Light flicker is a phenomena of quick repeated changes in the brightness of the light. Flicker is probably most known from computer monitors, especially old ones, which were blinking and flickering, causing many people annoyance and even headaches. Flickering lights can also cause many different negative health effects. Flicker is often caused by AC (alternating current) electrical system where the electricity is turning on and off 100 or 120 times a second (50 Hz or 60 Hz system). This constant on and off in the electric system causes also the lights to turn on and off as the electricity turns on and off. Basically all electricity that is produced by electrical companies is provided in alternating current.
Figure 1. Alternating current (AC) waveform.
As seen in the picture above, in one cycle of alternating current, the light turns on and off two times. This means that in 50 Hz electrical system (used for example in North America) the light turns on and off 100 times a second and in 60 Hz system (used for example in Europe) the light turns on and off 120 times. However, different lighting technologies produce flicker in different frequencies so many lights flicker much more faster than just 100 / 120 times a second.
All lights, that are connected to AC electric grid, flicker more or less. However, there are many aspects in flicker that vary between different types of lights and affect the severity and the detectibility of the flicker.
The different aspects affecting the flicker and the severity of it are:
The frequency of the flicker (Hz)
The modulation of the flicker (%)
The ambient light (natural light) levels in the space
The frequency is the number of times the light turns on and off in a second. It is measured in Herz (Hz). The lowest frequency flicker (50 - 120 Hz) is produced by incandescent, halogen, most LED and old fluorescent lights with magnetic ballasts. Some LEDs and new fluorescent lights with electronic ballasts flicker in much more higher frequency; fluorescent lights can flicker in up to 40,000 Hz frequency whereas LEDs flicker around 100 - 400 Hz.
The modulation is the change in the intensity of the light as the light turns on and off.
In different bulbs the change of the intensity that follows the voltage drops vary. This is due to the differencies in the way the bulbs themselves work.
Incandescent lights work by heating a filament that lights up as the filament's temperature rises. The filament in the bulb, however, reacts fairly slowly. This means that, as it takes a little bit of time for the filament to reach full light output, it also takes time for the filament to cool down completely. As the electricity turns on and off 50 or 60 times in a second, the filament doesn't have enough time to cool down so the drop in the light output is very small, only about 5 - 13 %.
Halogen lights work very much the same way as incandescent lights and thus produce flicker of only about 10%.
In LEDs there's a lot of different technologies and drivers that are used so the flicker modulation varies a lot between different LEDs. Basically, the flicker modulation-% of LEDs can vary anywhere from 0 to 100. Old and cheap LEDs can have flicker close to 100% but many modern LEDs have drivers that causes flicker of only 0 - 20 %.
Old fluorescent lights that used magnetic ballasts have very strong flicker, as they flicker in 50 - 60 Hz and have also high flicker modulation. Modern fluorescent lights use high frequency electronic ballasts (20,000 Hz or higher) which have been shown to cause 50 % less negative health effects.
Figure 2. Flickering of different lamp bulbs. The values are not absolute and can differ between different light bulbs.
Figure 3. Flickering frequencies and modulations.
Ambient light refers to the amount of natural light in the room. The more there is natural non-flickering light in the space, the less effect the flicker of the lighting has. It has also been noted that people on higher floors tend to have fewer headaches than people in lower floors, probably due to higher levels of natural light in the space.
Other causes of flicker
Modern dimmer switches that use phase-cut controls cause flicker. This is due to the phase-cut system where the electricity is turned on and off repeatedly which causes the light to be on less time and is perceived by the human eye as a dimmer light. In reality, the light is just made to flicker (in a lower frequency). Dimmable and smart LEDs also flicker if the driver uses pulse-width modulation (PWM) to reduce the average light output.
The health Effects of Flicker
The negative health effects that can occur due to flicker vary from small annoyances to epilectic seizures. These different health effects can occur even if the eyes are closed.
The flicker can be annoying and cause irritation when the frequency is so low that it can be detectable by eye. Flicker cannot usually be seen when it's above the critical flicker fusion frequency (CFF), which sets around the frequencies between 60 and 90 Hz, depending on the individual.
The flicker can cause eyestrain and discomfort. It can increase the incidence of headaches by 50% with nausea and visual disturbances and also trigger migranes in some individuals.
