What are Photocells and How Do They Work?
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- Опубликовано: 9 фев 2025
- Most electricians, heck even most PEOPLE, understand that actuating a light switch will result in the lights turning On and Off! That works great for inside of a room, but what about parking lots or the entire exterior of a building? In the latest episode of Electrician U, Dustin talks about Photocells- what they are and how they work.
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In essence, a photocell is a light switch, just with more moving parts. When you buy it off the shelf, a photocell is in a Normally Closed State. Normally closed means that with no external help, the circuit within it is closed and electron flow can happen. For reference, with a Normally Open device, without any external influence, the circuit is open and electron flow CANOT happen. With both of these, the control circuit operates a coil, that when energized, will change the state of the device to the opposite of what it is when it’s just sitting there. For most photocells, there are 3 wires- a black, a white, and a red. The white is the neutral for the control circuit, the black being the incoming hot of the control circuit, and the red being the switch leg.
The photons from the sunlight act as the catalyst here. During daylight hours, the photons change the resistor inside the photocell and it provides so much resistance that current cannot flow and the circuit stays open and the lights off. When the sun goes down, the resistance lessens in the resistor, current can flow and the lights come on.
Something to be aware of is that photocells have ratings- both to voltage and amperage. This means if you are attempting to have the photocell directly control a light fixture(s) that you have to match it with the circuit it is attempting to control. If you are controlling several fixtures (say a parking lot full of pole lights or an entire building exterior), having the photocell control a contactor may be necessary. Contactors generally have a much larger amperage rating than a photocell alone. In this type of scenario, the photocell is still controlling something, but it is now controlling the coil of the contactor. Same result, just more fixtures are able to be controlled.
There are also several different types of photocells to choose from. Your standard photocell, a photocell that has a knuckle so it can be precisely aimed, even small photocells that can be mounted IN a fixture (or right next to it in a bell box) and are hardly noticeable. Since photocells have “moving parts” they are susceptible to failure over time (much like GFCI receptacles or motion sensors). A great tip to troubleshoot a lighting circuit to see what the issue is would be to trick the photocell into thinking its dark outside forcing the lights to come on. To do this, simply use black electrical tape and completely cover the sensing eye of the photocell. If the lights come on, then it may be something other than the photocell being the problem. If the lights stay off, then the photocell is probably your issue. Another way to sort of test this theory would be to bypass the photocell from the circuit and see if the lights come on. If they do, then its probably a photocell issue.
Did you know that the safety beam of a garage door is a photocell. It shines a light, the light reflects off of a reflector, then the photocell sees the light. I installed hundreds of these type of photocells in a ups processing facility. This place was 1 million sq ft and packed with layers of conveyors & chutes. We drilled holes on each side of the metal conveyors and welded strut to the outside and installed our relectors and photocells on the strut. That's how system could tell if packages are moving as normal or a blockage. Everything was built from scratch on site. Very industrial, very loud, all imc conduit and lots of controls. 160 union electricians working 7, 12's back then in 2019 we only made 43.69hr. That was 5,500wk. We make 56hr now 66hr in the next county over.
In what city/ state? That's awesome
Isnt it an photeye, not cell?
@shanemichael7978 Technically, it's whatever the manufacturer names it. Alot of times, with lots of material, people call things different names / slang name. And then the supply houses list it as those slang names. But technically it's whatever the manufacturer named it, they created the thing. But I have found it's eaiser to go through this trade accepting the slang name, rather than pissing everyone off by proving everyone wrong, which they are. By calling it the proper name, rather than the majority used slang name, makes you look dumb in their eyes, even though you're right. In any case just google the thing, and make sure the site you're looking at is a manufacturers website, not supply house. 😁🤔
Yeah i agree. I try to use text book names to avoid confusion, but in the end using local nomenclature is better to avoid just that.
Dang that's $800k-$900k in just electrical weekly payroll. Vastly expensive project there.
There is also the twist lock photo eyes. Those are my favorite because they are the easiest to replace.
Yep mostly on street lamps
I think covering ballasts would be a great video, there are so many that don't understand
Ballast are kinda of a outdated technology with LEDs now it cheaper to bypass the Ballast and convert over to LED
Awesome. In the instruction manual for the same photocells you are showing, it will say north is the best direction to point them towards, and that if north is not possible, then east is second best. I have seen them fail because the installer pointed them directly upwards toward the sky
I liked the troubleshooting tips. I feel like it's the most challenging part of our work. Ty.
Next, motion detectors explained. 😎
They make photocells that are 120-277 volts now which is nice as you only need to keep one type on the truck. They are also very fast acting.
Lessons learned, Thanks D...you are 1 away from 500,000 subs, congrats!!
Hey, Electrician U, you should gives us a tour of all your Electrical Books.
