Abstract:
A photocuring device and a method of photocuring using it. The device includes a housing and a light emitting semiconductor array mounted to the housing, capable of emitting light energy having a light output wavelength suitable for initiating a photoreaction. The device also has a power source for providing power to energize the array to emit light energy and a controller coupled to the power source for varying the power provided by the power source to the array.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of radiation delivery systems, including photocuring systems. 
     BACKGROUND OF THE INVENTION 
     The utilization of photopolymerized materials, adhesives and encapsulants in industrial manufacturing applications has increased dramatically in the past decade. For the most part, this has been a result of the advances in photochemistry. 
     Correspondingly, light source technology has evolved utilizing medium pressure linear ultraviolet (UV) lamps, microwave powered UV lamps, xenon lamps and high-pressure mercury vapour and metal halide lamps. These lamps provide photons in the absorption bandwidth of the photo-initiators utilized in the chemistry required to complete the photochemical reaction. 
     In general, the available old lamp technology required to provide the energizing photons operates with an efficiency of 1-10% in order to provide broadband energy between 248 nanometres (nm) to 500 nm in wavelength required for the photochemical reaction. Typically these lamps require a warm up time to reach full output power, cannot be turned off and on rapidly, generate a great deal of electromagnetic interference (EMI) necessitating extensive shielding, require venting for ozone produced and often contain mercury, an environmentally hazardous substance. Other commonly used light technologies have a limited lifetime (greater than 1,000 hours) with continuous degradation over time. 
     There is accordingly a need for apparatus which efficiently emits light energy suitable for initiating a photoreaction. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards a light curing device, which has common, but by no means exclusive application to industrial manufacturing applications involving photoreactive materials. When used herein, it should be understood that “curing”, “photocuring” and “photoreaction” are intended to include the concepts of “thermal curing”, “polymerizing” and “photoinitiating”, each of which terms (and variations thereof) may be used interchangeably herein. 
     The device according to the present invention includes a housing and a light emitting semiconductor array mounted to the housing, capable of emitting light energy having a light output wavelength suitable for initiating a photoreaction. The device also has a power source for providing power to energize the array to emit light energy and a controller coupled to the power source for varying the power provided by the power source to the array. 
     The invention is also directed towards the use of the present photocuring device invention described above to cure photoreactive materials. Similarly, the invention is directed towards a method of curing photoreactive products using the photocuring device invention. The method comprises the steps of: 
     A. providing a light curing device of the present invention; 
     B. positioning a photoreactive product proximate the light curing device; and 
     C. causing the device to emit light energy suitable for initiating a photoreaction onto the product until the product is sufficiently photocured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example only, with reference to the following drawings, in which like reference numerals refer to like parts and in which: 
     FIG. 1A is a schematic diagram of a photocuring device made in accordance with the present invention. 
     FIG. 1B is a side schematic diagram of the array head cooling system of FIG.  1 A. 
     FIG. 1C is a schematic diagram of the base unit cooling system of FIG.  1 A. 
     FIG. 1D is a schematic diagram of an alternate configuration of a base unit cooling system. 
     FIG. 1E is a schematic diagram of an alternate configuration of a photocuring device made in accordance with the present invention, having a different cooling system than the device of FIG.  1 A. 
     FIG. 1F is a side view schematic diagram of a photo sensor configuration of FIG.  1 A. 
     FIG. 1G is a top view schematic diagram of an alternate photo sensor configuration than in FIG.  1 F. 
     FIG. 2A is a perspective view of a first alternative embodiment of a modular LED (light emitting diode) array head assembly. 
     FIG. 2B is a side schematic view of the modular LED array head assembly of FIG.  2 A. 
     FIG. 2C is a side schematic view of a microlens configuration for an LED array head assembly. 
     FIG. 2D is a chart indicating the light energy output of LED die having different peak output wavelengths. 
     FIG. 2E is a chart indicating the additive light energy output of the LED die of FIG.  2 D. 
     FIG. 3 is a front perspective view of a first alternate configuration of an LED array head assembly. 
     FIG. 4 is a top perspective view of a third alternative configuration of an LED array head assembly having a concave surface. 
     FIG. 5 is a top perspective view of a fourth alternative configuration of an LED array head assembly having a tubular configuration. 
