Passive Infrared (PIR) sensors are the most common type used in ceiling light applications due to their affordability and simplicity. They operate by detecting changes in infrared radiation emitted by warm objects, such as human bodies, moving within their field of view. A pyroelectric material senses heat differentials, generating pulses when motion causes positive or negative changes in infrared levels. Fresnel lenses focus the IR energy, filtering to wavelengths close to human body heat (8-14 micrometers) to minimize false triggers from non-human sources.
Advantages include low power consumption, making them ideal for battery-powered or wireless setups, easy installation, and adjustable sensitivity/timer settings. They provide reliable detection in enclosed spaces with clear lines of sight, saving energy by automatically switching lights on/off.
- Disadvantages: They require unobstructed views, so partitions or furniture can block detection. They're less effective at sensing minor movements like typing and may false-trigger from heat sources like vents or sunlight.
- Applications: Ceiling-mounted in offices, hallways, restrooms, warehouses, and classrooms for occupancy-based lighting control, offering 10-90% energy savings in intermittently used areas.
