How do Dusk-to-Dawn Photocells Work?

light-photo-controller

As the push to cut energy usage continues, one method is to eliminate the use of light sources when they are not needed. To this end, most quality outdoor LED fixtures now come equipped with a factory-installed photocell which tells the fixture when it should operate. This is primarily used to turn exterior lights off at dawn and back on when the sun sets.

There are numerous types of photocells in the market but the technology behind them is all the same, as they utilize semiconductors to control the electric current. When the semiconductor is exposed to a certain level of light, current starts to flow and the fixture will be shut off. Some photocell sensors come adjustable, allowing you to choose the light level that will activate the semiconductor. As the light fades during the evening, the flow stops and the fixture is powered on. This allows for “Dusk-to-Dawn” light output.

Being that photocells sense ambient light levels, they will automatically adhere to seasonal changes and are not affected by daylight-savings time. This results in maintenance-free energy efficiency in addition to providing the security of having lights on in the evening to deter intruders.

outdoor-barn-light-photocell

Photocells are most commonly hard-wired via 120-277V line voltage to control an entire electrical circuit that operates outdoor LED fixtures. But there are also photocells that screw into light bulb sockets, allowing nearly any lamp or fixture to become a dusk-to-dawn lighting system. The difference being that a photocell has to be installed into each individual socket. There are also photocells that work with a standard wall outlet and control a pass-through plug.

Timers and motion sensors are other types of controls that are sometimes used in conjunction with (or to replace) photocells. Timers are useful for on-demand lighting controls, for example to turn off lights at a work site during set times. More complex timers are set up to allow input of multiple time configurations. But they lack the ability to work well with environmental factors. Local sunrise and sunset patterns change over time and would have to be manually set, whereas a photocell will sense this automatically. Timers also won’t be able to react to a rainy or cloudy day like a photocell would.

Ultimately, the needs of your particular application will decide which controls make sense but photocell sensors have proven to be essential components for many outdoor lighting systems.

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29 Responses to “How do Dusk-to-Dawn Photocells Work?”

  1. WarrenMarch 8, 2019 at 11:50 am #

    With dusk to dawn switch fixture comes on at dusk 2 or 3 nights and then will not come on 2-3 nights. Why

    • PremierMarch 8, 2019 at 11:57 am #

      The sensor could be defective or not installed correctly

      • GraceJuly 12, 2020 at 1:48 pm #

        Are they more complicated to install than regular outdoor lighting?

  2. Bruce BoylesJune 11, 2019 at 10:47 pm #

    I have a problem w/ my photocells coming on an hour before dark & going off an hour after the sun is up. With 500 lights drawing 300 watts each there is 150,000 watts or 150 KW every hour. This is 2 hrs. a day of wasted power. Do you have a unit that would help me? Bruce Boyles Electrical Connection ranchonogota@gmail.com. Thank you.

    • LesSeptember 1, 2019 at 10:00 pm #

      I sound like the sensor is located in the shade. The best location is where it could be pointed due south with an unobstructed view of the sky.

  3. JulieJune 23, 2019 at 12:55 pm #

    Is a dusk to dawn plunged into an electrical source, or solar? I have a lamp base that I want to take the wiring out of and make it outdoor solar. Does dusk to dawn light bulbs screw into a light fixture but require no electricity?

    Please help needs to finish this project

    Thank you

  4. joanneJune 28, 2019 at 9:02 pm #

    i’m having dificulty with my neighborhood lamp sensor going on at times. It’s pitch black and not on. The previous 3 days it went on at dusk. Those days where not as bright as today. WHAT IS THE BEST WAY FOR IT TO BE POSITIONED TO GO ON AT DUSK. It’s an ambien sensor

    • Greg mcqueenNovember 3, 2019 at 5:41 pm #

      I put dusk to dawn LED bulbs with built in sensors in my outside motion light fixtures and one fixture on the west side of the house works great, but the east side fixture is still working like a motion light. WHY ?

  5. John D NeyAugust 4, 2019 at 11:33 am #

    put a new bulb in our outside electric light. put my hand over the sencer,light did not go on . what should i do?.