     FIG. 6 is a top perspective view of a fifth alternative configuration of an LED array head assembly having a tubular configuration. 
     FIG. 7 is a top view of sixth alternative configuration of an array head assembly having LEDs configured in a shape approximating the periphery of a circle. 
     FIG. 8A is a top view of a seventh alternative configuration of an array head assembly having LEDs configured in a shape approximating the periphery of a square. 
     FIG. 8B is a top view of an eighth alternative configuration of an array head assembly having LEDs configured in a shape approximating a triangle. 
     FIG. 9 is a side view of a ninth alternate configuration of an LED array head assembly having opposed arrays of LEDs. 
     FIGS. 10A-10C show top views of a tenth alternate configuration of an LED array head assembly having an array of addressable LEDs. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1A, illustrated therein is a first embodiment of the subject invention. The photocuring device, shown generally as  10 , typically comprises a base unit  12  and a remote LED array head assembly  14  operationally coupled to the base unit  12 . 
     The base unit  12  typically includes a base unit housing  16  which may contain a controller  18  (typically a suitably programmed CPU (central processing unit) having RAM (random access memory) and ROM (read only memory) operationally connected to a power source  20 . Preferably, the device  10  also has a cooling system  22  and a control data interface  24  operatively coupled to the controller  18  which displays operational data to the user on a display  26 , and which receives input control instructions via an input device  28  from the user to the controller  18  which controls the operation of the device  10 . 
     Alternatively, as will be understood, the controller  18 , control data interface  24 , input device  28  and display  26  may be replaced with similar components (controller  18 ′, control data interface  24 ′, input device  28 ′ and display  26 ′) operatively coupled to, but remote from, the base unit  12 . 
     The head assembly  14  includes a head assembly housing  30  holding an array  32  of LED die  34 . Preferably, the assembly  14  also comprises a temperature sensor  36  for detecting the operating temperature of the array  32 , as well as a photo, photodiode or optical sensor  38  for detecting the levels of light energy generated by the array  32 . 
     Typically, the power source  20  will be adapted to provide regulated current to the LEDs during operation, using pulse width modulation to control the radiance of the LEDs (as controlled by the controller  18 ). 
     The cooling system  22  includes base unit  12  cooling system components  23  and array head assembly  14  cooling system components  25 . The head assembly  14  is operatively coupled to the base unit  12  through flexible connectors  50  which include tubing for circulating liquid coolant between base unit cooling system  23  and the array head cooling system  25 , as will be described in greater detail below. The connectors  50  also include electrical cabling to supply power to the array  32 , as well as to conduct data signals from the sensors  36 ,  38  to the controller  18 . Preferably the head assembly  14  and the connectors  50  are designed such that the assembly  14  may be operatively coupled and decoupled from the base unit  12 , to enable the assembly  14  to be replaced, or exchanged with an assembly having an alternate configuration. 
     FIG. 1B illustrates a side view of the array head assembly  14  cooling system components  25 . The head cooling system  25  typically includes a liquid cooled cold plate  40  mounted behind the LED array  32 , for absorbing heat generated by the LED die  34  when in operation. The LED die  34  are mounted on a thermally conductive substrate  39 , typically ceramic, to spread and conduct heat to the cold plate  40 . The cooling system  25  also has an inlet  41  for receiving liquid coolant from the base unit cooling system  23 . The coolant travels through a circulatory channel  37  passing through the cold plate  40  to an outlet (not shown). 
     FIG. 1C illustrates a side schematic view of the various base unit cooling system  23  components. The base unit cooling system  23  preferably includes a cold plate  42 , a thermo electric cooler  43 , as well as a heat sink  44 , a fan  45  and a liquid reservoir  46  for storing the liquid coolant. A pump  48  is also provided for circulating the coolant throughout the cooling system  22 . As will be understood, the base unit cooling system  23  has an inlet  52  for receiving heated coolant from the array head assembly  14  cooling system  25 . The heated coolant travels through a circulatory channel  53  passing through the cold plate  42 . The heat stored in the coolant is transferred to the cold plate  42 , which in turn conducts the heat energy to the thermo electric cooler  43 . The heat energy is transferred to the heat sink  44 . The fan  45  is preferably located proximate an exterior wall of the base unit housing  16 , to draw external air across the heat sink  44  thereby increasing its cooling efficiency. The cooled coolant is then directed by the pump  48  to the reservoir  46 . Coolant may then be circulated through the outlet  54  to the array head assembly  14  cooling system  25  through the connectors  50 . 
