Patent Document

STATEMENT OF RELATED CASES 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 13/690,609, filed Nov. 30, 2012, which is a continuation of U.S. patent application Ser. No. 12/572,471, filed Oct. 2, 2009 and now U.S. Pat. No. 8,324,817, which claims priority from U.S. Provisional Patent Application Ser. No. 61/108,354 filed Oct. 24, 2008, all of which are hereby incorporated by reference in their entireties. 
     
    
     FIELD 
       [0002]    An LED-based light as described herein relates to “smart buildings” that can automatically control lighting in response to various environmental conditions. 
       BACKGROUND 
       [0003]    Lights in buildings are generally controlled by switches, such as wall-mounted switches in the vicinity of one or more lights. The switch can include a dimmer for varying the brightness of one or more lights. However, lights are often left on when not needed, such as when no people are around the lights or when sources of light besides the lights (e.g., sunlight passing through windows and/or skylights) provide sufficient illumination. 
       SUMMARY 
       [0004]    Known smart buildings that can automatically control various environmental characteristics, such as a lighting brightness level, of one or more rooms of a building are typically expensive to manufacture and install. For example, known smart building components typically are not compatible with standard building fixtures, such as conventional fluorescent tube fixtures, and thus can require an electrician to install. 
         [0005]    Embodiments of LED-based lights described herein can be used to transform a building with standard fixtures, such as standard fluorescent tube fixtures, into a smart building. Many advantages are offered by the LED-based lights described herein, such as allowing for a low-cost smart building and automatically providing an alert when an efficiency of the LED-based light becomes too low. 
         [0006]    In one embodiment, a system of LED-based lights comprises: a first LED-based light having a first electrical connector configured for engagement with a first conventional fluorescent fixture, a first LED configured to produce light in an area when the first electrical connector is engaged with the first fixture and a first controller electrically coupled to the first LED; a second LED-based light having a second electrical connector configured for engagement with a second conventional fluorescent fixture, a second LED configured to produce light in the area when the second electrical connector is engaged with the second fixture and a second controller electrically coupled to the second LED; and one or more sensors operable to detect a brightness level in the area and output respectively one or more signals indicative of the brightness level, wherein: the first and second controllers are configured to control an amount of power provided to the respective first and second LEDs at least partially based on a signal to adjust the light produced in the area towards a desired brightness level. 
         [0007]    In another embodiment, a system for measuring an efficiency of a plurality of LED-based lights comprises: a first LED-based light having a first electrical connector compatible with a first standardized light fixture, a first LED configured to produce light in an area when the first electrical connector is engaged with the first fixture and a first controller electrically coupled to the first LED; a second LED-based light having a second electrical connector compatible with a second standardized light fixture, a second LED configured to produce light in the area when the second electrical connector is engaged with the second fixture and a second controller electrically coupled to the second LED; and one or more sensors operable to detect a brightness level in the area and output respectively one or more signals indicative of the brightness level, wherein: the brightness level in the area is a function of the light produced by the first and second LEDs, and at least one of the first and second controllers is operable to estimate an efficiency of the system of LED-based lights at least partially based on the brightness level in the area. 
         [0008]    These and other embodiments will be described in additional detail hereafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an example of an LED light tube; 
           [0010]      FIG. 2  is a schematic perspective view of a smart building system; 
           [0011]      FIG. 3  is a schematic perspective view of yet another example of an LED light tube; 
           [0012]      FIG. 4  is a flowchart illustrating operation of an example of an LED light tube; 
           [0013]      FIG. 5  is a schematic perspective view of another example of a smart building system; and 
           [0014]      FIG. 6  is a flowchart illustrating operation of multiple LED light tubes. 
       
    
    
     DESCRIPTION 
       [0015]      FIGS. 1-6  are discussed in reference to a light and a light sensor. As shown in  FIG. 1 , a light fixture  14  can accept an LED-based light  16 . The light fixture  14  can be designed to accept standard fluorescent tubes, such as a T-5, T-8, or T-12 fluorescent tube, or other standard sized light, such as incandescent bulbs. Alternatively, the fixture  14  can be designed to accept non-standard sized lights, such as lights installed by an electrician. 
