Outdoor Light Won’t Turn On at Night: Photocell and Timer Checks
Exterior lighting that stays off at night may be controlled by a photocell, astronomical timer, BAS schedule, contactor, breaker, or fixture driver. Identify the control method first.
Last reviewed 2026-09-12 · General facility-maintenance information, not a substitute for site procedures, manufacturer instructions, codes, or qualified professional judgment.
Safety boundary
Likely causes
- Photocell failure
- Wrong timer setting
- Bas schedule issue
- Contactor fault
- Fixture driver failure
Symptom → cause → first move
Photocell failure
Check: Define the affected group
First move: Correct time or schedule
Wrong timer setting
Check: Identify the control method
First move: Clean or expose photocell appropriately
Bas schedule issue
Check: Check current time and date
First move: Replace failed photocell or fixture through qualified service
Contactor fault
Check: Inspect photocell for obstruction
First move: Document control-zone behavior
Fixture driver failure
Check: Check visible control indicators
First move: Correct time or schedule
What to check first
Bring these
- Flashlight
- Camera
- Known-good compatible lamp or plug-in tester when appropriate
- Manufacturer instructions
Before touching anything
- Confirm the exact location and complaint.
- Photograph labels, settings, fault codes, and the original condition.
- Determine whether the failure affects one item or several nearby items.
- Know how to safely isolate the system if the task requires it.
Step-by-step procedure
- 1Define the affected groupRecord whether one fixture, a pole group, or all exterior lights are affected; use ground-level observations after dark when safe.
- 2Identify the control methodIdentify schedule, photocell, or BAS control from records rather than opening a live cabinet.
- 3Check current time and dateCheck operator-visible date, time zone, daylight-saving setting, and programmed on/off periods; preserve original settings before approved changes.
- 4Inspect photocell for obstructionLook for dirt, shading, or a new light shining on the photocell from safe access; do not climb or bridge the photocell circuit.
- 5Check visible control indicatorsRecord control indicators and arrange qualified supply/fixture testing if the command is correct. Verify the repaired group through its actual dusk or schedule cycle.
Routine fixes that make sense here
- Correct time or schedule
- Clean or expose photocell appropriately
- Replace failed photocell or fixture through qualified service
- Document control-zone behavior
Stop and call a licensed professional when
- Panel or contactor wiring diagnosis is required
- Multiple safety or security areas are dark
- Fixture is overheated or damaged
Common mistakes
- Replacing parts before proving the failure.
- Changing several settings or components at once.
- Failing to photograph the original condition.
- Ignoring whether nearby equipment has the same symptom.
- Crossing into electrical, refrigerant, life-safety, structural, or plumbing work beyond training.
FAQ
What should I check first?
Start by deciding whether the problem is local to one fixture or piece of equipment. Then begin with the simplest safe observation: define the affected group.
What is the most common mistake?
Replacing parts before proving the failure. BuildingWrench recommends documenting the symptom, changing one thing at a time, and testing after each change.
When should maintenance stop?
Stop when the repair crosses your training or site-safety boundary. In this case, one clear handoff point is: panel or contactor wiring diagnosis is required.
What should I document?
Record the exact location, model or asset tag, what the equipment was doing, what you checked, what you changed, and whether the fix held through repeated testing.