     Referring now to FIG. 1D, illustrated therein is a schematic diagram of an alternate configuration of a base unit cooling system  23 ′. In place of the heat sink  44 , the thermo electric cooler  43  and the cold plate  42  of the cooling system  23  illustrated in FIG. 1C, the alternate cooling system  23 ′ utilizes a heat exchanger  56  positioned proximate a fan  45  near an external wall of the base unit housing  16 . Heated liquid coolant is received through the inlet  52 , and is circulated by a pump  48  through a circulatory channel  53 ′ passing through the heat exchanger  56 , before it exits through the outlet  54 . 
     A further alternate configuration of the cooling system  122  is illustrated in FIG.  1 E. The device  110  is generally similar to the device  10  illustrated in FIG.  1 A. In place of the heat sink  44 , the thermoelectric cooler  43  and the cold plate  42  illustrated in FIG. 1A, the alternate cooling system  122  may include a heat exchanger  156  external to the base unit  112 , coupled to a coolant reservoir  146  and pump (not shown). Connectors  150  (connecting the head assembly  114  and heat exchanger  156  to the base unit  112 ) provide tubular conduits for the circulation of liquid coolant, and also electrical cabling to supply power to the array  132  in the head assembly  114  (generally similar to head assembly  14 ) and the heat exchanger  156 . Connectors  150  also conduct data signals from the photo sensors  136  and temperature sensors  138  to the controller  118  (generally similar to controller  18 ). Instead of being coupled directly to the base unit  112 , alternatively, a heat exchanger  156 ′ may be directly coupled to the head assembly  114 , as will be understood. 
     While LEDs typically provide relatively stable radiance output, some degradation occurs over time. Referring back to FIG. 1A, the photo sensor  38  will preferably comprise semi-conductor photodiodes, and will provide continuous monitoring of the light energy output of the array  32 , to enable the system  10  to provide measurable quantities of light energy, providing a high level of confidence that the required light energy has been delivered to the workpiece. Irradiation control is important when photocuring products and materials having narrow tolerance levels, such as bonding photonic components including solid state lasers and single mode fibers. 
     Referring now to FIG. 1F, illustrated therein is a side schematic view of a photo sensor  38  arrangement. The array  32  of LED die  34  should preferably be protected. An output window  57  may be positioned above the LED die  34 , thereby providing some protection to the LED die  34 . Preferably the output window  57  is made of clear plastic or other material which has been selected such that the majority of light energy (preferably at least 90%) emitted by the LED die  34  (as indicated by light vectors  58 ) passes directly through the output window, with a small percentage of the light energy (typically less than 10%) being internally reflected within the output window  57  (as indicated by light vectors  59 ). 
     Preferably, a photo sensor  38  will be positioned and configured to measure light  59  which is internally reflected within the output window  57  of the array  32 . The light which is reflected internally can be measured by the photo sensor  38 , which may include photodiodes. Such a configuration minimizes or prevents light energy reflected from the workpiece or from external sources from being detected by the photo sensor  38  and affecting the accuracy of the readings. As a result, the reflectivity of the workpiece or the proximity of the workpiece to the array  32  will have a reduced impact on the accuracy of the data generated by the photo sensor  38 . As will be understood, a series of photo sensors  38  positioned around the perimeter of the output window  57  of the array  32  will detect any changes in average optical power. 
     A top schematic diagram of an alternate photo sensor configuration is illustrated in FIG.  1 G. Optical fibers  61  may be positioned between the LED die  34  in the array  32 . Preferably, the optical fibers  61  will be made of material which is able to receive sidewall light emissions from the LED die  34 , and direct the received light energy (through internal reflection) toward photo sensors  38 , such as photodiodes. 
