Abstract:
The present invention is an illuminator for CCTV surveillance and security applications that maintains constant optical output from an array of LEDs by employing output compensation, feedback and enhancement. This constant optical output illuminator system enables reliable long-duration low-light imaging and data capture for surveillance and security applications, via an array of LEDs, LED power supply circuitry, and output feedback and compensation circuitry in which a photodetector circuit provides a voltage signal proportional to an amount of light falling on a photosensor and the voltage signal is fed to a drive control circuit for electrical current to the LEDs to achieve a desired optical output as measured by a photosensor voltage setpoint across the photodetector circuit.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates to the general field of surveillance illumination devices, particularly light emitting diode (LED) illumination devices, and power supplies for LEDs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Surveillance illuminator systems using arrays of LEDs mounted on metal heatsinks are widely used in the security industry to provide visible or infrared (IR) illumination for CCTV cameras, imaging or data capture devices. LED illuminators are claimed to offer lifetimes in excess of 100,000 hours, however their effective output decays from the moment the LEDs are activated. Lifetime output reductions of 20% to 50% have been quoted in manufacturer&#39;s data, and LED output is often specified at 50% of the maximum operating current at a particular ambient temperature. The need for increased illuminator range and output necessitates that LEDs be driven to their current limits in surveillance applications, a practice that reduces illuminator effectiveness, reliability, and operational lifetime. 
         [0003]    Factors that can also degrade LED output &amp; lifetime of surveillance illuminator systems include, but are not limited to: operation of LED arrays at fixed output currents; operation at high ambient temperatures which reduces LED efficiency (even when constant current power supplies are used); production spreads in LED die quality, LED efficiency, and inefficient lensing can represent a variation of up to +/−20% in optical output power between different illuminator units. 
         [0004]    Known prior art surveillance illumination systems utilize and may combine illuminator feedback, heat sinking, and pulse width modulation to prolong LED lifetime. However, the lifetime of even the best of these systems is still limited by their high current operation, and high temperature operation due to their use of encapsulated LEDs. Less applicable prior art uses less reliable current sensor feedback instead of direct light sensor feedback to maintain nominal illuminator output. The effective range of prior art LED illuminators can vary dramatically with temperature and time, and from unit to unit. No prior art LED illuminator system produces surveillance images of sufficiently reliable quality over the maximum operational lifetime of the monitoring equipment. 
         [0005]    A number of patents exist which utilize photo detectors to provide feedback on optical power output for LED arrays or other light sources. At least one patent (U.S. Pat. No. 6,028,694—Schmidt) uses pulse width modulation to increase LED light output for a given heat load. A number of patents or publications seek to provide constant or ‘stable’ brightness or optical power, often through the feedback provided by photo detectors. Other patents seek to ‘maximize’ optical output from the LEDs by altering the voltage or current. A patent application that combines a limited number of the features most relevant to the present invention is LED Array Package with Internal Feedback and Control by Mazzochette, et al (US 20060012986). 
       SUMMARY OF THE INVENTION 
       [0006]    This invention provides a constant optical output illuminator system to enable reliable long-duration low-light imaging and data capture. This disclosure describes an illuminator for CCTV surveillance and security applications that maintains constant optical output from an array of LEDs by employing output compensation, feedback and enhancement. The constant illuminator system overcomes a number of problems with common LED illuminators where optical output varies:
   a) with temperature   b) with manufacturing tolerance   c) over time as LEDs and components in power board age   d) during initial calibration   
 
         [0011]    During daylight there are sources of illumination outdoors from sunlight and indoors from sunlight coming through windows as well as indoor visible light sources for work and ambience. CCTV cameras use this on-scene light to capture images, but are reliant on proper camera setup to ensure the best possible image is captured with the light available. CCTV system installation is a challenging field where the performance of a surveillance system is measured not only by the resulting image quality, but the ability to maintain that quality in all environments, lighting conditions, and during the full lifetime of the product. 
         [0012]    At night, surveillance scenes are either without any illumination, or are artificially illuminated for human activity. Both of these night-time scenarios are far from optimal when the quality of CCTV images for security and surveillance applications is considered. 
         [0013]    Previous pioneering work in illuminators has resulted in widespread use of infrared (IR) illumination in conjunction and support of CCTV systems for surveillance and security. For example, the patented illuminator sold as the UF500 (TM of Extreme CCTV International Inc.) provides a usable night-time CCTV image that does not rely on ambient lighting on scene. As the industry matures however, higher demands are placed on the CCTV infrastructure including the use of advanced video analytics software to monitor video from CCTV cameras. 
