Solid-state light sources for curing and surface modification

The systems and methods described herein relate to solid-state light sources capable of generating radiation beams for, but not limited to, the treatment of surfaces, bulk materials, films, and coatings. The solid-state ultraviolet source optically combines the light output of at least two and preferably as many four independently controllable discrete solid-state light emitters to produce a light beam that has a controllable multi-wavelength spectrum over a wide range of wavelengths (i.e. deep UV to near-IR). Specific features of this light source permit changes in the spectral, spatial and temporal distribution of light for use in curing, surface modification and other applications.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to an apparatus and method of providing substantially improved radiation beams for the treatment of surfaces, thin films, coatings, fluids or objects. More particularly, the present invention pertains to an apparatus and method for optically combining the light output of at least two arrays of solid-state light emitters to produce a light beam that has a selected spectrum chosen for applications requiring a wide range of wavelengths to improve or accelerate a treatment process with a controllable irradiance.

2. Description of the Prior Art

Radiant energy is used in a variety of manufacturing processes to treat surfaces, films, coatings, over layers, and bulk materials. Specific processes include but are not limited to curing, fixing, polymerization, oxidation, purification, or disinfections. By way of example, the manufacture of components for motor vehicles involves the application of under coatings, paints or clear coatings on vehicle surfaces for various purposes including corrosion resistance, decoration or surface protection (e.g. scratch resistance). The coatings or paints are resins or polymer-based materials that are applied as liquids or powders and require thermal or radiant energy processing to become solids. The processing of coatings or paints by thermal methods is slow and requires times ranging from minutes to hours to complete. In addition, some materials (for example, substrates or coating components) may be heat sensitive and damaged by thermal treatments.

Non-thermal curing using radiant energy to polymerize or effect a desired chemical change is rapid in comparison to thermal treatment. Radiation curing can also be localized in the sense that curing can preferentially take place where the radiation is applied. Curing can also be localized within the coating or thin film to interfacial regions or in the bulk of the coating or thin film. Control of the curing process is achieved through selection of the radiation source type, physical properties (for example, spectral characteristics), temporal variation, or the curing chemistry (for example, coating composition).

A variety of radiation sources are used for curing, fixing, polymerization, oxidation, purification, or disinfections of a variety of targets. Examples of such sources include but are not limited to photon, electron or ion beam sources. Typical photon beam sources include but are not limited to arc lamps, incandescent lamps, electrodeless lamps and a variety of electronic (that is lasers) and solid-state sources (that is solid state lasers, light-emitting diodes and diode lasers). Selection of a specific radiation source for an application is contingent on the requirements of the treatment process and the characteristics of the radiation source. These characteristics are related to but are not limited to the physical properties of the source, its efficiency, economics, or characteristics of the treatment process or target. For example, arc lamps or radio-frequency or microwave driven “electrodeless” ultra-violet sources efficiently produce high levels of radiated power having applications in many “industrial” processes where rapid treatment using significant levels of irradiance or energy density over large areas are needed. Arc or electrodeless lamps require high voltage, microwave or radio frequency power supplies and in the case of microwave-driven systems, a microwave tube (that is a magnetron). These high-powered lamps also require cooling and heat rejection systems. Such operational requirements limit the application of such photon sources to situations were this need can be met.

The spectral emissions of arc and electrodeless lamps are controlled by the conditions under which the lamp is operated, the particular gases used to fill the bulb and the selection of various additives placed in the bulb. Those skilled-in-the-art formulate specific lamp fills meeting curing needs for many photochemical processes, but gaps exist in spectral coverage in certain spectral ranges.

Solid-state light sources, such as, but not limited to, light emitting diodes (LEDs), diode lasers, diode pumped lasers and flash lamp-pumped solid-state lasers provide emission sources that can tuned to the needed wavelength or can be combined as arrays to provide a multi-wavelength source for applications needing broadband source. Advances in solid-state source technology provide high-brightness ultraviolet LEDs suitable as sources for radiation treatment.

