A motion sensor is a switch that turns on your outdoor porch light or shed floodlight when it detects an appropriate change in the surroundings. Most sensors for outdoor lights are tiny radar emitters, but some operate by detecting infrared radiation. When your light won't come off -- or it won't go off -- you can usually fix the problem by adjusting the sensor range and sensitivity. Sometimes all that's needed is to give the sensor cover a good cleaning.
Adjusting the Sensor
Although it's possible to operate a light from a remote sensor, in most cases the sensor is part of the light fixture. It's usually a semi-cylindrical attachment located under the lights. If your lights won't come on, start by cleaning the frosted plastic with soapy water and a rag; it's possible that dirt is blocking the radar signal. Once the plastic is clean, adjust the range and sensitivity using a simple procedure:
Aim the sensor by loosening the screws holding it to the fixture and tilting it up or down or rotating it. Once the sensor is roughly centered in the area you want to monitor, tighten the screws and set the toggle switch under the sensor to the "Test" position.
Walk across the area you want to monitor and verify that the light comes on. Tilt the sensor up to expand the borders of the detection zone and down to contract them.
Fine-tune the range detection with the "Sensitivity" dial. Adjust it all the way to maximum sensitivity, then turn it down to contract the range. If you want the sensor to detect only what's in front of it, cover the outside edges of the sensor with electrical tape.
Flip the switch away from the "Test" position when the adjustments are complete.
The procedure is easier if you have a helper who can walk across the detection range while you make adjustments.
The Light Won't Come On
If the light won't come on after adjusting and cleaning the sensor, try a simple trick. Turn off the circuit breaker that controls the light circuit and leave it off for 30 minutes. Turn on the breaker and see if the light comes on. If it does, adjust the sensor range and sensitivity as needed.
If the light doesn't come on when you turn the breaker back on, try replacing the bulb. If that doesn't work, the sensor may be bad. To find out, turn off the breaker again and disconnect the wires connecting the sensor to the light fixture. Connect the light directly to the circuit wires and turn on the breaker. if the light comes on, replace the sensor.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.