Patent Document

FIELD OF THE INVENTION 
       [0001]    This invention, in general, relates to emergency lighting apparatus and, more particularly, to the use of light emitting diodes (LEDs) in high luminance emergency lighting systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    High brightness light emitting diode (LED) light sources are in high demand for challenging applications including emergency lighting. Prior art in the emergency lighting field typically utilize either tungsten or tungsten halogen lamps with colored filters or, more recently, systems incorporating pre-packaged high brightness LEDs. Emergency lights are used on vehicles such as police, fire, ambulance, tow trucks, construction vehicles, plows, as well as on vehicles in the aviation and marine fields. 
         [0003]    Generally, emergency lighting is relatively narrow in spectral width, with the most widely used colors including blue, green, amber, and red. In some cases there is a demand for white light as well. Filtered halogen or tungsten halogen lamps by the physics of their material structure and design have a wide spectral distribution ranging from the ultraviolet to well into the infrared spectrum. Thus, creating narrow spectrum single color light from tungsten or tungsten halogen lamps is very inefficient and results in limited luminance. 
         [0004]    Prepackaged LEDs are devices comprising an LED die or die array sitting on top of one or more thermally and electrically conductive materials, each with associated thermal impedance with electrical leads and thermal backplane that are then intended to be attached to yet another board with additional thermal impedance. Examples of prepackaged devices include the Luxeon™ and Rebel™ product lines now sold by Philips, the Osram Dragon™ and Ostar™ product lines, and the CREE X-Lamp™ product line. Companies including Code 3/PSE of St. Louis, Mo. and Whelen Engineering Company of Chester, Conn., have successfully launched products incorporating prepackaged LED devices in the emergency lighting market sector. 
         [0005]    Consequently, there is a need for high performance, low cost, compact and reliable emergency lighting, and it is a principal object of this invention to satisfy this need. 
         [0006]    Other objects of the invention will be obvious and will in part appear hereinafter with the following detailed description is read in conjunction with the drawings. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention herein describes an emergency light system which incorporates light emitting diode (LED) light sources with one or more distinct colors including broad band white light. The LED die or die array is mounted to a high thermal conductivity circuit board comprising “Chip on Board” (COB) technology which can include both the LED die and electronic drive components thus resulting in a more compact and reliable design with improved thermal and optical performance at lower cost relative to pre-packaged based LED systems. 
         [0008]    The light from the typically blue, green, amber, red or phosphor coated blue (for white light) LED die or die arrays is collected by one or more typically non-imaging concentrators. The light is then directed toward one or more additional optical elements for the purpose of imaging the output of the non-imaging collection optic to the far field with low divergence in both the horizontal and vertical planes. The magnitude of the far field angle is fundamentally limited by the limitations of the overall package size available. The properties of the non-imaging collection optic result in substantially filling the rectangular aperture of the light module resulting in a system with improved appearance from near to far viewing distances. 
         [0009]    A final optical element comprising a diffuser acts to increase the far field angular spread by a desired amount and profile along the horizontal and vertical planes. Typically, it is desirable to have an emergency light which can be viewed over a large range of angles about the normal in the horizontal plane and a relatively narrow range of viewing angles in the vertical plane. That is, a complete light bar assembly that would typically be mounted on top of a police car, for instance, should be viewable from all angles to an observer with an eye height above the ground roughly equivalent to that of the light bar, but without sending light upward into space or downward onto the ground (beyond angles required to account for vehicles sitting on the top of or bottom of a hill or valley respectively), which would only act to minimize the brightness available to the eye of the observer. The present invention fundamentally acts to provide a narrow beam of light in the horizontal and vertical planes which can then be redistributed as desired by passing through an appropriately structured diffuser element. A particular advantage of the invention is that different far field intensity distributions can be readily obtained simply by changing out the diffuser element only, with no change to the balance of the system. For example, if it is desirable to have different far field distributions for a system incorporating both blue and red light modules, the only change in the design between the two color light modules other than the LED die would be the diffuser. This commonality of parts further reduces the cost both to develop and to manufacture which translates to lower cost to the customer and a greater competitive advantage for the seller. Alternatively, the far field in the horizontal plane can be set primarily by the divergence from the collection optic without the need for a diffuser element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The structure, operation, and methodology of the invention, together with other objects and advantages thereof, may best be understood by reading the following detailed description in connection with the drawings in which each part has an assigned numeral or label that identifies it wherever it appears in the various drawings and wherein: 