The biggest health issues come with flicker at frequencies between 3 and 70 Hz. Flicker at these frequencies have been shown to cause epilectic seizures in small percentage of people, the biggest risk produced by frequencies in the range of 15 Hz to 20 Hz. The severity also depends on the area of retina exposed, and the frequency and modulation of the flicker. Luckily, most lights, except old fluorescent lights with magnetic ballasts, flicker in frequencies higher than that.
Flicker can also cause blurryness and light trails in the vision. This can be noticed often in car (LED) taillights at dark. When you look directly to the taillights, the lights appear normal, but when you are moving your eyes rapidly (saccade) and glancing at other objects, a blurry trail of lights can appear. This phenomena is called a phantom array.
Fluorescent lighting with a flicker of 100Hz has been observed to affect the plasma corticosterone levels in birds and to affect the choice of their mating partners.
Flicker has also been shown to disrupt the natural eye movements across text and to impair visual performance in visual tasks.
Low frequency flicker can cause a stroboscopic effect that is associated with apparent slowing or stoppage of rotating machinery. This can lead to dangerous situations when operating heavy machinery.
Flicker has also been showed to increase repetitive behavior in autistic individuals.
Below you can see an illustrative chart on which flicker frequencies and modulations are known to cause health effects:
Figure 4. The health effects of different flicker frequencies and modulations.
How to know if your lighting flickers?
An easy way to test your lighting for flicker is to use your phone camera. Put the camera on, point it at a lamp and look at the phone screen; flicker will cause dark fringes to appear around the lamp. The frequency of the fringes is related to the flicker frequency and the frame rate of the camera. The contrast of the fringes can also give a clue on the flicker modulation: the bigger the contrast between the fringes, the higher the flicker modulation. If fringes appear, the modulation is likely higher than 20%.
Another way to spot flicker with your phone is to record a video pointing at a light and then using a video editor to slow the video down. The possible flicker can be seen as rapid blinking in the slowed down video. However, some cameras come with automatic flicker reducing technology, which will automatically correct the flicker, so before using your camera for this, check your camera instructions or your manufacturer if the camera uses such a technology.
The most accurate result you get when you hire a building biologist or other lighting professional to measure the flicker. There's also a lot of different flicker meters on the market, prices ranging from 50€ to thousands of euros. As the cheaper meters may not be the most accurate compared to expensive professional models, they can still give you more accurate results than your camera.
Some lower frequency flicker can also be detected with bare eyes. Focus your glance slightly to the side of the light. If the light flickers in low frequency you might see the light blinking rapidly. This can also be seen in TV:s, monitors and other screens.
How to avoid flicker and mitigate its negative effects?
All lighting should be designed so that as much natural light as possible is used. Even though glazing blocks certain frequencies of light, natural light is usually still superior to any artificial light sources. Natural light will also mitigate the negative health effects of possible flicker produced by the lighting.
Use lights that have higher flicker frequency and/or lower flicker modulation. These kind of lights include incandescent, halogen and some LED lights. As incandescent and halogen lights have naturally fairly high flicker frequency and low flicker modulation, LED lights can differ from catastrophic headache-causing lights to almost perfect zero-flicker lights, so always check the flicker levels from the package/website of the light or ask directly from the manufacturer before buying.
Take breaks from artificial light sources and screens and relax your eyes outdoors in natural light. This will calm down your nervous system in many ways and mitigate the negative health effects of flicker.
Use direct current (DC) lighting. DC electricity doesn't fluctuate as alternating current (AC) does, meaning that it provides a steady flow of electricity that doesn't turn on and off multiple times a second. This provides a steady, non-flickering light. DC lighting systems usually operate in low-voltage (12-24V) and are powered by solar panels, windmills or other renewable energy sources.
So what kind of lights do you use? Do you notice negative effects when spending time under flickering light? Is there something that the post failed to answer to? Leave a comment below or contact us here!
