Direct answer
PIR describes a passive-infrared sensing technology that detects changes in infrared radiation, usually from moving people. “Occupancy sensor” describes a control function and can use PIR or other sensing technologies. A day/night switch responds to ambient light level, not people. A timer responds to time. The best control depends on what event should turn the light on and off.
The fastest way to choose
| If you want the light to respond to… | Use / consider | Example application |
|---|---|---|
| Movement / presence | PIR or occupancy sensor | Passage, storeroom, bathroom, driveway approach. |
| Daylight level | Day/night photocell | Exterior wall lights that should operate from dusk to dawn. |
| Clock time | Timer | Signage or predictable exterior operating hours. |
| App / rules / remote status | Smart controller or smart switch | Home automation, schedules, energy monitoring. |
| Both darkness and movement | Combined photocell + motion strategy | Security/entrance lighting that activates only at night when motion is detected. |
PIR is a technology, not a complete behaviour description
A PIR sensor detects changes in infrared energy across its detection zones. That makes it effective for moving people, but its performance depends on placement, detection angle, target movement and environmental conditions. A sensor pointing across a walking path can behave differently from one aimed directly down the path. Product detection range and mounting height should therefore be treated as actual specifications, not marketing decoration.
Occupancy and vacancy strategies
US Department of Energy guidance distinguishes occupancy controls, which can operate auto-on/auto-off, from vacancy controls, which are manual-on/auto-off. The distinction matters because a room with sufficient daylight may not need the lights to turn on every time somebody enters. In homes, this logic can be useful in bathrooms, garages and utility spaces — provided the sensor can reliably detect occupants who may remain relatively still.
Day/night switches solve a different problem
A photocell or day/night switch measures ambient light and changes state around a set threshold. It is useful for dusk-to-dawn lighting but has no knowledge of occupancy. If the aim is to reduce unnecessary outdoor lighting, combine daylight logic with a timer or motion strategy where appropriate. DarkSky recommends timers and motion sensors so exterior lighting is used only when needed.
Why sensors sometimes become annoying
- The detection zone does not cover where people actually spend time.
- Sensitivity is too high and traffic, pets or vegetation trigger the light.
- The time delay is too short and the light switches off while someone is still present.
- The photocell sees light from the fitting itself or a nearby source and cycles unpredictably.
- The connected LED load is not compatible with the sensor electronics.
- The product is installed at the wrong height or orientation.
Indoor vs outdoor sensors
An outdoor sensor must be suitable for the environment, including ingress protection and operating conditions. For entrance and security lighting, sensor placement should support visibility without aiming intense light into neighbours, roads or eye level. The separate Whitehouse outdoor-lighting guide in this pack should be linked directly from this section.
Frequently asked questions
Is a PIR sensor the same as a motion sensor?
PIR is one common type of motion-sensing technology. “Motion sensor” is the broader category.
Does a PIR sensor detect people who are not moving?
PIR works best when there is a change in infrared pattern. Very still occupants can be harder to detect depending on the sensor and placement.
What is the difference between a day/night sensor and a motion sensor?
A day/night sensor responds to ambient light; a motion sensor responds to movement or presence.
Can a motion sensor work only at night?
Many outdoor PIR products include an adjustable light-level function, or the system can combine motion sensing with a separate photocell. Check the exact product.
Should a passage use a timer or occupancy sensor?
If use is irregular, occupancy sensing usually matches the need better. If use follows a predictable schedule, a timer may be simpler.
Technical references and further reading
- US DOE/FEMP: Wireless Occupancy Sensors for Lighting Controls — Occupancy/vacancy control strategies and application guidance.
- DarkSky International: Home Outdoor Lighting Assessment — Guidance on controls, shielding, light level and warm outdoor light.
- Publishing note: product availability and specifications can change. Verify current Whitehouse product pages and manufacturer documentation before publication, purchase or installation.
