Motion Sensor Light Not Turning On

Common Symptoms

• Motion sensor light doesn't turn on when walking in front of it
• Light turns on briefly then shuts off within 10 seconds
• Motion sensor light stuck on — never turns off
• Light only triggers when standing directly in front of sensor
• Outdoor motion light won't come on at night

Most Likely Causes

1. 1

   Sensitivity Adjustment Too Low

   Most motion sensor lights have a sensitivity dial on the sensor head (labeled SENS or SENSITIVITY). If this dial is turned to the minimum setting, the sensor only detects motion within 3–5 feet instead of 20–30 feet. Turn the sensitivity to maximum and test — if detection range improves, calibrate to the desired range from there.

2. 2

   Daylight Photocell Blocking Night Operation

   Outdoor motion sensor lights typically have a built-in photocell (light sensor) that prevents the light from triggering during daylight hours. If the photocell is faulty, pointed at a light source, or calibrated incorrectly, it may keep the light disabled even after dark. Some sensors have a DAYLIGHT SAVING or DUSK setting — verify it's set correctly. Covering the photocell with your hand during testing forces a 'dark' reading.

3. 3

   Time Delay Set Too Short

   The TIME or DURATION dial on the sensor head sets how long the light stays on after motion stops. Most sensors offer 10 seconds to 10 minutes. If set to the minimum, the light turns on and shuts off within seconds — which looks like a failure but is actually correct operation at a short time setting.

4. 4

   Detection Zone Obstruction

   PIR motion sensors detect infrared heat moving through the lens. Overgrown shrubs, a newly installed awning, or a decorative cover over the sensor can block the field of view. The sensor may work perfectly when approached from one angle but not another if part of the lens is blocked.

Quick DIY Checks

1. 1Locate the sensitivity dial on the sensor head (usually on the underside or back). It's labeled SENS, LUX, or SENSITIVITY. Turn it fully clockwise (maximum). Walk in front of the sensor from 20–30 feet away. If the light triggers at max sensitivity, dial it back to the desired range.
2. 2Locate the time delay dial (labeled TIME or DURATION). Set it to the maximum setting (usually 5–10 minutes) for testing. If the light now stays on longer after triggering, the time delay was the issue — adjust to your preferred duration.
3. 3Test the TEST/WALK mode: most motion sensor lights have a mode where the light turns on for only a few seconds when motion is detected, allowing you to walk through the detection zone and see coverage. Enter TEST mode (usually by turning the TIME dial fully counter-clockwise). Walk through the area to map the detection zone and identify any dead spots.

1. 4Check the photocell override: cover the sensor's photocell (the small clear dome separate from the motion sensor body) with electrical tape or your thumb. This simulates darkness. If the light now triggers when you walk past, the photocell settings or orientation is the problem — verify the photocell isn't aimed at a lamp post or security light that's keeping it in 'daytime' mode.
2. 5For smart occupancy switches (Lutron Maestro, Leviton Decora): verify a neutral wire is connected. Smart occupancy switches require a neutral (white) wire to function correctly. In older homes with switch loops (only hot and switched hot, no neutral in the switch box), these smart switches may not work at all without a neutral wire adapter or running a new wire.
3. 6If all adjustments are correct and the sensor still doesn't trigger: replace the sensor. Motion sensor heads (the oval or rectangular sensor unit on floodlight fixtures) are sold separately for $10–$25 and are typically universal screw-in replacements.

Repair vs Replace

Recommended Tools & Parts

• Universal Motion Sensor Head (replacement)

  Universal replacement motion sensor head for outdoor floodlight fixtures. Threaded screw-in replacement — verify your fixture uses the standard E26/E27 or direct wire mounting. Includes sensitivity and time delay adjustment.

  $12–$25

  Buy on Amazon →

• Lutron Maestro Occupancy Switch

  Smart occupancy sensor wall switch for indoor motion-activated lighting. Requires neutral wire. Compatible with LED, CFL, and incandescent fixtures.

  $20–$35

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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