           [0011]      FIG. 1  is an exploded diagrammatic perspective view of a preferred embodiment of a 6-LED “Chip-on-Board” illumination module with application to emergency lighting comprising a heat sink, an LED metal core board with attached index matched collection opitc, a collimating lens array cover, and a diffuser to spread light preferentially along one axis; 
           [0012]      FIG. 2  is an exploded diagrammatic side elevational view of the system of  FIG. 1 ; 
           [0013]      FIG. 3  is an unexploded diagrammatic side elevational view of the system of  FIG. 2 ; 
           [0014]      FIG. 4  is a diagrammatic side elevational cross section of the system of  FIG. 3  with the heat sink removed; 
           [0015]      FIG. 5  is a diagrammatic plan view of the system of  FIG. 4  with parts removed; 
           [0016]      FIG. 6  is an exploded diagrammatic view of the system of  FIG. 4 ; 
           [0017]      FIG. 7  is an exploded diagrammatic view of the system of  FIG. 5 ; 
           [0018]      FIG. 8  is an isometric diagrammatic view of one set of the collection and collimating optics of the system of  FIG. 1 ; 
           [0019]      FIG. 9  is a diagrammatic elevational view of one set of optics from the elevational, side-on view of  FIG. 4 ; 
           [0020]      FIG. 10  is a diagrammatic top view of one set of optics from the perspective of  FIG. 5  which is orthogonal to  FIG. 9 ; 
           [0021]      FIG. 11  is a diagrammatic perspective view of the system of  FIG. 8  with a collection optic input aperture increased in size to accommodate two side by side LED die for the purpose of increasing luminance; 
           [0022]      FIG. 12  is a diagrammatic perspective view of an optical system similar to the system of  FIG. 8  with the non-imaging collection optic replaced by a rectangular θ by θ concentrator for use without index matching, such as could be done for white LEDs; 
           [0023]      FIG. 13  is a diagrammatic perspective view of the system of  FIG. 12  with the non-imaging collection optic replaced with a substaintially straight walled taper; 
           [0024]      FIG. 14  is a graph showing the far field distribution of the system of  FIG. 1  without the diffuser in place; 
           [0025]      FIG. 15  is a graph showing a plot of the far field distribution for an 80 degree, and a 60 degree holographic diffuser convolved with the horizontal distribution of the source of  FIG. 1  shown in the plot of  FIG. 14 ; 
           [0026]      FIG. 16  is a graph showing the horizontal and vertical far field distributions of the system of  FIG. 1  with the 80 degree diffuser of  FIG. 15  partially covering the output aperture producing a far field, which is the linear combination of the plots of  FIGS. 14 and 15 ; 
           [0027]      FIG. 17  is a diagrammatic perspective of an alternative embodiment to the system of  FIG. 1 ; 
           [0028]      FIG. 18  shows a top view (X-Z plane) of the system of  FIG. 17  with parts removed; 
           [0029]      FIG. 19  is a diagrammatic top view of a detail of the diffuser of the system of  FIG. 18 ; 
           [0030]      FIG. 20  is a diagrammatic perspective view of the bottom of the diffuser of  FIG. 19 ; 
           [0031]      FIG. 21  is a diagrammatic perspective view of another alternative embodiment of a “Chip-on-Board” LED emergency light module; 
           [0032]      FIG. 22  shows the system of  FIG. 21  with the cylindrical collimation optic removed; 
           [0033]      FIG. 23  is an enlarged diagrammatic view of the collection optic array and LED die of the system of  FIG. 21 ; 
           [0034]      FIG. 24  is an enlarged diagrammatic section view of one of the collection optics of the system of  FIG. 23 ; 
           [0035]      FIG. 25  is a diagrammatic cross-sectional view in the Y-Z plane of the system of  FIG. 21 ; 
           [0036]      FIG. 26  is a diagrammatic perspective view showing the LED “Chip-on-Board” printed circuit board of the system of  FIG. 21 ; 
           [0037]      FIG. 27  is an enlarged diagrammatic perspective view of the system of  FIG. 26  showing detail of the LED die and wire bonds; 
           [0038]      FIG. 28  is a diagrammatic perspective view of another alternative embodiment of a “Chip-on-Board” LED emergency light module using a hybrid total internal reflection (TIR) collection optic; 
           [0039]      FIG. 29  is a diagrammatic elevational view in the Y-Z plane of the system of  FIG. 28 ; 
           [0040]      FIG. 30  is a diagrammatic sectional view of the system of  FIG. 28  showing individual collection optics associated with each LED; 
           [0041]      FIG. 31  is a diagrammatic elevational view of an alternative embodiment of the system of  FIG. 29  indicating replacement of the solid TIR collection optic with a hollow non-imaging collection optic and prism-shaped cylindrical mirror; 
           [0042]      FIG. 32  is a diagrammatic perspective view with parts broken away of another alternative embodiment of a “Chip-on-Board” LED emergency light module using a cylindrical lens, but no collection optic; 
           [0043]      FIG. 33  is a diagrammatic elevational view in the Y-Z plane of the system of  FIG. 32 ; 
           [0044]      FIGS. 34A and 34B  are diagrammatic cross sectional elevational views of a rotationally symmetric LED emergency light which produces a 360 degree azimuthal beam with narrow divergence in the elevation plane. The light ray paths are indicated by dotted lines in  FIG. 34B  of the system of  FIG. 34A ; and 
           [0045]      FIG. 35  is a diagrammatic isometric view of one half of the sectioned system of  FIG. 34A . 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    The present invention relates to Light Emitting Diode (LED) emergency lighting. In particular, the present invention is an LED based light source for improved luminance in a compact form factor and low cost relative to prior art. 