     Referring now to FIG. 2A, illustrated therein is a first alternative embodiment of a modular array head assembly  14   A , with some of the LED die  34  removed for illustrative purposes. The assembly  14   A  comprises a platform  60  designed to operatively engage a plurality of array modules  62  which collectively form an array  32   A . Each module  62  is typically square or rectangular and comprises an array of LED die  34  and sensors  36 ,  38 , mounted onto a printed board substrate, as will be understood by one skilled in the art. The modules  62  are typically formed of thick film or plated metal circuitry on an electrically insulating substrate, such as a ceramic alumina. Alternatively, the circuit can be printed directly onto a metal substrate. Preferably, the substrate will in turn be mounted onto a metal heat sink  63 . The platform  60  also comprises array connectors  64  for electronically and physically engaging the array modules  62 . 
     The platform  60  also preferably includes locating holes  65 , designed to receive locating pegs positioned on the back of the modules  62 , for accurately positioning the modules  62  on the platform  60 . 
     The platform  60  also includes a liquid coolant inlet  66  and a liquid coolant outlet  68  for releasably engaging the connectors  50 . Typically, the base of the platform  60  will be a liquid cooled cold plate formed of metal or other heat conductive material, having a circulatory path for the coolant commencing at the inlet  66  and passing beneath the various array modules  62  and ending at the outlet  68 . Preferably, the heat sink  63  is mounted to the cold plate to assist in transferring the heat generated by the LED die  34  to the cold plate. The platform  60  also has an input connector  70  adapted to releasably engage the electrical cabling portion of the connectors  50 , to provide an electrical connection between the controller  18  (and power source  20 ) and the modules  62 . The input connector  70  preferably comprises a communications protocol chip  72  for coordinating the communication of the data generated by the sensors  36 ,  38  to the controller  18  (illustrated in FIG.  1 A). 
     FIG. 2B illustrates a side schematic representation of the modular array head assembly  14   A  substantially illustrated in FIG.  2 A. As described in relation to FIG. 2A, modules  62  comprise an array of LED die  34  (collectively forming an array  32   A ) mounted on the plated metal or thick film circuitry  80  of a ceramic alumina circuit board  69 . In turn, the circuit board  69  is mounted to a metal heat sink  63 . The module  62  also includes electrical connectors  84 , to electrically engage the platform&#39;s  60  array connectors  64  (illustrated in FIG.  2 A), and provide power to the circuit board  69 . A liquid cooled cold plate  86  is provided at the base of the platform  60 . Liquid coolant circulates throughout the cold plate  86  through a circulatory channel  88  commencing at the inlet port  66  and exiting at the outlet port  68  (illustrated in FIG.  2 A). The platform  60  also preferably includes locating holes  65  passing through the cold plate  86 , designed to engage locating pegs  90  mounted to the base of the module  62 . The pegs  90  are fixed to the platform  60  through the use of removable fasteners  92  to provide close physical contact between the cold plate  86  and the heat sink  63 . With the fasteners  92  removed, the modules  62  can in turn be removed from the platform  60 . 
     As should be understood, by making the array modules  62  square or rectangular, the overall size of the array  32  is scalable, since the platform  60  may be designed to accommodate multiple LED modules  62 , each of which can abut another module  62  on each of its four sides. Large area planar light sources can thus be constructed using these LED module  62  building blocks. Another advantage of this configuration is that modules  62  can be individually replaced, if desirable, as a result of damage or long use. 
     Preferably, each module  62  comprises a series of current limiting resistors, to equalize current through each module  62 . Additionally, preferably the array connectors  64  (and the modules  62 ) are wired in a series-parallel configuration, as will be understood by one skilled in the art. 
     As illustrated in FIG. 2C, preferably, the array  32  also incorporates a grid  93  of reflectors or refractors which direct any sidewall emission of light (illustrated by light vectors  94 ) from each LED die  34  towards the workpiece to be cured. The LED array  32  also preferably incorporates a conformal coating  95  with a refractive index between that of the LED material and air to increase the coupling of light from the LED die  34 . Additionally the array  32  also preferably incorporates a microlens array  97  positioned between the LED die  34  and the workpiece, configured to collimate the emitted light (illustrated by light vectors  98 ). The microlens array  97  also serves to protect the LED die  34  from contact. 
