Abstract:
A compact passively-cooled solid state illumination system is provided as a replacement for conventional arc light, metal halide and Xenon white-light sources for photocuring applications. The solid state illumination system utilizes LED modules to generate high intensity light output suitable for photocuring. The light output is continuous in the visible spectrum from 380 nm to 530 nm and is suitable for photocuring using a wide range of photoinitiators. A touchscreen interface allows programming of spectral output, intensity and duration. Output can be initiated using the touchscreen interface and/or a foot pedal.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority to U.S. Provisional Patent Application entitled “Solid State Light Source For Photocuring” Application No. 61/660,386, filed on Jun. 15, 2012 which application is incorporated herein by reference. 
       RELATED APPLICATIONS 
       [0002]    The present application is related to the following patents and patent applications which are incorporated herein by reference in their entireties: 
         [0003]    U.S. Pat. No. 7,846,391, granted Dec. 7, 2010, entitled “Bioanalytical Instrumentation Using A Light Source Subsystem,” U.S. Publication No. 2007/0281322 filed May 21, 2007; 
         [0004]    U.S. Pat. No. 7,709,811, granted May 4, 2010 entitled “Light Emitting Diode Illumination System,” U.S. Publication No. 2009/0008573 filed Jul. 2, 2008; 
         [0005]    U.S. Pat. No. 8,098,375, granted Jan. 17, 2012 entitled “Light Emitting Diode Illumination System,” U.S. Publication No. 2009/0040523 filed Aug. 5, 2008; 
         [0006]    U.S. patent application Ser. No. 13/012,658, filed Jan. 24, 2011 entitled “Light Emitting Diode Illumination System,” U.S. Publication No. 2011/0116261; and 
         [0007]    U.S. patent application Ser. No. 12/691,601, now U.S. Pat. No. 8,242,462, granted Aug. 14, 2012, entitled “Lighting Design of High Quality Biomedical Devices,” U.S. Publication No. 2010/0187440 filed Jan. 21, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0008]    The present invention relates to systems for providing light to induce curing, hardening, and/or polymerization of monomeric, oligomeric or polymeric materials. Photocuring applications include, by way of example only, dentistry, coatings, imaging, inks, manufacturing, plastic, electronics, and packaging. 
       BACKGROUND OF THE INVENTION 
       [0009]    Photocuring systems have been developed in which visible and/or ultraviolet light is used to induce curing, hardening, and/or polymerization of monomeric, oligomeric or polymeric materials. Generally speaking, a photocurable resin/adhesive includes a photoinitiator responsible for initiating free-radical polymerization of the resin. The resin remains in a liquid/workable condition until polymerization is initiated. In order to initiate polymerization, light source is used to provide light of a wavelength suitable for absorption by the photo initiator. The photoinitiator enters an excited state upon absorption of photons of the correct wavelength inducing the creation of free-radicals. The free-radicals induce curing, hardening, and/or polymerization of monomeric, oligomeric or polymeric resin/adhesive. 
         [0010]    Light energy is typically provided by one of four types of curing lights: quartz-tungsten-halogen (QTH), arc lamps, light-emitting diode (LED), arc lamps, and argon laser. Both QTH and arc lamps have broad emission spectra suitable for initiating polymerization in a broad range of resins. However, QTH and arc lamps also emit a great deal of heat/infrared. The heat/infrared output is reduced utilizing filters which may also be used to select output wavelengths suitable for particular photoinitiators. The large heat output however requires the QTH and arc lamp systems to have substantial thermal management systems and also reduces the life span of the lamps such that costly replacement parts are required. Moreover, both QTH and arc lamps have significant warm-up periods before spectral output is stable. Thus, in practice the lamps must be kept running continuously while light output is controlled using a shutter. This further reduces the effective lifespan of the lights. 
         [0011]    Argon laser systems can be used to provide light for photocuring applications. The light output is coherent and can thus be used to generate high intensity illumination with photons of a selected wavelength. However, the emission spectra of the Argon laser is very narrow and may not be compatible with some photocurable resins. Moreover, Argon laser systems are expensive and have significant thermal regulation requirements 
         [0012]    LEDs (light-emitting diodes) have matured significantly within the last decades. LEDs emit light in specific wavelengths and generate much less heat relative to arc and QTH lamps thereby providing for longer lifespan, easy switching, consistent output and lower power consumption. However LEDs presents trade-offs with respect to emission wavelength dependent intensity, broad emission spectrum (spectral half width on the order of 30 nm or more), poor spectral stability, and the wide angular range of emission. The narrow band emission may not be compatible with some photocurable resins. In addition, the process used to manufacture LED&#39;s cannot tightly control their spectral stability; anyone wishing to use LED&#39;s in applications requiring a good spectral stability typically works directly with a supplier to essentially hand-pick the LED&#39;s for the particular application. Moreover the spectral output of an LED varies with temperature. Also, LED&#39;s emit light over a wide angular range (50% of light intensity emitted at) 70°). While optics can narrow the emission band and focus the light output, the resulting loss in power and increase in thermal output further complicates the use of LEDs for photocuring. Thus, it can be difficult to provide sufficient light at a wavelength suitable for exciting a particular photoinitiator. 
         [0013]    While lighting manufacturers cannot provide all things to all applications, it is precisely this breadth of demand for which a light engine can be designed. To that end, products are not simple sources, but rather light engines, sources and all the ancillary components required to provide pure, powerful, light to the sample or as close to it as mechanically possible. A qualitative comparison of light engine performance as a function of source technology is summarized in Table I. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 A qualitative comparison of light source technology. 
               
