Motion sensor lighting: sensor types, wiring diagram and settings

Short answer: A motion sensor switches the light on when it detects movement and off after a set time. The supply live (L) and neutral (N) go into the sensor; the sensor's switched output (L' or L-out) goes to the lamp, and the lamp's neutral goes to N. In corridors, stairs, car parks and toilets it cuts energy use considerably. Wiring should be done by a qualified electrician with the circuit breaker off.

Sensor types: PIR or microwave?

• PIR (passive infrared): detects the movement of body heat. Best at movement across its field; it cannot see through glass. The most common and economical type for homes, stairs and outdoors.
• Microwave (radar): measures changes in the reflected wave, picks up small movements and walking straight towards it, and works behind thin plastic or plasterboard, so it can be hidden inside a fitting. Set the sensitivity carefully, as it can react to movement behind walls.
• Presence sensor: a more sensitive type for offices that also detects the small movements of someone sitting at a desk.

Motion sensor wiring diagram

• L (live): the live from the breaker to the sensor's L terminal.
• N (neutral): neutral to the sensor's N terminal and the lamp's neutral.
• L' / L-out (switched output): from the sensor to the lamp's live terminal.
• Earth (PE): to metal-bodied luminaires.

A switch wired in parallel with the sensor output (bypass) lets you keep the light on when needed. If several sensors must switch the same lamps, connect their outputs in parallel according to the manufacturer's diagram.

Settings: TIME, LUX and SENS

• TIME: how long the light stays on after the last movement. 1–3 minutes for corridors and 2–5 minutes for stairs are usually enough.
• LUX (light threshold): stops the sensor switching on when there is enough ambient light, avoiding daytime operation.
• SENS (sensitivity/range): detection distance. Too high a setting causes triggers from passing cars or plants moving in the wind.

Mounting height and position

Ceiling 360° sensors are usually fitted at 2.5–4 m and cover a circle around that point. Wall 180° sensors work best at 1.8–2.5 m. Place a PIR so that people cross its field sideways, and away from heaters, air-conditioning vents or direct sunlight.

Compatibility with LED lights

LED drivers draw a short high current at switch-on (inrush). The sensor's relay must suit the total power and inrush of the LED fittings; for many fittings on one sensor, use a sensor with a high-inrush relay or a contactor. Some sensors need a minimum load; if very low-power LEDs flicker or will not switch off, choose a suitable sensor type.

Where to use them

• Stairwells and corridors in apartment blocks
• Car parks, storage and plant rooms
• Toilets, dressing rooms, pantries
• Garden paths, entrances and driveways (IP44 or higher outdoors)

Luminaires with built-in sensors need less cabling and labour than a separate sensor and fitting, and are usually preferred in new projects.

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