         [0047]      FIGS. 1 ,  2  and  3  show, respectively, an exploded isometric view of a preferred embodiment of the LED module designated generally at  100 , an exploded view of LED module  100  in the Y-Z plane, and a collapsed side view of LED module  100  in the Y-Z plane. The LED module  100  comprises a “Chip-on-Board” (COB) metal core substrate printed circuit board (PCB)  106  with six (6) individual LED die  112  shown optically coupled to an associated individual collection optic  114 , one each for each LED die  112 . Each collection optic  114  has an input aperture on the order of the size of a square LED die  112 , 1.1 mm, for example. The collection optic  114  is described in detail below. 
         [0048]    The light that exits the output aperture of an individual collection optic  114  is converged by means of an associated corresponding lens section  116  toward lens array  120  which acts to collimate the light output with low far field divergence in both the horizontal and vertical directions. While the figures indicate refractive dielectric lens elements comprise lens elements  116  and  120 , other means such as Fresnel lenses, kinoforms, mirrors, or diffractive lenses could be used as alternatives. 
         [0049]    The light propagating from the collimation lens array  120  in the positive Z direction then enters a downstream diffuser  124  that is structured by design to spread the light predominantly in the horizontal (X-Z) plane. A preferred embodiment of the diffuser  124  would be of the type described as a randomized non-periodic structure which can be made by the interference of coherent light (holography) such as light shaping diffusers offered by Luminit of Torrance, Calif. or by engineered diffusers such as those offered by RPC Photonics of Rochester, N.Y., which are made by direct laser writing on photo resist to make the master followed by replication onto assorted substrates. These diffusers can be made on substrates such as plastic or glass with a primary advantage of high transmitted efficiency relative to other diffusers such as frosted glass and also offer greater control over the far field patterns that can be obtained. A typical diffuser for the system  100  would be made out of a material substrate such as polycarbonate with a thickness on the order of 0.250 mm. Diffusers can be made to affect the spread of light differently along the horizontal and vertical axes. Such diffusers are typically referred to as elliptical diffusers, as the far field distribution that results from collimated, normally incident, low divergence incoming light is elliptical in profile. Thus, the design provides a large range of far field distributions that are the result of convolving the far field distribution of the optical system without the diffuser with the far field distribution of the diffuser response to normally incident collimated light with no divergence. The diffuser response is described in more detail below. 
         [0050]    There are benefits to both performance and cost in using COB metal core PCB&#39;s to directly attach the LED die or die arrays relative to prior art, which typically use pre-packaged LED devices. The thermal impedance between the LED die  112  and a preceding heat sink  102  is much lower with the directly attached COB approach. Pre-packaged LED emitters have many additional layers of higher thermal impedance which means that at high current densities the COB system results in a much lower LED junction temperature which, in turn, leads to improved optical power and lower temperature operation. This translates into longer and more reliable product life. Additionally, fewer LED die can be used due to the higher performance for the COB approach further reducing system cost. 
         [0051]    The COB approach is also much lower in cost relative to the use of pre-packaged LED devices since there are fewer parts and fewer process steps to make a finished unit. The thermal performance advantage is particularly acute with respect to amber LED die with a photometric peak around 590 nm, as this LED material structure is much more sensitive to increased temperature which results in a drop in optical power. The thermal impedance with a COB LED solution can be as low as one (1) C.°/W or lower in comparison to typical values on the order of eight (8) to ten (10) C.°/W for pre-packaged devices. Examples of pre-packaged devices include the Luxeon™ and Rebel™ product lines now sold by Philips, the Osram Dragon™ and Ostar™ product lines, and the CREE X-Lam™ product line. There are now several vendors producing COB metal core LED boards such as those available from The Bergquist Company of Chanhassen, Minn. The lowest thermal impedance is obtained by mounting the LED die  112  directly to the metal core, typically copper or aluminum substrates. However, that approach requires that the LED die have common anodes (bottom contact). Other high performance board substrates include, but are not limited to, composite materials such as aluminum or copper and silicone carbide, graphite or CVD diamond. To be able to drive the LED die  112  in series, however, which is required for some applications and drive circuits, there must be a thermally conductive, but electrically insulating layer with a copper foil above it to attach the die to. The thickness of the copper foil can be increased from one (1) oz. to the order of ten (10) oz. to act as a heat spreader thereby reducing the heat flux in passing through the electrically insulating layer. The dielectric is typically on the order of 0.075 mm or less and typically has a thermal conductivity on the order of 2 W/m-K in comparison to the order of 160 W/m-K for aluminum and 370 W/m-K for copper. The facts that the dielectric is very thin and the heat flux is reduced by thermal spreading in the foil layer that the die is directly attached to in the case of series operation, minimizes its effective thermal impedance. 
