RELATED U.S. APPLICATION DATA 
       [0001]    This application is a continuation-in-part of application Ser. No.11/867,876, filed Oct. 5, 2007, published as Pub. No. US 2008/0025013 A1 on Jan. 31, 2008. The disclosure of the previously referenced U.S. patent application is hereby incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to apparatus that produce visible light. It is particularly directed to an electrically powered light source including a light emitting diode (LED) having variable chromaticity, which is adapted for use in a dental operatory. 
       BACKGROUND 
       [0003]    It has been known for an extended period of time that electricity may be harnessed to create visible light. Incandescent light emitting elements powered by electricity have been used for substantially the same period of time. However, such incandescent lights suffer from an inefficient conversion of electricity to visible light. The inefficient conversion process causes production of a considerable amount of heat, and emission of a significant amount of radiation in, or near, the infrared spectrum. Such infrared emission inherently casts a heat load onto a target along with an illuminating beam. The heat generated by incandescent lighting may sometimes place an undesirable burden on environmental control systems, such as cooling systems used in dwellings. Both the inefficient conversion process, and removing the undesired heat load from the area near the light, lead to a correspondingly larger than necessary electric utility bill. Furthermore, in use on an operatory to illuminate an operating site on a patient, the infrared emissions may undesirably dry illuminated tissue, or may produce a feeling of discomfort in the patient. 
         [0004]    Alternative light emitting elements include fluorescent light bulbs. Such fluorescent bulbs advantageously produce a reduced heat load compared to incandescent bulbs. However, fluorescent bulbs tend to be bulky, and generally produce light of a less desirable color and intensity for many applications. Furthermore, certain electrical components required in the electric circuit powering the fluorescent bulbs, such as the ballast, tend to produce an undesirable amount of noise. In use in an operatory, it is generally desired to reduce the bulk of a lamp fixture, to reduce its intrusion into the operating arena, and to facilitate ease of manipulation of the lamp fixture. 
         [0005]    The majority of currently marketed dental exam lights use incandescent bulbs as light sources. These incandescent dental exam lights possess a number of disadvantages, such as: emission of infra-red (IR) radiation that must be removed with filters or so-called ‘cold-mirrors’ to prevent excessive warming of the patient and user; relatively short bulb life-time; inability of the user to adjust light color temperature and chromaticity of light; color temperature becoming lower and the light becoming “warmer” (i.e., shifting from white to orange/red), when light intensity is reduced (dimmed); and production of significant ultraviolet (UV) and blue light which causes undesired and uncontrolled curing of dental composites and adhesives. 
         [0006]    It would be an improvement to provide a more energy-efficient lamp fixture capable of producing a reduced heat load, and casting illumination having a desirable color and intensity that can be adjusted to obtain desirable spectra in a single lamp. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    A particular embodiment of the invention includes a dental operatory lamp used to illuminate an operating area which comprises a thermally conductive housing having a front directed toward the operating area and a rear away from the operating area; a generally elliptical reflector located on the rear of the thermally conductive housing; at least one heat pipe; a plurality of color LEDs projecting light toward the elliptical reflector, the plurality of LEDs being in thermal contact with the at least one heat pipe; and an optical light guide for combining light from said LEDs. 
         [0008]    Another embodiment of the invention is drawn to a dental operatory lamp used to illuminate an operating area that includes: a plurality of color LEDs; an optical light guide for combining light from said LEDs; and at least two user selectable light spectra, one of said spectra providing white light with color temperature in the range 4000° K-6000° K and one spectra having reduced output in the wavelength range 400-500 nm. 