         [0014]    The demand for improved night-time performance has led to LED illuminators with Black Diamond (TM of Extreme CCTV International Inc.) patent-pending illuminators that use micro-diffractive refractive elements which channel light from the LEDs so as to alter the distribution of illumination on the target and/or to make illumination more efficient by conserving light. (See  FIGS. 2 &amp; 4 ) The Black Diamond technology provides far more even and efficient distribution of optical energy from a micro-diffracted illuminator (see  FIG. 15 ) than traditional LED illuminators (see  FIG. 14 ). 
         [0015]    To further evolve security and surveillance illumination performance Extreme CCTV has created a family of CCTV illuminators that maintain constant optical power output over time and across varying environmental conditions for the life of the product. Maintaining even illumination for the life of the product ensures the quality of the image from the CCTV system will be as good as the day it was installed. 
         [0016]    It is common for illuminator products to be quoted as having a lifetime of between 3 years and 10 years. Depending on the quality of the manufactured product, and assuming no catastrophic failures, the illumination power on scene will degrade over time. Typical illuminator lifetime quoted from manufacturers is stated from 80% to as low as 50% of rated output. The rate of drop of optical output from LED illuminators is directly related to the internal operating temperature of the LED itself. 
         [0017]    The combined effects of manufacturing variance, temperature variation and lifetime degradation are additive, making a worst case variation in the region of +/−50% optical output power under various conditions. The constant illuminator system  20  will guarantee 100% constant optical power over the same conditions giving confidence in security system design. 
         [0018]    By monitoring and maintaining optical power output from the illuminator, the quality of the CCTV image will not change over time and will therefore greatly enhance the image quality as well as extend the useful life of the security/surveillance system. 
         [0019]    The constant illuminator system is designed to provide reliable long-duration illumination for low-light imaging and data capture. By packing higher power LEDs closer together and running them with less current, then making more efficient use of their light output by focusing through a lens, then an asymmetric diffuser, the resultant light output is at least equal to the prior art, but provides constant illumination over a much longer operational lifetime. Photodetectors also monitor total LED output and increase drive current or activate additional auxiliary LEDs to maintain optimal LED output longer than other solutions. Overheating is prevented by lowered operating current, pulse width modulation and by use of efficient heatsinking The constant illumination system may use surface mount or through-hole LEDs in either visible or infrared wavelengths, depending on the surrounding light available and monitoring equipment used. 
         [0020]    To summarize, the invention provides a constant optical output illuminator system to enable reliable long-duration low-light imaging and data capture for surveillance and security applications, comprising an array of LEDs, LED power supply circuitry, and output feedback and compensation circuitry, in which a photodetector circuit provides a voltage signal proportional to an amount of light falling on a photosensor and the voltage signal is fed to a drive control circuit for electrical current to the LEDs, to achieve a desired optical output as measured by a photosensor voltage setpoint across the photodetector circuit. It also provides the innovation of a constant optical output illuminator system to enable reliable long-duration low-light imaging and data capture for surveillance and security applications, comprising an array of LEDs, LED power supply circuitry, and output feedback and compensation circuitry, in which optical output from the LEDs is controlled based on feedback from at least one photodetector that is embedded in the array of LEDs. 
         [0021]    More detailed innovative embodiments of the invention include such systems in which:
   a) the voltage setpoint is adjustable via potentiometer for manual control, or having a the voltage setpoint is adjustable via microcontroller for dynamic control and remote control;   b) optical output from the LEDs is controlled via current control based on feedback from a plurality of photodetectors is embedded in the array of LEDs, each photodetector sending a light output feedback signal for current control of the optical output from the LEDs and via pulse modulation based on feedback from one or more photodetectors embedded in the array of LEDs;   c) a microcontroller receives feedback from the photodetectors and uses that feedback to control electrical current to the LEDs via pulse modulation;   d) the array of LEDs is surface-mounted on an insulated metal substrate material;   e) the array of LEDs uses infrared wavelengths that are not substantially visible to a human eye but are visible to IR sensitive CCD and CMOS cameras;   f) the LEDs are compacted closely together and are lensed, not limited to being lensed with tessellated hexagonal lenses;   g) the photodetectors are spread throughout the LED array so as to obtain substantially average measurements of light output;   h) a microcontroller determines maximum allowable current drive for the LEDs;   i) a bandpass filter is used on each photodetector sensors and the bandpass filter corresponds to light output wavelength of the LEDs;   j) a step pass filter is used to pass substantially all of light output wavelength of the LEDs to each photodetector;   k) the photodetectors are oriented within the LED array so as to capture light from the LEDs rather than external ambient light;   l) a microcontroller monitors junction temperature and ensures it does not exceed a predetermined maximum level;   m) a microcontroller triggers an alarm when the LEDs decay beyond a predetermined level;   n) feedback and compensation circuitry adjusts optical output from the LEDs to compensate for the optical output varying with ambient and system temperature and with aging of the LEDs and power board components;   o) the control circuitry compensates for input voltage variations, temperature which affects both the control circuit as well as LED output, component tolerances in the drive circuit, and LED panels as well as performance degradation of the power components and LEDs.   