At the present time, commercial UV emitting diodes emitting radiation down to an output of 370 nm. are available from Nichia, Cree, Agilent, Toyoda Gosei, Toshiba, Lumileds and Uniroyal Optoelectonics (Norlux).

UV emitting LEDs and laser diodes are constructed using large band gap host materials. InGaN based materials can be used in LEDs emitting at peak wavelengths ranging from 370 to 520 nm (for example, from the ultra-violet (UV-A) to visible green). The band gap of GaN is 3.39 eV and can accommodate luminescent transitions as large as 363 nm. The substitution of In into the GaN host provides localized states that can radiate in the ultraviolet down to 370 nm.

Other nitride materials such as InAlGaN can emit ultraviolet radiation in wavelengths as short as 315 nm. InAlGaN is already being used to make high brightness LEDs and laser diodes that operate in the range of 315 to 370 nm. Hirayama et al (Appl. Phys. Lett. 80,207 (2002)) reports devices employing layered structures of InxGa1-xN or quaternary InxAlyGa1-x-yN grown on AlxGa1-xN (x=0.12-0.4) have been used in multiple quantum well structures to produce sources emitting comparable flux at 330 nm to InGaN devices operating at 415-430 nm. Hirayama et al. (Hirayama et al, Appl. Phys. Lett, 80, 1589 (2002)) has also reported a room temperature LED source using an improved multiple quantum well (MQW) structure and InAlGaN materials which emits intense UV radiation at 320 nm and significant emission at 300 nm.

Hirayama et al. (Appl. Phys. Lett. 80, 37 (2002)) report that AlxGa1-xN(AlN)/AlyGa1-yN MQWs exhibit efficient photoluminescence between 230 to 280 nm and that the photoluminescence is as high as that of the InGaN-based materials used in the violet diodes now commercially available. AIN-based materials are likely candidates for making ultraviolet LEDs operating in the UV-B or UV-C ranges. Other researchers are studying carbide and diamond materials as hosts for deep-UV based on the fact that their band gaps are as large as AlN.

LEDs operating in the blue, violet and UV-A (390 nm) wavelengths are of sufficient radiance to be used in ultraviolet and photochemical curing as “spot” curing sources. U.S. Pat. No. 6,331,111B1 (Cao) and EP 0-780-104 (Breuer et al) describe hand held portable spot curing light systems using solid state light sources consisting of light emitting diodes or diode laser chips. The light source of Cao may contain sources that emit multiple wavelengths so that numerous components in materials whose photo initiators are sensitive to different wavelengths may be cured at once. In the preferred embodiment described in Cao, the light travels directly to the curing surface without going through an optical device like a light guide or optical fiber. Breuer et al. describe a similar device optimized to cure dental resins and also extend claims to apparatus where the irradiator is a stationary curing apparatus whose light source chips are fixed to the walls of the curing chamber.

Various light sources have been used for the purposes of curing composite materials. These include plasma, halogen, fluorescent, and arc lamps. Various lasers have been incorporated in curing apparatus. Lasers emitting ultraviolet beams include frequency doubled or re-doubled sources like the 266 nm Nd—YAG systems, argon-ion systems and Nd—YAG pumped OPOs (optical parametric oscillators). Cao cites U.S. Pat. Nos. 5,420,768, 5,395,769, 5,890,794 and 5,161,879 where LEDs have been employed as curing light sources. The application of solid state sources to the curing process are also described in U.S. Pat. Nos. 6,127,447 and 5,169,675.

Technology necessary for the application of solid-state sources in the treatment process can be found in the development of LED and laser diode equipped systems for illumination and solid-state displays. These systems include an apparatus for LED illumination that can be incorporated into a hand-held lamp, are battery powered and equipped with electronics that provide pulsed power to control lamp radiance and compensate for the decrease in battery voltage during battery discharge. Published U.S. Patent Application 2002/0017844 A1 teaches the use of optical systems to modify the field of view for LED emitters in displays where the field-of-view is restricted.

