Abstract:
An optical sensor controlled lighting system comprises an ambient light sensor responsive to ambient light levels for generating an output signal proportional to the ambient light level. A light source having on and off states is controlled by circuit elements providing for developing a rate of change for the output signal and further providing for, responsive to the rate of change, selectively switching the light source between on and off states based on characteristics of the rate of change.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure relates to an optical sensor which can detect light level and light level rate and direction of change. 
         [0003]    2. General Description of the Problem 
         [0004]    Kitchen and bathroom cabinets, particularly those below countertops, are often dark even with the cabinet door open and the room where the cabinet is located has a high level of ambient lighting. Adding light sources within cabinets is often difficult because these areas do not typically have outlet plugs. To simplify the installation of lighting, battery operated lights have been used. The use of lighting in these areas is typically brief and intermittent and to conserve battery power the lights are designed to switch states, such as from on to off or off to on, with opening and closing of the cabinet door, and sometimes after a short period after opening of the door. This has been accomplished by any one of a number of devices including mechanical switches, magnetic switches, ultrasonic motion sensors, microwave motion sensors, active and passive infrared motion sensors and photoelectric sensors combined with timers. 
         [0005]    Mechanical and magnetic switches can be attached directly to the cabinet door and/or door frame and if properly installed reliably detect whether or not the door is open or closed. The light operated by the switch turns on immediately when the door is opened and turns off immediately upon its closure. A timer can also be built in to turn the light off after a predetermined period of time if the door is left open. In order to make sure the contacts are closed when the cabinet door is closed, these types of switches must be mounted to the door and/or door frame in such a manner that they align properly when the door is closed. Achieving proper alignment of contacts during installation can make installation difficult where poor installation might keep the product from operating properly. In cases where two doors are used, as is often the case under sinks, two sets of switches are installed, which increases the chance of installation error. These types of switches use wires that run from the switch on the door frame to the lighting device which is usually installed off the door inside the cabinet. The wires are vulnerable to damage as items are placed in or removed from the cabinet. 
         [0006]    Using motion sensors to control interior cabinet light activation can simplify installation by reducing the number of components to install and eliminating exposed wires inside the cabinet. A variety of motion sensor technologies exist including, ultrasonic, microwave and passive infrared motion sensors that can reliably generate signals in response to cabinet door movement. They tend to be less reliable in distinguishing the direction of movement. They also distinguish poorly between opened and closed stationary doors. As a result they can fail to turn a light off immediately upon closure of the door and in some instances can turn the light on when the door is being closed. Passive infrared motion sensors may not work if an object is placed in the cabinet at a location which obstructs the field of view of the light collecting lens. Passive infrared motion sensors tend to exhibit a noticeable delay from initial movement of the door until the light turns on. Microwave motion sensors generate microwaves which can penetrate the door and turn on the light when there is motion adjacent to the cabinet even if the door is not moved. 
         [0007]    Active infrared motion sensors respond to motion and are used for lighting control. These devices typically use a light emitting diode (LED) to emit infrared light in front of the sensor. An infrared photodiode or transistor detects the infrared light upon reflection by nearby objects. Changes in the detected amount of infrared light indicate motion in front of the sensor. One such device is the General Electric LED Motion Sensing Light Model # 17433. This device detects motion within a few inches in front of the sensor. When used in a cabinet the system does not respond immediately when the door is opened but responds upon someone reaching into the cabinet. As with passive infrared motion sensors, this type of sensor is sensitive to field of view considerations. 
         [0008]    Photoelectric sensors can also be used to turn on a light when a door is opened. This type of sensor detects the increase in light level when a door is opened and turns on a light. 
         [0009]    An example of a photoelectric sensor product is the Automatic Closet Light; model EZT-ACL, from Touch and Glow Lighting Solutions. This alternating current (AC) product is screwed into an ordinary light bulb socket and then a light bulb may be screwed into it. The light bulb turns on when the door is opened for a period of time that is user selectable. The product uses a single, fixed light level threshold to determine if the door is open or closed. Under conditions of low ambient room lighting the light level in the closet may never rise above the threshold when the door is opened. In a bright environment the light level may not drop below the threshold when the door is closed and again the light will not turn on when the door is opened. The product does not differentiate between slowly changing light levels, as when a door opens, and fast changes in light level as when a room light is turned on. 
