A dusk to dawn light uses a photocell: it measures ambient light and switches on when daylight fades, staying lit until morning. A PIR light uses movement and stays on for a few minutes at a time. Both are “outside lights with a sensor” and they are not substitutes for each other.
This is the single most common outdoor lighting mix-up across our counter. Somebody wants a light that comes on when it gets dark, buys a PIR floodlight, and then wonders why the front of the house is black until somebody walks past it.
1. Photocell or PIR — pick by what you want the light to do
Ask one question: do you want light present, or light triggered?
Photocell (dusk to dawn) gives you presence. On at dusk, off at dawn, every night, with no movement needed. Right for:
- Front doors, porches and house numbers — so visitors and deliveries can see where they are going.
- Paths, steps and level changes, where a light that comes on after you have already tripped is no use.
- Signage and shop frontages.
- A general lived-in look while you are away.
PIR (motion) gives you alert. Off until something moves, then bright for a few minutes. Right for side gates, back yards, driveways and bin stores — anywhere the point is to notice someone, and to keep running costs and light pollution down. That is a different job, and we cover it in our guide to security lights.
Our position: photocell at the front where people need to see, PIR at the back and sides where you want to be told. Plenty of houses want both, and there is nothing wrong with that.
Trade Tip: If somebody asks for “a sensor light”, always ask whether they want it on all night or only when someone comes. That one question settles the whole purchase — and it is the question that stops a return three days later. The word “sensor” does not distinguish the two.
2. Fittings with the cell built in
The tidiest answer for a front elevation is a wall light with the photocell integrated — one fitting, one cable, nothing extra to site.
The Knightsbridge OWALL2BCP is a GU10 up-and-down wall light with a photocell sensor, IP54, brushed steel finish, 2 × 20 W. The same fitting comes in white as the OWALL2WP. Up-and-down fittings suit a front door because they wash the wall in both directions rather than glaring straight out at head height.
Where you want a more traditional look, the LANT3BKP is an LED half wall lantern with a photocell, 8 W, 440 lumens, cool white, IP54, in black — an integrated LED, so there is no lamp to change.
3. Converting lights you already have
If the fittings are fine and you just want them switching automatically, you do not need to replace anything. A separate photocell control unit switches an existing circuit.
The Knightsbridge OSPCKIT is a 230 V 10 A IP66 automatic photocell control sensor in black, rated for 1000 W incandescent or 300 W LED.
Note those two figures carefully, because they are not a typo and they trip people up. The LED limit is far lower than the incandescent limit. LED drivers draw a brief high inrush current at switch-on, and it is that surge — not the running wattage — that the relay contacts have to survive. Load a photocell to its incandescent rating with LED fittings and you will be replacing the photocell, not the lamps.
Trade Tip: Add up the LED wattage of every fitting on the circuit and check it against the LED rating, never the incandescent one. If you are anywhere near the limit, split the load across two photocells. They cost less than the call-out to work out why one keeps failing.
4. IP ratings, and what they mean on a wall
Two figures: solids, then water.
- IP54 — dust-protected and resistant to splashing. Correct for a wall light under normal exposure, including British rain running down a wall.
- IP66 — dust-tight and resistant to powerful water jets. Worth having on a control unit that will sit fully exposed, or anywhere it may be hosed.
The sensible pattern is what the products above already do: IP54 on a sheltered wall fitting, IP66 on the exposed control sensor.
5. Where not to put the cell
A photocell only knows how much light is falling on it, which makes siting the whole game. Get it wrong and you get the two classic faults.
Light that never comes on: the cell can see a street lamp, a security light, a neighbour's floodlight or an illuminated sign. It reads that as daylight and stays off all night.
Light that flickers on and off: the cell can see the lamp it is controlling. It switches on, sees its own output, decides it is daytime, switches off, goes dark, switches on again. Round and round.
So: point the cell away from the fitting it controls and away from other light sources. North-facing is generally the safest aspect. And check it at night before you make good — a cell that behaves perfectly at four in the afternoon can hunt all night.
Summary: photocell or PIR
| You want | Fit |
|---|---|
| Light on all night, front door and paths | Photocell — dusk to dawn |
| Light only when someone approaches | PIR — motion |
| New fitting, tidy front elevation | Wall light with integrated photocell, IP54 |
| Automate lights already fitted | Separate photocell control unit, IP66 |
| LED load | Check against the LED rating, not the incandescent one |
| Siting the cell | Away from the lamp it controls and from other light sources |
Expert Help in the West Midlands
Villa Road, Birmingham, since 1975. Tell us what you want the light to do — be on, or come on — and how many fittings are on the circuit, and we will point you at the right sensor and check the load with you before you buy.
Browse outdoor lighting or the full lighting range.
Frequently asked questions
What is the difference between a dusk to dawn light and a PIR light?
A dusk to dawn light uses a photocell to sense daylight and stays on all night. A PIR light detects movement and stays on for a few minutes. One gives constant light after dark; the other only responds to someone approaching.
Why does my dusk to dawn light keep switching on and off?
The photocell can almost certainly see the lamp it is controlling. It switches on, reads its own light as daylight, switches off, and repeats. Reposition or reorient the cell so it cannot see the fitting.
How many LED lights can I run from one photocell?
Check the LED rating rather than the incandescent one — they differ a lot, because LED drivers draw a high inrush current at switch-on. The OSPCKIT is rated 1000 W incandescent but 300 W LED. Split the load across two units if you are close to the limit.