     As should be understood, LEDs typically have a long operational life and provide a steady output intensity level over the operational life of the LED. However, LEDs do degrade slowly over time. Referring back to FIG. 1A generally, the photo sensor  38  will preferably comprise semi-conductor photodiodes, and will provide continuous monitoring of the light energy output of the array  32 , to enable the system  10  to provide measurable quantities of light energy, providing a high level of confidence that the required light energy has been delivered to the workpiece. Irradiation control is important when photocuring products and materials having narrow tolerance levels, such as bonding photonic components including solid state lasers and single mode fibers. 
     As should also be understood, the miniature size of the LED die  34  (approx 10×10 mil) permit array densities up to 4,000 LED die per square inch which can provide a significant quantity of energy and homogeneity of output light energy. 
     As an alternative to LEDs, organic LEDs (such as organic planar light devices) or any other semi-conductor light source can be used such as laser diodes and vertical cavity emitting lasers. As well, the LEDs may be selected such that they emit light energy in the infrared or near infrared range for heat curing applications. 
     As will be understood by one skilled in the art, the controller  18  is preferably programmed to receive data from the control data interface  24  corresponding to user requirements for light output power (irradiance), exposure time (or multiple exposure times), and on/off rates of the array  32  and variation of irradiance throughout an exposure cycle. The controller  18 , periodically monitors the feedback data generated by the photo sensor  38 , then controls the power supplied to the array  32  to generate the required light energy output. 
     Similarly, one or more thermal sensors  36  are preferably placed proximate or within the array  32  to generate and forward temperature data to the controller  18  to control the cooling system  22  or to terminate the supply of power to the array  32  to ensure that the LED die  34  are operating within the manufacturer&#39;s recommended temperature range. 
     Depending on the absorption characteristics of the material to be photoinitiated, all of the LED die  34  or other light emitting devices in the array  32  may be selected to emit light energy having substantially the same peak wavelength. Alternatively, the LED die  34  or other light emitting devices in the array  32  may be arranged in groups such that each LED die  34  or other light emitting device emits light energy having substantially the same peak wavelength as every other LED die  34  or other light emitting device in its group, but different from the output wavelength of the LEDs or light emitting devices in a different group. Alternatively, multiple wavelength diodes can be spread randomly over the array to generate a light source with a broader bandwidth. Groups may comprise complete modules  62  (as illustrated in FIG.  2 A), depending on the size of the array  32 . As well, the controller  18  is preferably programmed to direct different quantities of power to each group, possibly at different times and for different durations, in accordance with the curing requirements of the workpiece. 
     Referring now to FIG. 2D, illustrated therein is a chart indicating the light energy output of four different types of LED die, each having different peak output wavelengths. The vertical axis represents the output power of the LED die in milliwatts (mW), while the horizontal axis represents the wavelength of the light energy emitted by the LED die in nanometers (nm). The first type of LED die emit light over a range of wavelengths  34   A  (as illustrated by the first roughly parabolic curve on the chart) and have a peak output wavelength of approximately 370 nm. The second type of LED die emit light over a range of wavelengths  34   B  (as illustrated by the second roughly parabolic curve on the chart) and have a peak output wavelength of approximately 405 nm. The third type of LED die emit light over a range of wavelengths  34   C  (as illustrated by the third roughly parabolic curve on the chart) and have a peak output wavelength of approximately 430 nm. The fourth type of LED die emit light over a range of wavelengths  34   D  (as illustrated by the fourth roughly parabolic curve on the chart) and have a peak output wavelength of approximately 470 nm. 
     The continuous curve  34   E  on the chart of FIG. 2E indicates the cumulative light energy output of the LED die  34   A ,  34   B ,  34   C ,  34   D  of FIG.  2 D. Accordingly, as should be understood, if the LED die  34  of an array  32  are selected in groups matching the output wavelengths of the LED die  34   A ,  34   B ,  34   C ,  34   D , respectively, and if all such LED die  34  are energized to emit light energy simultaneously, the array  32  would function as a light source having a broad bandwidth. 
     In use, a user manipulates the device  10  such that the head assembly  14  is positioned proximate a workpiece intended to be irradiated with photoinitiating light energy. The user then inputs the curing parameters for the workpiece using the control data interface  24 , which are stored by the controller  18 . Such curing parameters may include the quantity of light energy required for the cure, or may simply include the desired power level and the duration of the cure period. If the LED die  34  in the array  32  are arranged in groups (of different types or configurations of LEDs), the control data interface  24  may include specific curing parameters including the timing and duration of a cure period for each group to be energized to emit light energy. 