There are many examples in the prior art of the use of LEDs in arrays to synthesize multi wavelength emissions. U.S. Published Patent Application No. 2001/0032985 A1 teaches the installation of arrays of colored LEDs on a chip to make multicolored or white solid-state illumination sources. U.S. Pat. Nos. 6,016,038 and 6,150,774 disclose the method and electronics needed to generate complex, predesigned patterns of light in any environment. The use of computer controlled LED arrays to provide light sources capable of rapid changes in illumination and spectral selection are detailed in U.S. Pat. No. 6,211,626, which describes a system using sub-arrays of primary colored (red, green and blue) LEDs whose individual elements are addressable and which can be controlled by pulse modulation to emit varying amounts of light to synthesize a third color. U.S. Pat. No. 6,211,626 indicates that such computer-controlled arrays of light emitters are not new but that previous systems had limitations, which reduced the flexibility or efficiency of the illumination system. The use of computer control for lighting networks used in illumination is described in U.S. Pat. Nos. 5,420,482, 4,845,481 and 5,184,114.

U.S. Published Patent Application No 2002/0191394 teaches the use of a diffractive optical element (diffraction grating) for mixing light from monochromatic light sources like LEDs and making multicolor or white beams. The monochromatic light sources are positioned relative to the grating where light of that frequency is found in the diffracted order beams higher than the zeroth order. The mixed beam is the zeroth order beam. A white beam will be provided if sufficient frequencies are represented in the first and higher order beams being directed on the grating. Fraunhoffer diffraction is used to mix the monochromatic beams. This is different from the use of Fresnel Zone plates to accomplish the coupling of the multiple radiation sources

SUMMARY OF THE INVENTION

The present invention provides a solid-state light source and method which optically combines (mixes) the light output of at least two and preferably additional independently controllable discrete solid-state light emitter arrays to produce a light beam that has a selected multi-wavelength spectrum over a wide range of wavelengths such as from deep UV to near-IR to provide irradiance of a target surface with a controlled power level. Optical mixers combine light spectrums which are provided from the light emitter arrays to produce the controllable multi-wavelength spectrum.

Specific features of this light source permit changes in the spectral, spatial and temporal distribution of light for use in curing, surface modification and other applications.

This light source can be adjusted to precisely match the physical characteristics of the applied light to the chemical properties of materials to provide a means to improve the process at both nanometer and greater length scales by:(1) optimizing the degree and rate of cross-linking of polymeric materials;(2) selecting specific cross-link bonding in polymers;(3) matching light source characteristics to specific photo-initiators;(4) controlling the distribution, penetration or rate of light energy deposition in materials to create new morphologies; and(5) optimizing light source characteristics for surface processing.

A preferred embodiment of the invention comprises at least two solid state light emitting arrays which preferably are LED arrays, each of which has a characteristic emitting frequency (wavelength), an optical mixer to mix the radiation from the LED arrays, a reflector to concentrate radiation from the arrays and to provide a two-dimensional energy distribution on the target surface to be treated which is optionally substantially uniform. An optional cooling system may be provided to provide high stability of the spectral output and to improve lifetime of arrays.

The invention increases the flexibility of the photochemical processes (especially, but not limited to, UV-curing of inks and the like, plastic, thermal paper, liquid crystal and the like) by either optimizing existing ultraviolet treatment processes and outcomes, or creating entirely new treatment processes or outcomes. The invention performs these tasks by providing a light source whose spectral emissions can be varied to provide changes in the ultraviolet light such as to changes in the brightness, chromaticity, calorimetric purity, hue, saturation and lightness of visible light. Modification of physical characteristics of light provides configuration of a light source to make the best use of the physical and chemical properties of curable materials.

Other problems which the invention overcomes include curing applications where the use of technology normally included in light sources cannot be used for technical, process or economic reasons. This includes but is not limited to:(1) high voltage cabling, electronics and power supplies;(2) RF or microwave cabling, wave guides, electronics and power supplies;(3) gaseous electronic components including electrode and electrode-less bulbs(4) high power electronics and the needed heat dissipation systems.