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1 . is an isometric exterior view of the constant illuminator system. 
           [0038]      FIG. 2 . is an isometric exploded view of the constant illuminator system. 
           [0039]      FIG. 3 . is a side view of LED array board with feedback sensor. 
           [0040]      FIG. 4 . is a side exploded view of the constant illuminator system. 
           [0041]      FIG. 5 . is a rear view of the constant illuminator system. 
           [0042]      FIG. 6 . is a graph showing constant illuminator output maintained across a wide temperature range by varying current. 
           [0043]      FIG. 7 . is a graph showing prior art illuminator output reduction at higher temperature. 
           [0044]      FIG. 8 . Is a graph comparing constant illuminator output with prior art across a wide temperature range. 
           [0045]      FIG. 9 . is a graph showing prior art output degradation during warm-up. 
           [0046]      FIG. 10 . is a graph showing constant illuminator output during warm-up and lowered current requirements. 
           [0047]      FIG. 11 . is a graph of extrapolated plot of prior art illuminator output degradation. 
           [0048]      FIG. 12 . is a block diagram outlining the functional elements of the LED regulator/control board (LRB). 
           [0049]      FIG. 13 . is a schematic of LED regulator/control board (LRB) electronics. 
           [0050]      FIG. 14 . is a graph showing area power output of prior art illuminators. 
           [0051]      FIG. 15 . is a graph showing area power output of the constant illuminator using asymmetric diffusion. 
       
    
    
     DETAILED DESCRIPTION 
       [0052]      FIG. 1  shows the exterior of a constant illuminator system  20 , with its faceplate  22 , heatsink  28 , mounting bracket  40 , LRB (LED Regulator/Control Board) enclosure  30 , and its top coverplate  34 . 
         [0053]      FIG. 2  shows an exploded view of the constant illuminator system  20 , with its faceplate  22 , micro-diffractor  50 , faceplate gasket  24 , and LED array board  26 . The heatsink  28  and LRB enclosure  30  are cast as one unit, but are defined as separate functional elements. The elements listed above are assembled onto the front of the heatsink  28 . Any heated gas or moisture from the LED array board  26  escapes through the internal wall of the heatsink  28 , into the LRB enclosure  30 . Pressure and moisture are then passed out of the LRB enclosure  30  by means of a pressure relief valve  38 . The LRB enclosure  30  houses an LED regulator/control board (LRB)  32 , sealed from external environments by means of a coverplate  34  and a gasket  36  with fasteners  52  (shown in  FIG. 4 ). Attached to the LRB  32 , is an ambient photocell assembly  42 , which fits through a hole through the rear wall of the LRB enclosure  30 , and is sealed from external environments. The LRB  32  electrically attaches to the LED array board  26  by means of a connector  56  passing through the inner wall of the heatsink  28 . A mounting bracket  40  is shown, which attaches by means of mounting bolts  54  to the sides of the LRB enclosure  30  (shown in  FIGS. 4 &amp; 5 ). 
         [0054]      FIG. 3  shows a side view of the LED array board  26  with its light emitting diodes (LEDs)  44 , which are each covered by a lens-like focuser  48 , which are surrounded by an opaque housing  60 , and whose output is monitored by a multiplicity of photocells  46 . 
         [0055]      FIG. 4  shows a side view of the same elements of the constant illuminator system  20  shown in  FIG. 2 , but also includes the fasteners  52  required to seal the unit from external environments, secure internal components and the mount the bracket. 
