleds operat |
e at substantially lower efficiency than inorganic crystaline leds the best efficiency of an oled so far is about one zero these promise to be much cheaper to fabricate than inorganic leds and large arrays of them can be deposited on a screen using simple printing methods to create a color graphic display considerations in use unlike incandescent light bulbs which light up regardless of the electrical polarity leds will only light with positive electrical polarity when the voltage across the pn junction is in the correct direction a significant current flows and the device is said to be forward biased if the voltage is of the wrong polarity the device is said to be reverse biased very little current flows and no light is emitted leds can be operated on an ac voltage but they will only light with positive voltage causing the led to turn on and off at the frequency of the ac supply close up of a typical led showing the internal structure the correct polarity of an led can usually be determined as follows it sho |
uld be noted that looking at the inside of the led is not an accurate way of determining polarity while in most leds the large part is the in some it is the terminal the flat tab or the short pin are more accurate ways of determining polarity because the voltage versus current characteristics of an led are much like any diode they can be destroyed by connecting them to a voltage source higher than their turn on voltage most leds have low reverse breakdown voltage ratings so they will also so be damaged by an applied reverse voltage of more than a few volts since some manufacuters don t follow the indicator standards above if possible the data sheet should be consulted before hooking up an led or the led may be tested in series with a resistor because of the risk of excess voltage damaging the device a good led driver circuit is a constant current source if high efficiency is not required an approximation to a current source made by connecting the led in series with a current limiting resistor to a voltage sou |
rce may be substituted to increase efficiency the power may be applied periodically or intermittently so long as the flicker rate is greater than the human flicker fusion threshold the led will appear to be continuously lit parallel operation is generally problematic the leds have to be of the same type in order to have a similar forward voltage even then variations in the manufacturing process can make the odds of satisfactory operation low for more information see nichia application note some led units contain two diodes one in each direction that is two diodes in inverse parallel and each a different color typically red and green allowing two color operation or a range of apparent colors to be created by altering the percentage of time the voltage is in each polarity other led units contain two or more diodes of different colors arranged in either a common anode or common cathode configuration these can be driven to different colors without reversing the polarity led units may have an integrated multivibra |
tor circuit that makes the led flash advantages of using leds leds are capable of emitting light of an intended color without the use of color filters that traditional lighting methods require the shape of the led package allows light to be focused incandescent and fluorescent sources often require an external reflector to collect light and direct it in a useable manner leds are insensitive to vibration and shocks unlike incandescent and discharge sources leds are built inside solid cases that protect them making them hard to break and extremely durable leds have an extremely long life span typically ten years twice as long as the best fluorescent bulbs and twenty times longer than the best incandescent bulbs further leds fail by dimming over time rather than the abrupt burn out of incandescent bulbs leds give off less heat than incandescent light bulbs with similar light output leds light up very quickly an illumination led will achieve full brightness in approximately zero zero one seconds one zero times fa |
ster than an incandescent light bulb zero one second and many times faster than a compact fluorescent lamp which starts to come on after zero five seconds or one second but does not achieve full brightness for three zero seconds or more a typical red indicator led will achieve full brightness in microseconds or possibly less if it s used for communication devices leds are produced in a staggering array of shapes and sizes though the color of the plastic lens cannot be guaranteed to correlate with the actual color of light emitted by the led for instance purple plastic is often used for infrared leds when not completely clear it is often a good indicator disadvantages of using leds leds are currently more expensive than more conventional lighting technologies the additional expense partially stems from the relatively low lumen output requiring more light sources and drive circuitry power supplies needed a good measure to compare lighting technologies is lumen dollar led performance largely depends on the ambie |
nt temperature of the operating environment driving an led hard in high ambient temperatures may result in overheating of the led package eventually to device failure adequate heat sinking is required to maintain long life this is especially important when considering automotive military applications where the device must operate over a large range of temperatures with government regulated output led applications led panel light source used in an experiment on plant growth the findings of such experiments may be used to grow food in space on long duration missions list of known applications for leds some of these applications are further elaborated upon in the following text leds are used as informative indicators in various types of embedded systems status indicators e g on off lights on professional instruments and consumers audio video equipment in toys especially as light up eyes of robot toys continuity indicators seven segment displays in calculators and measurement instruments although now mostly repla |