The invention also provides a solution to the problem of unwanted light emissions such as infrared from curing sources. Ultra-violet solid-state light emitter arrays generate little or no emissions in the infrared. If infrared radiation is needed in the curing process, infrared emitters of the desired wavelength and energy can be configured into the solid state UV generating arrays providing the selected wavelengths which are included in the curing light system to provide the desired missed spectrum.

The frequency spectrum of the individual light emitting arrays is chosen either (1) to provide a composite frequency made up of the mixed spectrum from the individual arrays required for the desired application, or (2) each array provides the identical common frequency spectrum to increase the power level of irradiance of the common frequency spectrum.

Like reference numerals identify like parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a solid state light source and a method of irradiating a target surface with a solid state light source which utilizes solid state light emitting arrays each preferably comprising a plurality of light emitting diodes (LEDs) which are mounted on a flat surface. Each diode emits light away from one side of the flat surface toward a target surface with at least one wavelength which is chosen to satisfy the desired application. At least one optical mixer is provided with each mixer mixing the output of a pair of solid state light emitting arrays. Each optical mixer is positioned symmetrically with respect to a pair of light emitting solid state arrays. Each optical mixer reflects part of the light output from a symmetrically disposed diode array and transmits part of the light output from another symmetrically disposed light array to provide a composite mixed light spectrum to irradiate the target surface with mixed light which has a selected frequency spectrum with the irradiance level of the spectrum being controllable by a variable control parameter such as voltage, but it should be understood that the invention is not limited thereto. The at least one optical mixer may be designed to substantially split (50-50) the light incident thereon from each array into a part which is reflected and a part which is transmitted through the optical mixer. With respect to the portion of the light which is transmitted through the optical mixer from the first light emitting array, the light incident on an opposite surface of the optical mixer from the other light emitting array which is reflected is optically mixed with the portion transmitted through the optical mixer from the first light emitting array. A composite wave front comprised of the mixed components of light from each of the symmetrically disposed solid state light emitting arrays is transmitted toward the irradiated target surface. As is described below, a controller controls the power applied to the light emitting arrays to control the irradiance which is incident on the target surface. Each light emitting array may have a substantially similar frequency spectrum or have a different frequency spectrum.

When the frequency spectrums of the symmetrically disposed light emitting arrays are different, the overall frequency of the irradiance on the target surface is a summation of the individual frequency spectrum output by the individual light emitting arrays. In each of the embodiments of the invention, mixing is produced by one or more optical mixers which may be a partially reflective and partially transmissive mirrors which may transmit and reflect substantially equal parts or transmit and reflect unequal parts or a prism which is irradiated by the light from the individual solid state light arrays to provide mixing thereof.

FIGS. 1A and 1Billustrate a first embodiment10of the present invention.FIG. 1Ais an elevational view with a section taken through a curved internally reflective housing21;FIG. 1Bis a perspective view of the embodiment10; andFIG. 1Cis an illustration of a suitable light emitting array which may be used with the practice of the invention.

The first embodiment10is illustrative of a basic solid state light source in accordance with the present invention. Each of light emitting arrays12A and12B may be manufactured in accordance with any well-known technique. The surface14of each of the pair of symmetrically disposed solid state light emitting arrays which, in a preferred embodiment, are LEDs output light rays16which pass directly to the target surface18. Other light rays17produce a combined irradiance produced by optical mixing element20on which the rays17are incident thereon. As may be seen inFIG. 1A, the interior of housing21has an internally reflective surface22which functions to reflect any light output from either of the light emitting arrays12A or12B toward the target surface18to provide controlled irradiance which, in a preferred embodiment, is preferably substantially uniform thereon as described below in conjunction withFIGS. 2-6in view of the curvature of surface22being elliptical with the optical mixer being near the focal axis of the elliptical curvature. Light rays16,17and19, which are output from the light emitting arrays12A and12B and do not pass through the optical mixer20, are shown as solid lines and light rays22passing through the optical mixer20, from either of the light emitting arrays12A or12B are shown as dotted rays. Parallel solid line rays19and dotted rays22symbolize the net mixing performed by the optical mixer20for the rays emitted from the surfaces of the light emitting arrays12A and12B which partially transmits and partially reflects the light emitted from the pair of light emitting arrays. The degree of reflection and transmission may be varied from an equal splitting.