There are two different "photocells". One type generates voltage when sunlight is present such as roof panels etc. Normally called solar cells
The other kind is called an LDR or light dependant resistor. This is the type you are referring to..
In this circuit the LDR is in series with a healing element. This heating element heats up in the presence of sunlight. This heat causes a bi-metalic strip to flex acting like a relay. The purpose if this is to avoid false triggering of headlights, flashlights etc. This heating/cooling cycle takes time thus giving a small time delay. This heating element is the thing that usually wears out over time The LDR never controls the load as this is beyond the capacity of any LDR. Instead the only load it controls is the heater. So even with no load, this device pulls current.
The type that generate voltage with sunlight are also called "Photovoltaic Cells" or just "PV Cells" for short.
I wasn't sure how the electronics inside the LDR photocells works, so I'll take your explanation as typical. (My expertise is electronics, so I'm more familiar with the bare CdS cell element which is a 2 pin device.) There is another reason why the LDR doesn't have the load going through it. LDRs are analog devices, meaning that they are rarely ever fully on or fully off. Something else is needed to trip either fully on or fully off somewhere in the circuitry, and the bimetalic strip (hopefully configured as a snap switch to accelerate the load contacts opening and closing quickly to mitigate contact burnout) would do this nicely.
@@Sembazuru some Cadmium Sulfide (CDS) photoresistors are still used & some circuits use a Silicon (SI) transistor. One of the issues with SI is that they are sensitive to IR light and act erratic because of this. You would need an IR filter to correct this problem. The CDS and heating element seems to be a far simpler device rather than a silicon transistor and supporting circuitry so I assume a CDS device is still used
@@rty1955 Thanx for the good info. The simplicity of the CdS cell is very enticing to a designer, but good luck getting a RoHS certification on the end product since Cadmium is one of the prohibited materials under RoHS. 😉 Though, if the CdS cell is small enough and is the only Cadmium in the product, one might be able to fall under the 0.01% limit to be able to get a RoHS certification.
I'm a 5 month sparky apprentice in Texas loving work getting really good at work can fix 3 ways and troubleshoot now I'm replacing ceiling fans and moving switches on the wrong side of a door and running new switch legs and getting the in coming hot to fly over fixing everything around the multi family apartments I'm so glad my company is smaller than big huge companies but 30 employees with a lot of foreman's and journeymans and they hire subcontractors so there's a lot of stuff on big jobs that I'm learning
Excellent description sir. Thanks for your time
Thanks, I installed a PC for landscape lights and the lights did not shut off when I uncovered the sensor. Your explanation about the resistance taking time to build-up cleared up the confusion. I though it would operate like instant on-off switch, the PT-PC1 needs about 5 minutes of light to open.
Thank you. Very helpful bit of information!
You’re an amazing instructor and the graphics and drawings help SO much! Thank you and GOD bless!!!🙏🏽👍🏼😎 ⚡️
Almost 500K pre-congratulations!
Your videos are pretty awesome brother! Keep up the good work! Love the t shirts !
Hi Dustin ,I am a level 1 apprentice from Canada …can you make a detailed explanation on contactors, relays and control centres
At work we have a photocell cover hat extension pole (insulated) to test the hard to get ones without getting a lift
Thank you so much bro love this channel man changed my life
What’s the best brand photocell I get tired of changing so often
been waiting for this one thank you
Can you do more code time videos please the three that I watched turned out to be extremely helpful.
Can you do a video on motors and calculations? I really struggled with that on my Journeymans test.
I think he has in the past. If you are speaking about the 125% , 115% etc service factors etc . NEC should have a code online course.. the CEC does. I just took it as a refresher because I was dealing with some MCC on a service call
You might check out Jeremy Fielding's channel. Good luck. :)
Grab a Tom Henry Calculations book
Another phenomenal video! Thank you
I had to troubleshoot a brand new one that would repeatedly turn its lights on and off every few seconds. Turns out it was seeing the light it was controlling! I had to relocate it and it’s been running for years now without fail.
Thanks for the video I have learned some things
According to Tork you are supposed to install the Photoeye either North or South. Doing so gives it a more even light line of site vs mounting East and West which will give you a brighter light at one part of the day or Not enough at another part, which causes either a premature disengagement or prolonged engagement (aka turning on or off at the wrong time). There are multi-voltage rated models that cover everything but 480V. The new ones are designed for LED which has kind of a solid-state interior component, and they take the inrush of LED Drivers a lot better.
Great video! But what happened to your amperage video you recently made?????
what if the outside light fixture I bought already has a built in photocell? Can I still connect it to a photocell that controls multiple light fixtures? I probably need to disable my lights photocell correct?
A lot of good advice
hey man quick question, who edits your videos? i like the way the bottom visuals pop up.
I had a problem with a neighbor's light sometimes shining in the direction of one of our lights outside that has a built in photocell. I put a little white nail polish over the sensor and now it comes on. It wasn't turning on at all while the other light did. That's the benefit I guess of these central ones they can be placed where something else probably won't interfere with them.