         [0009]    Yet another embodiment of the invention relates to a dental operatory lamp used to illuminate an operating area that includes: a housing having a front directed toward the operating area and a rear away from the operating area; a reflector module located at the rear of the housing; a plurality of color light emitting diodes (LEDs) on the reflector module; and an optical light guide configured to direct the light from the color LEDs toward the front of the lamp in a pattern that focuses white light from the lamp to a central area of illumination of high intensity, with significantly reduced intensity illumination outside the central area. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, this invention can be more readily understood and appreciated by one of ordinary skill in the art from the following description of the invention when read in conjunction with the accompanying drawings in which: 
           [0011]      FIG. 1  is a perspective view of a dental operatory lamp according to a particular embodiment of the invention; 
           [0012]      FIG. 2  illustrates a component arrangement and a representative LED light output in a dental operatory lamp; 
           [0013]      FIG. 3  illustrates an embodiment of an optical light guide in a dental operatory lamp of the invention; 
           [0014]      FIG. 4  illustrates a representative illumination pattern for the dental operatory lamp according to one embodiment of the invention; and 
           [0015]      FIG. 5  is a cross-section of a light module having a reflective interior reflective surface according to a particular embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some representative embodiments. Similarly, other embodiments of the invention may be devised that do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. 
         [0017]      FIG. 1  illustrates a perspective view of a current embodiment of the invention, generally indicated at  100 , of a light source structure constructed according to principles of the invention. Light source structure  100  may generally be characterized as a lamp. Lamp  100  is powered by electricity, and functions to provide illumination to a work area disposed a distance from the lamp front, generally indicated at  102 . Desirably, the work area illuminated by lamp  100  is shadow-free, and appears relatively uniform in illumination color and intensity. For most applications, the illuminated target work area is considered to have an approximately flat footprint and a depth normal to that footprint. That is, the illuminated region is generally structured to encompass a volume disposed proximate the footprint. 
         [0018]    Illustrated lamp  100  can include an attachment structure (not shown) operable to connect lamp  100  to suspension structure in the work area. Such an attachment structure is typically attached at a back  106  of lamp  100 , although any convenient arrangement is operable. Typical suspension structure in a dental operatory permits a user to orient the lamp in space operably to aim the light output of lamp  100  at the desired target area. Certain embodiments of the invention provide a lamp having reduced weight and/or intrusive volume compared to commercially available lamps. Such reduced weight lamps permit a corresponding reduction in mass of the lamp suspension arrangement, thereby increasing ease of manipulation of the lamp to orient its output toward a target. 
         [0019]    In use in an environment such as a dental operatory, a front shield (not shown) can be provided as a protective cover to block migration of dust and contaminated aerosols into the lamp interior. A front surface of such a shield may be structured to provide an easily cleanable surface, whereby to maintain sterility of the operatory area. In certain embodiments, the shield may incorporate one or more lenses to focus, or otherwise modify, the light output of lamp  100 . Whether or not a focusing lens is provided, a shield made from Lexan®, or other similar optically useful and formable material, can be provided to completely encase the front of a dental lamp to resist contamination of, and to facilitate cleaning of, the lamp. The shield may be injection molded and may include focusing lenses. Desirably, the shield, or a portion of lamp housing  114 , can be hinged, or otherwise openable by a user, to provide access to the interior of lamp  100  for maintenance or replacement of a light generating element. 
         [0020]    With reference to  FIG. 2 , an LED  118  emits light indicated by a plurality of rays  120 . An operable LED can include a 3 watt LED, such as that sold by Lumileds Lighting US, LLC under the Brand name Luxeon, part number LXHL-LW3C. 
         [0021]    Typically, a reflective element, generally indicated at  116 , is provided to direct the LED&#39;s light output toward a target. In a particular embodiment, reflective element  116  can be a concave aspheric reflector which collects the light emanating from the mixing rod and focuses it onto the plane of the patient&#39;s face (“image plane”). The reflector surface contour can be a simple 2D ellipse section revolved around the central optical axis. A focusing lens  122  may be included in an arrangement effective to collimate rays  120  and further direct them to an illuminated area indicated at  126 . In certain embodiments of the invention, area  126  corresponds to the target footprint of the lamp  100 . In such case, it is desired that the illumination emitted from each module  108  is substantially uniform over area  126 . Certain rays  128  may be emitted in a direction other than desired for impingement on area  126 . Such rays  128  are characterized as stray light. As indicated by the illustrated collection of rays  120 , area  126  sometimes has a higher intensity of illumination at its center, and may fade to a decreased intensity near its perimeter, as discussed with reference to  FIG. 4 . In another embodiment, the LED  118 , mirror  122 , and all associated optics are arranged in harmony to produce a substantially uniform intensity over its illuminated footprint at a selected focal distance. 