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Mwangaza wa mwangaza ni jambo linalotokana na mabadiliko ya haraka ya mwangaza wa mwanga. Flickering ni kawaida katika kompyuta, hasa zile za zamani, ambazo zilikuwa zikipeperusha na kusababisha watu wengi kuchanganyikiwa na hata maumivu ya kichwa. Taa zinazong'aa-ng'aa pia zaweza kusababisha madhara mengi mabaya kwa afya. Flicker ni kawaida kusababishwa na AC (mzunguko wa kubadilishana) mfumo wa umeme ambapo umeme ni kugeuka juu na mbali mara 100 au 120 kwa sekunde (mfumo wa 50 Hz au 60 Hz). Mzunguko huu wa mara kwa mara katika mfumo wa umeme husababisha pia taa kuwasha na kuzima wakati umeme unawasha na kuzima. Kimsingi umeme wote unaozalishwa na makampuni ya umeme hutolewa kwa umeme wa kubadilishana. Picha ya 1. Mzunguko wa sasa (AC) waveform. Kama inavyoonekana katika picha iliyo juu, katika mzunguko mmoja wa umeme wa kubadilishana, taa huwaka na kuzimwa mara mbili. Hii inamaanisha kwamba katika mfumo wa umeme wa 50 Hz (kutumiwa kwa mfano katika Amerika ya Kaskazini) taa inazunguka na kuzima mara 100 kwa sekunde na katika mfumo wa 60 Hz (kutumiwa kwa mfano katika Ulaya) taa inazunguka na kuzima mara 120. Hata hivyo, teknolojia tofauti za taa hutokeza mwangaza wa mara kwa mara kwa masafa tofauti, hivyo taa nyingi huwaka kwa kasi zaidi kuliko mara 100 kwa sekunde. Taa zote, ambazo zimeunganishwa na mtandao wa umeme wa AC, huangaza zaidi au chini. Hata hivyo, kuna mambo mengi katika flicker kwamba kutofautiana kati ya aina tofauti ya taa na kuathiri ukali na detectability ya flicker. Vipengele tofauti vinavyoathiri flicker na ukali wake ni: Mzunguko wa flicker (Hz), Modulation ya flicker (%) na viwango vya mwanga wa mazingira (mwanga wa asili) katika nafasi. Ni kipimo katika Herz (Hz). Mwangaza wa chini zaidi wa frequency (50-120 Hz) hutengenezwa na incandescent, halogen, LED na taa za zamani za fluorescent na ballasts za sumaku. LEDs na taa za fluorescent zenye umeme na umeme wa umeme huwaka kwa masafa ya juu zaidi, na taa za fluorescent zinaweza kuwaka kwa masafa ya juu ya 40,000 Hz, wakati LEDs huwaka karibu na 100-400 Hz. Modulation ni mabadiliko katika nguvu ya mwanga kama mwanga inageuka juu na nje. Katika balbu tofauti mabadiliko ya nguvu ambayo ifuatavyo voltage matone kutofautiana. Hii ni kwa sababu ya tofauti katika njia balbu wenyewe kazi. Taa za incandescent hufanya kazi kwa kupasha joto nyuzi ambayo huwaka wakati joto la nyuzi inapopanda. Hata hivyo, nyuzi zilizo ndani ya balbu hiyo huitikia polepole sana. Hii inamaanisha kwamba, kama inachukua muda kidogo kwa filament kufikia pato kamili la mwanga, pia inachukua muda kwa filament baridi kabisa. Kama umeme inageuka juu na mbali mara 50 au 60 katika sekunde, filament haina muda wa kutosha baridi chini, hivyo kushuka katika pato mwanga ni ndogo sana, tu kuhusu 5-13%. Halogen taa ni moja ya taa ya incandescent na kwa hivyo hutoa mwangaza wa 10% tu. Kwa sababu ya teknolojia tofauti za LED, moduli ya flicker inatofautiana sana. Kwa mfano, kiwango cha modulation ya flicker ya LED inaweza kuwa 0 hadi 100. LEDs za zamani na za bei nafuu zinaweza kuwa na flicker karibu na 100% lakini LEDs nyingi za kisasa zina madereva ambayo husababisha flicker ya 0 - 20% tu. Taa za zamani za fluorescent ambazo zilitumia ballasts za sumaku zina mwangaza mkali sana, kwani zina mwangaza wa 50 - 60 Hz na pia zina moduli ya mwangaza wa juu. Taa za fluorescent za kisasa hutumia