             
          
           
               
                 Source 
                 Useable 
                   
                 Temporal 
                 Heat 
                   
                   
               
               
                 Technology 
                 Light 
                 Uniformity 
                 Response 
                 Generation 
                 Durability 
                 Cost 
               
               
                   
               
               
                 Arc Lamp 
                 med 
                 poor 
                 none 
                 high 
                 low 
                 high 
               
               
                 Laser 
                 high 
                 poor 
                 none 
                 low 
                 low 
                 very high 
               
               
                 LED 
                 low 
                 poor 
                 fast 
                 low 
                 high 
                 medium 
               
               
                 QTH 
                 low 
                 poor 
                 none 
                 medium 
                 low 
                 medium 
               
               
                 LED 
                 high 
                 high 
                 fast 
                 low 
                 high 
                 low 
               
               
                   
               
             
          
         
       
     
         [0014]    A wide range of photoinitiators are available. To initiate polymerization it is essential to provide sufficient light energy at a wavelength which can be absorbed by a selected photoinitiator. However, each photoinitiator has a particular absorption spectra. Additionally, the light energy may have to pass through the resin and other materials in order to reach the photoinitiator. Resins incorporating a photoinitiator can affect transmission and absorption of light in different ways. Accordingly, it may be difficult to ensure sufficient light energy is provided at a wavelength suitable for exciting the photoinitiator. Without proper absorption, free radical polymerization may not occur uniformly throughout the resin. Moreover, where narrow band light sources, such as LEDs, are used the wavelength provided will not be suitable for exciting all photoinitiators in all compositions and manufacturing environments. 
         [0015]    Accordingly it would be desirable to provide an LED light source for photocuring that overcomes limitations of the prior art. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention provides an LED light engine system suitable for photocuring. The LED light engine system is a compact, passively cooled, durable, inexpensive solid state lighting solution, uniquely well suited to the production of light for photocuring. In an embodiment of the invention, this light engine can provide powerful, stable, inexpensive light across a range of wavelengths suitable for photocuring. The LED light engine system is designed to directly replace the entire configuration of light management components with a single, simple unit. Power, spectral breadth and purity, stability and reliability data demonstrates the advantages of the LED light engine system for photocuring applications. Performance and cost analyses are superior to traditional optical subsystems based on QTH, arc lamps, and lasers. Moreover the LED light engine has relatively small footprint, and low heat output such that it has lower power requirements and no need for moving parts—such as a fan. 
         [0017]    In an embodiment, the present invention provides a compact passively-cooled solid state illumination system usable as a replacement for conventional arc light, metal halide and Xenon white-light sources for photocuring applications. The solid state illumination system utilizes LED modules to generate high intensity light output suitable for photocuring. The light output is continuous in the visible spectrum from 380 nm to 530 nm and is suitable for photocuring using a wide range of photoinitiators. A touchscreen interface allows programming of spectral output, intensity and duration. Output can be initiated using the touchscreen interface and/or a foot pedal. 
         [0018]    Embodiments of the present invention are directed to an LED light engine system suitable for use as a replacement for conventional QTH and arc light photocuring lamps. In particular embodiments, the LED light engine generates a broad band of wavelengths between 380 nm and 530 nm suitable for exciting a wide range of photoinitiators. 
         [0019]    Another embodiment of the present invention relates to an improved system for cooling the LED modules of the LED light engine system which reduces contamination of the LED modules and optical pathway from cooling airflow. The system includes means for conductive transmission of heat away from LED modules to a remote heat sink which is passively cooled. 
         [0020]    Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description of the various embodiments, when read in light of the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0021]    Various embodiments of the present invention can be described in detail based on the following figures. 
           [0022]      FIG. 1A  shows a view of an LED light engine system according to an embodiment of the present invention. 
           [0023]      FIG. 1B  shows the spectral power output of the LED light engine system of  FIG. 1A . 
           [0024]      FIGS. 2A and 2B  show exterior views of LED Light Engine according to an embodiment of the invention. 
           [0025]      FIG. 2C  shows a perspective internal view of the LED Light Engine of  FIGS. 2A &amp; 2B . 
           [0026]      FIGS. 2D and 2E  show side internal views of the LED Light Engine of  FIGS. 2A &amp; 2B . 
           [0027]      FIG. 2F  shows a bottom view of the LED Light Engine of  FIGS. 2A &amp; 2B . 
           [0028]      FIG. 2G  illustrates a control system of the LED Light Engine of  FIGS. 2A &amp; 2B . 
           [0029]      FIG. 3A  shows a perspective view of a LED module of the LED Light Engine of  FIGS. 2A &amp; 2B  according to an embodiment of the invention. 
           [0030]      FIG. 3B  shows a partial perspective view of the LED module of  FIG. 3A . 
           [0031]      FIG. 3C  shows a sectional view of the LED module of  FIG. 3A . 
           [0032]      FIG. 4A  shows a top view of an output optics subsystem of the LED Light Engine of  FIGS. 2A &amp; 2B  according to an embodiment of the invention. 
           [0033]      FIG. 4B  shows a top view of the optical components of the output optics subsystem of  FIG. 4A . 
           [0034]      FIGS. 4C and 4D  show different sectional views of the output optics subsystem of  FIG. 4A . 
       
