You mount an outdoor light with a motion sensor at 1.8 to 2.5 metres, choose IP44 as a minimum (on the wall under an overhang) up to IP65 (fully exposed to the weather), and connect it to a circuit with 30 mA RCD protection. The sensor gets live and neutral, and passes the switched live on to the lamp through terminal L1. Set it up in this order: LUX to sun first (then it works in daylight and you can test it), TIME on the shortest setting and SENS halfway. Test, adjust, and only when everything is right do you turn LUX to moon. For a front door, 400 to 800 lumens at 2700 to 3000 kelvin
is plenty. Anything over 3,000 lumens on a house wall stops being security and starts being a nuisance. And the most important rule, the one that appears on no packaging anywhere: a PIR sensor sees you far better when you walk across its view than when you walk straight at it. So mount it at right angles to the route people walk, not looking along it.
There is no job with a bigger gap between “that should take ten minutes” and reality than this one.
You buy a light with a sensor. You screw it to the wall. You connect three cores. And then it starts: it comes on when your neighbour turns their car around, it burns all night, or it does absolutely nothing when you walk up to your own front door with two bags of shopping.
That is almost never the light’s fault. It is down to where it hangs, how it is set up, and which type of sensor is inside it.
I will walk you through the whole thing. Choosing, mounting, wiring, setting up and fixing problems. Including the bits the instructions skip: why your sensor works worse in summer than in winter, why an LED keeps glowing faintly after it switches off, and how to avoid half the street having a word with you about it.
Here we go:
First the choice: light with a built-in sensor, separate sensor, or smart
There are three ways to get sensor light onto your house. They do not solve the same problem.
1. A light with a built-in sensor. One fitting, with the sensor inside it or underneath it. Simplest to mount, cheapest to buy. The downside: the sensor and the lamp face the same way and sit at the same height. For a front or back door that is fine. For a drive or a path around the corner, often not.
2. A separate sensor that switches one or more lights. You put the sensor where it sees well and the light where the light needs to fall. That can be three lights if you want. More expensive and more cable, but far more control. It is also the only way to automate existing outdoor lights you like without replacing them.
3. A smart light or camera with motion detection. Zigbee, Wi-Fi or Matter, linked to an app or to a system like Home Assistant. You set it so the light only comes on between sunset and 1am, or only when nobody is home. Most options, most faff, and it depends on your network and sometimes on a cloud subscription.
My advice for most houses: a good light with a built-in sensor at the doors, and a separate sensor for the drive and the path. You can always make it smart later, and then you do it where it actually helps.
Sensor types: PIR, high frequency, or both
This is where most choices go wrong. There are two technologies, and their strengths and weaknesses are completely different.
PIR (passive infrared) does not see movement. It sees differences in heat shifting across the segments of its lens. A person at 37 degrees walking past a cold fence gives a clear signal. That same person on a summer evening at 28 degrees, on a driveway that has been warming up all day, gives a much weaker one. That is why your sensor performs better in January than in July. It is not a fault, it is the physics of the thing.
HF or radar (high frequency, sometimes called microwave) transmits its own signal and measures the reflection. It sees movement, not heat. The advantage: it works through glass, thin timber and plastic, so you can hide it behind a housing. The disadvantage: it works through glass, thin timber and plastic, so it also sees your neighbour behind the fence, the cat on the windowsill and, now and then, a flapping tarpaulin.
| PIR (infrared) | HF / radar | |
|---|---|---|
| Detects | Moving difference in heat | Movement, heat or no heat |
| Typical range | 5 to 12 metres | 5 to 15 metres |
| Detection angle | 90 to 360 degrees | 180 to 360 degrees |
| Sees through material | No | Yes (thin timber, glass, plastic) |
| Affected by sun and heat | Yes, noticeably | Barely |
| Affected by rain and wind | Barely | Yes, moving water and branches |
| Price on its own | 15 to 60 euros | 25 to 80 euros |
| Best for | Walls, doors, drives, garden paths | Hidden in a housing, porches, covered areas |
Outdoors on a wall, PIR is the right choice nine times out of ten. You use HF when you want the sensor hidden away, or when it sits under a canopy and you want it tucked neatly behind a cover. There are also dual sensors that only switch when both technologies see something. Those cost more and are mainly there to stop false triggers in awkward spots.