         [0052]    An additional benefit of using COB PCB technology is that electrical drive circuit devices  110  and  202 , such as one of the commercially available current controlling integrated circuits (IC&#39;s) that have recently been developed for LED applications along with the required auxiliary components including resistors, capacitors, inductors, and diodes, can be attached directly to the COB PCB by standard surface mount techniques well know in the art thereby eliminating the need for the added cost, space, and complexity of additional external drive circuitry. A wire harness or electrical connector can be mounted directly to the COB PCB to get power and or control signals to and from the board. A temperature sensing device such as a thermistor is often added to the COB PCB to monitor temperature. If closed loop intensity operation is required, a light detection and control circuit can also be added to the COB PCB to account for changes in light output as a function of time and temperature. COB PCB&#39;s can have multiple layers attached by standard electrical vias with successive foil layers separated by the same dielectric described above. 
         [0053]    The heat from the COB PCB  106  is conducted to the heat sink  102  by use of a thermally conductive conformal pad  104 . Such thermal pads  104  are available from companies such as The Bergquist Company referenced above. They are available in a range of thicknesses, thermal impedances, electrical conductivity, and material compliance. Alternatively, a thermally conductive paste can replace the thermal pad  104 , but pastes can be awkward in volume production and are not generally preferred. The fins on the heat sink  102  are generally oriented in the vertical direction to work best in free convection if forced air was not available. 
         [0054]    Collection optics  114  and associated output-lenses  116  are shown molded as three (3) sections per part, and in a preferred embodiment, are made out of a highly transparent optical grade thermal plastic, such as acrylic, polycarbonate, cyclic olefins (such as is available from Zeon Chemicals), or other transparent materials such as glass or silicone. Depending on the application, the effect of short wavelength light, such as blue or ultraviolet, should be considered with respect to yellowing with time. Some grades of the above materials offer superior transmission in the shorter wavelengths and should be considered in such cases. The motivation for not molding all six (6) collection optics  114  and associated lenses  116  into one molded part is driven by the differential thermal expansion between the metal core substrate material and the dielectric material of the optics. By splitting the optics into two parts, the issue is reduced to a tolerable level. Each group of three collection optic  114  and associated lens  116  has 6 legs  108  each with opposite corners having a round pin and oval pin which engage into tightly toleranced holes in the PCB to assure that the input apertures of the collection optic  114  match up with respect to position in the X-Y plane to the LED die  112  in a kinematic geometry. If the dielectric optics were to be made out of a single molded piece rather than two, the differential expansion between the PCB  106  and the optic would move the input apertures relative to the LED die. This movement would have two effects. First, it would potentially reduce the amount of light that would couple from the LED die  112  into the collection optic  114 , and secondly, it could cause delamination between the refractive. index matching silicone gel and the input aperture of the collection optic  114  or between the LED die  112  and the gel, which would result in loss of light. The purpose of the index matching gel is to increase the extraction efficiency of the light generated within the LED die junction out of the LED die by means well know in the art and understood by Snell&#39;s Law and is driven by the high index of refraction of the LED junction itself. Low durometer two-part silicone gels specifically formulated for index matching to high brightness LED die are typically used and are available from companies such as Nusil Technology LLC, of Carpinteria, Calif. 
         [0055]    A cover  118  (See  FIG. 3 ) is provided and is structured to snap to the PCB  106  while serving several functions. First, the cover  118  comprises a collimating optic array  120  that is comprised of individual refracting surfaces having a one-to-one correspondence with the individual lenses  116 . The refracting surfaces of collimating optic array  120  redirects the light exiting the collection optic lens portion  116 , which images the output of the non-imaging collection optic section  114  to infinity. Secondly, the cover  118  acts as a protective cover for the balance of the optics. Thirdly, cover  118  acts as a support for the optics array  120  and contains four (4) symmetrically located self tapping holes  122  which allow self tapping screws entering from the far side of the heat sink  102  to sandwich the thermal pad  104  and PCB  106  together as indicated in  FIG. 3  with sufficient pressure to achieve the required thermal conduction between the PCB  106  and heat sink  102 . Similarly, self taping screws hold the collecting optics to the PCB  106 . The metal core substrate of the PCB  106  acts to spread the heat from the six (6) LED die  112  prior to transferring through the thermal pad  104  to the heat sink  102  thereby minimizing the thermal impedance resulting from the thermal pad  104 . 