     In accordance with the curing parameters, the controller  18  causes the power source to supply electrical energy to the array  32 , causing the LED die  34  to emit light energy which is directed onto the workpiece. Throughout the curing period, the controller  18  monitors the temperature of the array  32  (as sensed by the temperature sensor  36 ), and controls the cooling system  22  to ensure that the temperature remains within acceptable parameters. Additionally, the controller  18  monitors the intensity of the light emitted by the array  32  (as sensed by the photo sensor  38 ) and adjusts the supply of power provided by the power source  20  as necessary to maintain the intensity within the curing parameters. 
     As shown in FIG. 3, illustrated therein is a second alternative embodiment of a head assembly  314  shown with a head assembly housing  330  enclosing an array  332  of LED die  334 , with the connector  350  attached to the assembly  314 . As should be understood, these components  330 ,  332 ,  334 ,  350  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     FIG. 4 illustrates a third alternative embodiment of a head assembly  414  with the connector  450  attached to the assembly  414 . The assembly housing  430  as well as the array  432  are configured to form a concave surface where the LED die  434  are mounted. Typically, such a contoured configuration will be adopted to match the shape of the corresponding surface area portion of the workpiece to be cured. As will be understood, the head assembly  414  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should also be understood, these components  430 ,  432 ,  434 ,  450  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     FIG. 5 illustrates a fourth alternative embodiment of a head assembly  514 , with the connector  550  attached to the assembly  514 . The housing  530  has a tubular configuration, in which the LED die  534  of the LED array  532  are positioned throughout the interior of the tube. With such a configuration, a workpiece to be cured may be inserted into the interior of the head assembly  514 , for curing. As will be understood, such a configuration provides 360° of essentially uniform light emission (about the tube&#39;s longitudinal axis) within the tube. Alternatively, the array  532  may extend only partway around or cover only certain portions of the interior of the tube, depending on the requirements of the workpiece to be cured. As will also be understood, the head assembly  514  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should further be understood, these components  530 ,  532 ,  534 ,  550  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     FIG. 6 illustrates a fifth alternative embodiment of a head assembly  614 , with the connector  650  attached to the assembly  614 . The housing  630  has a tubular configuration, in which the LED die  634  of the LED array  632  are positioned about the exterior of the tube. While the array  632  may extend around the entire periphery of the tube, alternatively, the array  632  may extend only partway around or cover only certain portions of the periphery, depending on the requirements of the workpiece to be cured. With such a configuration, the tubular head assembly  614  may be inserted into the interior of a workpiece, for internal curing. As will be understood, the head assembly  614  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should further be understood, these components  630 ,  632 ,  634 ,  650  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     Referring now to FIG. 7, illustrated therein is a sixth alternative embodiment of an array head assembly  714  with the connector  750  attached to the assembly  714 . The LED die  734  in the array  732  have been arranged in a shape approximating the periphery of a circle. Such a configuration may be selected when the portion of the workpiece to be cured is ring-shaped. The array head assembly  714  may be provided with a cylindrical hole  731  passing through the assembly housing  730 , in the center of the LED die  734  circle. As will be understood, the head assembly  714  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should further be understood, these components  730 ,  732 ,  734 ,  750  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     Referring now to FIG. 8A, illustrated therein is a view of a seventh alternative embodiment of an array head assembly  814 , with the connector  850  attached to the assembly  814 . The LED die  834  in the LED array  832  have been arranged in a shape approximating the periphery of a square. Such a configuration may be selected when the portion of the workpiece to be cured roughly matches such a shape. The array head assembly  814  may be provided with a square hole  831  passing through the assembly housing  830 , in the center of the LED die  834  square. As will be understood, the head assembly  814  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should further be understood, these components  830 ,  832 ,  834 ,  850  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     Illustrated in FIG. 8B is a view of a eighth alternative embodiment of an array head assembly  814   b , with the connector  850   b  attached to the assembly  814   b . The LED die  834   b  in the LED array  832   b  have been arranged in a shape approximating a filled square. Also illustrated are a temperature sensor  836   b  and a plurality of photo detectors  838   b  positioned about the array  832   b . As will be understood, the head assembly  814   b  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should further be understood, these components  830   b ,  832   b ,  834   b ,  850   b  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     As should be understood by the examples illustrated in FIGS. 4,  5 ,  6 ,  7  and  8 A, the two and three dimensional shape of the LED array may be configured to approximate the surface area of the portion of the workpiece to be cured. 
