Occupancy Sensors

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Occupancy and vacancy sensors are devices that detect when a space is unoccupied and accordingly automatically turn OFF (or dim) the lights, thereby saving energy. The device may also turn the lights ON automatically upon detecting the presence of people, providing convenience and a potential security aid. 

According to the Lawrence Berkeley National Laboratory, occupancy-based strategies can produce average lighting energy savings of 24%.

Due to their relative simplicity and high energy-savings potential, coupled with energy code mandates, these sensors are a staple in new construction. They are also a common control feature in retrofit projects.

The sensor’s sensitivity defines at what distance it can detect major (i.e., body) and minor (i.e., hand) motion. The resulting coverage is expressed as coverage area and pattern. Coverage area defines the boundaries within which the sensor can detect motion. Coverage shape is the resulting shape of these boundaries, which may be a circle, rectangle, ellipse, tear drop, etc.

Occupancy sensors may be specified as manual-, partial- or full-ON devices.

The majority of commercial building energy codes require manual- or partial-ON operation. Manual-ON sensors (also called vacancy sensors) require the occupant to turn the lights ON using a manual switch, which may be integral to the sensor (shown here is an example). Partial-ON sensors activate the lights to a designated level such as 50%, and the occupant then uses a switch to bring the lights to full output. Full-ON sensors activate the lights at full output.

Manual- and partial-ON sensors tend to save more energy because the occupant may want to leave the lights OFF or at a lower level. Full-ON sensors provide convenience, which may be regarded as an amenity.

Occupancy and vacancy sensors may turn the lights OFF or reduce the lighting via stepped switching or dimming. While ON/OFF is more common, light reduction is well suited to applications where the lights must stay ON but are frequently unoccupied, such as this stairwell, or where the lamp does not start quickly, as in the case of HID lamps.

The sensor’s sensitivity defines at what distance it can detect major (i.e., body) and minor (i.e., hand) motion. The resulting coverage is expressed as coverage area and pattern. Coverage area defines the boundaries within which the sensor can detect motion. Coverage shape is the resulting shape of these boundaries, which may be a circle, rectangle, ellipse, tear drop, etc.

Most commercial building energy codes require lighting be turned OFF or reduced when it is not being used. These codes apply to new construction and renovation projects and, in some states, lamp-plus-ballast retrofits as well. The majority of codes now specifically require sensors in a wide range of spaces. Increasingly, codes mandate use of manual- or partial-ON sensors. The maximum time delay is trending from 30 to 20 minutes. See our Energy Codes course for information that may be applicable to your project.