         [0010]    Ambient light sensors are also used in vehicles and with hand held electronic devices to control the illumination levels of displays, typically increasing brightness of the display as ambient light levels increase. U.S. Pat. No. 7,297,929 teaches a multi-element sensor for detecting light over wide angles and in multiple optical zones. Detected light level values are stored and luminosity of a light source determined based on historic (i.e. the stored) light readings. 
       SUMMARY 
       [0011]    An optical sensor controlled lighting system comprises an ambient light sensor responsive to ambient light levels for generating an output signal proportional to the ambient light level. A light source having states including full on and off is controlled by circuit elements providing for developing a rate of change for the output signal and further providing for, responsive to the rate of change, switching the light source between states where the rate of change has specified characteristics or falls within a given range. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a block diagram of a typical prior art optical sensor controlled lighting system. 
           [0013]      FIG. 2  is a block diagram of an optical sensor using multiple signal channels to provide operation over a broad range of illumination levels. 
           [0014]      FIG. 3A  is a block diagram of an optical sensor using average values to provide operation over a broad range of illumination levels. 
           [0015]      FIG. 3B  is an alternate block diagram of an optical sensor using average values to provide operation over a broad range of illumination levels. 
           [0016]      FIG. 4  is a block diagram of an optical sensor that uses a log converter to provide operation over a broad range of illumination levels. 
           [0017]      FIG. 5  is a block diagram of an optical sensor that dynamically determines the threshold values used in the comparators. 
           [0018]      FIG. 6  shows typical output signals from the amplifier of  FIG. 5  when a door is opened. 
           [0019]      FIG. 7  shows a typical output signal from the amplifier of  FIG. 5  when an incandescent lamp is turned on. 
           [0020]      FIG. 8  shows a typical output signal from the amplifier of  FIG. 5  when a fluorescent lamp is turned on. 
           [0021]      FIG. 9  shows a typical output signal from the amplifier of  FIG. 5  when a compact fluorescent lamp is turned on. 
           [0022]      FIG. 10  shows typical output signals from the amplifier of  FIG. 5  when a door is closed. 
           [0023]      FIG. 11  shows a typical output signal from the amplifier of  FIG. 5  when an incandescent lamp is turned off. 
           [0024]      FIG. 12  shows a typical output signal from the amplifier of  FIG. 3  when a fluorescent lamp is turned off. 
           [0025]      FIG. 13  shows a typical output signal from the amplifier of  FIG. 5  when a compact fluorescent lamp is turned off. 
           [0026]      FIG. 14  is a circuit schematic for one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    In the following detailed description, like reference numerals and characters may be used to designate identical, corresponding, or similar components in differing drawing figures. 
         [0028]    Referring to  FIG. 1 , a prior art sensor controlled lighting system  60  is illustrated. A light sensor  1  is made up of a photo sensitive resistor  2  and a fixed resistor  3  connected in series between a voltage source Vcc and ground to operate as a simple voltage divider generating an output signal on output  4 . Devices such as photo diodes and photo transistors can be substituted for the photo sensitive resistor  2 . Typically the resistance of the photo sensitive resistor  2  decreases with increasing light level. The value of the fixed resistor  3  is typically chosen so that at a fixed light level the resistance of the photo sensitive resistor  2  is approximately equal to the value of the fixed resistor  3 . At the selected light level the voltage level on output  4  of the light sensor  1  will be equal to the input voltage threshold of the logic circuit  5 . If the light sensor output  4  transitions from below this voltage threshold to above the threshold, the logic circuit  5  will turn on the controlled light  6 . The use of a single threshold results in there being only one light level that causes the controlled light  6  to turn on. The circuit does not distinguish between different rates of change in light level. 
         [0029]    Referring to  FIG. 2 , a sensor controlled lighting system  61  is illustrated that employs multiple channels to operate over a broad range of illumination levels and discriminates between slowly and quickly changing ambient light levels. Light sensor  1  converts light intensity to an electrical signal on output  4  as described in  FIG. 1 . The output of light sensor  1  is applied to amplifiers  7 , and  8 . The amplifiers  7 ,  8  amplify the signal on output  4  to levels that, at a nominal light level selected by fixed resistor  3 , cross the input threshold of signal processor  9  at different times. Because higher gain amplifier  8  and amplifier  7  have different gains, the result will be two different light level thresholds that result in the amplifier outputs crossing the input threshold of signal processor  9 ; a first lower light level threshold and a second higher light level threshold. If the signal on light sensor output  4  is increasing from below the nominal light level, the output of higher gain amplifier  8  will cross the input threshold before the output of amplifier  7  crosses the input threshold. This time differential is proportional to the speed with which the light level is changing. Similarly, if light levels are decreasing from above the nominal light level, the output of amplifier  7  will cross the input threshold before the output of higher gain amplifier  8  crosses the input threshold. Different rates of light level change may now be discriminated against. Making the gain differential between higher gain amplifier  8  and amplifier  7  small results in a short delay between when their output signals cross the input threshold of signal processor  9 . This allows the signal processor  9  to turn on the controlled light  6  very quickly. 
