A sensor light that comes on once you are already at the door, or every time a possum crosses the fence, is almost never a faulty unit. It is aimed wrong or set wrong. Both are fixable, and both are avoidable at install time.
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Sensor lights are one of the cheapest genuinely useful things you can add to a house. They stop you crossing a dark yard with your arms full, they light the way to the front door for anybody arriving, they make a property distinctly less appealing to walk up to uninvited, and they cost nothing to run while nothing is moving.
They also generate more complaints than almost any other fitting we install, and the complaints are remarkably consistent. It comes on too late. It comes on for no reason. It floods the neighbour’s bedroom. It stays on for twenty minutes.
None of those are product faults. They come from how the sensor is aimed and how its three adjustments are set, and both of those are done in about ten minutes at the end of an install by somebody who understands what the sensor is actually looking at.
Which brings us to the part almost nobody is told: a passive infrared sensor is not watching for movement. It is watching for warmth moving between the segments of its lens. That single fact explains both the late trigger and the phantom ones.
A PIR lens splits its field into a fan of separate segments. The sensor reacts to warmth passing from one segment into the next, which means the direction you approach from matters enormously.
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How to read it: the fan is the sensor’s field of view, split into alternating detection segments. Cross it and you pass through segment after segment, so the sensor sees a strong, fast change and reacts straight away. Walk straight down the middle of it and you stay inside one segment for most of the approach, so it barely registers until you are close. The practical rule: aim the fan across the way people actually walk in, not along it.
Because the sensor is looking for moving warmth rather than movement, the usual suspects are not the ones people expect.
Possums, cats and the local wildlife
On the North Shore this is the number one cause by a wide margin. A warm animal crossing a fence line or a roof is exactly what a PIR is built to notice.
Solved by lifting the aim so the fan sits above fence height, masking the lower segments of the lens, or dropping sensitivity so a possum-sized heat signature no longer qualifies.
Foliage moving in the wind
Sun-warmed leaves swinging in and out of the detection fan look a lot like a person to a sensor. It is why a light that behaved all summer suddenly plays up once a shrub has grown.
Either re-aim past the planting or trim it back. This is the one that most often returns a year after installation.
Heat, not motion
An air conditioning condenser, a dryer vent, a hot metal roof shedding heat after sunset or a barbecue will all trip a sensor pointed at them. There is no movement involved at all in the way we normally mean it.
Aiming away from heat sources is a five-second decision at install time and a nuisance to fix afterwards.
Headlights and the street
If the detection fan spills over your front boundary it will pick up cars, pedestrians and anyone walking a dog past your house at eleven at night.
Pull the fan back inside the property line. A sensor light covering the footpath is not providing security, it is providing a strobe for the neighbours.
Almost every domestic sensor has these three dials, and almost every one we are called out to has been left exactly where it came out of the box.
| Adjustment | What it does | Set too high | Set too low |
|---|---|---|---|
| Lux (daylight threshold) | Decides how dark it has to be before the sensor is allowed to switch the light on at all | Triggers in daylight and wastes energy | Will not come on at dusk when you actually want it |
| Time delay | How long the light stays on after the last movement it detected | Burns for twenty minutes after a cat walked past | Drops out while you are still unlocking the door |
| Sensitivity | How large a change in infrared is needed before it counts as a trigger | Every possum, breeze and warm draught sets it off | Misses people, especially in summer when the temperature difference is smaller |
Worth knowing about that last row: a PIR works on the difference between a body and its background, so the same sensor is noticeably less sensitive on a hot night than on a cold one. A unit set on a mild evening in May can feel sluggish by January. It is not failing, it is doing exactly what it was set to do.
We set all three on site with you, at night, walking the approaches rather than guessing from the ladder.
All three exist for a reason. Only one of them is an electrician’s job, so here is the honest version rather than the sales version.
Stick it up, done. Genuinely useful for a shed, a side gate or somewhere you visit occasionally, and no electrician required.
The trade-offs are real though: modest brightness, and a battery that will go flat at some point without telling you, usually in the middle of winter when you need it most.
Works well where the panel gets genuine direct sun for a good part of the day, which rules out a lot of shaded southern side paths and anywhere under the tree canopy.
Output tends to fade through a wet stretch of winter, and the internal battery has a finite life. Good for a back fence, less good as your only entry light.