         [0056]      FIG. 4  shows a diagrammatic side elevational view, in the Y-Z plane, of portions of the module  100  and  FIG. 5  shows a diagrammatic plan or top view, in the X-Z plane, of system  100  of  FIG. 1 . The dotted lines indicate how the light exiting the collection optic  114  at position  206  is imaged by lens section  116  and collimating lens array  120 . Thus, the far field angles in the horizontal and vertical directions are proportional to the dimensions of the output of the collection optic  114  at  206 . The narrower height of the output aperture at  206  in the Y-Z plane results in a larger divergence angle more fully filling the lens section  116  and collimating lens  120  in comparison to the smaller divergence exiting section  114  at  206  in the X-Z plane. This is evidenced by the smaller extent of the rays depicted by the dotted lines with arrows in  FIG. 5  relative to  FIG. 4 . Generally, the requirements for the type of emergency light of the system of  FIG. 1  are used within a car top mounted light bar on police cars for which it is desirable to have the light visible over a large angle in the horizontal plane, but not to have too much light diverging into the vertical plane, which would only be launched into the ground or up into space and would thereby reduce the light to the intended observer. For this reason, it is desirable to maintain a small dimension of the aperture  206  in the Y-Z plane as is accomplished by the present invention of the system of  FIG. 1 . The details of the exact design are established using well-known ray tracing programs (e.g. Code V, TRACEPRO, or ZEMAX) with knowledge of the material composition, geometry of the optical elements, and operating wavelengths. 
         [0057]      FIGS. 6 and 7  show exploded diagrammatic elevational and top plan views, respectively, of the embodiments of  FIGS. 4 and 5 . Note that a complementary configured pocket is molded into the cover  118  to accept the diffuser  124  which could be attached by a number of methods including optical adhesive. It is important to note that the diffuser  124  works most effectively with the light entering the patterned side and exiting the smooth non-patterned side which would be facing outward. It is possible to achieve a large degree of divergence from having the pattern on the outside, but not to the same extent as it is for the pattern on the inside. Thus, an alternative embodiment of the diffuser would be molded directly onto the outer surface of the lens array  120 . 
         [0058]      FIG. 8  shows a detailed diagrammatic perspective (isometric) view of one representative or typical set of collecting and light shaping optics out of 6 of the system of  FIG. 1 . The LED die is positioned in close proximity to an input aperture  802  and is refractive index matched with a dielectric material such as silicone gel as previously described. Thus, the angular extent just inside the non-imaging collection optic section  114  is substantially hemispherical. Opposite sides of the optical concentrator  114  are symmetric. The sections  804  and  806  are compound parabolic concentrator (CPC) sections of the type described by Winston and Welford in a book entitled “High Collection Nonimaging Optics” published by Academic Press and are made of tilted and shifted parabolic sections according to the edge ray principle. For the practical reason of assuring that the optic can be released from the mold, sections  810  and  812  are drafted. Ideally, the draft is made tangent to the CPC sections  804  and  806  respectively. The draft has minimal impact on the output relative to that which would be obtained by extending the section  806  all the way to its normal length. The rectangular cross section is extended beyond its normal CPC length to increase the length of the collection optic section  114  for the purpose of increasing the light uniformity at its exiting aperture at  814  and  816  representing the long horizontal and narrow vertical outputs of the collection optic section  114 . The lens  116  is attached to the collection optic  114  by means of the material  818  bridging the gap. This is primarily for the purpose of minimizing losses due to Fresnel reflections and reducing the total number of optical elements for reduced complexity and cost. The reason for having the lens section  116  is for the purpose of reducing the overall physical distance between the LED die and the output at the diffuser  124 . If sufficient length were available for a given application, the lens section  116  could be eliminated and the optical system would consist of the collection optic section  114  and the collimating lens  120  only. The length of the side of the lens  120 , in the horizontal plane depicted by side  820 , is dictated by the requirement for maintaining minimal dimensions between the first and last LED die. The motivation for having the vertical dimension  822  of the lens  120  to be greater than the length of side  820  is that of achieving the smallest possible divergence in the vertical plane within the confines of the maximum allowable height of the entire module. One important aspect of the output of a rectangular cross section CPC such as represented by  114  is that it has a substantially rectangular far field which means the rectangular lens aperture defined by sides  820  and  822  are substantially filled with light. Thus, from the outside, the entire rectangular aperture of lens array  120  is substantially filled with light, which is a desirable quality to the viewer and leads to a higher perceived brightness. This is related to the fact that the human eye has a logarithmic response to light. If all the light, when observed from a distance, appears to be coming from a small point in comparison to a more extended source, with the same amount of optical energy, the slightly more extended source will appear brighter because it appears to be of similar intensity, but larger in size giving the perception of more light. That is, once your eye approaches the point of light saturation, a physically brighter source may not appear any brighter, so a larger source of equivalent total energy will be perceived as brighter (photometric power per unit solid angle). Thus, it is advantageous to be able to use the total area of the output aperture of the light source as opposed to substantially circular beams of light or substantially point sources observed in prior art. In terms of compactness, this approach provides overall dimensions for the combined envelope around the CPC  114  and following shaping optics a package of about 30 mm high by 130 mm wide (looking head-on) by about 130 mm deep (from front to back). 
