Patent Publication Number: US-6340864-B1

Title: Lighting control system including a wireless remote sensor

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to the field of lighting control. More particularly, the present invention relates to a lighting control system including a wireless, integrated circuit, sensor for detecting light and/or occupancy in an area. 
     BACKGROUND OF THE INVENTION 
     As is well known, fluorescent lamps offer large energy savings as compared to incandescent lamps. Additional energy savings can be obtained through the use of dimmable fluorescent lamp ballasts. These ballasts can be controlled by ballast control circuitry which reduces the level of the light produced by the fluorescent lamp. In this regard, conservation of energy is always an economic and environmental consideration in designing lighting systems. 
     In addition, as will be appreciated by one skilled in the art, the level and type of background illumination has a profound effect on the optimum artificial light needed for a work area. Besides the ergonomic aspects involved in providing adequate lighting, the light level in an area also affects the human physiology. It is well accepted that lighting can dramatically affect the circadian rhythm of the human physiological system. Accordingly, it is desirable to control the level of the artificial light to provide an optimum amount of light, see, e.g., U.S. Pat. Nos. 5,648,656 and 5,459,376, the contents of which are incorporated herein by reference. 
     Lighting systems are known that control, i.e., decrease or increase, the level of artificial light in relation to the level of daylight in an area. Generally, these conventional lighting control systems are hampered by the lack of adequate light sensors for flexible daylight harvesting applications. Typically, conventional sensor technology uses a single photodiode that senses the light on a work surface so that the light can be adjusted accordingly to maintain a constant value during the day. 
     Since such sensors detect light from either one limited position or possibly an averaged value over a predetermined area, it is necessary to carefully position and angle the sensors. This is required to ensure that the sensors detect adequate and accurate illumination data so that a desired light level can be provided throughout the day. 
     Furthermore, as will be appreciated by one skilled in the art, conventional sensor technology normally requires independent calibration for each application to achieve adequate results. One reason is that typical light sensors, for example, are analog devices that are prone to drift and inaccuracies. 
     In addition to the light sensors discussed above, separate motion sensors may also be used to detect the movement of an occupant in an area, as described in U.S. Pat. No. 5,489,827, the contents of which are incorporated herein by reference. A light source is turned “on” or “off” depending on the presence, or lack thereof, of an occupant in the sensing area. However, determining the state of occupancy within an area can be difficult depending on the positioning of the motion sensor. For example, the motion sensor&#39;s field of view may be limited or obstructed. Moreover, after placement of the motion sensor, subsequent rearrangement of an area&#39;s contents (e.g., furniture) may impair the field of view. 
     Another shortcoming of such motion sensors is that they are typically battery powered. Eventually, these batteries need to be replaced. This is not only inconvenient from a maintenance perspective, but the need for replacement may not always be readily apparent. 
     Conventional light and motion sensors also typically have wired connections to the control unit, e.g., ballast. This requirement adds extra cost for installation, as well as the extra cost for the wired interface in the control ballast, which must be isolated for safety reasons. These hard-wired sensors may be in addition to the need for a separate infrared (IR) sensor used by many ballast systems (e.g., Philips ballast systems) to provide a wireless control interface between the ballast and a handheld or wall mounted remote control unit. This IR sensor is usually mounted on the ceiling near the fixture with a wired connection to the ballast, which again adds to the overall system expense and installation time. 
     Some improvement in lighting control technology has been achieved by using multiple light sensors. In this arrangement, the sensors are tied to a control unit that generates a control signal based on the inputs from the multiple sensors. Illustratively, in the prior art, a ballast dimming signal based on some algorithm of multiple sensor inputs to control a light source is known. This type of arrangement, however, results in complex installation/setup procedures and expensive equipment requirements. Moreover, this arrangement fails to address the shortcomings of conventional sensor technology discussed above. 
     There thus exists in the art a need for a lighting control system that provides improved performance as well as reducing the cost, complexity and installation/setup time of the system. It is also desirable to provide a sensor that is not encumbered by hard-wired connections and limited-lifetime, power supplies. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to address the limitations of the conventional lighting control systems and sensor technology discussed above. 