Watch the detection angle against the position. A 180 degree sensor on a flat wall makes sense. A 360 degree sensor belongs on a ceiling or under a canopy, not against a wall: half its field of view is then staring into the brickwork.
Where to put it: the four rules that decide everything
Rule 1: mount it at right angles to the route people walk. A PIR sensor works with vertical lens segments. Walk across its field of view and you jump from segment to segment, so it switches almost instantly. Walk straight at it and you stay inside the same segment, so it only notices you much later, sometimes at two metres. This is by far the most common mistake: the light above the front door that comes on when the key is already in the lock.
Rule 2: mount it at 1.8 to 2.5 metres. The manufacturer’s range figures (say “12 metres”) apply at a stated mounting height, usually around 2.2 metres. Mount it higher and the field of view grows but the sensitivity drops and the range shortens. Mount it lower and the odds of false triggers from cats and wildlife go up sharply. Is a height given in the instructions? Follow the instructions.
Rule 3: point it away from heat sources and moving greenery. A PIR reacts to the steaming flue of a boiler or a tumble dryer, an air conditioning unit kicking in, a metal shed door warming up in the morning sun, washing on the line and swaying branches. Keep those out of the field of view, or make the field of view smaller (more on that below).
Rule 4: leave the street and the neighbours out of it. Point the sensor at your own property. A sensor that takes in the pavement will be switching all evening and becomes a source of irritation within two weeks: for you, because the light flickers through your curtains, and for the neighbours, because it shines into their bedroom.
The lighting plan: which spot, how much light
More lumens is not better. Light that is too fierce dazzles you, makes the shadows around it darker, and works against you when you actually want to see something.
| Spot | Guide figure | Type of fitting | Run-on time |
|---|---|---|---|
| Front door, back door | 400 to 800 lumens | Wall light, light aimed down | 1 to 2 minutes |
| Garden path to the shed | 200 to 400 lumens per point | Low bollard or wall light | 1 to 3 minutes |
| Drive, parking space | 1,000 to 2,000 lumens | Floodlight, shielded | 3 to 5 minutes |
| Back garden, large patio | 1,000 to 2,000 lumens | Floodlight under the overhang | 2 to 5 minutes |
| Carport, garage door | 800 to 1,500 lumens | Ceiling fitting with a 360 degree sensor | 2 to 3 minutes |
Choose 2700 to 3000 kelvin (warm white). Cool white at 6000 kelvin is cheaper to produce, which is why so much of it is sold, but it dazzles harder, feels cold and causes more light pollution for wildlife. The 20 lumens per watt you gain is something you will never notice in your own garden.
And here is the point almost no DIY guide mentions: aim the light downwards and shield it. The Dutch consumer organisation Milieu Centraal recommends exactly that for garden lighting, along with keeping it on as briefly as possible and using as few fittings as possible, to give nocturnal wildlife a break. Bats avoid lit routes around their roosts, and insects gather around the light and drop out of the night-time food chain there. A sensor light is a good answer to that: it burns for a few minutes at a time rather than all night. Just set it to a short run-on time, then, and not to a quarter of an hour. Source: Milieu Centraal
IP rating: what you actually need
The IP code has two digits. The first covers dust and touch, the second covers water.
| Spot | Minimum | Better | Why |
|---|---|---|---|
| Under a deep overhang or in a porch | IP44 | IP54 | Splashing only, but condensation happens |
| Flat wall, out in the rain | IP44 | IP65 | Driving rain gets everywhere |
| Under a carport or canopy | IP44 | IP44 | Sheltered, but damp |
| Just above ground level, along a path | IP65 | IP66 | Splashed water and mud |
| Ground light, set into paving | IP67 | IP68 | Sits under water from time to time |
Also look at the IK rating (impact resistance) if the light hangs at football or bicycle height, and at the housing: powder-coated aluminium lasts far longer near the coast than chromed steel. Rust almost always starts at the screws, so swap the supplied fixings for stainless steel if you have any doubt.