    
    
       [0035]    In the figures common reference numerals are used to indicate like elements throughout the drawings and detailed description; therefore, reference numerals used in a drawing may or may not be referenced in the detailed description specific to such drawing if the associated element is described elsewhere. The first digit in a three digit reference numeral indicates the series of figures in which the referenced item first appears. Likewise the first two digits in a four digit reference numeral. 
       DETAILED DESCRIPTION OF THE INVENTION 
     LED Light Engine System for Photocuring 
       [0036]    While no one lighting solution can best satisfy all instrument architectures, an LED light engine according to an embodiment of the invention combines the best of solid state technologies to meet or outperform the traditional technologies listed in Table I on the basis of all figures of merit across all wavelengths desired for photocuring. In an embodiment of the invention, an LED light engine can emit light exceeding 500 mW/color with intensifies up to 10 W/cm 2  at wavelength suitable for photocuring. The present invention offers a smart alternative for light generation. The capabilities of the LED light engine are highlighted in Table II. The high performance illumination provided by the LED light engine is embodied in a single compact unit designed to replace the entire ensemble of lighting components. The sources, excitation filters, multicolor switching capabilities and fast pulsing are contained within one box with a small footprint such that no external optics or mechanics are required. 
         [0000]    
       
         
               
             
               
             
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 Led Light Engine Metrics. 
               
             
          
           
               
                 Key Metrics: 
               
               
                   
               
             
          
           
               
                 Spectral Output 
                 Three selected wavelengths suitable for photocuring 
               
               
                   
                 &gt;_ 100 mW/spectral band 
               
               
                   
                 1-10 W/cm 
               
               
                 Peak Wavelength 
                 Optimal for different floors, adjustable bandwidths 
               
               
                 Power Stability 
                 &gt;99% over 24 hours 
               
               
                 Spectral Width 
                 10 to 50 nm 
               
               
                 Spectral Drift 
                 &lt;1% in 24 hours 
               
               
                 Color Dependence 
                 None 
               
               
                 Lifetime 
                 &gt;5000 hrs 
               
               
                 Footprint 
                 Amenable to portability 
               
               
                 Maintenance 
                 None, no consumable components for the light 
               
               
                   
                 engine&#39;s lifetime 
               
               
                   
               
             
          
         
       
     
