BACKGROUND

Motion/occupancy sensors are known to provide an economical solution for controlling energy delivery to various electrical systems, such as lighting systems in a residence, commercial building, outdoor area, or any other place where it is desired to limit energy delivery to those times when the controlled space is occupied. One of the primary benefits of utilizing occupancy sensors for this purpose is substantial energy savings which results in corresponding cost savings, not to mention conserving valuable natural resources. Occupancy sensors are often considered to be most suitable when the area to be controlled is intermittently occupied, for example, when a room is unoccupied for two or more hours per day, and where one or more lights in the area is regularly left ON when the space is unoccupied. This type of situation makes occupancy-based lighting control a very desirable solution for areas such as parking garages and exterior lighting applications. Studies have shown that Motion/Occupancy detection systems used to control parking garages and exterior lighting can provide energy savings of up to 30% to 60%, and possibly more.

In addition to providing a cost-effective method for reducing energy consumption, additional uses for occupancy sensors include security (e.g., by indicating that a particular area is occupied, or not), and reducing light pollution (e.g., by limiting the amount of lighting operated at night). Historically, due to reasons that include relatively low energy costs, security concerns, and the lack of a truly robust low-cost occupancy detection technology, the market has been reluctant to deploy occupancy detection for parking garage and outdoor lighting applications. This reluctance is waning, however. Recent code changes, such as to the California Energy Code (CEC), Title 24, and the addition of new wide-reaching energy-related standards, such as ASHRAE/IES 90.1, have led to strengthened language in Codes of many jurisdictions and led to the addition of more energy-delivery control requirements that now include parking garages and exterior lighting. These changes include, for example, adding a requirement for occupancy detection as a means of reducing lighting levels when these lighting zones are unoccupied. The development of a new robust luminance and motion/occupancy sensor capability for lighting applications provides a solution that addresses these new code and standard requirements, as well as additional concerns.

SUMMARY

According to one aspect of the present application, a control system based on Digital Image Processing is presented that provides a superior solution to those currently on the market. In accordance with at least one embodiment such digital image-based occupancy sensing uses a much higher resolution method compared to conventional alternatives. For example, a passive infrared (PIR) sensor is basically a 2-pixel camera that provides a yes/no decision. In accordance with an exemplary embodiment of the present application, however, a digital camera with greater than 100,000 pixels provides a much more robust solution. Both the PIR and the embodiment mentioned provide an indication of motion in the field of view. However, the additional information captured and processed by a Digital Signal Processor (DSP) allows for improved object Motion of Interest (MOI) detection and eliminates false detections.

According to this and other embodiments, by analyzing digital video data and removing selected background information, the system disclosed herein uses the change in the remaining image, and a characterization of that change, to determine if relevant movement has taken place in the field of view. According to further embodiments, additional processing on the image data is performed to increase the reliability of the system because there are many events that can result in image frame data modification that are not necessarily related to actual occupancy or MOI. Such events could potentially lead to inaccurate or erroneous MOI detection and are addressed by the additional processing. Situations that could lead to this type of erroneous MOI determination include sudden changes in light, such as lightning flashes or vehicle headlights sweeping across the field of view, falling snow or rain, insects on or near the sensor, and moving trees, grass or other foliage.

FIGS. 1 and 2respectively illustrate two exemplary issues addressed by embodiments of this application.FIG. 1shows a large number of swarming insects100flying in close proximity to an outdoor light fixture110equipped with an imager, such as a camera, (not shown). In this embodiment the fixture and sensor are fixed atop a pole120of, for example, a street light. This type of motion, i.e., the random motion of one or more swarming insects, is exemplary of the type of motion that is typically not intended to result in energy-delivery, e.g., the turning the street light ON. Moreover, recent scientific studies have shown that blue-light LEDs, which are becoming more and more common in lighting fixtures, attract more flying insects than do other types of light sources, such as yellow-hued sodium lights. Even a small number of bugs or insects can deceive an image-based detector into determining an occupancy condition as the bugs or insects are in motion and their proximity to the imager makes them appear much larger than they really are. This perspective-distance effect makes it difficult to differentiate the insects from relevant motion, such as vehicular or pedestrian traffic on the ground. In accordance with exemplary embodiments of this application, specific processing is performed on the image data to enable the system to distinguish this type of undesired motion from that which is desired to be used to turn ON the light.

Another situation addressed by exemplary embodiments of the application occurs when the pole, or other structure on which the sensor is mounted, does not remain stationary. For example, the pole may wobble, or sway, due to mechanical resonance imparted by incident wind force. The pole swaying will cause the imager to move, creating frame-to-frame changes of the image that, if significant enough, will result in a false detection of desired motion, e.g., MOI. In an exemplary embodiment illustrated inFIG. 2, a sensor (not shown) is mounted on the fixture210at the top of the pole220. The sensor includes an imager which perceives significant apparent motion as the pole220sways back and forth as indicated by the dashed-line arrows. In accordance with embodiments of the application this non-useful relative motion perceived by the swaying sensor/imager is differentiated from the Motion Of Interest (MOI) so only detected MOI is used to control the light.

Other aspects will become apparent by considering the detailed description and accompanying drawings.