One trap: the IP rating only holds if the light is mounted the way the manufacturer intended. Run the cable into the fitting from above instead of through the gland underneath, or use a gland that is too big for your cable, and your IP65 is worth nothing in practice.
The electrics: what has to be right and where the line sits
Straight talk first. In England and Wales, replacing an existing outdoor light or adding one to an existing circuit is not notifiable work under Part P of the Building Regulations, so you may do it yourself. Installing a new circuit to feed outdoor lighting, or any work inside the consumer unit, is notifiable and must either be done by a registered electrician or signed off by building control. Source: Approved Document P Either way, the work has to comply with BS 7671, the wiring regulations. Rules differ in Scotland and Northern Ireland, so check locally before you start.
What that means for this job in practice:
RCD protection. Anything mounted outdoors belongs behind a 30 mA RCD. If you are in an older house with no RCD on the lighting circuits, this is the moment to sort it. Outdoor lighting is exactly where moisture and earth faults turn up.
Earthing. If the light has a green-and-yellow terminal or a metal body that has to be earthed (class I), you connect the earth. Full stop. If the light is double insulated (class II, marked with the symbol of one square inside another) it does not need an earth, but you still run the earth core through neatly and terminate it in a connector. Never cut it off: the next light may well need it.
Cable through the wall. Drill the hole sloping upwards from outside to inside, so lower outside than inside. Water running along the cable then drips back out instead of into your cavity. Use a wall sleeve, or fill the hole afterwards with a flexible sealant, not a hard filler.
Cable along the wall or through the garden. Above ground along a wall: in conduit or trunking, with the junction in an IP65 or better junction box, at least 30 centimetres above ground, with the cable entering the box from below and a drip loop in it. Through the garden: steel wire armoured cable at a depth of at least 600 millimetres, with the last 600 millimetres up to roughly 300 millimetres above ground level in protective conduit. That is not overkill: at 600 millimetres you are below the frost line and below the spade of the next person who lives here.
Cable size. For lighting, 1.5 mm² is enough in the vast majority of cases. If you are running a long cable down the garden (more than about 25 metres) or you plan to hang a socket off it later, go straight to 2.5 mm².
Wiring it up, step by step
What you want to hand: a cross-head screwdriver, wire strippers, a drill with a masonry bit, a spirit level, a voltage tester (a proper one, not a screwdriver with a bulb in it), connectors, a wall sleeve, sealant and stainless steel screws with the right plugs.
Step 1: power off and prove it. Circuit off at the consumer unit, and then test with a proper voltage tester that it really is dead. Lock the circuit off with tape or a lock-off clip so nobody switches it back on while you are up the ladder.
Step 2: work out the position and mark it. Hold the light against the wall and look, literally from the route people walk, at whether the sensor sits at right angles to the direction they arrive from. Mark the holes and note where the gland or cable entry comes out: that belongs on the underside of the light or behind the mounting plate, never on top.
Step 3: drill and feed through. Drill the fixing holes and, if the cable is new, the feed-through hole sloping upwards. In cavity walls: be careful with long drill bits, you do not want to hit a cable or a frame. Blow the hole clean before you put the plug in.
Step 4: feed the cable in and connect it. Standard arrangement for a light with a built-in sensor: brown to L, blue to N, green-and-yellow to earth. Done.
With a separate sensor it looks different. The sensor usually has four terminals:
| Terminal | Where it goes |
|---|---|
| L | Live from the supply (brown) |
| N | Neutral from the supply (blue) |
| L1 (sometimes L’) | Switched live to the light |
| Earth | Earth carried through to the light |
The neutral for the light connects straight to the supply neutral, so not through the sensor. Only the live runs through the sensor. That is the whole principle: the sensor is a switch that operates itself, and to do that it needs a neutral of its own.
Step 5: seal it and close it up. Tighten the gland properly onto the right cable diameter, rubber seal in place, cover on. Seal along the top edge of the mounting plate so water cannot run in behind it, but leave the bottom edge open so any moisture that does get in can get out again. This is the classic mistake in reverse: sealing all the way round, after which the light turns into a bathtub.
Step 6: power on and test. Switch the circuit back on and work through the settings (next section).
Combining a sensor with an ordinary switch
Often you want two things: automatic light when something moves, and the option to keep the light on by hand while you are working in the garden.