         [0030]    The output of light sensor  10 , directed into parallel amplifiers  11 ,  12 , provides a second channel at a second nominal light level. Light sensor  13  and amplifiers  14 ,  15  provide a third channel at a third nominal light level. By adding additional channels, a large number of light levels can be monitored. Sufficient light level changes at light sensor  10  results in changes in the outputs of each of these channels as input thresholds are crossed providing the ability to detect absolute and time rate of changes across a wide variety of lighting conditions and to generate a rate of change signal related to the time rate of change of ambient light levels. 
         [0031]    Referring to  FIG. 3A , an alternate embodiment of sensor controlled lighting system  62  is shown which operates over a wide variety of lighting conditions. In sensor controlled lighting system  61  shown in  FIG. 2 , each channel detects one light level and a large number of channels are required to detect a comparably large number of distinct threshold levels of ambient light. In sensor controlled lighting system  62  a single channel can detect increases or decreases in light level over a wide range of light levels. More than one channel may still be used to expand the range of light levels the system operates over, but the number of channels necessary will be reduced compared to sensor controlled lighting system  61  to achieve the same range of operation. 
         [0032]    As with sensor controlled lighting system  61 , the difference in gain between amplifier  7  and higher gain amplifier  8  results in a first light level threshold and a second light level threshold. The output of amplifier  8  is connected to average value generator  17 , typically made up of a simple low pass filter. The output of average value generator  17  changes slowly compared to the signals expected at the output of amplifier  8  when light levels change in the environment of the device. The term “expected” relates to the expected rates of change in ambient light levels stemming from turning a light on or opening a door within a “normal” range of speeds. Comparator  18  compares the average value of the output of amplifier  8  to the current output of amplifier  8 . If the output of amplifier  8  exceeds the average value  17  by a threshold  19 , the output of comparator  18  will switch high. If the current signal is not changing, it will be close to the average value and the output of comparator  18  remains low. If the output of amplifier  8  is increasing, it will rise above the output of average value generator  17  and the comparator will switch high if the threshold is exceeded. Similarly, the output of comparator  16  will also switch high in response to increasing light levels, but at a later time due to the lesser gain of amplifier  7 . The difference in time between when comparators  16  and  18  go high is proportional to the speed with which the light level is changing. To detect decreasing light levels, the comparators  16  and  18  would be arranged to detect when the outputs of amplifiers  7  and  8  were below the output signals from average value filters  55  and  17 , respectively, by threshold  19 . The gains of the two amplifiers  7 ,  8  can be chosen so that the time between each comparator going high is very short allowing the signal processor  9  to turn the controlled light  6  on very quickly when, for example, light levels increase due to opening of a door. The points defining the rate of change correspond to the points in time where the gains of the respective amplifiers  7 ,  8  cross the preset threshold. It may be observed that a door could be opened very slowly to produce a very slowly increasing ambient light level at the location of the sensor controlled light system  62  in order to defeat operation of the sensor controlled light system  62 . 
         [0033]      FIG. 3B  shows an alternate sensor controlled lighting system  62 . Only one amplifier  7  and average value filter  55  are used. Each comparator  20 ,  21  has its own threshold for generating a rate of change, threshold 1 (applied to input  22 ) and threshold 2 (applied to input  23 ), respectively. If threshold 2 is larger than threshold 1,the output of comparator  21  will switch high a little later than the output of comparator  20 . The time difference between when the two comparators  20 ,  21  switch high will be proportional to the speed with which the light level is changing. Threshold 1 and threshold 2 can be chosen so that the time between each comparator going high is very short allowing the signal processor  9  to turn the controlled light  6  on very quickly. 