         [0016]    The LED light tube  16  can include a housing  22 , a circuit board  24 , LEDs  26 , a pair of end caps  28 , a controller  25 , and a receiver  27  as shown in  FIG. 1 . The housing  22  as shown in  FIG. 1  is a light transmitting cylindrical tube. The housing  22  can be made from polycarbonate, acrylic, glass or another light transmitting material (i.e., the housing  22  can be transparent or translucent). For example, a translucent housing  22  can be made from a composite, such as polycarbonate with particles of a light refracting material interspersed in the polycarbonate. While the illustrated housing  22  is cylindrical, housings having a square, triangular, polygonal, or other cross sectional shape can alternatively be used. Similarly, while the illustrated housing  22  is linear, housings having an alternative shape, e.g., a U-shape or a circular shape can alternatively be used. Additionally, the housing  22  need not be a single piece as shown in  FIG. 1 . Instead, another example of a housing can be formed by attaching multiple individual parts, not all of which need be light transmitting. For example, such a housing can include an opaque lower portion and a lens or other transparent cover attached to the lower portion to cover the LEDs  26 . The housing  22  can be manufactured to include light diffusing or refracting properties, such as by surface roughening or applying a diffusing film to the housing  22 . For compatibility with the fixture  14  as discussed above, the housing  22  can have a length such that the light  16  is approximately 48″ long, and the housing  22  can have a 0.625″, 1.0″, or 1.5″ diameter. 
         [0017]    The circuit board  24  as illustrated in  FIG. 1  is an elongate printed circuit board. Multiple circuit board sections can be joined by bridge connectors to create the circuit board  24 . The circuit board  24  as shown in  FIG. 1  is slidably engaged with the housing  22 , though the circuit board  24  can alternatively be clipped, adhered, snap- or friction-fit, screwed or otherwise connected to the housing  22 . For example, the circuit board  24  can be mounted on a heat sink that is attached to the housing  22 . Also, other types of circuit boards may be used, such as a metal core circuit board. Or, instead of a circuit board  24 , other types of electrical connections (e.g., wires) can be used to electrically connect the LEDs  26  to a power source. 
         [0018]    The light  16  can include two bi-pin end caps  28  (i.e., each end cap  28  can carry two pins), one at each longitudinal end of the housing  22 , for physically and electrically connecting the light  16  to the fixture  14 . The end caps  28  can be the sole physical connection between the light  16  and the fixture  14 . The end caps  28  can be electrically connected to the circuit board  24  to provide power to the LEDs  26 . Each end cap  28  can include two pins, though two of the total four pins can be “dummy pins” that do not provide an electrical connection. Alternatively, other types of electrical connectors can be used, such as an end cap carrying a single pin. Also, while the end caps  28  are shown as including cup-shaped bodies, the end caps  28  can have a different configuration (e.g., the end caps  28  can be shaped to be press fit into the housing  22 ). One or both of the end caps  28  can additionally include electric components, such as a rectifier and filter. 
         [0019]    The LEDs  26  can be surface-mount devices of a type available from Nichia, though other types of LEDs can alternatively be used. For example, although surface-mounted LEDs  26  are shown, one or more organic LEDs can be used in place of or in addition thereto. The LEDs  26  can be mounted to the circuit board  24  by solder, a snap-fit connection, or other means. The LEDs  26  can produce white light. However, LEDs that produce blue light, ultra-violet light or other wavelengths of light can be used in place of white light emitting LEDs  26 . 
         [0020]    The number of LEDs  26  can be a function of the desired power of the light  16  and the power of the LEDs  26 . For a 48″ light, such as the light  16 , the number of LEDs  26  can vary from about five to four hundred such that the light  16  outputs approximately 500 to 3,000 lumens. However, a different number of LEDs  26  can alternatively be used, and the light  16  can output a different amount of lumens. The LEDs  26  can be evenly spaced along the circuit board  24 , and the spacing of the LEDs  26  can be determined based on, for example, the light distribution of each LED  26  and the number of LEDs  26 . 