         [0037]    In various embodiments of the present invention, an LED light engine includes LED modules having light emitting diodes which emit wavelengths of light, which suitable for exciting a range of photoinitiators. The LEDs operate through the process of spontaneous emission, which results in a much larger selection of available wavelengths than is available for efficient stimulated emission (laser action). The outputs of LED modules each including LEDs which emit one or more color of light are combined using optics into a single output to produce multiple colors simultaneously or in sequence. The LED modules can be illuminated continuously, can be controlled in intensity, and can be pulsed on and off rapidly as necessary or desired to excite the photoinitiator in a particular application. The LED modules can be switched off between uses to eliminate the heat output. This can be contrasted with alternatives such as QTH lamps, arc lamps, and lasers which are unstable unless they are operated continuously. 
         [0038]    Because of the solid state nature and independently operable designs of the LED modules, coupled to fast (approximately 10 ns) decay times of typical materials employed, an LED light engine outperforms any broad spectrum source in terms of support for switching control. QTH and arc lamp based sources are coupled to filters and/or shutters with mechanical supports that relegate them to 1 to 50 millisecond regimes and require continuous operation of the lamp. The LED light engine incorporates all that capability into its highly integrated design. Therefore switching times are limited today by the electronics of the boards controlling the sources. Rise times of less than 20 μs and fall times of less than 2 μs are can be achieved. Moreover each color can be switched independently and is compatible with triggering by TTL, RS232 and USB and intensity control by RS232, USB or manually. 
         [0039]    Using an LED light engine, effectively instantaneous excitation of photointiators can be performed to achieve desired curing effects with no external hardware beyond the light engine itself. Moreover, because the LED light engine is based on solid state technologies, they are extremely stable both in short duration experiments and over long term use. The LED light engine is powered by 24 V power supplies operated in DC mode, therefore there is no 60 Hz noise. All colors perform similarly. In 24 hours of continuous operation, the output fluctuates on the order of 1%. Short term stability on the order of 1.0 ms is approximately 0.5%. Short term stability for 0.1 ms is diminished by a factor of ten to 0.05%. 
         [0040]      FIG. 1A  shows a view of an LED light engine system  110  according to an embodiment of the present invention. As shown in  FIG. 1A , LED light engine system  110  includes, LED light engine  100 , light guide  102 , control device  104 , a foot pedal (not shown) is also provided with LED light engine system  110 . LED light engine  100  includes LED modules for each discrete output based on solid state technologies tailored to best satisfy that output requirement complete with collection and delivery optics. Light guide  102 , receives the light output from the LED light engine  100  and transmits it to the location and/or equipment where the light is to be used for Photocuring. Light guide  102 , may be, for example, a liquid light guide or fiber optic light guide. Light guide  102 , connects to an adapter  108  on the exterior of LED light engine  100 . Control device  104 , is in this embodiment a touchscreen tablet running software which allows the control device  104  to control operation of LED light engine  100 . The touchscreen tablet, enables the user to set intensity, a countdown timer and even program custom curing cycles. Initiation of such programmed outputs can be actuated by the touchscreen or a foot-pedal (not shown). Control device  104  is connected to LED light engine  100  by USB cable  106 , however, in alternative embodiments, a wireless or network connection can be used (Bluetooth, Wifi, NFC, Ethernet etc). 
         [0041]    LED light engine  100  has a compact and novel fan-free design. The use of solid state light sources in combination with optimized thermal management allow for cool operation without the use of fans. LED light engine  100  has a long lifetime and is ideal for durable, reproducible, robust curing. A dual interlock system prevents light output from LED light engine  100  both mechanically and electronically when the light guide  102  is removed. The LED light engine  100  has no replaceable parts and no maintenance. Instant warm-up time and superior stability result in highly reproducible optical output power. LED light engine  100  is capable of fast on/off times that can be precisely controlled as well as intensity control. In an embodiment, LED light engine system  110  has the features shown Table III. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE III 
               
               
                   
               
               
                 Photocuring LED Light Engine System Features. 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Source 
                 Multiple solid state sources operating 
               
               
                   
                 simultaneously 
               
               
                 Wavelength Range 
                 380-530 nm (see FIG. 1A). 
               
               
                 Power Intensity 
                 13 W/cm2 with a 3 mm diameter liquid light guide 
               
               
                 Switching Speed 
                 5 kHz with turn on/off ~10 μs 
               
               
                 Light Delivery 
                 3 or 5 mm diameter light guide adapter (LLG sold 
               
               
                   
                 separately) 
               
               
                 Easy to install 
                 Pre-aligned, simple to operate, no maintenance 
               
               
                 Lifetime 
                 ~20,000 hours, 18 month warranty to end user 
               
               
                 Safety Features 
                 Dual electronic and mechanical safety interlock 
               
               
                   
                 system 
               
               
                 Interface 
                 7-inch, 1280 × 600 resolution touchscreen LCD 
               
               
                   
                 control pad 
               
               
                 Power requirements 
                 41 W, 24 V DC, 1.7 A power supply. 
               