         [0059]      FIGS. 9 and 10  diagrammatic elevational views of the Y-Z plane and the X-Z plane, respectively, illustrating the inverse relationship between the dimensions of the output apertures  816  and  814  to the heights  822  and  820  of the collimating lens  120 . 
         [0060]      FIG. 11  shows an alternative embodiment  1000  to the non-imaging portion  114  for the system  100  of  FIG. 8 . The input dimension of an entrance aperture  1002  has the same vertical dimension  1006  as that of  100 , but has twice the horizontal dimension  1004 , allowing for the use of a 1×2 array of the LED die used in system  100 . Thus, the far field extent in the vertical dimension of  1000  is the same as that of  100 , but the horizontal extent of the far field is twice that of  100 . Given that the second LED is operated at the same current density as that of the system of  100 , the system of  1000  yields approximately twice the large angle luminance in the horizontal direction in the far field, but approximately the same luminance in the center as the non-diffused far field would have twice the dimension in the horizontal direction only. This assumes that the extent of the width of  822  is designed as not to vignette the light exiting  116  in the horizontal (X-Z) plane. In this case, section  1010  may not have added draft as not to be too long in comparison to section  114  of  100 . 
         [0061]      FIG. 12  represents a single optical system  1100  similar to that of system  100  of  FIG. 8 , but with non-imaging section  1150  replacing section  114 . Section  1150  has an input dimension equivalent to a two by two (2×2) array of LED die sized similar to the LED die depicted in the system of  FIG. 1 . In the case of system  1100 , the array is not refractive index matched as would be the preferred configuration for a white LED array comprised of 4 blue LED die in a 2×2 configuration covered by a phosphor. The phosphor is of a type such as cerium doped YAG (Ce:YAG) that is well know to the art or one of the alternative yellow phosphors available from companies such as Intematix of Fremont, Calif. A portion of the blue light emitted by the LED die is absorbed by the phosphor and re-emitted as yellow light which, in combination with the scattered, but non-absorbed blue light, produces the appearance of white light. Typically, the phosphor is held in place on the emitting surface of the LED die with a silicone material. Since the LED is already index matched by the silicone/phosphor matrix, there is no further advantage to index matching and higher brightness is achieved without the use of index matching silicone gel between the phosphor coated LED die and the input aperture  1102 , as understood from the index of refraction contribution to the well know Etendue (area—solid angle-refractive index squared-product). Thus, since the light just inside the dielectric material of section  1150  does not extend over a hemisphere, but is reduced by the well know Snell&#39;s Law, the CPC sections  1114  and  1112  are truncated with straight conical sections  1110  and  1108 , respectively, as described by Winston and Welford as a θ by θ compound parabolic concentrator. Sections  1118  and  1116  comprise the drafted walls analogous to sections  812  and  810  of the system  100  of  FIG. 8 . 
         [0062]    This type of optical system in conjunction with white LEDs functions as a very effective white take down light replacing tungsten halogen systems found in prior art. 
         [0063]      FIG. 13  shows a system  1200  with a section  1250  replacing section  1150  of system  1100  in  FIG. 12 . This non-imaging collection optic section  1250  has the same dimension input aperture  1102  and output aperture dimensions  1206  and  1208  as  1120  and  1122  of system  1100 . However, the sections connecting the input and output apertures are comprised of straight walls as in a taper. This works for the non-index matched system and results in better homogenization of the light distribution at the input aperture relative to that of  1150 , but is characterized by a somewhat more elliptical, rather than rectangular far field than that which is obtained from  1100  at lens  120 . 
         [0064]      FIG. 14  represents the normalized far field distribution of the system of  FIG. 1  prior to the diffuser  124 . Note the narrow extent in the vertical plane as described above. The solid line represents the distribution in the horizontal plane and the dashed line represents that of the vertical plane. 
         [0065]      FIG. 15  represents the horizontal far field distribution of the system of  FIG. 1  with an 80 degree full width half maximum (FWHM) Gaussian holographic diffuser, represented by the dotted line, and that of a 60 degree FWHM represented by the solid line, both of which are such as is available from Luminit. The illustrated distributions represent the convolution of the far field distribution in the horizontal plane of system  100  of  FIG. 1  prior to the diffuser  124  with that of the near Gaussian distribution of the diffuser  124 . If the diffuser  124  does not cover the entire output aperture of the collimating lens array  120 , or has a specific ratio of patterned versus non-patterned areas either on a macroscopic or microscopic scale, then for a particular ratio or of patterned versus non-patterned area, the distribution of  FIG. 16  results. The ratio of the peak on-axis luminance to that of the off-axis (beyond the far field extent of the system  100  prior to the diffuser) can be controlled to yield any desired value. This is a significant advantage of the invention, as the system&#39;s far field distribution can be controlled and readily changed merely by changing the diffuser element only, as opposed to the prior art for which the optical system would have to be changed and retooled to affect such a change in the far field distribution, if even feasible. The solid line of  FIG. 16  represents the broad far field obtained in the horizontal plane, and the dashed line represents that of the vertical plane. It is important to note that the shape of the far field in the vertical can be tailored to that which is desired by an appropriate change in the vertical distribution of the elliptical diffuser  124 . The composite far field distribution of  FIG. 16  represents the linear combination of the distribution that is unmodified by the non-patterned portions of the diffuser  124  and that of the patterned portion, which, again, is the convolution of the pre-diffuser far field distribution with that of the Gaussian distribution of the patterned portion of the diffuser  124 . 