         [0022]    LEDs  118  are typically mounted onto a bracket  112  associated with lamp housing  114 . Desirably, the bracket  112  assembly is structured to provide simple and rapid installation and removal of LED  118 , and includes connection structure for the electricity supplied to the LED and may further include a metal core circuit board  130 . It is further desirable for bracket  112  to be formed from a material capable of conducting heat or, alternatively, to be associated with heat conducting pipes  134 . Advantageously, bracket  112  and/or heat pipe  134 , together with housing  132  may be structured and arranged to dissipate any heat generated by LED  118  in a direction away from the front  102  of the lamp  100 . In some embodiments, use of heat pipe  134  is particularly desirable since a large heat sink positioned directly behind the metal core board with the heat-generating LEDs may significantly obscure the light focusing onto the image plane. Through use of a heat pipe  134  or equivalent structure, the heat can be conducted away via heat pipes  134  to a heat sink housing positioned on the back of the reflector where it does not obscure the light. An exemplary heat sink housing can include heat sink fins  142 . The heat sink fins  142  can be integral with the outer housing of the lamp and constructed of any heat conducting or dissipating material, such as cast aluminum. To increase cooling, a fan can be used to draw air into a gap  144  between the reflector and the heat sink housing. To maximize surface area and thus cooling, the inside of the heat sink/housing includes fins or ribs  142  that form air channels therebetween. 
         [0023]    In order to produce homogenous light from multiple LEDs of different colors (for example, red, greed, blue, and amber), the light emitting from each individual LED should sufficiently overlap the light from all the other LEDs. In a particular embodiment, a clear rectangular rod made of acrylic serves this function and is referred to herein as an optical light guide or a light mixing rod  136 . It is understood that the mixing rod  136  can be made out of any suitable material capable of acting as an optical light guide. The performance of the mixing rod  136  can be significantly enhanced with the addition of periodic features or “ripples”  150  on the outside walls of the mixing rod, as shown in  FIGS. 1 and 3 . As illustrated in  FIG. 3 , light from multiple LEDs of different colors  154  (e.g., red, green, blue, and/or amber) are introduced through one end of the mixing rod  136  and emanate from another end of the mixing rod  136  as a composite white light  158 . One particular embodiment combines the light from four different colored LEDs (red, blue, green, and amber) to produce white light. By varying the ratios of the different colors, the character of the white light can be changed. Specifically, white light with coordinated color temperatures (CCTs) of 4200° K and 5000° K can be produced while maintaining a high color rendering index (CRI), typically in excess of 75. Blue light typically occurs in the peak wavelength range of 445 nm to 465 nm. Green light typically occurs in the dominant wavelength range of 520 nm to 550 nm, amber light in the range of 584 nm to 597 nm, and red light in the range of 613 nm to 645 nm. A rod support 138 can be used to secure mixing rod 136 in place. 
         [0024]    Multiple LEDs of each color can be mounted using reflow surface mount techniques to achieve optimum optical density. In a particular embodiment, a conventional metal core board (MCB)  130  can be used. Alternatively, a conventional fiberglass laminate (FR4) printed circuit board (PCB) material can be used. LEDs, particularly red and amber LEDs, have the characteristic that their light output decreases significantly as their temperature raises. Heat management can be critical to maintaining optimum light output and therefore the proper ratios of light intensity to maintain the desired CCT and CRI. 
         [0025]    The lamp  100  of the present invention includes a number of different operating modes which provide different light characteristics, as described in Table 1. 
         [0000]                                                                                                                              TABLE 1                           Nominal   Approximate relative peak                    CCT       intensity                Mode   (°K)   CRI   Blue   Green   Amber   Red   Comments                    “Cool   5,000   70+   0.72   0.70   0.75   1.00   Meets European user       white”                           preference for cooler                                   white light.       “Warm   4,200   70+   1.00   0.80   0.75   1.00   Meets US user preference       white”                           for warmer white light.       “No-cure”   N/A   N/A   ~0   0.30   0.60   1.00   Greatly reduced flux                                   below 500 nm will not cure                                   dental adhesives.                    