         [0034]    Referring to  FIG. 4 , still another sensor controlled lighting system  64  is shown which handles a wide dynamic range of the ambient light levels. A log converter  24  is used to reduce the dynamic range of the light sensor  1  output. For instance, the log function would reduce a 1000:1 ambient light level change to only 3:1 which can easily be accommodated by a single amplifier. The remaining components in sensor controlled lighting system  64  are the same as those in sensor controlled lighting system  62 . 
         [0035]    Referring to  FIG. 5 , a sensor controlled lighting system  65  incorporates a signal processor  27  which monitors the outputs of amplifier  7  and average value filter  55  as provided above. These two output are analyzed and values for threshold 1 (applied to input  25 ) and threshold 2 (applied to input  26 ) are calculated dynamically. This analysis provides that:
       1. Instead of using fixed values for threshold 1 and threshold 2,the thresholds can be calculated as a percentage of the output of either average value filter  55  or amplifier  7 , thus insuring a uniform response over a broad range of light levels;   2. The thresholds applied at inputs  25  and  26  can be selected as either positive or negative allowing for the detection of both increasing light levels and decreasing light levels as occurs when a door opens or closes, respectively;   3. The calculation of threshold 2 can be delayed relative to the time that comparator  20  indicates that threshold 1 has been passed. This allows the signal processor  27  to ignore a brief period of time after comparator  20  has indicated that the light level is increasing. This delay can be selected so that the relatively fast changes in light level that occur when a room light is turned on are ignored. If threshold 2 is calculated after this delay as a percentage of the output of amplifier  7 , the threshold will not be met if the light level change was fast enough that it was done changing at the time threshold 2 was calculated. If the delay is chosen so that slower changes in light level will still be increasing after threshold 2 is calculated, it is possible to discriminate between lighting level changes associated with lights turning on and doors opening.   4. The time between when threshold 2 is calculated and the time that comparator  21  indicates that the threshold has been passed is proportional to the speed with which the light level is changing. This time difference can also be used, alone or in conjunction with a delay, to discriminate between fast and slowly changing light levels.   5. A variation of this system would not measure rate of change in ambient light levels. A single light level trigger could be used but short duration signals, as might occur as a result of turning a light on in a room with a cabinet door open, could be ignored while a more sustained difference, as would result from opening a door to a lit room would result in the light source being turned on.   6. Another variation would be to use different light levels and delays as triggers without developing a rate of change signal.       
 
         [0042]    Many of the function blocks shown in  FIG. 2 ,  FIG. 3 ,  FIG. 4 , and  FIG. 5  can be implemented using analog components, digital components, firmware in a microprocessor, or a combination of all three. In some cases an analog to digital (A/D) converter may be used to convert analog signals into a format that can be manipulated as per the above block diagrams within a microprocessor. Although not shown in the block diagrams, the use of such converters is contemplated under some circumstances. 
         [0043]    Referring to  FIG. 6 , several output signals  28 ,  29 ,  30  from the amplifier  7  in  FIG. 5  are shown. The sensor controlled lighting system  65  was located in a cabinet and the signals resulted from opening a cabinet door to an area fully illuminated at a constant level. Increasing output signals  28 ,  29 ,  30  correspond to increases in light level in the cabinet as the door is opened at a steady speed over periods varying from about 0.4 seconds to 1.0 seconds. Signal levels will vary depending on how well lit the room is, but the signals shown are typical. Signal  28  is the result of opening the door at a slow rate. The signal level is seen to increase gradually as the cabinet door is opened. Opening the door more slowly results in a slower signal  29 , while opening it more quickly results in a faster signal  30 . After about 50mS from the start of the light increase, all three signals have relatively slow rates of increase. However, the faster signal  30  has a fairly fast rate of increase during the first 50 mS, increasing over 200 mV in the first 50 mS. 
         [0044]    Referring to  FIG. 7 , the output signal from the amplifier  7  in sensor controlled lighting system  65  is shown changing in response to an incandescent light turning on where the sensor lighting system is exposed to an incandescent light in a modestly sized room. This signal strength grows considerably faster than the signals shown in  FIG. 6 . The signal has reached its final value in about 100 mS and it rises over 450 mV in the first 50 mS. 
         [0045]    Referring to  FIG. 8 , the change in the output signal from the amplifier  7  of sensor controlled lighting system  65  in response to a fluorescent light turning on under the same conditions as described with reference to  FIG. 7 . There is an initial slow increase in light level for about the first 100 mS, followed by a very fast increase to its final value. The final value is reached in about 120 mS from the initial increase in light level. 