         [0066]    Referring now to  FIG. 17 , there is shown a system  1300  that represents an alternative embodiment to the system  100  of  FIG. 1 . A housing represented by top and bottom sections  1304  and  1306 , respectively, act as a claim shell to house a collection optics array  1410  of the system shown in top plan view in  FIG. 18  along with a collimation lens array  1412 , a heat sink  1302 , and a diffuser  1308 . A COB PCB  1404  is shown comprising six (6) LED die and can contain drive electronic components analogous to PCB  106  of system  100  of  FIG. 1 . 
         [0067]      FIGS. 19 and 20  show close up views  1500  and  1600 , respectively, indicating details of a diffuser which is distinct from the design of that outlined in conjunction with the system  100  of  FIG. 1 . Here, plastic moldable macroscopic cylindrical segments protruding from the main diffuser substrate  1308  are comprised of aspheric cylindrical sections  1502  with symmetric sides  1504 . Low divergence angle light entering diffuser sections  1502  are refracted and then totally internally reflected by sides  1504  (or reflected if they are coated with a mirror on the outside) and, upon exiting into the main substrate  1308 , are deflected over a range of angles substantially in the horizontal, but not vertical plane. The light entering the flat sections between the cylindrical segments is not changed in angle upon passing through the substrate  1308 . Thus, by controlling the pitch of the cylindrical segments, the ratio of unaltered to diffused light in the horizontal plane is modified such as was described by the diffuser  124  of system  100 . 
         [0068]      FIGS. 21 through 27  represent another alternative embodiment of the LED emergency light of  FIG. 1 . A system  1700  of  FIG. 21  comprises a COB PCB  1702  comprising twenty one (21) individual LED die and associated corresponding hollow rectangular CPC&#39;s in a linear array  1802  of system  1700  as shown in  FIG. 22 . The hollow CPC&#39;s are formed into a molded holder  1704  which attaches to the PCB  1702  and to an aspheric cylindrical collimation lens  1706 . In this case, the far field distribution in the horizontal plane is obtained solely by the far field of the output of each of the individual CPC sections by walls  1906  and  2002  as seen in of  FIGS. 23 and 24 , respectively. Section  1906  is of the form of a CPC. Section  2002  is a straight walled conic section for the purpose of increasing the output divergence angle beyond that which would otherwise exit the CPC section  1906  and allows for a larger input aperture consistent with the size of the LED die, which is on the order of 1.1 mm per side, typically, but could be any desired size that is readily available. The shape of the cylindrical lens  1706  must be chosen carefully as not to result in total internal reflection of skew rays. Otherwise, the throughput would be compromised. 
         [0069]    The divergence in the vertical axis is controlled by the combination of the size of the output aperture  1908  (See  FIG. 24 ) and the lens focal length to be relatively small consistent with that of the system  100  of  FIG. 1 . One advantage of this approach is that it is feasible to use a reduced LED die to die spacing thereby increasing the number of LED die per unit length thus allowing for operation at a lower current density per die thus resulting in higher overall system level efficiency. The disadvantage of this embodiment relative to the system  100  of  FIG. 1  is that the far field distribution in the horizontal plane is necessarily flatter and therefore does not result in as high a near-zero angle luminance. 
         [0070]      FIG. 25  shows a diagrammatic cross-sectional Y-Z plan view of parts of the system  1700  illustrating ray paths through its optics The path of the rays exiting the CPC aperture  1908  are indicated for one side by the dashed arrows. The LED die  1904  can be seen at the input to the conical section  2002  of the CPC section  1906 . 
         [0071]      FIGS. 26 and 27  represent, respectively, the COB PCB  1702  shown in perspective and in partial close up view showing detail of the LED die  1904  attachment to the board  1702  as well as wire bonds  2302 . Typically, wire bonds  2302  for this system and the system  100  of  FIG. 1  are comprised of aluminum or gold between about 0.030 and 0.050 mm in diameter. The LED die for both systems are typically attached by means of solder, epoxy, or eutectic attachment. Generally, solder and eutectic attachment are preferred due to their superior thermal performance in comparison to thermally and electrically conductive epoxies. 
         [0072]    Yet another embodiment of the invention is represented by a system  2400  shown in  FIG. 28  with cylindrical total internal reflecting (TIR) element  2404  with solid dielectric CPC sections  2504  as shown in the systems of  FIGS. 29 and 30 , respectively. The path of the light rays is indicated by the dashed lines in traveling from an LED die  2506  through the CPC section  2504 , reflecting off section  2502 , and reflecting off a cylindrical parabolic section  2402 . The divergence in the horizontal plane is also dictated by that leaving the CPC section, as all other optical power elements are limited to affecting the horizontal far field only. 