ced by liquid crystal displays thin lightweight message displays e g in public information signs at airports and railway stations and as destination displays for trains buses trams and ferries red or yellow leds are used in indicator and alphanumeric displays in environments where night vision must be retained aircraft cockpits submarine and ship bridges astronomy observatories and in the field e g night time animal watching and military field use leds may also be used to transmit digital information remote controls for tvs vcrs etc using infrared leds in fiber optic communications in dot matrix arrangements for displaying messages leds find further application in safety devices where high brightness and reliability are critical in traffic signals led clusters are replacing colored incandescent bulbs in level crossing lights red leds have been used to replace incandescant bulbs in car brake and indicator lights where the quick on characteristic of leds enhances safety in bicycle lighting also for pedestrians |
to be seen by car traffic signaling and emergency beacons or strobes navigation lights on boats which are red green and white and shine in specific directions boats use direct current batteries to power their lights so not only does that match the requrements of leds but the efficiency of colored leds is a big advantage leds are also used for illumination in photographic darkrooms red or yellow leds are also used for providing lighting which does not lead to unwanted exposure of the film in flashlights us torches uk and backlights for lcd screens as a replacement for incandescent and fluorescent bulbs in home and office lighting an application known as solid state lighting ssl as disco club lighting products in projectors led projectors are smaller lighter and produce much less heat than incandescent technology finally leds have additional applications not categorized above movement sensors for example in mechanical and optical computer mice and trackballs in pulse oximeters both a red and an infra red led ar |
e used in led printers such as high end color printers in phototherapy the use of light for healing purposes more recently leds have been used as a replacement to incandescent bulbs for christmas lights illumination applications small spotlights made of many individual leds leds used as a replacement for incandescent bulbs and fluorescent lamps are known as solid state lighting ssl leds ssl leds are packaged as a cluster of white leds grouped together to form a light source leds are moderately efficient the average commercial led currently outputs three two lumens per watt lm w and new technologies promise to deliver up to eight zero lm w they are also more mechanically robust than incandescent light bulbs and fluorescent tubes leds today are not sold in many places require power source conversion in household applications and are relatively expensive although their costs are decreasing incandescent bulbs are much less expensive but also less efficient generating from about one six lm w for a domestic tungste |
n bulb to two two lm w for a halogen bulb fluorescent tubes are more efficient providing five zero to one zero zero lm w for domestic tubes average six zero lm w but are bulky and fragile and require starter or ballast circuits that sometimes buzz audibly compact fluorescent light bulbs which include a quiet integrated ballast are relatively robust and efficient fit in standard light bulb sockets and are currently the best choice for efficient household lighting proponents of leds expect that technological advances will reduce costs such that ssl can be introduced into most homes by two zero two zero however they are still not commercially viable for general lighting applications and so leds are found today in illumination applications where their special characteristics provide a distinct advantage due to their monochromatic nature led lights have great power advantages over white lights when a specific color is required unlike traditional white lights the led does not need a coating or diffuser that can abs |
orb much of the emitted light led lights are inherently colored and are available in a wide range of colors one of the most recently introduced colors is the emerald green bluish green about five zero zero nm that meets the legal requirements for traffic signals and navigation lights there are applications that specifically require light without any blue component examples are photographic darkroom safe lights illumination in laboratories where certain photo sensitive chemicals are used and situations where dark adaptation night vision must be preserved such as cockpit and bridge illumination observatories etc yellow led lights are a good choice to meet these special requirements because the human eye is more sensitive to yellow light about five zero zero lm watt emitted than that emitted by the other leds led display panels the one five zero zero foot long led display on the fremont street experience is currently the largest in the world there are two types of led panels conventional using discrete leds and |
surface mounted device smd panels most outdoor screens and some indoor screens are built around discrete leds also known as individually mounted leds a cluster of red green and blue diodes is driven together to form a full color pixel usually square in shape these pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution the largest led display in the world is over one five zero zero feet long and is located in las vegas nevada covering the fremont street experience most indoor screens on the market are built using smd technology a trend that is now extending to the outdoor market an smd pixel consists of red green and blue diodes mounted on a chipset which is then mounted on the driver pc board the individual diodes are smaller than a pinhead and are set very close together the difference is that minimum viewing distance is reduced by two five from the discrete diode screen with the same resolution indoor use generally requires a screen that is based on smd technolog |