In this design, the ratios of the four colors are controlled with a variation of pulsed width modulation of the current. During the assembly and test of the lamp  100 , each color is independently characterized for peak wavelength, spectral spread (full width half max), and illuminance (lux) at the image plane at a predetermined maximum current. Using test software based on both theoretical and empirical predictions, these values are used to generate a table of duty cycles for each wavelength at each of the three operating conditions: 4200K, 5000K, and “No Cure” modes at start up (board temperature equal to ambient temperature). These tables then can be stored on an electronic memory device (chip) that matches the serial number of the lamp. The PWM controller then looks up the duty cycle table on the memory chip and sets the duty cycles accordingly when the lamp is first started. At this time, the test software algorithm can also produce and store duty cycle tables for the full range of operating board temperatures, as discussed in more detail below.
 
         [0026]    In a particular embodiment of the invention, temperature compensation or measurement may be included. Since each color LED has a different sensitivity to heat, a compensation algorithm can be used to set the drive current values for each color as a function of temperature. The compensation algorithm may be adapted to assume that LEDs of a given color do not exhibit significant differences in temperature sensitivity. As a result, each lamp need not be characterized thermally but rather may depend on the theoretical and empirically determined temperature relationships in the algorithm. A thermistor on the LED circuit board may also be included to measure actual board temperature from which the LED temperature can be derived, based on previously determined empirical values, and the current to each LED color can be adjusted accordingly by software. 
         [0027]    In another embodiment, a dental operatory lamp used to illuminate an operating area comprises a housing having a front directed toward the operating area and a rear away from the operating area, and a reflector module located at the rear of the housing. An electrical power supply is provided for supplying electrical power to the LEDs for illuminating the LEDs, with the power supply being selectively operable to provide an intensity adjustment for the LEDs. The electrical power supply can be selectively operable to control the level of power transmitted to each LED independent of the level of power transmitted to the other LEDs. The lamp can be configured to have a variable color output. For example, the intensity adjustment can range from 0 to about 2500 FC. The intensity adjustment can be continuous throughout its range of adjustments or, alternatively, can be adjustable at discrete settings within its range of adjustments. The lamp may further include a microprocessor in communication with the LEDs to control the level of power transmitted to the LEDs, and thus the output intensity of the light from the lamp. Suitable microprocessors for use with the present invention are well known in the art and include, but are not limited to, any programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). 
         [0028]    In an alternative embodiment of the invention, a dental operatory lamp used to illuminate an operating area comprises a housing having a front directed toward the operating area and a rear facing away from the operating area. A plurality of light emitting diodes (LEDs) can be included. An adapter configured for receiving at least one non-light emitting diode (non-LED) light source is located within the housing. The at least one non-LED light source may consist of a group of lights that can be selected from, for example, Quartz halogen, tungsten halogen, incandescent, xenon, fluorescent, fiber optics, gas plasma, laser, ultraviolet, and blue light. The at least one non-LED light source may also include the group of lights selected from, for example, dental curing light, oral cancer screening light, decay detection (cavities and caries) blood detection sterilization and tooth whitening light. 