         [0056]      FIG. 5  shows a rear view of the constant illuminator system  20 , with its mounting bracket  40  and mounting bolts  54  attached to sides of the LRB enclosure  30 , which is sealed by means of a coverplate  34  and coverplate gasket  36  at top and bottom. Shown passing through the rear wall of the LRB enclosure  30  while maintaining enclosure integrity is the ambient photocell assembly, and the pressure relief valve  38 . External components are connected through enclosed conduits (not shown) to the LRB  32  through threaded holes in the side walls of LRB enclosure  30 , which are sealed when not used by means of a gasketed conduit plug  58 . Fasteners  52  are also shown passing through the heatsink  28 , which are used to secure components on its other side. 
         [0057]      FIG. 6  shows the constant illuminator system  20  maintaining a constant optical power output (+/−1%) over a wide temperature range by varying the LED array board  26  current. The output current never reaches 100%, but does rise over the lifetime of the LEDs  44  by compensating for LED  44  degradation over time as well as temperature. 
         [0058]      FIG. 7  shows the corresponding graph for a standard uncompensated illuminator running in a constant current feedback loop. Here we can see that even with constant current, the optical output of the standard illuminator changes dramatically with temperature. 
         [0059]      FIG. 8  compares the optical output of prior art illuminators and the constant illuminator system  20  over the operational temperature range. 
         [0060]      FIG. 9  shows that from initial power up there is degradation of power output for various LEDs used in standard illuminators. This warm up period can last up to 1.5 hrs. During testing, calibrating and commissioning this output degradation can give misleading results if uncompensated. 
         [0061]      FIG. 10  shows that there is effectively no start up delay in the output for the constant illuminator system  20 , which reaches 99% of its specified output within 1 minute. The operating current is lower at the initial startup because the units are more efficient when they are not overheating. 
         [0062]      FIG. 11  shows an extrapolated plot of relative optical power output versus time for an uncompensated illuminator. Note that this extrapolation assumes continuous operation of the illuminator. Operational lifetime would be extended by an approximate factor of 3 due to 8 hrs/day of operation, on average throughout the year. This means that a 20% reduction would occur in 2 years of continuous use and in normal use this would take 6 years. The constant illuminator system  20  is designed to maintain its 100% output for a similar period of time at which point it will start to degrade in a manner similar to standard illuminators, but at a greater rate of decay, all things being equal. 
         [0063]      FIG. 12  shows a block diagram illustrating the basic elements of the electronic operation of the constant illuminator system  20 . 
         [0064]      FIG. 13  shows a schematic diagram of electronic components used in the operation of constant illuminator system  20 . 
         [0065]      FIG. 14  shows an area plot of optical power output of a standard LED illuminator array, in microwatts per square centimeter. 
         [0066]      FIG. 15  shows an area plot of optical power output of the constant illuminator system  20 , in microwatts per square centimeter. 
         [0067]    A preferred embodiment of the constant illuminator system will now be described in detail. 
         [0068]    A. LED Array Board: The LED array board  26  houses an array of light emitting diodes (LEDs)  44 , each of which is capped by a focuser  48 , which is registration mounted to the board  26 . Most LEDs spray light in all directions, which is an inefficient use of power and light. The focuser  48  is a plastic hexagonal tessellated lens which focuses the light from each LED  44  into a tight cylindrical pattern. 
         [0069]    B. LED Photocell: The LED photocell  46  is a photon sensing device such as photodetector, photodiode or phototransistor which is placed in the illumination cavity, connected in place of a current sensing resistor on the LRB  32  to provide direct control of current to LED array  26  based on voltage across the photodetector. The LED photocell  46  may include a filter to block extraneous wavelengths of light, enabling both day-time use, and to prevent intentional interference with the operation of the illuminator  20 . This filter may be a step pass filter restricting the LED photocell  46  to a specific part of the light spectrum or notch type filter that further restricts the sensitivity of the LED photocell  46  to a narrow region that corresponds to the spectral output of the LED array  26 .  FIG. 3  shows the arrangement of the LED photocell  46  at 90 degrees to the direction of the LED  44  output. This particular arrangement is such that the opaque plastic housing  60  of the focuser  48  shields the LED photocell  46  from stray light that could be reflected back into the board, which could provide inaccurate output feedback data to the LRB  32 . 
         [0070]    C. Ambient Photocell Assembly: The ambient photocell assembly  42  is an external photocell used to measure ambient light, and is shown in  FIGS. 2 ,  4 , &amp;  5 . By means of its associated hardware, the photocell  42  is connected to the LRB  32  through the rear wall of the LRB enclosure  30 . The function of the ambient photocell assembly  42  is to supply the ambient light level to the LRB  32  which then determines when the LED array board  26  should turn on by comparing the light level with a predetermined setpoint. 