There are three ways, and one of them is wrong:
A. A switch in the supply before the sensor. Simple and safe: switch off means everything off. Many sensor lights also have a permanent-on function: switch off and back on twice within about one to two seconds and the light stays on for a few hours until you switch it off again. Check the instructions to see whether your model does this, because the command (how many times, how quickly) varies by brand.
B. A separate manual switch that bypasses the sensor. A switch in parallel with the sensor output, so you can send live straight to the light as well. It works fine, but bear in mind: with the switch on, there is voltage on the sensor output. So always work with the whole circuit off, not just the switch.
C. The mistake: leaving out the sensor’s neutral. Some cheap sensors work on two wires and use the light itself as a path to power their own electronics. With filament lamps that was fine. With LED it guarantees trouble: afterglow, flicker, or refusing to switch off. Choose a sensor with a proper neutral connection.
Setting it up: LUX, TIME and SENS in the right order
Almost every sensor has three adjusters. In this order you will have them right in ten minutes, in broad daylight.
LUX (the dusk setting). Decides at what ambient light level the sensor is allowed to switch. Symbols: a sun (switches at any time, daylight included) and a moon (switches only in the dark). Turn it fully to sun first. Then you can test during the day. Only when everything is right do you turn it back towards moon, or just short of it if you want it coming on at dusk.
TIME (run-on time). How long the light stays on after the last movement, usually adjustable from about 5 seconds to 15 minutes. Put it on the shortest setting while you are setting up, otherwise you spend three minutes waiting after every test. Afterwards you set what the spot needs: 1 to 2 minutes for a door, 3 to 5 minutes for a drive where you have to unload a car.
SENS (sensitivity or range). Decides how far and how finely it looks. Start halfway. Too high and it picks up the pavement, too low and it only sees you at three metres.
The test routine
- LUX to sun, TIME on the shortest setting, SENS halfway.
- Wait about a minute after switching the power on; many sensors have a warm-up period in which they switch at random.
- Walk your normal route to the door. Does it come on in time? If not: SENS up, or turn the sensor head slightly.
- Now walk the route you do not want detected: along the pavement, along the neighbours’ fence. Does it come on? SENS down, or shield it (see below).
- Go out and look once more in the evening. Does it dazzle? Does it shine into a bedroom? Tilt the fitting further down.
- Only now turn LUX back to moon.
Shrinking the field of view without ruining the sensitivity
Winding the sensitivity down makes the sensor worse everywhere. It is smarter to shield only the direction you do not want. Plenty of brands supply blanking plates or sliders for the lens for exactly this, so do not throw them away. If nothing came with it, a strip of opaque tape on the inside of the lens segments on that side works perfectly well. Black insulating tape on the outside works too, but it leaves an ugly adhesive line after two summers.
With an HF sensor, taping does nothing: it looks straight through your tape. There you have to wind the sensitivity back or move the sensor.
Fixing problems: the table you came for
| Symptom | Most likely cause | Fix |
|---|---|---|
| Light stays on continuously | LUX is set to sun, or TIME to maximum | Work through the settings; leave the sensor without power for a minute to reset it |
| Light stays on even after a reset | Sensor is not reaching its minimum load (old sensor, small LED lamp) | Choose a sensor rated for LED, or a lamp with more wattage |
| LED glows faintly after switching off | Leakage current through the sensor electronics or through a single pole switch | Fit a bypass (load resistor) as close to the lamp as possible, or choose a lamp and sensor combination the manufacturer lists together |
| Comes on by itself, always in the same place | A heat source in view: boiler flue, dryer, air conditioning unit, a shed door warming up | Shield the field of view or move the sensor |
| Comes on by itself, at random | Moving greenery, washing, headlights, rain on the lens | SENS down, shield the field of view, clean the lens |
| Triggers off the neighbours or the pavement | Range too wide | SENS down and shield that side with the supplied plate |
| Flashes or pulses on and off | Light from the lamp falls back onto the sensor, or warm air from the fitting rises past it | Move the lamp further from the sensor, angle the sensor head down a little |
| Comes on too late at the front door | You are walking straight at the sensor | Turn the sensor a quarter turn so you cross the field of view |
| Works much worse in summer | Small temperature difference between you and the surroundings | Normal PIR behaviour; SENS slightly higher in summer, or consider an HF sensor |
| Stopped working after heavy rain | Water in the gland or behind the mounting plate | Unscrew, dry out, tighten the gland properly, leave the bottom edge open |
| Does nothing at all | Wrong terminal (lamp on L instead of L1), or no neutral at the sensor | Check the wiring, power off first |
One nuance on the afterglow: that faint glow is not dangerous and costs half a watt per light at most, but it is annoying and it shortens the life of the driver in the lamp. A bypass (sometimes sold as a “dimmer stabiliser”) in parallel with the lamp cures it by draining the residual voltage away.