         [0029]    A particular embodiment of the invention includes a dental operatory lamp used to illuminate an operating area having a housing with a front directed toward the operating area and a rear away from the operating area. The LEDs  118  are positioned with their longitudinal axes aligned toward predetermined points on the reflective element  116  for directing the light from the LEDs  118  toward the front of the lamp in a pattern that focuses light from the lamp to a central area of illumination of high intensity  204 , with significantly reduced intensity illumination  202  outside the central area, as shown in  FIG. 4 . Particular representative patterns of focused light emanating from the dental operatory lamps of the present invention include, for example, a pattern of focused light that can be elliptically shaped and may be about 3 inches by about 6 inches (7.62 cm by about 15.24 cm) in size. In a particular embodiment, the reduced intensity illumination  202  outside the central area of illumination  204  decreases in intensity by 50% of a maximum intensity relative to the central area of illumination of high intensity. The central area of illumination of high intensity  204  can have a pattern size of at least 50 mm by 25 mm. The reduced intensity illumination  202  outside the central area can be configured to decrease in intensity progressively and smoothly relative to the central area of illumination of high intensity. The pattern can be configured to have a brightness of greater than about 20,000 Lux at a focus height of 700 mm from a target. The illumination on the central area of illumination of high intensity 204 at a distance of 60 mm can be configured to be less than about 1200 Lux. Illumination at the maximum level of the dental operating light in the spectral region of 180 nm to 400 nm can be configured to not exceed 0.008 W/m2. 
         [0030]    Yet another embodiment of the invention is shown in  FIG. 5 , wherein a dental operatory lamp used to illuminate an operating area includes a lamp assembly  208  having a front  210  directed toward the operating area and a rear  212  away from the operating area. A reflector module  220  can be located within the lamp assembly  208 , and more specifically, can be located at the rear  212  of the lamp assembly  208 . A plurality of light emitting diodes (LEDs) can optionally be located in a reflector module  222 . Optionally, a light mixing rod (not shown) may be included as part of the reflector module  222  to produce homogenous light from the multiple LEDs of different colors. The lamp assembly  208  can include a curved or faceted interior reflective surface  220 . The LEDs can be directed toward the curved or faceted interior reflective surface  220  for directing the light from the LEDs toward the front  210  of the lamp in a pattern that focuses light from the lamp to a central area of illumination of high intensity, with significantly reduced intensity illumination outside the central area. The reduced intensity illumination outside the central area can be configured to decrease in intensity by 50% of a maximum intensity relative to the central area of illumination of high intensity. The reduced intensity illumination outside the central area may be configured to decrease in intensity progressively and smoothly relative to the central area of illumination of high intensity. The light pattern can have a brightness of greater than about 20,000 Lux at a focus height of 700 mm from a target. The illumination on the central area of illumination of high intensity at a distance of 60 mm may be less than about 1200 Lux. The illumination at the maximum level of the dental operating light in the spectral region of 180 nm to 400 nm may be configured to not exceed 0.008 W/m 2 . 
         [0031]    The lamp  100  of the present invention allows the user to set various chromaticity settings, such as sunlight equivalent D65 or simulated fluorescent lighting for improved dental shade matching. It also allows the addition of thermal, color, or intensity feedback to better maintain light characteristics over the life of the product, and permits adjustment of light intensity independent of color setting. The lamp  100  also is adapted to provide different configurations and forms of color mixing light guides. Specifically, the lamp  100  provides a user selectable mode with reduced irradiance in the near UV and blue wavelengths to allow adequate illumination while not initiating curing of UV-curable dental composites and adhesives. The lamp design can provide longer life through use of LEDs instead of incandescent bulbs and which can be further achieved through use of heat pipes, finned rear housing and fan cooling which maintain low LED temperature even at high currents. 
         [0032]    Although the foregoing description contains many specifics, these are not to be construed as limiting the scope of the present invention, but merely as providing certain representative embodiments. Similarly, other embodiments of the invention can be devised which do not depart from the spirit or scope of the present invention. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims, are encompassed by the present invention.
An electrically powered light source including a light emitting diode (LED) having variable chromaticity, which is adapted for use in a dental operatory. A dental operatory lamp includes a thermally conductive housing having a front directed toward the operating area and a rear away from the operating area; a generally elliptical reflector located on the rear of the thermally conductive housing; at least one heat pipe; a plurality of color LEDs projecting light toward the elliptical reflector, the plurality of LEDs being in thermal contact with the at least one heat pipe; and an optical light guide for combining light from said LEDs. Another embodiment of the lamp includes at least two user selectable light spectra, one of said spectra providing white light with color temperature in the range 4000deg K-6000deg K and one spectra having reduced output in the wavelength range 400-500 nm.