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.
Likely causes
Do not jump straight to the most expensive possibility. These are the common places to start:
- Photocell failure
- Wrong timer setting
- Bas schedule issue
- Contactor fault
- Fixture driver failure
| Possible cause | How to check | Routine first move |
|---|---|---|
| Photocell failure | Define the affected group | Correct time or schedule |
| Wrong timer setting | Identify the control method | Clean or expose photocell appropriately |
| Bas schedule issue | Check current time and date | Replace failed photocell or fixture through qualified service |
| Contactor fault | Inspect photocell for obstruction | Document control-zone behavior |
| Fixture driver failure | Check visible control indicators | Correct time or schedule |
Tools and preparation
Bring these
- Exact model manual and phone for documentation
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 checks
Define the affected group
Record whether one fixture, a pole group, or all exterior lights are affected; use ground-level observations after dark when safe.
Identify the control method
Identify schedule, photocell, or BAS control from records rather than opening a live cabinet.
Check current time and date
Check operator-visible date, time zone, daylight-saving setting, and programmed on/off periods; preserve original settings before approved changes.
Inspect photocell for obstruction
Look for dirt, shading, or a new light shining on the photocell from safe access; do not climb or bridge the photocell circuit.
Check visible control indicators
Record 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
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.
When to stop and hand it off
- Panel or contactor wiring diagnosis is required
- Multiple safety or security areas are dark
- Fixture is overheated or damaged
Frequently asked questions
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.
Related BuildingWrench guides
BuildingWrench provides general educational information for commercial-facility maintenance. Manufacturer instructions, applicable codes, site procedures, and required trade qualifications always take priority.