Making it smart: when it is worth it
A sensor light does one thing: light on when something moves. A smart setup can do more:
- Only on between sunset and a time you choose
- Brighter when nobody is home, softer when you are sitting in the garden
- All the outdoor lights on at once when the camera at the back door sees something
- A notification on your phone instead of just light
You can do that with Zigbee or Matter devices and a hub, or with a video doorbell that drives other lights. Realistic costs: a smart outdoor sensor 30 to 80 euros, a smart outdoor fitting 60 to 200 euros, a hub 60 to 150 euros.
Two warnings. First: anything that depends on Wi-Fi and a cloud stops working when your internet goes down or the manufacturer pulls the service. Prefer systems that keep working locally. Second: put up a camera that looks onto a public road or your neighbours’ garden and you are into data protection territory. Point it at your own property.
What does it cost?
| Item | Range |
|---|---|
| Basic LED wall light with PIR | 20 to 60 euros |
| Branded fitting with PIR (Steinel, Ledvance, Philips and the like) | 60 to 150 euros |
| LED floodlight 20 to 50 W with sensor | 25 to 80 euros |
| Separate PIR sensor | 15 to 60 euros |
| Separate HF/radar sensor | 25 to 80 euros |
| IP65 junction box | 5 to 15 euros |
| Wall sleeve, glands, sealant, stainless screws | 10 to 25 euros |
| 2.5 mm² steel wire armoured cable | roughly 3 to 5 euros per metre |
| Adding an RCBO in the consumer unit | 40 to 90 euros in parts |
| Electrician, hourly rate | roughly 60 to 100 euros per hour |
| Electrician, replacing an outdoor light on an existing point | 100 to 250 euros all in |
An average job (two sensor lights on existing connection points) costs 80 to 250 euros in materials and takes half a day. If it turns into a new supply from the consumer unit plus a cable down the garden, reckon on 250 to 600 euros in materials and a full day.
Maintenance: ten minutes, twice a year
- Clean the lens with a damp cloth. Dust, cobwebs and limescale will quietly take a couple of metres off your range.
- Clear out spiders and insects from the housing. A spider building its web in front of the lens is one of the most common causes of random switching.
- Check the gland and mounting plate for cracks and loose screws, especially on south and west facing walls where the UV hits hardest.
- Reassess the settings when the season changes: what is right in winter is sometimes just a shade too insensitive in summer.
- Test the RCD with the test button. Twice a year, and definitely after you have changed anything on the outdoor installation.
Nine mistakes worth avoiding
- Mounting the sensor along the walking direction. It only sees you at the last moment. Mount it at right angles.
- Going too bright. A 5,000 lumen work light on your house wall dazzles you, your visitors and your neighbours, and makes the rest of the garden darker rather than lighter.
- Cool white light. 6500 kelvin is cheaper but feels cold, dazzles harder and does more harm to nocturnal wildlife.
- Running the cable into the fitting from above. Water runs along the cable and straight in. Always from below, with a drip loop.
- Sealing all the way round. The light has to be able to shed moisture. Sealed on top, open at the bottom.
- Putting a 360 degree sensor on a wall. Half its field of view is wasted.
- Skipping RCD protection. Outdoors is where moisture and earth faults meet. 30 mA, no discussion.
- Cutting off the earth core because the light is class II. Run it through and terminate it. The next light may need it.
- Setting it up on the first evening, in the dark, from the top of a ladder. Do it in daylight with LUX on sun and TIME short. Saves you three evenings of irritation.
