PIR Motion Sensor (PIR)

A PIR (passive infrared) sensor detects the moving heat signature of a person or vehicle and tells the fixture to react — typically taking a light from a dim standby level to full brightness for a set hold time, then easing back down. “Passive” is the key word: it emits nothing and detects nothing on its own. It only sees change in the infrared pattern across its field of view.

How It Works, and What That Implies

The sensor element is split into zones behind a faceted Fresnel lens. A warm body crossing from one zone into another produces a differential signal; a warm body sitting still produces none. Three practical consequences follow directly:

• Movement across the beam is detected far more reliably than movement toward it. Someone walking straight at the fixture crosses fewer zone boundaries than someone walking past it, which is why approach corridors need the sensor oriented across the path of travel rather than along it.
• A stationary person disappears. Hold times exist precisely because of this — set them long enough that someone working or waiting is not left in the dark.
• Ambient temperature reduces contrast. On a hot night, body and background temperatures converge and effective range shortens. This is normal PIR behaviour, not a fault.

Detection Range and Mounting Height

Ranges vary with the sensor and the target, but the shape of the table does not: PIR is a low-mounting-height technology. Above roughly 6 m, the angle to a pedestrian flattens, the target occupies fewer zones, and detection degrades. That is why the feature belongs on path, perimeter, wall and garden lights rather than high-mast or main-road fixtures.

Why PIR Matters Most in Solar Lighting

On a grid fixture, motion control saves electricity. On a solar fixture, it changes what the product can do at all.

A residential path may see only minutes of real traffic per night. Running at 20–30% standby and boosting to 100% on approach cuts nightly consumption dramatically, and in an off-grid system that saving converts directly into one of three things:

1. A smaller panel and battery for the same performance, which lowers cost and wind loading.
2. Longer autonomy through cloudy spells on the same hardware.
3. A brighter peak than a constant-output configuration could sustain.

This is why sizing a solar light always requires the dimming profile, not just the LED wattage. Panel watts × your worst-month sun-hours must exceed nightly consumption — and nightly consumption is a function of the profile.

Typical Configuration Parameters

• Standby level — 20–30% is the usual compromise between visible presence and energy saving. Dropping to zero makes the area feel abandoned and startles users when it snaps on.
• Hold time — 30 seconds to a few minutes. Too short is worse than no control at all: repeated on/off cycling annoys users and reads as a fault.
• Fade — a ramp of a second or two up and several seconds down feels engineered; instant switching feels broken.
• Sensitivity — reduce it where foliage, flags or heat plumes cause false triggers.

PIR vs Microwave vs Photocell

PIR and photocell are complements rather than alternatives, and most well-specified fixtures use both: the photocell decides whether it is dark enough to be on at all, and the PIR decides how bright it should be right now.