         [0073]      FIG. 31  shows a similar system  2700  to that of system  2400  of  FIG. 28  for which the composite dielectric CPC and reflector are replaced with a hollow CPC  2702  and front surface reflecting prism  2706 . Legs  2710  are used to support a front surface  2704  mirrored prism  2706 . 
         [0074]    A final linear array LED emergency light module alternative embodiment is shown as system  2800  in  FIGS. 32 and 33 . A COB PCB  2804  is shown with multiple LED die, each with its own plastic dome typically filled with index matching gel. Alternatively, the domes could be over-molded out of a material such as silicone. With reference to  FIG. 33 , the light exiting in the Y-Z plane is either redirected by refraction by a cylindrical lens  2808  or by a cylindrical parabolic section  2810  in the Z direction. In the orthogonal X-Z horizontal plane, the far field is substantially Lambertian (falls off as cos θ). If, however, the LED die is not positioned near the center of curvature of the dome, but is further away, then the dome acts as a lens to redirect some of the light in the horizontal plane to smaller angles and a tighter distribution than that which would otherwise be obtained. The ends of the parabolic reflector section  2810  can be parallel to the Y-Z plane in which case they have no affect on the horizontal far field distribution, or they can be tilted as represented by end caps  2812  (See  FIG. 32 ) on each side, in which case they act to redirect some of the light in the horizontal plane that would otherwise map into larger angles, to smaller angles thereby increasing on-axis luminance. 
         [0075]      FIGS. 34A ,  34 B and  35  show a system  3000  comprising an LED emergency light which transforms the symmetric output of a single CPC  3002  with one or more LED die at its input aperture, to a beam of light with complete 360 degree azimuthal coverage and limited divergence in elevation symmetric (or non-symmetric) about the X-Y horizontal plane. This is the type of emergency light that would replace rotating tungsten halogen beacons with 360 degree (by rotation) azimuthal coverage that would be used on emergency vehicles such as tow trucks and snow plows. It also has application in aviation and marine lighting. The advantage to this approach is that there are no moving parts and it can be pulsed at much higher luminance relative to the tungsten halogen solutions observed in prior art. An LED module  3006  of the type represented by the 40 degree half angle divergence LumiBright offered by Innovations in Optics, Inc. of Woburn, Mass., is located on top of a heat sink  3010  that acts secondarily as a base for an outer cylindrical window  3014  which is made out of materials such as optically transparent plastics, rigid silicones or glass. The output of the LED source&#39;s CPC  3002  is directed downward by parabolic reflector  3012  such that the focus of the parabolic section is substantially coincident with the output face of the CPC  3002 . The downward directed light is then reflected off of a straight conical mirrored section  3016  to the far field. If desired, the reflective cone  3016  can have some curvature to redistribute the light in the elevation plane. The light then passes un-deviated in angle through the cylindrical window  3014 , which also acts to hold the parabolic reflector  3012  in position. Alternatively, the parabolic mirror  3012  can have other shapes including spherical, elliptical, hyperbolic, compound parabolic, flat or conical, or combinations thereof, which would act in concert with the form of the reflector  3016 , which could also take on similar shape profiles. The hole in the reflector  3016  is small in area in comparison to the lighted portion of the reflector so it represents minimal loss in light and any light that does re-enter the CPC has an opportunity to be reflected back out off the LED die or die array, thereby representing a negligible loss in light. The top portion of the window, above the rays passing through the window, as indicated by the dashed lines representing the path of light in  FIG. 34B , show that it could be opaque with only the area through which light passes being required to be transparent. Alternatively, the system  3000  could be oriented upside down such that only the area through which light exists need be visible, which would allow for a much shorter profile. This would also allow fins to be located on the heat sink for better heat transfer to the air. Any wires required for power or control can be routed up the inner wall of the window  3014  or alternatively straight up the central axis, with negligible blockage of light or alternatively, transparent conductors can be deposited on the inside of the window  3014 . If desired, the input to the CPC  3002  can have a premixing segment preferably faceted with an even number of sides between about 4 and 10 to act to mix multiple colored LED die if it were desired to have multiple colors emitted either simultaneously or sequentially. If desired, for example, the LEDs could be red, amber (A), green, and blue, which can produce any desired color, including white and saturated red, amber, green, or blue. Alternatively, white LEDs can be used with or without index matching between the phosphor coated LEDs and the input aperture of the CPC  3002 . Alternatively, the CPC  3002  can be replaced with a taper which can be round or square at its input and or output, which can also act as an effective light homogenizer if multiple colors were desired. 
         [0076]    Having described preferred and alternative embodiments of the invention, those skilled in the art will recognize that other variants of it are possible in accordance with the teachings herein.

Technology Category: 2