Ambient and Spectral Light Sensors

Abstract

Silicon photocells have been used for years to inform a lighting unit of the simple presence or absence of other light in the vicinity. The most common outdoor application has been street lighting, which lends itself to the straightforward on/off control information. The needs of an advanced lighting system, however, differ from those of a streetlight or other dark/light, on/off decision scenarios. Among its other distinguishing characteristics, an advanced lighting system will be expected to adapt to specific human-centered needs within a space. While adaptation capabilities in some systems may include the ability to adjust the color qualities or color temperature of a space, it will most certainly be expected to be able to vary illuminance levels in order to maintain a fixed level of brightness suitable to the user or task at hand, regardless of the variance in sunlight or other ambient lighting within the space. In order to accomplish this, a lighting decision engine will require knowledge of the specific amount of light within a space at any given point in time, measured in a human-centered fashion. This is the role of an ambient light sensor or ALS. This chapter will discuss the technical aspects of the ALS, including how it differs from a normal photocell, and will explore the communications and intelligence extensions that will be required for a complete sensor subsystem. A functional model will also be addressed to provide an illustration of how this important technology can be expected to be applied.