Frequently asked questions
Can I fit an outdoor light with a motion sensor myself?
In England and Wales, yes, as long as you are replacing an existing light or adding one to an existing circuit. That is not notifiable work under Part P of the Building Regulations. A new circuit for outdoor lighting, or any work inside the consumer unit, is notifiable and needs a registered electrician or building control sign-off, and the rules differ in Scotland and Northern Ireland. Either way the work has to meet BS 7671. In practice that means: 30 mA RCD protection, the right IP rating, proper earthing and sound connections inside a waterproof box. If you are unsure about the circuit at the consumer unit, have just that part done for you.
What height should you mount an outdoor light with a motion sensor?
Usually between 1.8 and 2.5 metres. The manufacturer’s range figures apply at a stated height, often around 2.2 metres. Mounting higher widens the field of view but reduces sensitivity and range; mounting lower brings more false triggers from cats and wildlife.
Why does my outdoor sensor light come on by itself?
The most common causes: a heat source in the field of view (boiler flue, tumble dryer, air conditioning unit, a metal door warming up), moving branches or washing, car headlights, rain or cobwebs on the lens, and with high frequency sensors, movement behind a fence or a window. Fix it by shielding the field of view with the supplied plate rather than winding the sensitivity all the way down.
Why does my LED keep glowing faintly after the sensor switches it off?
That is leakage current. The sensor’s electronics, or a single pole switch, lets a tiny current through, and that is already enough to make a modern LED driver glow. It is not dangerous and costs half a watt at most, but you cure it with a bypass (load resistor) as close to the lamp as possible, or by choosing a sensor with a proper neutral connection that the manufacturer lists as suitable for LED.
Does a motion sensor work worse in summer?
Yes, with PIR sensors it does. They measure the temperature difference between you and your surroundings. On a warm summer evening, with a drive that has been heating up all day, that difference is small, so the sensor reacts later or at a shorter distance. That is normal behaviour. Turn SENS up slightly in summer, or pick a high frequency sensor for awkward spots, since those respond to movement rather than heat.
PIR or radar: which is better outdoors?
For walls, doors, drives and garden paths: PIR. It is cheaper, less bothered by rain and wind, and you can shield its field of view easily. Choose radar (HF) if you want the sensor hidden behind a cover or behind glass, or under a canopy where the temperature differences are small. Bear in mind that radar sees through fences and windows, so it can give you more false triggers.
How much electricity does sensor-controlled outdoor lighting use?
Very little. An LED fitting of 10 to 20 watts that runs for half an hour in total per evening uses roughly 2 to 4 kWh a year, so a few euros. The sensor itself usually draws less than 1 watt at rest, which works out at about 5 to 8 kWh a year. Compared with an outdoor light that burns all night (roughly 40 to 70 kWh a year at 12 watts), sensor switching saves a decent amount.
Can I add a motion sensor to an existing outdoor light?
Yes, with a separate sensor placed somewhere between the supply and the light. It can even sit indoors at the consumer unit or in a junction box, as long as the sensor itself has a clear view of the area it has to watch. There are also sensor adapters that screw in between the lampholder and the bulb, but those usually sit inside the fitting and therefore see too little. For a house wall, a separate wall-mounted sensor works better.
Finally
Sensor lighting stands or falls on three things: where the sensor looks, how bright the lamp is, and how long it stays on.
Mount it at right angles to the walking route. Choose warm light and aim it down. Set the run-on time to one to five minutes, not a quarter of an hour. Shield what you do not want it to see instead of wrecking the sensitivity.
Do that, and you have a light that comes on the moment you arrive, not when the cat from three houses down shoots across the garden.
Small tip. Big difference.
Working on the outside of the house anyway? At Fred’s DIY Plans you will find building plans with materials lists for garden and building projects: from a shed and a carport to a canopy you can tuck that lighting into neatly. Do yourself a favour. Have a quick look here.
Cheers from Fred Schouten, builder and DIYer through and through
PS: take a photo of the wiring diagram in the instructions before you throw them away, and keep it in your phone next to the photo of your consumer unit. In three years, when the light starts misbehaving and the instructions are long gone, you will know within ten seconds which core belongs on L1.