The housing21, while preferably having an elliptical cross section, may utilize other curved cross sections which facilitates converging divergent light rays produced by the solid state light arrays12A and12B being directed toward the target surface18as indicated by arrows24.

The pair of light emitting arrays12A and12B are illustrated as square flat panels. The light emitting arrays are comprised of a plurality of devices, such as LEDs, which emit radiation in the ultraviolet range but the invention is not limited thereto with a suitable construction being described below in conjunction withFIG. 1C. For example, in a high power irradiation apparatus in accordance with the embodiment10ofFIGS. 1A and 1B, the arrays12A and12B may respectively be an array of 40 LEDs as described inFIG. 1Cwhich individually emit at 400 mW at 405 nm mounted on an integrated circuit of approximately 1 square cm. The other radiation source12B may, without limitation, be an array of 40 LEDs as described below emitting 100 mW at 390 nm mounted on an integrated circuit of approximately 1 square cm. Additionally, the optical mixing element20may be semi-reflective mirror which substantially equally splits the emission from the rays16into reflected rays19and transmitted rays22which are mixed as indicated by the aforementioned parallel solid and dotted lines19and22such that the rays are superimposed onto each other. A semi-reflective mirror, which may be utilized as the optical mixer20, may be a UV transmitting quartz plate that is coated with a thin chromium film that reflects and transmits approximately 50% of the incident light. The light emitting diode arrays12A and12B are symmetrically positioned with respect to the optical mixer20such that virtual images of radiation sources are superimposed to create in a preferred embodiment a mixed light source comprising substantially equal amounts of light from each of the light emitting arrays.

FIG. 1Cillustrates a suitable construction for the light emitting solid state arrays12A and12B with a scale of approximately 5:1 for the first embodiment as described above and in the embodiments as described below. The array60is comprised of 40 LEDs62. A lower bus bar64has a group of 8 LEDs mounted thereon. Each of the LEDs62mounted on the lower bus bar64are in turn coupled by a wire66by means of wire bonds68which connect the wire extending from the individual LEDs to four upper bus bars64on which 4 LEDs are mounted. A lens70focuses light emitted by the individual LEDs62toward the optical mixer20. A thermal sensor72is utilized to provide temperature control for the LED array60. The LED array60is mounted on a hexagonal substrate74. Electrical terminals76are mounted on the hexagonal substrate74to provide suitable electrical contacts for electrical power of the array.

The light source represented by the light emitting solid state arrays12A and12B and the optical mixer20is positioned approximately at the focus of the elliptical reflector22which is preferably substantially one-half of an ellipse. However, the reflector22may be more or less than one-half of an ellipse if desired and may be a non-elliptical surface. Since the reflector22is part of an ellipse, the reflector22has a major axis, a minor axis, a first focal axis within the reflector, and a second focal axis outside the reflector. The light source comprised of the aforementioned light emitting and optical mixer is preferably positioned on the first focal axis. Light beams from the arrays of diodes12A and12B are transmitted and reflected by the optical mixer20and strike the elliptical reflector22that directs the light beams to the second focal axis of the elliptical reflector22proximate to the target surface18. The target surface18is placed substantially at the second focal axis where the light beams are directed to strike the irradiated surface thereof. The location of the target surface18at the second focal axis maximizes the irradiance at the second focal axis. The irradiated surface60can also be placed beyond the second focal axis such as at the far field to increase the area which is irradiated.

FIGS. 2-6illustrate the optical performance of the radiation on the target surface18using the first embodiment10. The spectral readings were obtained using an integrated sphere and a spectral radiometer (Ocean Optics model S2000) based on techniques well-known in the field of illumination. The radiation sources were 40 light emitting diodes which are high flux density solid state modules manufactured by Norlux Monochromatic Hex (NHX) emitting either ultraviolet UV-A at a peak emission at 390 nm or ultraviolet UV-B at 405 nm with a peak emission at 410 nm. The LED arrays12A and12B were independently connected to DC power supplies operated at a constant voltage mode. A forward bias voltage turned the diodes on to produce the UV spectra ofFIGS. 2-6.