               
                 Dimensions (W × 
                 110 mm × 230 mm × 190 mm (4.2 in × 
               
               
                 L × H) 
                 9.1 in × 7.5 in) 
               
               
                 Weight 
                 3.6 kg (~8 lbs) 
               
               
                 Shipment Contents 
                 LED Light Engine, DC Power Supply, Touchscreen 
               
               
                   
                 Control Pad, USB cable, foot pedal and cable, 3 mm 
               
               
                   
                 diameter light guide adapter, Power supply for 
               
               
                   
                 Touchscreen Control Pad. 
               
               
                   
               
             
          
         
       
     
         [0042]      FIG. 1B  shows the spectral power output of the LED light engine system  110  of  FIG. 1A . As illustrated by  FIG. 1B , and LED light engine system  110  is powerful, intense and produces a broad spectral light output over the range of wavelengths from 380 nm to 530 nm light, suitable for activating common photoinitiators. LED light engine  100  provides an output well matched for photocuring adhesives designed for UVA and visible wavelength curing. LED light engine system  110  is a high-performance device which generates nearly one watt of optical output power. 
         [0043]    As shown in  FIG. 1B , LED light engine system  110  produces high intensity visible light across a broad range of wavelengths suitable for photocuring LEDs (light-emitting diodes). The system exhibits good spectral stability, and focused emission. The wide emission band is compatible with most photocurable resins. Temperature is well controlled to maintain both lifespan and spectral stability. Thus, sufficient light is provided at wavelengths suitable for exciting particular photoinitiators. Moreover, the visible light generated by LED light engine system  110  has better penetration into photocurable resins than UV light, and the wide emission band means that the photoinitiator can be excited reliably across a wide range of compositions, environments, depths of resin etc thereby ensuring reliable and effective photocuring. 
       LED Light Engine For Photocuring 
       [0044]      FIGS. 2A-2G  show views of LED light engine  100  of the LED light engine system  110   FIG. 1A .  FIGS. 2A and 2B  show exterior views of LED light engine  100 .  FIG. 2C  shows a perspective view of LED light engine  100  with the cover removed.  FIGS. 2D and 2E  show side views of LED light engine  100  with the cover removed.  FIG. 2F  shows a bottom view of LED light engine  100 . 
         [0045]      FIGS. 2A and 2B  show exterior views of LED light engine  100 . As shown in  FIGS. 2A ,  2 B, LED light engine  100  is a fully enclosed in a housing  200  having a small footprint suitable for bench top use. In an embodiment LED light engine  100  has dimensions of 110 mm×230 mm×190 mm (4.2 in×9.1 in×7.5 in). A three-sided cover  210  covers the top, left and right surfaces of LED light engine  100 . The cover  210  includes vents  212  to allow cooling air to flow through the right side of the LED light engine  100 . Adapter  108  is fitted to the front plate  214  of LED light engine  100 . Back plate  220 , includes a power switch  222 , USB port  224 , power connector  226  and foot pedal connector  228 . LED light engine  100  sits on four feet  216  mounted to base plate  218 . Housing  200  thus consists of three-sided cover  210 , front plate  214 , back plate  220 , and base plate  218 . Housing  200  protects the LED light engine  100  and substantially prevents the entry/exit of light, and air except as provided by vents through housing  200 . 
         [0046]      FIG. 2C  shows a perspective view of LED light engine  100  with the three-sided cover  210  removed. As shown in  FIG. 2C , a platform  230  is mounted vertically between front plate  214  and back plate  220 . Platform  230  completely separates the left and right sides of the housing. The left side  232  of platform  230  is substantially planar for mounting and supporting the LED modules and optics. The right side  234  of platform  230  includes a large number of vertical fins  236  for cooling of platform  230 . Platform  230  is preferably machined from aluminum or another conductive metal or metal alloy. 
         [0047]    As shown in  FIG. 2C , the interior of solid LED light engine  100  is divided by a platform  230 . The left side  732  of platform  730  is substantially flat and supports the solid state light sources and associated optics. The right side  234  of platform  230  bears a plurality of fins  236  which provided a large surface area for the cooling of platform  230 . The fins are arranged vertically parallel to the axis of the air flow rising from the bottom of the housing and escaping through the top of the housing. Platform  230 , maintains the cooling air flow in the right portion of the housing between the platform  230  and the three-sided cover. This reduces the possibility of contamination of the optical components. 
