Installing a Photocell Sensor

What is a Photocell Sensor?

Automatic lighting, such as streetlights, often uses photocell sensors—also known as photoeyes—to sense how much ambient light there is. Once the photocell detects low enough light levels, the light turns on or conversely, rising external light levels will turn the light off.

The photocell is made up of a resistor attached to photosensitive plates. As more light hits the plates, the resistance (the amount of current that travels through the resistor) changes, turning the light on and off. This technology is convenient for all types of outdoor locations.

With no user input required, there’s no concern about setting timers or forgetting to turn the lights on. The photocell acts similar to how a light switch would—as such, photocell sensors are also sometimes called photoelectric switches.

Photocells work all year round, activating at dusk and turning off at dawn, even when the days are longer in summer or shorter in winter. As they sense the amount of light rather than operating at a set time, they don’t need to be adjusted when sunrise or sunset shifts with the seasons.

Many outdoor lighting setups use motion sensors. However, photocell sensors and motion sensors typically serve different purposes. While a motion sensor might be useful to keep stray animals away from dumpsters and garbage cans, for example, a photocell can keep a parking lot safely and consistently lit for long periods of time.

How to Install a Photocell Sensor for Outdoor Use

The following steps will guide you through the installation of a photocell sensor. This project requires some electrical work, so if you do not feel confident or safe performing these tasks, you should contact an electrician to install the photocell for you.

1. Turn off the circuit breaker to your outside light. If you do not know which breaker powers your light, turn off all breakers in the building to ensure that power is cut off. Double check that the power is off by flipping the switch to the outdoor light to make sure it doesn’t turn on.
2. Disassemble the housing that contains your exterior light. You may want to document how it comes apart with photographs so that you can easily put it back together.
3. You should see two black wires on the photocell. Those black wires need to be tapped in to the black wire that runs between the light fixture and your structure’s main power. Disconnect the black wire going from the house to the light fixture.
4. Connect one black wire on the photocell to the black wire that comes from the building. Be sure to twist the exposed copper wire so that it forms a tight connection.
5. Connect the second black wire on the photocell to the black wire on your light fixture, making sure that the copper wire is twisted together completely.
6. Cover the new connections you made with electrical caps. Ensure that the cap is tight around the wires.
7. Tape your connections completely with electrical tape. Make sure that there are no exposed copper wires.
8. To test the photocell, turn the power back on at the breaker. Make sure that the light switch is in the on position. Cover the photocell with your hand—if the light turns on when the photocell is covered, your photocell is working properly.
9. Finish installing the photocell by putting your light fixture back together.

If you are installing a new light fixture then the procedure is similar to the one above. To install a new light fixture, you may need the following:

• The new photoelectric switch
• Wire strippers
• Needle nose pliers
• A screwdriver
• A voltage tester
• Electrical tape
• Wire nuts
• Silicone sealant

Steps for installing a new fixture:

• Turn off the power at the circuit breaker.
• Remove the existing light fixture.
• Install the new light fixture with the pre-installed photoelectric switch using the mounting instructions that come with it.
• To wire your new light fixture, use your pliers to cut about 3/8″ of insulation away from the wires. Twist together the black wire of the light fixture and the black wire of your house. Cover the new connection with a wire nut and make sure it is tight. Do the same thing with the white wires. Always connect black wires to black wires and white wires to white wires.
• Cover all connections with electrical tape and tuck all the wires away.
• Finish installing your light fixture per the manufacturer’s instructions.
• Once everything is assembled, test your light as shown above.

ATG Electronics provides photocells that will fit in a variety of places, including outlet boxes, post lamps, or outdoor lights. Our products are well constructed and feature long service lives. If you are interested in photocells for LED lighting, please contact us.