y and has a minimum brightness of six zero zero candelas per square metre unofficially called nits this will usually be more than sufficient for corporate and retail applications but under high ambient brightness conditions higher brightness may be required for visibility fashion and auto shows are two examples of high brightness stage lighting that may require higher led brightness conversely when a screen may appear in a shot on a television show the requirement will often be for lower brightness levels with lower color temperatures common displays have a white point of six five zero zero nine zero zero zero k which is much bluer than the common lighting on a television production set for outdoor use at least two zero zero zero nits are required for most situations whereas higher brightness types of up to five zero zero zero nits cope even better with direct sunlight on the screen until recently only discrete diode screens could achieve that brightness level the brightness of led panels can be reduced from |
the designed maximum if required suitable locations for large display panels are identified by factors such as sight lines local authority planning requirements if the installation is to become semi permanent vehicular access trucks carrying the screen truck mounted screens or cranes cable runs for power and video accounting for both distance and health and safety requirements power suitability of the ground for the location of the screen check to make sure there are no pipes shallow drains caves or tunnels that may not be able to support heavy loads and overhead obstructions multi touch sensing since leds share some basic physical properties with photodiodes which also use p n junctions with bandgap energies in the visible light wavelengths they can also be used for photodetection these properties have been known for some time but more recently so called bidirectional led matrices have been proposed as a method of touch sensing in two zero zero three dietz yerazunis and leigh published a paper describing the |
use of leds as cheap sensor devices in this usage the led matrix quickly switches itself on and off when the leds are on they shine light onto a user s fingers or a stylus when the leds switch off again they function as photodiodes to detect reflected light from the fingers or stylus the voltage thus induced in the reverse biased leds can then be read by a microprocessor which interprets the voltage peaks and then uses them elsewhere the website of jeff han features a video demonstrating one such implementation of an led matrix multi touch sensor references salisbury david f quantum dots that produce white light could be the light bulb s successor exploration the online research journal of vanderbilt university october two zero two zero zero five more details regarding the use of quantum dots as a phosophor for white leds see also laser diode a coherent solid state light source nixie tube resources chart showing voltage drops of various colors light resource center spe method which results in eight zero l w |
vs six zero l w for fluorescent lighting light resource center information on developing a standard lifetime measurement for leds external links how leds work from howstuffworks com the led faq pages a compilation of questions and answers about light emitting diodes and infrared emitters led center information for hobbyists and articles on solid state lighting display technology optical diodes lighting luxembourgish or luxembourgian french luxembourgeois german luxemburgisch luxembourgish l tzebuergesch is a west germanic language spoken in luxembourg it was adopted as an official language in one nine eight four it is also spoken in small parts of belgium france and germany as well as by a few of the descendants of luxembourg immigrants in the united states and emigrants to transylvania romania siebenb rgen there are about three zero zero zero zero zero people who speak luxembourgish worldwide luxembourgish belongs to the central german group of high germanic languages luxembourgish has borrowed many french w |
ords for example the name for a bus driver is buschauffeur also dutch which would be busfahrer in german and chauffeur de bus in french it is relatively easy for german speakers to understand luxembourgish but more difficult to speak it properly because of the french influence on the other hand written luxembourgish often shows a marked influence from high german in syntax and idiom and often strikes the fluent reader of german as essentially pure german disguised as a foreign language it seems that the idea of how to properly write in luxembourgish is still heavily dependent on normative german grammar in this respect luxembourgish does come nearer to being merely a german dialect than does dutch which is also obviously related to german but markedly more divergent from that language in syntax word order and idiom some words are different from high german but have equivalents in german dialects an example would be the word potato which is gromper in luxembourgish but pomme de terre in french and kartoffel in |