         [0021]    The controller  25  can be mounted on the circuit board  24 , and can include a memory and a CPU for executing a program stored on the memory. That is, the controller  26  can be include a microprocessor or other digital or analog circuit that performs the tasks described herein. The controller  25  can be in communication with the LEDs  26 , the end caps  28 , and the receiver  27  via the circuit board  24 , though the controller  25  can alternatively be in communication with the LEDs  26 , end caps  28 , and/or receiver  27  using wires or another connection. The controller  25  can also be configured to regulate the amount of power provided to the LEDs  26 . That is, the controller  28  can govern the amount of power provided from the end caps  28  to the LEDs  26 . The controller  28  can be in communication with multiple subsets of LEDs  26  (such as individual LEDs  26 ) for providing a different amount of power to one or more of the subsets of LEDs  26 . Alternatively, a controller can be external of the light  16 . For example, a controller can be coupled to the fixture  14  to control a light attached to the fixture  14 . 
         [0022]    The light  16  can additionally include a receiver  27  mounted on the circuit board  24 . The receiver  27  can be in communication with the controller  25  as mentioned above and with a remote transmitter as is discussed below in greater detail. For example, the receiver  27  can be in communication with the transmitter using a standard wireless protocol (e.g., a radio standard, a cellular standard such as 3G, Bluetooth, or WiFi). The receiver  27  can alternatively be in communication with the transmitter in another manner such as hardwiring or via electric signals sent through the end caps  28 . The receiver  27  can be configured to receive signals from the transmitter, and the receiver  25  can transmit received signals to the controller  25 . 
         [0023]    While the light  16  is shown as being compatible with standard sized fluorescent fixtures, an LED-based light having another shape, such as an incandescent bulb or another type of light, can alternatively be used. Also, other types of light sources, such as fluorescent or incandescent based light sources, can be used instead of the LEDs  26 . 
         [0024]    As illustrated in  FIG. 2 , the fixture  14  can be in a building  11  including a light switch  31  and a light sensor  33 , and the light  16  can be installed in the fixture  14 . The light switch  31  can control whether power is provided to the fixture  14 . However, as is mentioned above and described below in greater detail, the controller  25  can control whether power is provided to the LEDs  26 , in which case the light switch  31  need not be included. Also, if the building  11  is a “smart” building, the controller  25  and switch  31  can be in communication (e.g., via a wired connection, or via a wireless transmitter and a wireless receiver) such that the controller  25  can override the switch  31  to turn on the light  16  even when the switch  31  is in an off position or vice versa. 
         [0025]    The light sensor  33  can detect a level of light in an area of the building  11  including the light  16 , such as an amount of light that strikes the sensor  33 . The light sensor  33  can include an integral transmitter for transmitting a light level signal α to the receiver  27 . The light sensor  33  can continuously transmit the signal, or the light sensor  33  can include a controller (e.g., a controller including a memory and a CPU for executing a program stored on the memory) for deciding when to transmit the signal. In addition to the light sensor  33 , other sensors can be in communication with the light  16 . For example, the building  11  can also include a motion sensor, a sensor for determining whether a door is ajar, a sensor for determining when a keypad or other type of lock is actuated, a voice-activated sensor, a clock or calendar, a light sensor for measuring an amount of light in the building  11  other than or including light provided by the light  16  (e.g., an amount of sunlight entering the building  11 ), a power supply monitor, and/or another type of sensor. 
         [0026]    In operation, as shown by in  FIG. 4 , the light  16  produces light in step S 1 . In step S 2  the light sensor  33  can measure the amount of light that strikes the sensor  33 , and the light sensor  33  can transmit the light level signal α to the receiver  27  as shown in step S 3 . The receiver  27  can communicate the light level signal α to the controller  25  as shown in step S 4 . 