         [0071]    D. Faceplate &amp; Gasket: The faceplate  22  protects the LED array board  26 , and when fastened properly, the faceplate gasket  24  allows IP68 rated submersion protection. In some implementations the faceplate  22  blocks visible light, but passes infrared light in order to prevent inaccurate LED photocell  46  feedback data. In these implementations, a step pass filter serves to reduce ambient light to/from the source. 
         [0072]    E. Micro-diffractor: Asymmetric diffusion of the focused output from the LED array  26  occurs by means of a sheet of micro-diffractor material affixed to the inside of the illuminator faceplate  22 . (see  FIGS. 2 &amp; 4 ) Current implementation of micro-diffractive material is by means of pressure sensitive adhesive, but other techniques could be used offering the same results. micro-diffractive material spreads and focuses light from the LED array  26  onto the imaged target in a pattern with greater efficiency than prior art. (compare  FIGS. 14 &amp; 15 ) 
         [0073]    F. Physical Layout: The heatsink  28  and LRB enclosure  30  are formed as a single unit out of 6063 aircraft aluminum. The chamber in which the LED array  26  is housed shares the same environment and pressure as that of the LRB enclosure  30 . Top and bottom coverplates  34  with their gaskets  36  are used to seal the LRB  32  into the LRB enclosure  30  by means of fasteners  52 . In order to allow external electrical connections, threaded holes are available on the sides of the LRB enclosure  30 , which are sealed when not used by plastic gasketed conduit plugs  58 . Incorporating the LED regulator/control board (LRB)  32  into the Illuminator  20  itself provides added performance and cost benefit by reducing the signal loss from the LED photocell  46  feedback. 
         [0074]    G. Pressure Relief Valve: Pressure is equalized to the outside ambient via the pressure relief valve  38 . The pressure relief valve  38  is simply there to prevent pressure buildup when the LED array  26  or LRB  32  heats the enclosed air during operation of the illuminator  20 . These units are IP68 rated, meaning they can withstand submersion—so they are effectively sealed from external environments. The problem with a sealed environment is Boyle&#39;s law where the contained gas expands as the Illuminator gets hot which pushes out the frontplate. This has undesirable aesthetic impact and may affect the actual performance of the product as well. The pressure relief valve  38  allows the internal and external pressures to equalize and lets moisture escape but will not admit moisture into the LRB enclosure  30 . The pressure relief valve  38  functions very much like the semipermiable membrane shell of an outdoor jacket that allows the wearer to vent heat and moisture but does not allow moisture back in. 
         [0075]    H. LED Regulator/Control Board (LRB): The LRB  32  is the current output regulator and control board used to drive and maintain the LED array board  26 . Refer to FIG.  12 —LRB Block Diagram for an overview of the LRB  32 , and FIG.  13 —Schematic for component details. The LRB  32  has both maximum current and maximum voltage limiting to prevent the LED array  26  from operating beyond the current &amp; heating ratings of its LEDs  44 . Controller features include: variable power output, passive IR triggering, and a timed profile where a specific power profile can be used. For example high power is used for 1 second and low power is used for 5 seconds, or high power is used for 1/15 second to illuminate for two video frames and off for remaining 14/15 second to save power. Adjustment and Calibration features include: high voltage limiting, high current limiting, measurement points for operating and maximum voltage and current. The LRB  32  controls and drives the LED array  26  by means of a connector  56  through the heatsink  28  wall. 
         [0076]    I. Constant Illuminator Power Output: The power output from typical switch mode power supplies includes buck, buck/boost, and boost topologies which vary with input voltage as well as temperature. Typical designs rely on a sensing resistor to provide feedback for the amount of current or voltage being supplied to the LED array  26 .  FIG. 13  shows a transimpedance amplifier used to convert the photoinduced current of the LED photocell  46  to an amplified output voltage, which determines how much current is supplied to the LED array  26 . 
         [0077]    CCTV imaging used for security and surveillance applications relies on light to capture images of the area of interest. As Ansel Adams said ‘if there is no light, there can be no picture’. The constant illuminator system  20  is particularly useful when combined with Extreme&#39;s patent pending Black Diamond (micro-diffraction) Illumination technology that provides even illumination for CCTV imaging over a 3 dimensional area. 
         [0078]    Use of surface mount technology also allows operating conditions to be set to the highest output levels expected on a standard product i.e. the output expected @−30 degrees at the start of life before warm up, and maintain this level to beyond the warranty period of 5 years. 