         [0046]    Referring to  FIG. 9 , the output signal from the amplifier  7  sensor controlled lighting system  65  is shown in response to a compact fluorescent light (CFL) turning on. In this case the signal reaches its final value in about 200 mS but the transition is very noisy. 
         [0047]    To illustrate the procedure for discriminating between a door opening and a light turning on  FIG. 4  is referred to. It may be assumed that the value for threshold 1 is 100 mV and the value for threshold 2 is 200 mV. From  FIG. 6  it is seen that the fast waveform  30  will cross threshold 2 about 20 mS after it crosses threshold 1.Similarly, waveform  28  will cross threshold 2 after about 50 mS and waveform  29  will cross threshold 2 after about 100 mS. Referring to  FIG. 7 , it is seen that the difference in time between threshold 1 and threshold 2 for an incandescent light turning on will be less than 10 ms. A criterion that simply required the time differential between threshold 1 and threshold 2 to be 20 mS or more would turn on the light when the door is opened and never turn on the light if an incandescent light were turned on with the door opened. 
         [0048]    Now referring to  FIG. 8  it is seen that a fluorescent light turning on will cross threshold 2 about 100 mS after it crosses threshold 1. In this case, the simple requirement that threshold 2 occur at least 20 mS after threshold 1 would fail and the controlled light  6  would turn on when the fluorescent light turned on. One solution would be to simply increase the values for threshold 1 and threshold 2,for instance to 150 mV and 250 mV, respectively. While this would successfully ignore a fluorescent light turning on, it would also ignore all signals smaller than 150 mV, such as might occur if a door is opened to a very dimly lit room. 
         [0049]    In order to successfully ignore the fluorescent light and still accurately detect a door opening in a dimly lit room, the method shown in  FIG. 5  can be used. Still referring to  FIG. 8 , the initial value of the signal is about 80 mV which would be the output from average value filter  55  for sensor controlled lighting system  65  in  FIG. 5 . The signal processor  27  would calculate a value for threshold 1, for instance 1.05×80 mV=84 mV. After a delay of, for instance, 150 mS, the signal processor  27  would calculate threshold 2 based on the current output of amplifier  7 , or about 510 mV in this illustration. For instance, threshold 2 might be calculated as 1.10×510 mV=561 mV. Since the signal never reaches this level in this example, threshold 2 will never be crossed and the controlled light  6  will not be turned on. For the fast signal  30  in  FIG. 6 , threshold 1 (84 mV) will be crossed at about 80 mS. A delay of 150 mS would be 230 mS and the signal is at about 420 mV. The value of threshold 2 would be calculated as 1.10×420 mV=462 mV. Threshold 2 would be crossed at about 290 mS. The difference in time between when threshold 2 is calculated and when threshold 2 is crossed is about 60 mS. Since this time is greater than 20 mS, the controlled light  6  will be turned on. If the time were less than 20 mS, the light would be left off since the signal was still moving too fast even after the 150 ms delay. 
         [0050]    Referring to  FIG. 9 , it is seen that the noisy transition of the CFL lasts longer than 150 mS. Since the signal is still moving up and down rapidly after this time it is likely that the time between when threshold 2 is calculated and when threshold 2 is crossed will be less than 20 ms and the controlled light will remain off. However, some CFL&#39;s may behave differently and there is a chance that the controlled light might turn on. To reduce this possibility, the signal processor  27  in lighting system  65  can monitor the signal between the times it crosses threshold 1 and when it crosses threshold 2,for instance counting peaks of a certain size. If there are many peaks it is likely that the signal is from a CFL and the controlled light would not be turned on. Other criteria for the shape of the signal between threshold 1 and threshold 2 can be implemented in order to reject specific types of lighting. 
         [0051]    If the criteria used to calculate threshold 2 is kept small, for instance 10% as in the above examples, then small signals from a door opening in a dark room can still be detected and the light turned on if it meets the criteria discussed above. If the criteria used to calculate threshold 2 is kept small, for instance 10% as in the above examples, then small signals from a door opening in a dark room can still be detected and the light turned on if it meets the criteria discussed above. 