         [0027]    In step S 5 , the controller  25  can analyze the light level signal α. For example, the controller  25  can estimate a brightness of an area of the building  11  including the light  16 , the controller  25  can compare the light level to a predetermined value (e.g., an amount of light comfortable for an ordinary person), or can analyze the light level signal α in some other manner. Depending on the light level signal α, the controller  25  can control the light  16  in various ways. For example, as shown in step S 6 , the controller  25  can adjust the brightness of light produced by the LEDs  26 . If the light level signal α indicates the amount of light detected is too high, the controller  25  can dim the LEDs  26  or turn a subset of the LEDs  26  off. Alternatively, if the amount of light is too low, the controller  25  can increase the brightness of the LEDs  26  or turn on a subset of the LEDs  26  that were previously off. Thus, the controller  25  can correct the amount of light provided by the light  16  in response to changes in ambient light, such as if a level of natural light entering the area of the building  11  including the light  16  increases or decreases, or if other lights are turned on or off. 
         [0028]    In another example not illustrated, the light  16  can initially not be producing light. The controller  25  can control the light  16  to begin producing light in response to the light level signal α. For example, the light level signal α can indicate that the amount of light in an area of the building  11  is below a predetermined level. 
         [0029]    To avoid interference with the light sensor  33  by the light emitted by the LEDs  26 , the light sensor  33  can sense ambient light during a short period, invisible to the eye, when the LEDs  26  are off. This short off period can occur due to line voltage zero-crossing, or a command from the controller  25 . 
         [0030]    Therefore, among other advantages, an occupant of the area of the building  11  including the light  16  can avoid having to make an effort to turn on the light. 
         [0031]    Returning to  FIG. 4 , as another example of operation of the light  16  shown in step S 7 , the light level signal α can be analyzed by the controller  25  to determine an efficiency of the light  16 . For example, the controller  25  can compare the amount of detected light with a reference value, such as an amount of light detected at a previous date if the light  16  includes a clock and/or calendar. The previous date can be a date when conditions such as ambient light conditions were similar, such as a recent day at approximately the same time. The difference between the current amount of light being produced and the previous amount of light being produced can be used to calculate a change in efficiency of the light  16 . The controller  25  can make this efficiency determination without turning the light  16  off, which can be beneficial if the light  16  is in a location such as a stairwell where a lack of light can be dangerous. As an alternative efficiency test, the controller  25  can compare the amount of detected light when the light  16  is on with an amount of light detected when the light  16  is off, with the difference being used to calculate an amount of light produced by the light  16 . 
         [0032]    The controller  25  can calculate the efficiency by comparing the amount of light produced by the light  16  with the reference value (e.g., an amount of light produced by the light  16  operating under ideal conditions), or by comparing the amount of light produced by the light  16  with the amount of power consumed by the light  16  (which can be measured with an ammeter and voltmeter, a wattmeter, or another power measuring device either integral with the light  16 , electrically coupled to the fixture  14 , or at another location). 
         [0033]    As shown in step S 8 , the controller  25  can also determine whether the light  16  should be replaced. For example, the controller  25  can compare the efficiency of the light  16  with a predetermined value to determine whether the light  16  should be replaced. The predetermined value can be a predetermined efficiency standard, such as the efficiency of the light  16  when new, the efficiency of an ideal light, a maximal output of the light  16 , or some other value. 
         [0034]    The controller  25  can also control the light  16  to indicate its efficiency, which can provide notice that the light  16  should be replaced. For example, the controller  25  can control the light  16  to display its efficiency using a digital read-out integral with the light  16 , a bar of light having a length equivalent with the efficiency, or in another manner. Alternatively, the controller  25  can control the light  16  to display when the efficiency of the light  16  is below a predetermined value, such as by illuminating at least one of the LEDs  26  having a different color than surrounding LEDs  26 , by causing at least one of the LEDs  26  to flash, or by controlling the light  16  in some other manner. Once the efficiency of the light  16  drops below the predetermined value, it can be understood that the light  16  should be replaced. Thus, the light  16  can signal to a maintenance worker or other personnel that the light  16  should be replaced. 