FIGS. 2 and 3show the spectral irradiance of the source12A which is a UV-A emitter and the source12B which is a UV-B emitter. Radiation source12A was operated at forward bias of 15.6 volts and a current of 200 nA. Array12A emitted UV-A ultra-violet radiation that peaked at 395 nm and extended from 385 to 405 nm (Full-Width-at-Half-Maximum) (FWHM). Diode array12B was operated at a forward bias of 19 volts and a current of 200 mA to produce UV-B ultraviolet radiation that peaked at 410 nm and extended from 400 to 418 nm (FWHM).

FIG. 4shows a measured spectral radiance of embodiment10when both radiation sources12A and12B were operated simultaneously. The composite spectrum peaked at 410 nm and extends from 392 to 418 nm FWHM. The LED array12A was operated at 15.6 volt forward bias, whereas the LED array12B was operated at 17.5 volts forward bias. The spectrum is a composite of the summed emission from the two LED arrays12A and12B.

FIG. 5illustrates the simulated spectrum produced by the summation of the individual emission spectra of the diode arrays12A and12B illustrated inFIGS. 2 and 3.

FIG. 6is a comparison of the simulated and measured spectra of the embodiment10. The measured spectra are identified by diamonds and simulated spectra are identified by lines. The measured spectrum matched a simulated spectrum over the entire range of emission from the light emitting arrays12A and12B and shows an excellent mixing of the beams from the two radiation sources.

The power levels of the light from the light emitting arrays12A and12B are controlled by varying the electrical bias applied thereto which changes the forward bias current of the diodes. The variation of voltage or another electrical parameter of the individual light emitting arrays12A and12B permits the variation of the spectral characteristic of the mixed light by choosing the magnitude and frequency of the spectra that are mixed by the optical mixer20.

FIG. 7shows how the spectral composition of a beam from the embodiment10can be changed continuously from (1) a spectrum90representing the wavelengths from the diode array12A, (2) a spectrum92with equivalent contributions from the diode arrays12A and12B, (3) a spectrum94with an increased spectrum from the array12B, and (4) finally to a spectrum96with the dominant contribution from the array12B. This demonstrates an important function of the embodiments of the invention including the representation of the spectral composition ofFIG. 1which permits generation of a spectrum with variable ultraviolet spectral weight.

FIG. 8illustrates a system120incorporating the embodiment10ofFIG. 1into a lamp housing130which is equipped with a cooling system for the LED arrays12A and12B. The air cooling system may be by forced air utilizing one or more fans inducting air into the housing and blown past the interior curved reflector21. As may be seen, pathways exist for the ingress and egress of cooling air. A controller170is coupled via connection172to the solid state light source. The curved reflector21is mounted in the lamp housing130with the reflector being attached to a base of the lamp enclosure that has a rectangular opening180from which light rays182pass to the target surface18. The LED arrays12A and12B are air cooled by two fans162which push air into the lamp enclosure130. A slot190is cut into the curved reflective surface21to permit air to be pushed into the lamp enclosure192to allow the air to impinge on heat sinks194of the LED arrays12A and12B which are attached thereto. The fans162may be powered from a 12 volt power supply. The LED arrays12A and12B will suffer a loss of light emitting power if a surface temperature of the substrate to which the LEDs12A and12B are attached exceeds 40° C. with current commercially available products. The power to the diode arrays12A and12B and the speed of the fans162is adjusted to keep the LED chip surfaces below the maximum temperature, such as 40° C. The controller170may be digitally controlled which permits programming of the voltage to be applied to each of the diode arrays12A and12B in order to produce a variation in the summed output radiation as reflected, for example by the curves90-96inFIG. 7once the frequency spectra is determined by the choice of the individual solid state light emitting elements of the array.