  6. John D NeyAugust 4, 2019 at 11:34 am #

    How do mi fix it

  7. SteveSeptember 7, 2019 at 8:47 am #

    Does the photo sensor consume any energy ? Either when the light is in or off
    Thanks

    • Guenter BruckmannNovember 13, 2019 at 3:37 pm #

      No, the photo sensor does not consume any power. On the contrary, it actually makes electricity. It is a miniature solar panel that converts light into electricity, which is then used to switch the light on.

  8. sujathaOctober 5, 2019 at 3:11 pm #

    Hi, My outdoor lights are all light up with one switch. Before they used to light up at dusk and turn off at dawn. But now they are turning on at night after 10PM only. And it is not fixed time. sometimes they light up at 10:30 too. What could be wrong? and how do I fix it. Thanks.

  9. William PorterOctober 9, 2019 at 5:15 am #

    I was wondering if a dusk to Dawn bulb uses more electric because the switch is always on. Verses a timer switch.

    • Guenter BruckmannNovember 13, 2019 at 3:34 pm #

      The bulb will use electric power only when it is lit. The sensor is actually a switch that is in series with the wall switch. Both have to be ON for the bulb to light – – and to use power.

  10. RalphNovember 12, 2019 at 2:40 pm #

    Hi, I want to control an outdoor led landscape light with a hard wired photocell timer. I do not want a timer that the light would plug into. Do you have that type of timer.

  11. Guenter BruckmannNovember 13, 2019 at 3:38 pm #

    The bulb will use electric power only when it is lit. The sensor is actually a switch that is in series with the wall switch. Both have to be ON for the bulb to light – – and to use power.

  12. Michael KeatingMarch 3, 2020 at 5:32 pm #

    i have replaced a bulb in the unit but its not coming on,,how do i switch the sensor switch on,presumeing its off

    • Sherrie EakinsMay 6, 2020 at 7:42 pm #

      We are having the same problem, the dusk to dawm worked when we bought our home. It went out last fall, we have bought 3 different bulbs. The last, current 60.00 bulb..it will flicker when hubby puts it in. Now tonight, nothing! Hoping for some ideas

  13. LindaMay 5, 2020 at 10:25 am #

    Why doesn’t our dust dawn light won’t go out we put a new timer on an new bulb nut just won’t go out in day light what could be wrong with it

  14. CheriJune 17, 2020 at 7:02 am #

    My 42 unit townhome community recently changed our outdoor lighting to LED light fixtures. The lights are controlled by 2 LED photo cells on each building. Ever since we installed the lights, we have had LED light bulbs burn out at an alarming rate. The LED bulbs are MaxLite dimmable filament bulbs (60W/8.5 W LED, 800 lumens). The lighting company who sold us the lights and the electrician who installed them have ghosted us. Can anyone provide some insight? Thanks in advance for your help.

    • Joni BoulwareOctober 15, 2020 at 8:05 am #

      Dark Sky rules don’t allow photocells because lights are only to be used when needed. Motion detection lights can provide the security function without being turned on disk to dawn.

  15. Can I plug in a dust to dawn light in a regular lamp holder and a regular outdoor electriJuly 27, 2020 at 10:36 am #

    Can I plug in a dust to dawn light in a regular lamp holder and a regular outdoor electrical plug-in thank you or does it have to be plugged into a dusk to dawn electrical plug-in

  16. Mary van ThielAugust 2, 2020 at 10:18 am #

    Can I order extra protocells

  17. Wallace phiriOctober 11, 2020 at 9:15 am #

    My photocell has been switching on early before it’s dark

  18. Wally RodriguezMarch 25, 2022 at 9:04 am #

    I had a little leaf in the way of our photocell that caused it to never go on. Fun…

  19. BrianApril 10, 2022 at 8:48 pm #

    Can a dusk to dawn switch be used w/ solar panel set up that uses battery 12 volt power with our an inverter?

  20. joel malasaOctober 1, 2023 at 12:03 am #

    My photocell does not light up if power went during the day and it comes during the night.what could be the problem

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