high german other words are exclusive to luxembourgish for example the word for match which is fixfeier standard german is called d itsch or sometimes preis sch prussian which has slightly xenophobic undertones in luxembourg its most common uses are in luxembourg s newspapers and in primary school the main administrative language in luxembourg is french luxemburgish is used by all the radio stations in luxembourg and is spoken by most of its citzens the alphabet of luxembourgish consists of the two six latin letters plus three modified letters and the laf l tzebuergesch als friemsprooch luxembourgish as a foreign language is a set of four language proficiency certifications for luxembourgish and follows the alte framework of language examination standards the tests are administered by the centre de langues luxembourg which is a member of the alte some phrases jo yes neen no vill icht maybe moien hello ddi goodbye merci thank you firwat why ech weess n t i don t know watgelift or ntsch llegt excuse me metzles |
chjong butcher s son a major suspect in the infamous one nine eight five bombings schw tzt dier d itsch frans isch englesch do you speak german french english politeschen anstand political decency sou so fr i free heem home ech i a and m in my iesel donkey mat with kand kid child wee way external links rtl lu radio t l l tzebuerg luxembourgish english dictionary introduction to the luxembourgish orthography schanen f pdf luxemburgische orthographie memorial one nine nine nine eng kleng h llef fir l tzebuergesch ze schreiwen luxdico universal deklaratioun vun de m nscherechter gefahr oder chance f r das luxemburgische centre for luxembourg studies university of sheffield uk the centre de langues luxembourg page at the alte site high germanic languages languages of belgium languages of france languages of luxembourg guttural r lev vladimirovich kuleshov in tambov two nine march one nine seven zero in moscow was a russian filmmaker known for his work on film editing and the impact it has on the viewers the kules |
hov experiment showed the ability of viewers to associate emotions with images this and other techniques were explored by kuleshov in his work in marxist film theory filmography one nine one eight the project of engineer prite one nine two zero on the red front one nine two four the extraordinary adventures of mr west in the land of the bolsheviks one nine two five the death ray one nine two seven by the law one nine two seven your acquaintance one nine two nine the merry canary one nine two nine two bul di two one nine three one forty hearts one nine three two the horizon one nine three three the great consoler one nine three four theft of sight one nine four zero the siberians one nine four one incident on a volcano one nine four two youthful partisans kartashova the teacher one nine four four we from the urals honours people s artist of the rsfsr one nine six nine order of lenin order of the red banner of labour see also film history of russia one eight nine nine births one nine seven zero deaths russian a |
nd soviet film directors people s artists of the ussr language interpretation may be roughly understood as the restating in speech language spoken uttered out loud in another language interpreters typically distinguish interpretation from translation which deals with the written word interpretations are uttered translations are written down interpretation may be either consecutive or simultaneous with consecutive interpretation the speaker frequently pauses to allow the interpreter to translate what was just spoken with simultaneous interpretation the interpreter using headphones to listen to the speaker voices the translation into a microphone immediately just in time dynamic recompilation of a programming language such as that used in an emulator parallels this process see translation of programming languages linguistics a legacy system is an existing computer system or application program which continues to be used because the user typically an organization does not want to replace or redesign it many peop |
le use this term to refer to antiquated systems legacy systems are considered to be potentially problematic by many software engineers for example see bisbal et al one nine nine nine for several reasons legacy systems often run on obsolete and usually slow hardware and sometimes spare parts for such computers become increasingly hard to obtain these systems are often hard to maintain improve and expand because there is a general lack of understanding of the system the designers of the system may have left the organization so there is no one left to explain how it works such a lack of understanding can be exacerbated by inadequate documentation or manuals getting lost over the years integration with newer systems may also be difficult because new software may use completely different technologies despite these problems organizations can have compelling reasons for keeping a legacy system such as the costs of redesigning the system are prohibitive because it is large monolithic and or complex the system require |
s close to one zero zero availability so it cannot be taken out of service and the cost of designing a new system with a similar availability level are high the way the system works is not well understood such a situation can occur when the designers of the system have left the organization and the system has either not been fully documented or such documentation has been lost over the years the user expects that the system can easily be replaced when this becomes necessary the system works satisfactorily and the owner sees no reason for changing it if legacy software only runs on antiquated hardware the cost of maintaining the system may eventually outweigh the cost of replacing both the software and hardware unless some form of emulation or backward compatibility allows the software to run on new hardware however many of these systems do still meet the basic needs of the organization the systems to handle customers accounts in banks are one example therefore the organization cannot afford to stop them and y |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.