         [0035]    Another light  40  as shown in  FIG. 3  includes the housing  22 , the circuit board  24 , the controller  25 , the LEDs  26 , and the end caps  28  similar to the light  16 . The light  40  can additionally include an integral light level sensor  42  and a transmitter  44 . The light sensor  42  can be mounted on the circuit board  24  to receive power via the end caps  28 , and the light sensor  42  can be in communication with the controller  25  and/or the transmitter  44 . The light level sensor  42  can protrude from the housing  22  as shown in  FIG. 3  or otherwise be positioned to sense an amount of light produced by at least some of the LEDs  26  (e.g., the sensor  42  can alternatively be contained within the housing  22 , and one or more reflectors can be included to direct a portion of light toward the sensor  42 ). Alternatively, the light level sensor  42  can detect an amount of ambient light. The amount of ambient light can include light produced by the LEDs  26 . The sensor  42  can communicate the light level signal α to the controller  25 . 
         [0036]    The transmitter  44  can be mounted on the circuit board  24  for receiving power via the end caps  28 . The transmitter  44  can be in communication with the controller  25  and/or the light sensor  24  for receiving the light level signal α. The transmitter  44  can be configured to transmit the light level signal α to a remote location, such as a smart building control center or another smart building component, or to controllers  25  of other lights  16 ,  40 . 
         [0037]    With this configuration, the controller  25  in the light  40  can control the LEDs  26  and calculate an efficiency of the light based on the light level signal α as discussed above in reference to the light  16 . The light  40  can also indicate whether the light  40  should be replaced similar to as described above in reference to the light  16 . Additionally, the inclusion of the transmitter  44  allows the light  40  to perform other functions. The transmitter  44  can transmit the light level signal α to the remote location, allowing the light level signal α to be used for controlling another component of a smart building (e.g., window shades, another light, or some other component of a smart building) or for another purpose. For example, the transmitter  44  can transmit an efficiency of the light  40  or an indication that the light  40  should be replaced to the remote location. 
         [0038]    The light  40  can also include another sensor, such as a motion detector, in communication with the controller  25  and/or the transmitter  44 . In this case, the controller  25  can take signals other than the light level signal α into consideration in controlling the LEDs  26 . For example, the controller  25  can turn the LEDs  26  off even though the light level sensor  42  detects a low level of light if the motion sensor has not detected movement for a certain amount of time. As a similar example, the controller  25  can turn the LEDs  26  off even though the light level sensor  42  detects a low level of light if a clock or calendar in communication with the controller  25  indicates the time is not during standard working hours. 
         [0039]    As illustrated in  FIG. 5 , multiple fixtures  14  can be in the building  11  including the light switch  31  and the light sensor  33 , and multiple of the lights  16  and/or  40  described above can be installed in the fixtures  14 . Each light  16 ,  40  may include a controller  25  configured to regulate the amount of power provided to the respective LEDs  26 , as described above. The controllers  25  can be external of the lights  16 ,  40 , for example, coupled to a fixture  14  to control a light  16 ,  40  attached to the fixture  14 . It will be understood that a controller  25  can be provided that performs the tasks described herein with respect to multiple of the lights  16 ,  40 , for example, those installed in a common fixture  14 . 