FIG. 9illustrates a third embodiment230of a solid state light source in accordance with the invention which is comprised of three LED arrays232A,232B and232C and three optical mixers250which intersect at a central point252within cylindrical reflector254. The three LED arrays232A,232B, and232C produce spectra which are mixed by the symmetrically disposed optical mixer250located therebetween. The aforementioned LED arrays and symmetrically positioned optical mixtures250perform the same function as described above with respect to the first embodiment10ofFIG. 1. The individual optical mixers250which intersect at central point252have an occluded angle of 120° between the adjacent optical mixers. The optical mixers250preferably are semi-reflective mirrors which split the emission substantially equally from the LED arrays232A,232B and232C into three transmitted and reflected beams of substantially equal intensity which are superimposed onto each other as indicated inFIG. 1by the superimposed light rays19and22. However, this embodiment may use optical mixers which do not transmit and reflect equal parts. The three optical mixers250are symmetrical when rotated through an angle of 120°.

FIGS. 10A and 10Bshow the results of ray tracing simulations to predict the irradiance distribution272in the XZ plane as illustrated inFIGS. 10A and 10Bfor the second embodiment230. The radiance profiles for traces parallel and perpendicular to the X or Z axis through the center of the irradiance distribution show small asymmetry272. The asymmetry is a consequence of a lack of symmetry of the embodiment230to rotations 90° along an axis perpendicular to the XZ plane through the center of the embodiment230.

FIGS. 11 and 12respectively show a third and fourth embodiment360and400. The designs respectively differ in the placement of the four LED arrays232A-232D arrays relative to the intersection362of the placement of the optical mixers350so that the diode arrays332A-332D are positioned between the edges352inFIG. 11and face the edges350inFIG. 12. In the third embodiment340, the LED arrays332A-332D face the point of intersection362while in the fourth embodiment370, the light emitting arrays332A-332D face the edges352of the optical mixers350. In the third and fourth embodiments, a cylindrical internally reflective housing360contains the LED arrays332A-332D and the four optical mixers350centrally disposed relative thereto which are joined together at central location362to form a cross. In the fourth embodiment370a solid line indicates light rays which are visible to the viewer and a dotted line indicates rays which are occluded from direct view. It should be understood that the connections to a suitable controller and cooling system for the light emitting arrays, such as illustrated inFIG. 8, are not illustrated for purposes of simplifying the illustration.

FIGS. 13 and 14show fifth and sixth embodiments400and420respectively of the invention which have been simplified to only show the LED arrays emitted. The internally reflective curved housing has been omitted along with the controller of the individual LED arrays which is used to produce a controlled application of power to the individual LED arrays to produce a variable spectrum as discussed above. The embodiment400ofFIG. 13has three pairs of LED arrays432A and432B which are symmetrically disposed relative to optical mixers440. Pairs of LED arrays432A and432B work in concert with their centrally disclosed optical mixer440to provide the same function as described above with respect to the first embodiment10to produce a controlled mixing of the light emitted from the surface of the pairs of the LED arrays. The difference between the embodiments400and420resides in the respective placement of the pairs of LED arrays432A and432B relative to the optical mixers440. In the embodiment of400, the pairs432A and432B face the point of intersection442of the optical mixers440and in the embodiment420, the pairs432A and432B face the edges444of the optical mixers440. The six optical mixers440are joined together at a central location442which is centrally disposed relative to the faces of the LED arrays432A and432B. The light from the three pairs of LED arrays432A and432B are combined by transmission and reflection of the six optical mixers440in accordance with the principal operation described above. While not illustrated, the embodiments400and420ofFIGS. 13 and 14may be placed inside of a cylindrical internally reflective housing of the type illustrated inFIGS. 1,9,10and11so as to cause light to be transmitted toward a target surface18. Additionally, a controller and a cooling system, such as that described above with respect toFIG. 8, may be utilized to control the emission of light from the LED arrays. The six optical mixers440in the embodiments400and420form a cross at a point of intersection442and preferably have the characteristic of reflecting and transmitting substantially equal intensity light. A solid line indicates light rays which are visible to the viewer and a dotted line indicates rays which are occluded from direct view.