         [0048]    As shown in  FIG. 2C , mounted to the left side  232  of platform  230  are three LED modules  241 ,  242 , and  243  for generating light of selected wavelengths. Each of the LED modules  241 ,  242 , and  243  includes a collimator  241   c,    242   c,  and  243   c  which forms the light output from the module into a collimated beam. The light output of LED modules  241 ,  242 , and  243  is combined into a single output beam using two dichroic mirrors  244 ,  245  which are also mounted to the left side  232  of platform  230 . The single output beam of light is directed to output optics  256  which focuses the combined beam into a light guide (not shown) inserted in adapter  108 . 
         [0049]    In an embodiment of the invention, LED light engine  100  includes three LED modules  241 ,  242 , and  243  each generating light of a different peak wavelength (color). The two dichroic mirrors serve  244 ,  245  color to create a single coaxial 3-color beam. In an embodiment the LED modules  241 ,  242 , and  243  generate violet (405 nm), blue (440 nm), and cyan (485 nm) light. In a preferred embodiment, the output beam is substantially continuous over the spectrum of 380 nm-530 nm such that it is suitable for exciting a wide range of photoinitiators. Each individual LED light source is collimated so as to be efficiently combined by dichroic mirrors  244 ,  245  and after combination, the single coaxial beam is refocused by output optics  256  into a light guide for transport to the device or system to be illuminated. Additional or different colors can be used by replacing one or more of LED modules  241 ,  242 , and  243 . For example, UV light LED module including UV LEDS in place of or in addition to the violet LED module. 
         [0050]    The cooling requirements for a solid state illumination system are substantially different than that for an incandescent light source. Incandescent lights typically release 90% or so of the heat they generate to their environment through radiation in the infrared and less than 10% through conduction. In comparison, LEDs typically release 90% or so of the heat they generate to their environment through conduction and less than 10% through conduction. Thermal dissipation is a key factor that limits the power output of an LED light source. Even though LEDs bulbs are considerably more efficient at converting electrical energy into light than incandescent light sources, but the LED components and the driver electronics can still create a considerable amount of heat. If this heat is not dissipated properly, the LED&#39;s quality of light, emission spectra, and life expectancy decrease dramatically. Thus, it is important in a solid state illumination system relying on LEDs to provide an effective solution for conductive cooling of the LEDs. Platform  230  provides both for mounting of LED modules  241 ,  242 , and  243  as well as thermal regulation as described below. 
         [0051]    As previously described cooling air is not circulated in the left portion of the housing. However, the LED modules  241 ,  242 , and  243  generate heat during operation. This heat must be removed such that the temperature of the solid state light sources is maintained at a desired level. In prior devices, the individual solid state light sources were provided with individual finned heat sinks and air was passed over the heat sinks using a common or individual fan to remove heat—however, this cooling system allowed for the entry of dust and/or other contaminants into the light sources and onto the optical components. The dust and/or other contaminants could cause a number of problems including: reduction in optical efficiency, scattering of light within the housing, burning, and burning odor. In the LED light engine  100  shown in  FIGS. 2A-2F , each of the LED modules  241 ,  242 , and  243  is in good thermal contact with platform  230 . The thermal contact is direct metal to metal contact or may be mediated by a thermal paste between the LED modules and the platform  230 . Platform  230  is made from a conductive metal/metal alloy such that heat from the LED modules is rapidly conducted away towards fins  236  through which cooling air may circulate. Thus platform  230  serves both as an optical table for mounting and aligning the LED modules, dichroic mirrors and output optics as well as a common heat sink for the LED modules. The LED modules are suitably designed to efficiently transmit heat from their components to the platform  720  as described with respect to  FIGS. 3A-3C  below. LED modules are arranged on the platform  230  based upon their heat output for example in an embodiment, LED modules  241 ,  242 ,  243  each put out 25 watts of heat each. Thus, the thermal output of the light sources is considered when arranging the light sources to ensure that each is adequately cooled by the cooling airflow on the finned side of platform  230 . Note, in  FIG. 2E , for example that the LED modules  241 ,  242 ,  243  are arranged so as to be horizontally displaced from each other such that each is effectively cooled. In a preferred embodiment passive cooling of fins  236  by air passing through the vents in housing  200  (see  FIGS. 2A ,  2 B) is sufficient to maintain the temperature of LED modules  241 ,  242 , and  243  without the use of a fan. Note also that platform  230  divides the internal volume of housing  200  such that cooling air only flows through the right side over fins  236 . The left side  230  of housing  200  is unvented such no external air passes around the optical components and LED modules  241 ,  242 , and  243 . This reduces the possibility of contamination by dust and the like. 