         [0079]    The object of the constant illuminator system  20  is to guarantee a constant optical power output for a specified minimum period of time, over a specified range of temperature, by producing constant illumination from an optimal number of individual LEDs  44 , and which results in a constant illuminator range and image quality performance. 
         [0080]    To achieve the above stated object, LED array boards  26  must have a higher output power density over a longer duration than the prior art. The first step of this object can be achieved by using higher power surface mount technology (SMT) LEDs  44  densely mounted on insulated metal substrate circuit boards  26 . However, when using high power LEDs  44  in an industry standard size illuminator, the heatsink  28  cannot remove enough heat to maintain the LED  44  junction temperature below its critical breakdown value. If the number of LEDs  44  is maximised to the available space, no advantage can be gained over using half the number of LEDs  44 , because heat cannot be removed quickly enough in a static system. For this reason, prior art solutions spread fewer LEDs  44  over a wider heatsink  28  area and use large circular lenses to narrow the output. 
         [0081]    The constant illuminator system  20  uses an array of high power LEDs  44  on insulated metal substrate material  26 , where LEDs  44  are compacted closely together and whose output uses tessellated hexagonal lenses as focusers  48 . The number of LEDs  44  is then maximised or significantly increased above the number of LEDs  44  that would normally constitute the maximum based on thermal limitations. The LED array board  26  is run at a lower operating current so as to give the same equivalent power output as that expected from the standard solution. A number of LED photocells  46  monitor the actual array  26  output, which is then applied to vary the drive current of the LEDs  44  to maintain constant optical power output. Additional backup LEDs  44  are mounted on the LED array board  26 , which may be activated to compensate for the decay in total array  26  output power over time, and thereby maintain constant illumination. 
         [0082]    To obtain output feedback, a number of photo detectors, known as LED photocells  46 , are placed within the LED array board, in the vicinity of the LEDs  44 , as shown in  FIG. 3 . A multiplicity of LED photocells  46  are spread across the array  26  to obtain an average illumination inside the front cavity of the illuminator. Using only a single feedback sensor  46  would give an inaccurate output reading because it would be responding to too small a sample of the entire LED array  26 . LED photocells  46  should ideally be bandpass filtered to correspond to the wavelength of the illuminator LEDs, thus reducing the potential for skewing feedback from external light sources. For this reason, LED photocells  46  should point 90 degrees from the illuminator output LEDs  44 , looking at the scattered light inside the illuminator, as is shown in  FIG. 3 . 
         [0083]    The another step towards fulfilling the object of constant illumination is to use a power supply topology that accepts pulse-width modulation (PWM) input to control the average current through the LED array  26  as governed by feedback from the LED Photocells  46 . (see  FIG. 13 ) A small microcontroller can also be used to add additional safety features like maximum allowable current drive and maximum junction temperature monitoring to extend LED array  26  lifetime. 
         [0084]    Inevitably there comes a point where the decay of the LEDs  44  can no longer be compensated for, and this point can effectively be designed to occur after a certain minimum number of hours. At this point an alarm output could be triggered to warn that the LEDs  44  are starting to decay beyond the performance specifications of the illuminator  20 . 
         [0085]    There are currently no known commercial illuminators in the CCTV industry or general lighting industry that use LED photocell  46  feedback to maintain constant optical power output. 
         [0086]    The constant illuminator system maintains constant optical power from a dense configuration of LEDs by utilizing pulse modulation technology and heat sink technology in conjunction with advanced features such as a sophisticated microcontroller and photo detectors. 
         [0087]    Other embodiments of the constant illuminator  20  are described below. Other embodiments are not ruled out or similar methods leading to the same result. 
         [0088]    The frontplate may block visible light for use with IR LED illuminator applications—but the constant illuminator  20  may be used for visible LED illuminator applications which would require frontplate material that passes visible wavelengths of light, such as clear or translucent plastic. 
         [0089]    The constant illuminator system  20  may use infrared LEDs emitting wavelengths of 730 nm, 808 nm, 850 nm, 880 nm or 940 nms (nanometers); as well as visible spectrum LEDs including blue, green, red, amber and white. LEDs  44  may be either plated through hole or surface mount and may be low power or high specific output type LEDs. 
         [0090]    The foregoing description of the preferred apparatus and method of implementation should be considered as illustrative only, and not limiting. Other forming techniques or materials, and equivalent electronic circuits or components may be employed towards similar ends. Various changes and modifications will occur to those skilled in the art, without departing from the true scope of the invention as defined in the above disclosure, and the following claims.