A homeowner fitted a PIR-controlled light at the front door expecting it to welcome visitors after dark. Every delivery driver and dinner guest arrived to a completely dark porch, because the light only triggered once they'd already stepped close enough to set it off, by which point they'd been fumbling for the doorbell in the dark.

Presence vs Alert: The Question That Actually Decides This

The mix-up is common because both sensor types sound similar on a spec sheet, automatic, dusk-triggered, energy-saving, but they solve different problems. A photocell answers "is it dark yet," and once it is, the light stays on continuously until daylight returns. A PIR answers "did something just move," and stays off otherwise, however dark it's gotten.

For a front door, house number, or entrance path, the job is to be visible on approach, not to react to it. A visitor walking up a dark path to a PIR-only porch light has already navigated the dark section before the light even triggers, which defeats the purpose for exactly the situation it's meant to help with. RoSPA's garden safety checklist flags well-lit, level paths and steps as a basic trip-prevention measure, which only works if the light is already on when someone arrives.

A Common Fault Worth Knowing Before You Blame the Sensor

If a photocell-controlled light seems to switch on and off repeatedly through the night rather than staying steady, the most common cause isn't a faulty sensor, it's the photocell detecting light from the fitting it's controlling. Repositioning or reorienting the cell so it can't see its own lamp usually resolves this without needing a replacement part.