         [0052]      FIGS. 2D and 2E  show side views of LED light engine  100  with the three-side cover  210  removed.  FIG. 2D  shows the right side  234  of platform  230  showing fins  236  which are vertically mounted such that heated air can pass up through base plate  218  and out through vents  212  in three-sided cover  210  thus facilitating convective cooling of fins  236  without the use of a fan. A control board  240  is also housed adjacent the right side  234  of platform  230  and is connected to includes a power switch  222 , USB port  224 , power connector  226  and foot pedal connector  228  through back plate  220 . Control board  240  also receives cooling air flow. Control board  240  includes the circuitry for driving the solid state light sources and sensors of LED light engine  100 . 
         [0053]      FIG. 2F  shows a bottom view of LED light engine  100 . Note that bottom plate  218  includes a plurality of slots  219  aligned with the gaps between fins  236  (not shown). Slots  219  are designed such that air can flow through slots  219  and between fins  236  thereby cooling platform  230  (not shown) by passive convection with requiring a fan. 
         [0054]    The LED modules  241 ,  242 ,  243  are controlled by the controller board  240  either together or individually to control the spectral content of the output beam. In embodiments of the invention, three LED modules  241 ,  242 ,  243  produce spectral components centered on colors violet 405 nm, blue 425-460 nm, and cyan 460-500 nm. All the and three LED modules  241 ,  242 ,  243  can be turned on at the same time such that the different colors are combined to create a substantially continuous spectrum over the range 380 nm-530 nm. 
         [0055]      FIG. 2G  illustrates a control system of the LED light engine  100 . As shown in  FIG. 2G , control board  240  includes a controller  270 . Controller  270  includes an input/output system  272  for receiving data from the various sensors, input port and input devices and sending data to the data output port and or any indicator/display devices. Controller  270  is coupled to power output system  274  which provides power to the electrical, optical and mechanical components of LED light engine  100 . Because of the solid state nature and independently operable designs of the light sources, coupled to fast (approximately 10 ns) decay times of typical materials employed, the solid state illumination system does not require a mechanical shutter and is capable of rise times of less than 20 μs and fall times of less than 2 μs under the control of controller  270  which is compatible with triggering by a control device  104  connected to USB port  224  and/or by a foot pedal connected to foot-pedal port  228 . Each light source is operated simultaneously to generate a continuous light output spectrum. Alternatively, each source can be switched independently to generate an output of the desired spectral power distribution and/or color. 
         [0056]    In the control system embodiment shown in  FIG. 2G , controller  270  is coupled by input/output system  272  to USB port  224 , foot pedal input  228 , safety flap sensor  276 , toggle switch  222 , additional sensor(s)  278 , display/indicators  280 , as well as the heat and light sensors of LED modules  241 ,  242 ,  243 . Controller  270  is coupled to power output system  274  which provides electrical power to drive the LEDs and laser diodes of LED modules  241 ,  242 ,  243 . Additional sensors  278 , display/indicators  280  and inputs/switches and outputs may be added to LED light engine  100  as necessary to support desired functionality for the system, however, typically a control device  104  connected to USB port  224  is used to control and monitor LED light engine  100  and provides control and data display flexibility through a software application. For example, as shown in  FIG. 1A  a control device  104 , in the form of a touchscreen tablet running software which allows the control device  104  to control operation of LED light engine  100 . The touchscreen tablet, enables the user to: set intensity for each LED module separately or as a group; set and initiate a countdown timer; and program custom curing cycles. Initiation of such programmed outputs can be actuated by the touchscreen or a foot-pedal (not shown). Control device  104  is connected to LED light engine  100  by USB cable  106 , however, in alternative embodiments, a wireless or network connection can be used (Bluetooth, Wifi, NFC, Ethernet etc). 
       LED Module For Photocuring System 
       [0057]      FIGS. 3A-3C  shows views of LED module  241  and collimator  241   c.  LED modules  242  and  243  have the same design though each of LED modules  241 ,  242  and  243  preferably includes LEDs which emit light of different wavelengths than the others of LED modules  241 ,  242  and  243 .  FIG. 3A  shows a perspective view of LED module  241 , collimator  241   c  and associated dichroic mirror  244 . As shown in  FIG. 3A , LED module  241  includes a base  300  adapted to be mounted to platform  230  (see  FIGS. 7C-7E ). Collimator  241   c  is mounted to base  300 . 
         [0058]      FIG. 3B  shows a partial perspective view of LED module  241 , collimator  241   c  and associated dichroic mirror  244 . As shown in  FIG. 3B , LED module  241  includes an LED die  310 . LED die  310  includes a plurality of light-emitting diodes on the same substrate. The substrate is mounted in direct or indirect thermal contact with base  300  such that heat generated by the light-emitting diodes during operation is transmitted to base  300 . Base  300  is secured in thermal contact with platform  230  such that heat is rapidly transferred to platform  230  and then dissipated from fins  236 . 