         [0040]    In operation, as shown by in  FIG. 6 , one or more of the lights  16 ,  40  produce light in step S 61 . In step S 62 , the light sensor  33  can measure the amount of light that strikes the sensor  33 , and transmit a light level signal α to one or more of the lights  16 ,  40 . In addition, or in the alternative, if a light  40  is installed, the light sensor  42  of the light  40  can measure the amount of light that strikes the sensor  42 , and transmit a light level signal α. It can therefore be seen that the light level signals α in this example may be generated by a remote sensor  33 , or by a light sensor  42  of a light  40 . Additionally, the light level signals α may be a function of multiple of the lights  16  and/or  40 . Each signal light level signal α may be indicative of the light produced by one light  16 ,  40 , multiple lights  16 ,  40  or all lights  16 ,  40 , and collectively, the light level signals α are indicative of the overall lighting conditions in the building  11 . The light level signal α (or optionally multiple light level signals α of more than one sensor  33 ,  42 , depending upon the specific configuration for the building  11 ) can be transmitted to one or more of the receivers  27  as shown in step S 63 . 
         [0041]    The receivers  27  can communicate the light level signal(s) α to the controllers  25  for processing and analysis as shown in step S 64 . In one example, multiple controllers  25  (e.g., one controller  25  for each light  16 ,  40 ) may exist in the system. The signal(s) α may be used among the controllers  25  to generate control signals indicative of the desired control for the LEDs  26  of the respective lights  16 ,  40  according to the operations described herein. For instance, each of the respective controllers  25  of the lights  16 ,  40  may communicatively receive one or more of the signals α for individual analysis, as generally described above, and then control the LEDs  26  of the respective lights  16 ,  40 . This analysis and control may be performed collaboratively with respect to the analysis and control of other controllers  25 , for instance. Alternatively, fewer than all of the controllers  25  can be perform certain of the tasks described herein, and can communicate with other controllers  25  of the respective lights  16 ,  40  to effect control of the LEDs  26 , for instance, via transmitters  44  and receivers  27 . However, in another example, the lights  16 ,  40  need not have individual controllers  25  where, for instance, a controller  25  is external of the lights  16 ,  40  and coupled to a fixture  14  common to multiple lights  16 ,  40 . 
         [0042]    In step S 65 , the one or more light level signals α are analyzed by the controllers  25 . For example, the brightness of an area of the building  11  including the lights  16 ,  40  can be estimated, and the light level can be compared to a predetermined value (e.g., an amount of light comfortable for an ordinary person), or the light level signal(s) α can be analyzed in some other manner. The light level signals α may be analyzed to estimate an overall brightness of the area of the building  11 , for example, or could be analyzed to estimate multiple brightness levels within the area. Depending on the light level signal(s) α, the lights  16 ,  40  may be controlled in various ways. For example, as shown in step S 66 , the controllers  25  can collectively function to adjust the brightness of light produced by the LEDs  26  of the lights  16 ,  40 . With respect to each of the individual lights  16 ,  40 , if the amount of light detected is too high, a controller  25  can dim the LEDs  26  or turn a subset of the LEDs  26  off. Alternatively, if the amount of light is too low, a controller  25  can increase the brightness of the LEDs  26  or turn on a subset of the LEDs  26  that were previously off. A control scheme accounting for multiple of the lights  16 ,  40  may also cause the LEDs  26  of one or more lights  16 ,  40  to be dimmed or brightened, or turned on or off, in accordance with a desired brightness level. Thus, the controllers  25  can collectively correct the amount of light provided by the lights  16 ,  40  in response to changes in ambient light, such as if a level of natural light entering the area of the building  11  including the lights  16 ,  40  increases or decreases, or if other lights are turned on or off. 
         [0043]    In another example not illustrated, one or more of the lights  16 ,  40  can initially not be producing light. The controllers  25  can control the light  16 ,  40  to begin producing light in response to the light level signal(s) α. For example, the light level signal(s) α can indicate that the amount of light in an area of the building  11  is below a predetermined level. 
         [0044]    To avoid interference with the light sensors  33 ,  42  by the light emitted by the LEDs  26  of the lights  16 ,  40 , the light sensors  33 ,  42  can sense ambient light during a short period, invisible to the eye, when the LEDs  26  are off. This short off period can occur due to line voltage zero-crossing, or via commands from the controllers  25 . 
         [0045]    Therefore, among other advantages, an occupant of the area of the building  11  including the light  16 ,  40  can avoid having to make an effort to turn on the lights. 