         [0052]    The above discussions have dealt for the most part with detecting an increase in light level. Detecting a decrease in light level, as when a door closes or a light turns off, is a very similar process. The primary difference being that the threshold levels must be below the average value of the light level instead of above it. It can be seen in  FIG. 12  and  FIG. 13  that when a CFL or a fluorescent light turn off the initial decrease in light level is very rapid for the first 50 mS or so and then the decrease becomes more gradual. For this reason it is preferable to shorten or eliminate the delay between when threshold 1 is crossed and threshold 2 is calculated. For instance in  FIG. 12 , the average value before the fluorescent light turns off is about 440 mV which sets the −5% threshold 1 value at 418 mV and threshold 1 is crossed at about 450 mS. Using a delay of zero, the −10% value for threshold 2 would be calculated to be 418 mV×0.9=376 mV and threshold 2 would be crossed at about 465 mS, or 15 ms later. Similar calculations for the CFL turning off ( FIG. 13 ) would also result in a time difference of about 15 mS between when threshold 1 and threshold 2 are crossed. Similar calculations on an incandescent lamp ( FIG. 11 ) result in a time difference of about 30 mS between when threshold 1 and threshold 2 are crossed. Finally, referring to  FIG. 10 , similar calculations when a door closes result in a time difference of about 110 mS between when threshold 1 and threshold 2 are crossed. Setting the minimum time difference that will turn off the controlled light  6  to 50 mS will prevent the controlled light  6  from turning off when a room light is turned off but will reliably turn off the controlled light  6  if the door is closed. 
         [0053]    One further complication when determining when to turn off the controlled light  6  is that when the controlled light  6  is on it becomes difficult to determine whether or not the door has closed since the light level will remain high. For this reason it is necessary to turn off the controlled light  6  in order to measure the light levels needed to determine whether or not the door has closed. (All waveforms in the figures were measured with the controlled light  6  turned off.) The necessary measurements can still made, but the controlled light must be periodically turned off for a period of time long enough to sample the ambient light level but short enough that it cannot be detected by the human eye. 
         [0054]      FIG. 14  shows a sensor controlled lighting system  66 . A phototransistor  28  is connected in series between a battery source Vdd and chassis ground with a 47 Kohm resistor and three bipolar NPN transistors  29 ,  30  and  31 . Phototransistor  28  sources current in proportion to the intensity of the light that falls upon it. The voltage across transistor  31  is proportional to the log of the current through the phototransistor  28 . An emitter follower arrangement comprising a pair of NPN bipolar transistors  32  and  33  apply the voltage at the collector of transistor  29  to resistor  37  connecting the emitter of transistor  33  to ground. This arrangement drains little current away from transistor  31 . Transistors  29  and  30  offset the base-emitter voltage drops of transistors  32  and  33  so that the voltage across resistor  37  is the same as the voltage across transistor  31 . Since voltage is proportional to the log of the current in the phototransistor  28 , the current in resistor  37  is also proportional to the log of the current in phototransistor  28  though greatly amplified. 
         [0055]    The current through resistor  37  causes a negative voltage ramp across capacitor  34 . When this ramp decreases below the logic threshold of Schmitt trigger inverter  35 , the Schmitt trigger inverter applies a signal to an input of microprocessor  36  which turns on a shorting transistor  38  connected across the terminals of capacitor  34 . This shorts capacitor  34  to restart the negative voltage ramp. The result is a waveform on input  3  of microprocessor  36  whose period is proportional to the log of the current sourced by phototransistor  28 . Microprocessor  36  counts or times the duration of this period and thus digitizes the analog signal from the phototransistor  28 . Algorithms within the microprocessor  36  then perform calculations to implement the functions shown in sensor controlled lighting system  65  in  FIG. 5 . Microprocessor  36  controls emission of light from a light emitting diode (LED)  40  serving as a low current light source by driving switching transistor  39  on and off or to an intermediate conduction state. The remaining resistors in the circuit diagram have conventional current limiting functions. Microprocessor  36  may also readily be programmed to implement any timer based shut off function for the LED  40 . 
         [0056]    In summary a battery operated, sensor controlled light which is simple to install within a cabinet and which is insensitive to mounting location is provided by the systems described here. False triggers occurring in response to changes in room lighting are minimized. The optical sensor response to opening and closing of a door is accurate. It operates over broad range of room illumination levels and the response can differentiate between a door being opened and a light being turned on as well as differentiating between a door being closed and a light being turned off and respond accordingly. The system operates with minimal delay in response to opening of a cabinet door.