Purpose

• Motion detecting lights provide security by illuminating an area in response to movement. While this in itself doesn't sound an alarm or trap an intruder, it does give any potential burglar or assailant the sense that they are being watched.
  
  

Types

• There are two basic ways that motion detecting systems function. Active systems send out a signal: light, sound or radar. When the signal is interrupted on its return journey to its source, movement is intercepted. These motion-detection systems are typically used in burglar alarms.
  
  Passive detection systems operate by reacting to changes in infrared energy, which is a form of light given off by living creatures. They are called "passive" because they don't send a signal out, but rather register variations.
  
  

Function

• Most motion-detecting lights use a passive detection system. The sensor built into the light fixture senses infrared energy at a range around 93 degrees F, a temperature roughly equivalent to that of the human body.
  
  Motion-detecting lights don't react to a stationary person because they are designed to pick up rapid changes in temperature. Generally, the sensor is placed below one or more security lights, but additional lights can also be grouped to operate off the same sensor.