Why use passive infrared sensors:

Passive Infrared (PIR) occupancy sensors help in saving energy by turning off unwanted lights. These sensors can be used in public places like offices and schools where people may keep moving in and out of a room and forget to switch off lights after use.

The amount of energy saved by using passive infrared sensors:

An infrared occupancy sensor can help reduce energy expenditures by 50%. The U.S. Environmental Protection Agency states that energy savings from using PIR occupancy sensors can range from 60 percent in conference rooms, 80 percent in corridors, 25 percent in private offices, 40 percent in classrooms, 30 to 90 percent in restrooms, and 45 to 80 percent in storage areas.