Motion sensors automatically turn outdoor lights on when they are needed (when motion is detected) and turn them off a short while later. They are very useful for outdoor security and utility lighting provided by incandescent lamps.

 

 

Because utility lights and some security lights are needed only when it is dark and people are present, the best way to control might be a combination of motion sensor and photosensor.

 

Incandescent flood lights with a photosensor and motion sensor may actually use less energy than pole-mounted high-intensity discharge (HID) or low-pressure sodium security lights controlled by a photosensor. Even though HID and low-pressure sodium lights are more efficient than incandescents, they are turned on for a much longer period of time than incandescents using these dual controls.

 

When turned on, HID and low-pressure sodium lamps can also take up to ten minutes to produce light. Therefore, they don't work well with just a motion sensor.