Photocells help lights turn on at night and off during the day. Simple, right? Until they stop working.
If you’re a homeowner dealing with lights that won’t behave, this guide is for you. You’ll learn what causes photocell issues, how to spot them, and what to do about it. Whether it’s wasted energy, safety concerns, or plain frustration, we’ll walk you through it.
Key Takeaways
- Photocells detect light to control your lighting systems.
- Most problems come from dirt, wiring, or the wrong sensor type.
- Flickering, unresponsive lights, and delays are common symptoms.
- Testing is easy with a flashlight and multimeter.
- Regular cleaning and replacing old units prevent future issues.
What Is a Photocell and How It Works
A photocell is a light-sensitive switch. It uses the photoelectric effect to detect changes in light. When it gets dark, it completes the circuit. When it’s bright, it opens the circuit.
There are two main types:
- Cadmium sulfide cells – older, cheaper, and more common.
- Digital sensors – newer, more accurate, often used in smart systems.
You’ll find photocells in dusk-to-dawn lights, street lights, and some motion sensors. They’re wired into your power supply and lighting systems to automate light control.
7 Common Problems with Photocells
Photocells are simple. But that doesn’t mean they don’t fail. Here are the issues that show up the most.
Light Stays On During the Day
The sensor may be shaded or covered in grime. Other causes include a short circuit or failed relay. Fix it by cleaning, moving the sensor, or replacing it.
Light Won’t Turn On at Night
Check the bulb and power supply first. If those are fine, the sensor might be wired backward or completely dead. Use a flashlight to test the sensor or inspect the wiring.
Light Flickers or Blinks Repeatedly
This usually means the sensor sees its own light. That creates a feedback loop. Loose wiring or incompatible LED bulbs also do this. Fix it by moving the sensor, shielding it, or replacing it.
Photocell Is Unresponsive
No click, no change, no nothing? The sensor might be dead. Check the breaker and voltage. If that’s fine, replace the sensor or the entire light fixture.
Delayed Activation or Deactivation
A dirty lens or bad installation angle slows things down. Clean the lens and aim it properly.
Works Intermittently
Moisture and rust are usually to blame. If the sensor housing is cracked, bugs or water may have gotten in. Replace the gasket or seal, or swap out the whole unit.
Light Turns On and Off Rapidly
Wrong sensor type. Some photocells don’t play nice with LED lights. If your system has both a motion sensor and a photocell, they might be fighting each other. Use a compatible sensor and make sure only one system is in control.
How to Troubleshoot a Photocell (Step-by-Step)
Think your photocell is shot? Test it. Here’s how to do it safely.
Step 1: Visual Inspection
Look for dirt, rust, broken parts, and poor installation angles.
Step 2: Flashlight Test
Shine a flashlight on the sensor. The light should shut off. Cover the sensor with black tape. The light should come on. No change? The sensor’s likely bad.
Step 3: Multimeter Test
Disconnect the sensor and test voltage at the wires. You should see current flow when the sensor is covered. Use continuity mode to check for internal failure. Always turn off power first.
When to Repair vs Replace
Clean or re-aim the sensor if that’s all it needs. If wires are burned or the electronics fail, replace it. Most photocells last five to ten years. If yours is old or unreliable, upgrade to a newer model.
How to Prevent Photocell Problems
- Clean sensors every spring and fall
- Keep leaves, snow, and other stuff away
- Use weather-rated sensors
- Only use bulbs and fixtures the sensor is designed for
- Replace the sensor every 5–7 years
When to Call an Electrician
If wires are fried or you’re not sure what’s wrong, don’t guess. Electrical shocks and fire hazards are real. Also, if your lighting system uses high voltage or you’re dealing with outdoor lines, it may be illegal to DIY the fix. Call a licensed electrician.
Need Photocell Services in Centennial, CO?
Genesis Electrical fixes photocell issues fast. We also install new units if yours is too far gone. If you live in Centennial, CO or the surrounding area, give us a call. Good day, and Gooooooood Genesis!
FAQs
Photocells confuse people. Here’s a short guide to common questions.
How long do photocells usually last?
About 5–10 years. Weather, dirt, and sun exposure speed up wear.
Can photocells work with smart lighting systems?
Some can. Look for digital sensors that list smart compatibility. Old ones don’t play nice.
Why do my lights stay on even when it’s sunny?
Your sensor is dirty, shaded, or broken. Clean it first. If that fails, replace it.
Can I install a photocell myself?
Yes—if you know electrical basics and follow safety steps. Turn off power. Double check wiring. If you’re unsure, call a pro.
Are photocells safe in wet climates?
Yes, if they’re rated for outdoor use and sealed well. Check for the IP rating and keep them clean.