     In one aspect of the present invention, a lighting control system includes a light source having a control unit and a wireless receiver. The system also includes a sensor having a plurality of pixels and a wireless transmitter, which are formed by a single integrated circuit (IC). The sensor transmits data to the light source using the wireless transmitter so that the control unit can control the light source in accordance with the transmitted data. 
     One advantageous embodiment of the present invention relates to the use of CMOS imaging technology for the sensor. This embodiment enables the integration of multiple functions into one integrated circuit (IC). This results in greatly reduced power requirements as compared to conventional sensors. The IC sensor architecture combines a wireless interface, as well as a pixel array for improved daylight harvesting and occupancy detection. The integration of these multiple functions into a single integrated component results in significant cost savings and reduced (installation/equipment) complexity for the lighting control system and sensor. 
     These and other embodiments and aspects of the present invention are exemplified in the following detailed disclosure. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The features and advantages of the present invention can be understood by reference to the detailed description of the preferred embodiments set forth below taken with the drawings, in which: 
     FIG. 1 is a diagrammatic view of a room in accordance with one aspect of the present invention. 
     FIG. 2 is a schematic diagram showing details of a remote sensor in accordance with a preferred embodiment of the invention. 
     FIG. 3 is a block diagram showing a lighting control system in accordance with another aspect of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, an area such as a room  10  (a portion of which is shown) includes a luminaire, such as a lamp fixture  20 , a sensor  30 , a work surface  40 , an occupant  50 , and a remote control unit  60 . The present invention of course is not limited to the office environment shown in FIG. 1, but may be used in any domestic environment or surrounding, such as buildings, sporting stadiums, aircraft or ships. It should also be understood that the lamp fixture  20  may be any controllable light source, such as a dimmable fluorescent lamp. 
     The sensor  30  is a standalone device that detects simultaneously illumination from various directions and surfaces in the room  10 . This is done to obtain improved control and balance of the light level in the room  10  as compared to conventional lighting control methods that depend on sensing the light level using a single or multiple photodiode sensors. 
     As shown in FIG. 2, the sensor  30  preferably comprises a CMOS pixel (imaging) array  31 . The present invention, however, is not limited to CMOS technology. Other types of low power dissipating logic technology may be used. The sensor  30  also comprises X-decoder  32 , Y-decoder  33 , A/D converter  34 , digital signal processor (DSP)  35 , wireless transmitter  36  and a power source  37 . In this embodiment, the pixel array  31  is arranged in rows (x-axis) and columns (y-axis). Of course, other pixel configurations are possible. X-decoder  32  and Y-decoder  33  are used to select a respective pixel from the array  31 . The A/D converter  34  converts the analog data from a respective pixel to digital data in a manner well known in the art. The DSP  35  processes the digital data for transmission by the wireless transmitter  36 . For a more detailed description of CMOS imaging sensors, the reader is referred to U.S. Pat. No. 5,841,126, the contents of which are incorporated herein by reference. 
     Compared to charged coupled devices (CCD) which are well known in the art, CMOS image sensors allow for integration of complex signal processing electronics on a single IC. This allow CMOS image sensors to have similar resolution while greatly reducing the power requirements as compared to CCD&#39;s. 
     For lighting applications, an optical resolution of several hundred pixels for the sensor  30  is preferred. Of course other resolutions may be used. For example, CMOS image sensors may have resolutions of tens to hundreds of thousands of pixels (primarily used for video and camera applications). But the preferred resolution results in significant size and cost advantages for the sensor  30 . Moreover, as compared to conventional photodiode sensors which offer a resolution of one pixel, the sensor  30 &#39;s resolution provides considerable improvement in the ability to sense illumination from various directions and surfaces in the room  10 . 