ballasts za elektroniki za masafa ya juu (20,000 Hz au zaidi) ambazo zimeonyeshwa kusababisha athari mbaya za afya kwa asilimia 50. Picha ya 2. Mwangaza wa balbu tofauti za taa. Thamani si kamili na inaweza kutofautiana kati ya balbu tofauti za taa. Picha ya 3. Frequency flickering na modulations. Nuru ya mazingira inahusu kiasi cha nuru ya asili katika chumba. Kadiri mwanga wa asili unavyoongezeka katika nafasi hiyo, ndivyo mwangaza unavyozidi kupungua. Watu walio kwenye ghorofa za juu huwa na maumivu ya kichwa kidogo kuliko wale walio kwenye ghorofa za chini, labda kwa sababu ya viwango vya juu vya mwanga wa asili katika nafasi. Sababu nyingine za flicker Switches za kisasa za dimmer ambazo hutumia udhibiti wa kukata awamu husababisha flicker. Hii ni kwa sababu ya mfumo wa kupasuka awamu ambapo umeme huwasilishwa na kuzimwa mara kwa mara, na kusababisha mwanga kuwa chini ya muda na ni kuonekana na jicho la binadamu kama mwanga wa giza. Kwa kweli, nuru hiyo huangaza tu (kwa mzunguko wa chini). LEDs dimmable na smart pia flicker kama dereva anatumia pulse-upana modulation (PWM) kupunguza wastani mwanga pato. Madhara ya afya ya Flicker: Madhara mabaya ya afya ambayo yanaweza kutokea kutokana na Flicker hutofautiana kutoka kwa usumbufu mdogo hadi mshtuko wa kifafa. Athari hizi tofauti za afya zaweza kutokea hata ikiwa macho yamefungwa. Mngurumo huo waweza kusumbua na kusababisha uchungu wakati mzunguko wake unapokuwa wa chini sana hivi kwamba unaweza kugunduliwa kwa jicho. Flicker ni kawaida ya juu ya kiwango cha muhimu cha fusion (CFF), ambayo inaweka karibu na masafa kati ya 60 na 90 Hz. Mwangaza huo waweza kusababisha uchovu wa macho na usumbufu. Inaweza kuongeza kiwango cha maumivu ya kichwa kwa 50% na maumivu ya kichwa na matatizo ya kuona na pia kusababisha migraines kwa baadhi ya watu. Kwa sababu ya hali ya afya, mlipuko wa sauti huanza wakati wa mzunguko wa 3 hadi 70 Hz. Flickering katika masafa haya imeonyeshwa kusababisha epileptic mashambulizi katika asilimia ndogo ya watu, hatari kubwa zinazozalishwa na masafa katika mbalimbali ya 15 Hz hadi 20 Hz. Ukali pia hutegemea eneo la retina linalofunuliwa, na mzunguko na mpangilio wa kuangaza. Kwa bahati nzuri, taa nyingi, isipokuwa taa za zamani za fluorescent zenye vifaa vya sumaku, huangaza kwa mzunguko wa juu kuliko huo. Mwangaza wa macho pia waweza kusababisha kutoeleweka na alama za nuru katika maono. Hii inaweza kuonekana mara nyingi katika taa za nyuma za gari (LED) wakati wa giza. Wakati unapoangalia moja kwa moja taa za nyuma, taa zinaonekana kawaida, lakini wakati unapoendesha macho yako haraka (saccade) na kutazama vitu vingine, mfuatano wa taa zisizo wazi unaweza kuonekana. Jambo hilo huitwa mfululizo wa viumbe wasioonekana. Mwanga wa fluorescent na flicker ya 100Hz umeonekana kuathiri viwango vya plasma ya corticosterone katika ndege na kuathiri uchaguzi wa washirika wao wa kuoa. Flicker pia imeonyeshwa kuvuruga harakati za asili za jicho kwenye maandishi na kudhoofisha utendaji wa kuona katika kazi za kuona. Flicker ya masafa ya chini inaweza kusababisha athari ya stroboscopic ambayo inahusishwa na kupunguza kasi au kusimamishwa kwa mashine zinazozunguka. Hilo laweza kusababisha hali hatari wakati wa kuendesha mashine nzito. Flicker pia imeonyeshwa kuongeza tabia ya kurudia-rudia katika watu wenye ugonjwa wa akili. Chati ya chini inaonyesha jinsi vipimo vya mlipuko vinavyoweza kuathiri afya. Athari