         [0059]    Referring again to  FIG. 3B , light emitted from LED die  310  is collected through plano-convex-lens  326  placed over die  310 . The light passes through plano-convex lens  326  and is collimated by plano-convex lenses  327 ,  328  of collimator  241   c.  A light sensor  329  is placed adjacent plano-convex lens  327  where it receives scattered light in order to monitor the light output of LED die  310 . After passing plano-convex lenses  327 ,  328  the collimated light beam is directed at dichroic mirror  244 . Dichroic mirror  244  is aligned such that the collimated beam of light is directed along an optical axis towards output optics  256  (see  FIG. 2E ). 
         [0060]      FIG. 3C  shows a sectional view of LED module  241  and collimator  241   c.  As shown in  FIG. 3C , LED module  241  includes an LED die  310 . LED die  310  includes a plurality of light-emitting diodes on the same substrate. The substrate is mounted in direct or indirect thermal contact with base  300  such that heat generated by the light-emitting diodes of LED die  310  during operation is transmitted to base  300 . Base  300  is secured in thermal contact with platform  230  such that heat is rapidly transferred to platform  230  and then dissipated from fins  236  (not shown, but see  FIG. 2D ). Referring again to  FIG. 3C , light emitted from LED die  310  is collected through plano-convex-lens  326  placed over die  310 . The light passes through plano-convex lens  326  and is collimated by plano-convex lenses  327 ,  328  of collimator  241   c.    
       Output Optics for Photocuring System 
       [0061]      FIGS. 4A-4D  illustrate output optics  256  of LED light engine  100  (see  FIGS. 2C and 2E ). As shown in  FIG. 4A , output optics  256  receives the collimated combined beam of light  254  from all the light sources of LED light engine  100 , focuses the combined beam  254  and directs it into the aperture  428  of light guide  102 . An adapter  108  connects light guide  102  to output optics  256  and positions light guide  102  such that the aperture  428  of the light guide is correctly positioned to receive the focused combined beam of light  254 . Output optics  256  are positioned against front plate  214  such that light guide  102  can be connected to output optics  256  through an aperture in front plate  214 . 
         [0062]    As shown in  FIG. 4B , output optics  256  includes two plano-convex lenses  426 ,  427 . Plano-convex lenses  426 ,  427  receive the collimated combined beam of light  254  from all the light sources of LED light engine  100 , focuses the combined beam  254  and directs it into the aperture  428  of light guide  102 . Light guide  102  transmits the combined beam to a location or instrument used to excite a photoinitiator. 
         [0063]      FIGS. 4C and 4D  are sectional views of output optics  256  illustrating attachment of a light guide  102 .  FIG. 4C  shows output optics without light guide  102  in place. As shown in  FIG. 4C , light guide  102  includes a housing  400  which defines a lumen  402 . Housing  400  is mounted to platform  230 . Housing  400  projects through aperture  424  in front plate  214  such that lumen  402  is accessible from the exterior of solid state illumination system  700 . As shown in  FIG. 4C , a safety flap  404  occludes lumen  402  to prevent the exit of light or entry of contaminants through lumen  402  when light guide  102  is not connected. Safety flap  404  is spring loaded such that it occludes lumen  402  automatically upon removal of a light guide  102 . Safety flap  404  pivots out of the way when a light guide  102  is inserted. One or more limit sensors (not shown) are coupled to safety flap  404  to sense the position of safety flap  404  (and thus the presence or absence of a light guide) and provide such information to controller board  240 . The safety flap  404  and sensor operate as dual interlock system to prevent light output from LED light engine  100  both mechanically and electronically when the light guide  102  is removed. 
         [0064]    As shown in  FIG. 4D , light guide  102  is received in an adapter  108  which connects light guide  102  to output optics  256  and positions light guide  102  such that the aperture  428  of the light guide  102  is correctly positioned to receive the focused combined beam of light  254 . When adapter  108  and light guide  102  are inserted into lumen  402  of housing  400 , safety flap  404  pivots out of the way. Aperture  428  is positioned coaxial with plano-convex lenses  426 ,  427  such that the combined beam of light  254  is focused into aperture  428  of light guide  102 . Light guide  102  transmits the combined beam to a location or instrument used to excite a photoinitiator. 
         [0065]    The foregoing description of the various embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art. Embodiments were chosen and described in order to best describe the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention, the various embodiments and with various modifications that are suited to the particular use contemplated. Other features, aspects and objects of the invention can be obtained from a review of the figures and the claims. It is to be understood that other embodiments of the invention can be developed and fall within the spirit and scope of the invention and claims.