Presence detector (detector de presencia, occupancy sensor)

What a presence detector is

A presence detector is a sensor that switches the light on when someone enters its zone and off when it has detected nobody for a programmed time. It avoids lights burning in empty spaces, which in communal stairs, garages and corridors account for a good part of consumption. In the US it is often called an occupancy sensor.

Types by technology

• Passive infrared (PIR): detects the heat of moving people. The most common and cheapest.
• Microwave: detects movement even through some materials, with more sensitivity. Useful where there are obstacles.
• Dual: combines both to avoid false triggering.

Presence or motion

The terms are used as synonyms, but there is a difference. A motion sensor reacts to clear movement, like someone crossing a hallway. A presence detector is more sensitive and picks up small movements, like a person sitting in an office or a toilet, and usually measures daylight so it does not switch on if there is enough. For corridors a motion sensor will do; where people stay still, choose presence.

Settings and mounting

• Switch-off time: how long it waits with nobody detected.
• Light threshold: the lux level at which it activates.
• Sensitivity and range.
• Mounting: on the ceiling it covers a full circle; on the wall, a fan in front.

With many LED fittings, the detector usually drives a relay or contactor so it is not overloaded.

Where it saves most

On stairs, entrances and communal garages, replacing push-button timers. Also in toilets in business premises, stores and storerooms. Fitted, it costs roughly 40 to 90 euros per point. See motion sensors and dimmers and communal area lighting in Seville, Spain.