za afya za masafa tofauti ya kuangaza na modulations. Jinsi ya kujua kama taa yako flickers? Njia rahisi ya kupima mwangaza wako kwa ajili ya flicker ni kutumia kamera ya simu yako. Weka kamera juu, lengo ni juu ya taa na kuangalia kwenye skrini ya simu; flicker itasababisha fringes giza kuonekana karibu taa. Mzunguko wa fringes ni kuhusiana na mzunguko flicker na frame kasi ya kamera. Tofauti ya fringes pia inaweza kutoa clue juu ya flicker modulation: kubwa tofauti kati ya fringes, juu ya flicker modulation. Ikiwa kuna mipaka, moduli ya kawaida ya juu ya 20%. Njia nyingine ya kuona flicker na simu yako ni kurekodi video kuonyesha mwanga na kisha kutumia mhariri video kupunguza kasi ya video. Flicker uwezekano inaweza kuonekana kama blinking haraka katika video kupunguza kasi. Kamera zingine zina teknolojia ya kupunguza flicker, ambayo itakusaidia kurekebisha flicker, kwa hivyo kabla ya kutumia kamera yako kwa hii, angalia maagizo ya kamera yako au mtengenezaji wako ikiwa kamera inatumia teknolojia kama hiyo. Kwa mfano, unaweza kupata matokeo sahihi zaidi kwa kuajiri mtaalamu wa biolojia wa ujenzi au mtaalamu mwingine wa taa kupima mwangaza. Kuna aina nyingi za vipima-moto kwenye soko, na bei zao zinaanzia € 50 hadi € 1000. Kwa kuwa mita za bei nafuu zinaweza kuwa sio sahihi zaidi ikilinganishwa na mifano ya kitaalamu ya bei ghali, bado zinaweza kukupa matokeo sahihi zaidi kuliko kamera yako. Baadhi ya miale ya masafa ya chini yaweza pia kugunduliwa kwa macho ya kawaida. Zingatia macho yako kidogo upande wa nuru. Kama mwanga flickers katika mzunguko wa chini unaweza kuona mwanga blinking haraka. Hii pia inaweza kuonekana katika TV:s, monitors na skrini nyingine. Jinsi ya kuepuka flicker na kupunguza athari zake hasi? Taa zote zinapaswa kubuniwa ili kutumia nuru nyingi iwezekanavyo. Ingawa kioo huzuia mwangaza wa masafa fulani, kwa kawaida mwanga wa asili bado ni bora kuliko mwangaza wa bandia. Nuru ya asili pia itapunguza athari mbaya kwa afya ya mwangaza unaoweza kutokezwa na taa. Tumia taa ambazo zina mzunguko wa juu wa kuangaza na / au modulation ya chini ya kuangaza. Aina hizi za taa ni pamoja na incandescent, halogen na baadhi ya taa LED. Kwa kuwa taa za halogen na incandescent zina frequency ya juu ya kuangaza na modulation ya chini ya kuangaza, taa za LED zinaweza kutofautiana kutoka kwa taa za kutisha za kichwa hadi taa za zero-flicker, kwa hivyo daima angalia viwango vya kuangaza kutoka kwa kifurushi au wavuti ya taa au uliza moja kwa moja kutoka kwa mtengenezaji kabla ya kununua. Punguza kutumia taa za bandia na kutumia vifaa vya kuangazia macho, na ufurahie kuona mwangaza wa asili. Hii itatuliza mfumo wako wa neva kwa njia nyingi na kupunguza athari mbaya za afya za kutikisa. Tumia taa ya mkondo wa moja kwa moja (DC). Umeme wa DC haubadiliki kama umeme wa mzunguko (AC), ambayo inamaanisha kwamba hutoa mtiririko wa umeme wa kudumu ambao hauzunguki mara nyingi kwa sekunde. Hilo hutoa nuru thabiti, isiyo na kung'aa-ng'aa. Mifumo ya taa ya DC kawaida inafanya kazi katika voltage ya chini (12-24V) na inaendeshwa na paneli za jua, mashine za upepo au vyanzo vingine vya nishati mbadala. Kwa hiyo ni aina gani ya taa unazotumia? Je, unaona athari mbaya za kutumia wakati chini ya nuru inayong'aa? Je, kuna jambo fulani ambalo chapisho hilo lilishindwa kujibu? Acha maoni hapa chini au wasiliana nasi hapa! Unahitaji msaada wa kubuni taa zako? Twaweza Kusaidia!