FIG. 15shows a seventh embodiment500having three pairs of light emitting diode arrays532A and532B which are symmetrically disposed about eight optical mixers550which are triangular semi-transparent mirrors which function to split the irradiation sources532A and532B into transmitted and reflected beams of substantially equal intensity which are superimposed onto each other in accordance with the mixing function as described above with respect to the first embodiment ofFIG. 1. The LED arrays532A and532B are placed at the vertices placed at the edges of the optical mixers550. It should be noted that the curved internally reflective housing, controller and target surface have been omitted from the embodiment ofFIG. 15. A solid line indicates light rays which are visible to the viewer and a dotted line indicates rays which are occluded from direct view.

The eighth embodiment560ofFIG. 16utilizes three pairs of LED arrays532A and532B which are positioned at the vertices of twelve optical mixers550which are partially reflective mirrors. Mixing of light from pairs of LED arrays532A and532B occurs in the manner described above. A solid line indicates light rays which are visible to the viewer and a dotted line indicates rays which are occluded from direct view.

FIG. 17illustrates a ninth embodiment600having four pairs of LED arrays632A and632B which face four optical mixers650configured in a structure with tetrahedral symmetry. It should be understood that the connections to a suitable controller and cooling system for the LED arrays, such as illustrated inFIG. 8, are not illustrated for purposes of simplifying the illustration. A solid line indicates light rays which are visible to the viewer and a dotted line indicates rays which are occluded from direct view.

FIG. 18shows a tenth embodiment700of the present invention having a configuration of four LED arrays332A,332B,332C and332D symmetrically disposed about four optical mixers350in a configuration similar toFIG. 11except that an ellipsoidal reflector740is provided as the housing. The ellipsoid740has a major access, which is also the axis of rotation of the ellipse that sweeps out the surface of the ellipsoid, a minor axis, a first focus within the ellipsoid and a second focus outside the ellipsoid which are not illustrated. The LED radiation source is positioned on the major axis of the ellipsoid reflector740at the first focus. Since the irradiation source is extended, the image of the irradiation source will not be brought into sharp focus. As described above with respect to other embodiments, the internally reflective curved cylindrical housing, controller and cooling system have been omitted. A solid line indicates light rays which are visible to the viewer and a dotted line indicates rays which are occluded from direct view.

FIG. 19shows the simulated irradiance of the embodiment700ofFIG. 18on the irradiated surface18. The radiance pattern of the beam shows a ring-like pattern near the peak irradiance. This pattern is due to the placement of the radiation sources332A-332D in a circle about the optical mixers350. As described above with respect to other embodiments, the internally reflective curved cylindrical housing, controller, cooling system and target surface have been emitted.

FIGS. 20 and 21show eleventh and twelfth embodiments800and900of the present invention that utilize elongated linear arrays of diodes12A′ and12B′ with the embodiment800having elongated optical mixer20′ which is a semitransparent mirror and the embodiment900utilizing an optical mixer902which is a prism for splitting and mixing beams from the arrays12A′ and12B′ using internal reflection rather than reflection from a mirror. As described above with respect to other embodiments, the internally reflective curved cylindrical housing, controller and cooling system have been emitted.

FIG. 22shows a twelfth embodiment1000which is similar to the embodiment800ofFIG. 20regarding the configuration of the elongated light emitting diode arrays12A′ and12B′ and the elongated optical mixer20′. The embodiment1000differs with regard to the curved internally reflective housing1002which is an elliptical reflector with a side reflector as an ellipse with semi-major and semi-minor axis being parallel and perpendicular to the optical mixer20′ or a prism such as902used in the embodiment900ofFIG. 21and replacement thereof. The side reflector1004is attached to an elliptical plate1006to form an elliptical housing. As described above with respect to other embodiments, the internally reflective curved cylindrical housing, controller, cooling system and target surface have been emitted.

While the invention has been described in terms of its preferred embodiments, it is intended that numerous modifications can be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. It is intended that all such modifications fall within the scope of the appended claims.