Consistently bright, always available, and able to be tied into your other lighting, a manual override switch, or a security and camera setup so the light and the recording work together.
It needs a licensed electrician and a circuit, which is the cost. In return it is the only option you can genuinely stop thinking about.
The one that matters most, and the one most often aimed straight down the path so it triggers late. Aimed across the approach instead, it lights up while somebody is still several steps away.
Keep the fan inside your boundary so the street does not set it off.
Useful for arriving at night with your hands full, but the classic spot for headlight triggering if the fan reaches the road. Aim it back toward the house rather than out toward the street.
A longer time delay suits here, since you are usually unloading rather than walking straight through.
Narrow, dark, and the route nobody legitimate uses at night, which makes it the most valuable security position on most properties. A narrow path also happens to suit a PIR perfectly, because anyone using it crosses the fan rather than walking down it.
Watch for fence-line wildlife here more than anywhere else.
Less about security, more about not falling down a set of wet sandstone steps carrying the bins. Lower output aimed downward works better here than a floodlight.
This is where light spill onto neighbours is most likely, so the aim wants to be down and inward.
There is an Australian standard specifically about the obtrusive effects of outdoor lighting, and while it is aimed mostly at larger installations, the thinking behind it applies just as well to a house. Light that spills across a boundary, glares into a neighbour’s window or throws straight up into the sky is doing nothing useful for you and quite a lot that is unwelcome for everyone else.
In practice the answer is almost always to aim down and inward, and to choose an output that suits the area being lit rather than the biggest number on the shelf. A very bright light pointed badly creates deep shadow beside it, which is worse for security than a moderate light aimed well.
If you already have a light causing friction with a neighbour, re-aiming it and adding a shield is usually a short job and a great deal cheaper than the conversation continuing.
We walk the property and work out where lights genuinely earn their place, which is usually fewer positions than people expect. You get advice on placement and type, and a fixed price before anything starts.
Hardwired units are run back to a suitable circuit, which can mean working through roof spaces or under the house and drilling through external walls. Fittings are chosen with an ingress rating that suits an exposed position, which matters a great deal near the harbour.
The part that gets skipped. We set lux, time and sensitivity, then walk the approaches after dark to confirm it triggers when it should and stays quiet when it should not. Then we issue your Certificate of Compliance for Electrical Work and tidy up.
Because of how the sensor sees. A PIR works by detecting infrared moving between the segments of its lens, so somebody crossing the detection fan trips it almost immediately, while somebody walking straight down the middle of it stays inside a single segment and barely registers until they are close. The fix is aiming rather than a better unit: point the fan across the path people actually walk in on, not straight down it.
In this part of Sydney it is usually possums, cats or foliage moving in the wind. After that it is heat sources, an air conditioning condenser, a dryer vent or hot air off a roof, because a PIR is looking for moving heat rather than for movement itself. Headlights and passing cars will do it too if the fan spills over the front boundary. Nearly all of it is solved by re-aiming, masking part of the lens or dropping the sensitivity, rather than by replacing the light.
They have their place. Battery units are easy and cheap and are fine for a shed or a spot you rarely use, but you have to remember to change the batteries and they tend to be dim. Solar avoids that and works well in a spot with real sun, though performance drops through a wet Sydney winter and the built-in battery eventually dies. Hardwired is the only option that is consistently bright, always available, and able to be tied into other lighting or a security system.
Yes, and it is worth doing. Most units support an override, commonly by flicking the switch off and on quickly, which holds the light on until you switch it off again. It is useful when you are working outside at night or want the light on deliberately. We set it up and show you how it works before we leave.
It can, and that is worth designing out rather than apologising for later. Light spilling across a boundary or straight into a bedroom window is what generates complaints, and AS/NZS 4282 exists specifically to deal with the obtrusive effects of outdoor lighting. Practically it means aiming the light down and into your own property, choosing an output suited to the area rather than the brightest unit on the shelf, and keeping the detection fan off the footpath and the neighbour's yard.
Attending your job is a chargeable callout. We confirm what it costs when you book, and the price for the work itself is agreed before we start, so there are no surprises on the invoice.
Based in Castlecrag, covering all of Sydney. A few of the suburbs we work in most:
Covering all 48 North Shore suburbs. See the full list of locations we service.
Upfront pricing, with the price agreed before we start. Call before 11am for same-day service.