     This resolution enables the sensor  30  to differentiate simultaneously light from various directions and sources in the room  10 . This light may originate from, or be reflected from different sources or surfaces in the area. For example, as shown in FIG. 1, the sensor  30  detects light  11 ,  12  and  13  from the work surface  40 , as well as from windows (i.e., daylight) and wall surfaces around the room  10  (i.e., background or ambient light). This information is collected by the sensor  30  so that an optimum level of artificial lighting for daylight harvesting can be determined as discussed below. Secondly, this resolution also allows the pixel array  31  of the sensor  30  to detect movement of the occupants in the room so that the sensor  30  can also be used as an occupancy detector. 
     In operation, the sensor  30  collects data in each pixel of the pixel array  31 . This data is then converted into digital form by the A/D converter  34 . The digital data is then processed/analyzed by the DSP  35  to extract key information, such as objects in motion, light levels from various sources and identification of specific features. This information is then formatted by the DSP  35  for transmission by the wireless transmitter  36 . 
     The sensor  30  can be automatically calibrated through a digital circuit  38 , e.g., included in the A/D converter  34 , to eliminate analog errors such as drift and offset. The digital circuit  38  can also be programmed to adapt the sensor  30  to different environments and lighting conditions, resulting in rapid and trouble-free installation. In addition, the sensor  30  may have a plurality of predetermined environment settings and operational modes such as: 
     Office-window (an Office with windows in which the ambient light may fluctuate greatly during the day); 
     Office-no-window; 
     Residential-kitchen (a residential kitchen in which bright light is required during the day, but, at night, only directional lighting is needed when an occupant is detected, i.e., providing a pathway to the refrigerator for the late-night snacker); 
     Freq-Fast (a mode in which updated information is transmitted frequently to control/adjust the artificial light level in a rapidly changing environment); 
     Freq-Slow; 
     Light-Only (a mode in which only light levels are detected); 
     Occupant-Only; 
     Light-&amp;-Occupant; and 
     Night-On (a mode in which the lamp fixture  20  is automatically turn on when no daylight is detected or falls below a predetermined threshold level). 
     As shown in FIG. 3, the lamp fixture  20  includes a wireless interface  21  and a control unit  22 . The information transmitted by the sensor  30  is received by the wireless interface  21 . The control unit  22  then processes the information to derive the correct control information (e.g., reduction or augmentation of the light output) based on the room lighting levels and/or the presence of occupants. 
     As will be appreciated, algorithms (e.g., implemented by software or firmware) and hardware are used by, and/or incorporated in, the control unit  22  to process the information accordingly. The control unit  22  may include ballast control hardware and a microprocessor for executing such algorithms and functions. 
     The control unit  22  also processes the information received from the sensor  30  to interpret information transmitted by the sensor  30  in accordance with the various predetermined settings and modes. It is also understood that the environment and mode settings are not necessarily mutually exclusive. Different environment and mode settings may be used together to tailor the lighting control system as needed. 
     The information transmitted by the sensor is preferably in a compressed digital format. Various compression formats may be used as will be appreciated by one skilled in the art. Compression reduces the transmission power consumption of the sensor  30 . In addition, the information is preferably transmitted at low data rate because such transmission can be performed reliably and using low-power. Preferably the peak transmission data rate is in the range of 10 Kbits/second or less. 
     As should be appreciated, the sensor  30  addresses the problem of wiring costs by incorporating the wireless transmitter  36 . CMOS passive or active RF transmitters are known in the art and have been used for applications such as identification badges. Preferably, the wireless transmitter  36  is a low-power RF transmitter. A short range RF transmitter can operate reliably at a power level of one milliwatt or less. Moreover, if the data is transmitted in short bursts periodically (e.g., every second), then the low duty cycle can reduce the average RF power level to less than 100 microwatts. This type of RF transmitter will provide a short-range link (1-2 meters) between the sensor  30  and the lamp fixture  20 . Of course, other types of wireless interfaces may be used rather than RF, such as IR or ultrasonic interfaces. 
     When using a low-power RF transmitter, the sensor  30  is placed in close proximity to the control unit  22 . For example, by mounting the sensor  30  to the ceiling near the lamp fixture  20 . The wireless communications link is then automatically established. No wiring or drilling holes in the ceiling is required. Moreover, system setup is quick and easy. 