     FIG. 9 illustrates a side view of a ninth alternative embodiment of an array head assembly  914 . In this embodiment, the array  932  comprises two planar arrays of LED die which oppose each other, an upper array  933  and a lower array  935 . The arrays  933 ,  935  are capable of simultaneously irradiating two sides of a workpiece  990  passing between them. Preferably, a transparent table or conveyor  992  (or other device which enables the required wavelengths of light energy indicated by light rays  994  to pass through to the workpiece) may be used to carry the workpiece  990  between the arrays  933 ,  935 . Alternately, the arrays may be positioned vertically on either side of the conveyor  992 , such that no light energy is required to pass through the conveyor  992  in order to reach the workpiece. As should be understood, the arrays  933 ,  935  are both generally similar to the array assembly  14   A  discussed in relation to FIG.  2 A. 
     Referring now to FIGS. 10A-10C, illustrated therein is a tenth alternative embodiment of an array head assembly  1014 , with the connector  1050  attached to the assembly  1014 . The LED die  1034  in the LED array  1032  are addressable. Such addressability provides the ability to selectively supply power to groups of LED die  1034  and direct configurations of light onto the workpiece more precisely matching the surface area of the part of the workpiece to be cured. Additionally, as discussed in relation to FIG. 2D, the types or groups of LED die  1034  may be selected such that every LED die  1034  in a particular group emits light energy having substantially the same peak output wavelength as every other LED die  1034  in that group. Different groups of LED die  1034  would have different peak output wavelengths. Accordingly, as will be understood, addressability provides the ability to selectively supply power to different groups of LED die  34  having different peak output wavelengths, thereby generating light energy more precisely matching the curing requirements of the workpiece to be cured. As will be understood, the head assembly  1014  comprises a cooling system similar to that discussed in relation to FIG.  1 B. As should further be understood, these components  1030 ,  1032 ,  1034 ,  1050  are generally similar to corresponding components  30 ,  32 ,  34 ,  50  illustrated in FIG.  1 A. 
     As shown in FIG. 10A, the LED die  1080  addressed and energized to emit light energy form the periphery of a square. LED die  1081  are not energized to emit light energy. LED die  1080  may form a first group of LED die which all emit light energy having substantially the same peak output wavelength. The remaining LED die  1081  may form a second group of LED die which all emit light energy having substantially the same peak output wavelength, but which is different from the peak output wavelength of the first group of LED die  1080 . As shown in FIG. 10B, the LEDs  1082  addressed and energized to emit light energy form the periphery of a square rotated 45 degrees from the square  1080  of FIG.  10 A. As shown in FIG. 10C, the LEDs  1084  addressed and energized to emit light energy form two solid squares intersecting at one corner. 
     In an eleventh alternate embodiment of the head array assembly substantially similar to the array head assembly  1014 , the LED die in the array may be grouped by alternating rows, such that odd rows of LED die would form one group, and even rows of LED die would form a second group. As will be understood, the power source and controller are configured to independently supply power to the first group and to the second group. The power supply is also configured to independently detect current flow from each group. Thus, when the first group of LED die is energized to emit light energy, sidewall emissions of light energy impinge upon the second group of LED die, generating a current proportional to the intensity of the impinging light energy, which is detected by the power source. The power supply then generates a signal to the controller correlated to the intensity of the detected light energy. Accordingly, the second group of LED die is capable of functioning as a photo sensor to detect the intensity of the first group of LED die. Similarly, the power source is also able to detect current generated by the first group of LED die, such that the first group of LED die can function as a photo sensor to detect the intensity of the second group of LED die. 
     Thus, while what is shown and described herein constitute preferred embodiments of the subject invention, it should be understood that various changes can be made without departing from the subject invention, the scope of which is defined in the appended claims.