         [0046]    In  FIG. 6 , as another example of operation of the lights  16 ,  40  shown in step S 67 , the light level signal(s) α can be analyzed to determine an efficiency of the lights  16 ,  40 , either individually or on a collective basis. For example, the controllers  25  can collectively function to compare the amount of detected light with a reference value, such as an amount of light detected at a previous date. The previous date can be a date when conditions such as ambient light conditions were similar, such as a recent day at approximately the same time. The difference between the current amount of light being produced and the previous amount of light being produced can be used to calculate a change in efficiency of the lights  16 ,  40 . The controllers  25  can make this efficiency determination without turning the lights  16 ,  40  off, which can be beneficial if the lights  16 ,  40  are in a location such as a stairwell where a lack of light can be dangerous. As an alternative efficiency test, the controllers  25  can compare the amount of detected light when the lights  16 ,  40  are on with an amount of light detected when the lights  16 ,  40  are off, with the difference being used to calculate an amount of light produced by the lights  16 ,  40 . The controller  25  can calculate the efficiency by comparing the amount of light produced by the lights  16 ,  40  with the reference value (e.g., an amount of light produced by the lights  16 ,  40  operating under ideal conditions), or by comparing the amount of light produced by the lights  16 ,  40  with the amount of power consumed by the light  16 ,  40  (which can be measured with an ammeter and voltmeter, a wattmeter, or another power measuring device either integral with the lights  16 ,  40 , electrically coupled to the fixtures  14 , or at another location). 
         [0047]    It will be understood that the comparisons described above can be completed with respect to individual lights  16 ,  40 , for example, or with respect to subsets of lights  16 ,  40  or all lights  16 ,  40  collectively. Where less than all of the lights  16 ,  40  are under consideration, for instance, the output of those lights  16 ,  40  may be factored out of the analysis, e.g., by turning the lights  16 ,  40  off or by otherwise accounting for their light output, power consumption, etc. 
         [0048]    As shown in step S 68 , the controllers  25  can also determine whether one or more of the lights  16 ,  40  should be replaced. For example, the controller  25  can compare the efficiency of the lights  16 ,  40  with a predetermined value to determine whether one, some of all of the lights  16 ,  40  should be replaced. The predetermined value can be a predetermined efficiency standard, such as the efficiency of the lights  16 ,  40  when new, the efficiency of an ideal light, a maximal output of the lights  16 ,  40  or some other value. The determination in this step may be made according to individual lights  16 ,  40 , for example, or with respect to subsets of lights  16 ,  40  or all lights  16 ,  40  collectively. 
         [0049]    As shown in step S 69 , the controllers  25  can also control the lights  16 ,  40  to indicate efficiency, which can provide notice that one, some, or all of the lights  16 ,  40  should be replaced. For example, the controllers  25  can control one or more lights  16 ,  40  to display efficiency using a digital read-out integral with the lights  16 ,  40 , a bar of light having a length equivalent with the efficiency, or in another manner. Alternatively, the controllers  25  can control the lights  16 ,  40  to display when the efficiency of the lights  16 ,  40  is below a predetermined value, such as by illuminating at least one of the LEDs  26  of a respective light  16 ,  40  having a different color than surrounding LEDs  26 , by causing at least one of the LEDs  26  to flash, or by controlling the lights  16 ,  40  in some other manner. Once the efficiency one or more lights  16 ,  40  drops below a predetermined value, it can be understood that the lights  16 ,  40  should be replaced. Thus, the lights  16 ,  40  can signal to a maintenance worker or other personnel when one or more of the lights  16 ,  40  should be replaced. Once again, it will be understood that the indication of efficiency in this step may be made according to individual lights  16 ,  40 , for example, or with respect to subsets of lights  16 ,  40  or all lights  16 ,  40  collectively. 
         [0050]    The above-described embodiments have been described in order to allow easy understanding of the invention and do not limit the invention. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure as is permitted under the law.

Technology Category: f