     Also, in such a configuration, the sensor  30  is used to control only its neighbor lamp fixture  20 . This allows for easy control of individual lighting in cellular light arrangements. In lighting fixtures in large office rooms, for example, this makes it possible to achieve good daylight harvesting by allowing the fixtures near the windows to respond separately from fixtures that are further removed from the windows. It also permits personalized light setting by the occupant  50 , who may wish to control the illumination on the work surface differently when working on the computer or drafting a memorandum. 
     Alternatively, the sensor  30  may incorporate identification codes as part of each transmitted information packet. Other control/selection information can also be transmitted in the information packet. In this embodiment, the control unit  22  of the lamp fixture  20  only accepts information packets with a particular code. This enables the sensor  30  to control multiple lamp fixtures within an area individually. For example, as shown in FIG. 3, a second lamp fixture  20 A also receives and decodes the transmission from the sensor  30 . 
     The wireless interface to the lamp fixture  20  also results in design improvements and advantages in the control unit  22 . A CMOS receiver can be easily integrated into a small low-cost IC, perhaps even as part of a main microcontroller IC of the lamp fixture  20  or control unit  22 . Only access to a small and inexpensive antenna structure is needed. 
     At the same time, by using the wireless interface embodiment of the present invention, conventional two-wire interfaces typically used for control in fluorescent lamps, for example, can be eliminated. This two-wire interface is expensive because it must have high-voltage isolation for safety reasons, for example, typically a transformer or a dual optoisolator circuit is required. Accordingly, this embodiment provides significant cost savings in ballast design and reduces the physical size of the printed circuit (PC) boards required in such lamp fixtures. 
     In another embodiment of the present invention, the sensor  30  includes circuitry for a wireless receiver  39  (shown in FIG.  2 ). While a separate circuit block for the wireless receiver  39  may be used, it is preferable that the DSP  35  include this functionality. The wireless receiver  39  preferably functions as an infrared (IR) detector so that the lamp fixture  20  can be controlled using the handheld or wall mounted remote control unit  60 . The use and popularity of these types of remote control units are increasing. 
     The DSP  35  can filter the IR signals from other optical signals detected by the pixel array  31 . The pixel array  31  can detect both white light and IR signals with efficiency, so that a separate IR photo-detector deceive is not needed. Typically, IR signals modulate at a high frequency (e.g., 36 kHz from a typical television remote control device) and are digitally encoded. The DSP  35  can filter and decode this IR signal from slower varying white light signals. 
     Information based on the infrared signals from the remote control unit  60  is combined with other information that is transmitted to the control unit  22  by the sensor  30 . As discussed above, the wireless interface eliminates the need for wiring and reduces installation costs, particularly for retrofit installations. 
     In another embodiment of the present invention, the sensor  30  functions as a passive device, or at least operates without a power-source such as batteries or a connection to an external power source. This can be achieved through the use of low-power CMOS circuit techniques. By performing the signal processing and data compression (discussed above) on the sensor  30 , and using a low-power transmitter only for short periods of time, results in very low IC power requirements, e.g., power levels of less than a 100 microwatts. Since, the power requirements are so low, the sensor  30  can maintain operation via the power source  37  (shown in FIG. 2) using only electromagnetic radiation, i.e., “free” power, which emanates from ambient energy sources. For example, the free power can be obtained from either ambient light, or RF energy from a nearby ballast of the lamp fixture  20 . 
     In yet another embodiment, the sensor  30  may received “free” power from ambient energy sources and also include a battery backup. In this embodiment, the power source  37  provides power to the sensor  30  to operate using the “free” power and/or the battery supplied power. This allows the sensor  30  to conserve the battery energy level by using the “free” power when possible. 
     While the present invention has been described above in terms of specific embodiments, it is to be understood that the invention is not intended to be confined or limited to the embodiments disclosed herein. On the contrary, the present invention is intended to cover various structures and modifications thereof included within the spirit and scope of the appended claims.