I spent about an hour trying to figure out a photocell light fixture that wasn’t working. A brand new one. I finally put a black plastic bag over it and it came on. There was a small gap in the cell housing that allowed light in so it didn’t work until it was completely dark.
i work on these alot and black electrial tape works every time.....
Pretty sure 2020. All switches now require a neutral to be pulled.
Also are you sure they come with a varying resistance conductor? I was pretty sure they used a DC transistor.
That is a negative. Neutrals are not required to be pulled to all switches
Nice explanation. I wonder what happens if you install one pointing at your neighbors light which is shining on your bedroom window? Do the lights both stay off or do they battle it out all night?
Could you do a video on dimmer switch loading. There seems to be a lot of confusion for folks on that. I’ve seen some people load a dimmer switch up thinking the max wattage was still 600w etc when it cleary states on lost dimmers incandescent 600w and led 150w etc. I see videos online and guys are still saying it’s 600w with led but they do t know it’s usually 25% of the that for led ( this is straight from the manufacturers)
I point the eye south if possible. thank you.
On the side of the development the lights have been out five weeks. We have told the management of the condo. Apparently they are not fixing it with no explanation we do pay a maintenance is this a costly thing to do? It is very dark and we are elderly. What should we do? We are getting no feedback.
Should talk about sensors in general pnp, npn or even both. Also 2 wire 3,4 or even 5 wires.
Prefer to use the photo eyes that are on a twist lock plug. So many times the circuit breaker that feeds luminare is not marked. For some reason they seldom last more then 6 to 8 years. They are so much better then cheap say Intermatic think its T100 single pole timer. Nice they are fail safe = when they burnt out circuit stays on. Knuckle style should be the only PE to stock. Type with straight nipple often require you to loosen the hell or even remove the box to screw it on to side of a box.
so no update on the health status for the digital multimeter ?
Are they still ok? after being used to measure current? 😄
don't get me wring, I love all your video and i understand people make mistake... but we haven't hear anything after the video being taken down...
Yea I noticed he made it private. I assume the fuses just need to be replaced. To be fair, there's not really any reason for an electrician in the field to use anything other than clamp-on ammeters. For 60 Hz AC, they work very well.
@@barryomahony4983 of coz, for general electrician, there is really not much point to break the circuit up in order to measure current if we are dealing with AC
most of us just use clamp meter to do it , it is quicker , safer, and easier.... i doubt anyone will reject that...
there are some of the clamp can do DC current , may be not as accuracy but it should get the job done...
however, he is teaching others how to do it and he is doing it the wrong way.... at least he should make a clarification on that so people will not make the same mistake...
and blowing their multimeter fuse....
Where would a photocell normally be located in a landscape lighting trees? Is it in a box by a building? Is it by the lights by the trees
Hey great electrician, I'm in cayman islands a fan of your RUclips channel. I'm trying to get a full time job with a electrical company but they want me to have a electrical licence even though I have a certificate. can tell me how to get the licence?
The photo cells I've installed have lasted over 15 years😁
They aren't really made for heavy loads. Usually only like 6-10 amps. If you want to run it at minimal load, use the photocell to close a double pole contactor. Even if you tie the hot of the photocell to a contactor line side, the photocell will only use like .8 amps even if the contactor is pulling 10 amps on that same leg.
DUSTIN, try to make a video lesson about what Contractors are used for and how to troubleshoot the common failures contractors cause. The Purpose of the contractor is to turn on multiple high current high voltage lamps/lights but the contractor has current/voltage ratings and other purposes to use contractors.
Way too specific
That is where my old boss would put photo cells anywhere shady. He didn't believe in science.
The led specific ones are terrible where I’m from. I don’t use them . I continue to use the built in time delay ones. the led ones seem to be way more sensitive and go off from car headlights
1--5fc ON, 3-15fc OFF. What is an 'fc' and how do you measure it?
If you are controlling a mechanically held contactor with a photocell, how would you unlatch the contactor?
It cause a metal strip to open or close (the resistor)
Most instructions advise to face the photo North I think
Exactly
For the life of me I can't find a DAWN to DUSK switch like this (On during daylight, off during night.) I'm using a dusk to dawn combined with a relay to facilitate, but can't find a commercially available switch like this with a normally open contact. I specifically want to run a pump only during strong sunlight, not on a timer or temperature or such else.
Funny how Conner's brogue goes away when talking about photo cells....
I want hope to be honest I always thought that it had a small coil in there and that the photo receiver was some type of solar panel that provided power for. Interesting
So this may sound like a silly question, but do LED's create photons? How am I able to turn off a photocell with my flashlight.
Basically it is a switch? That works of light?
Contactors please!
WHERE IS IT CANT FIND MINE CAN IT BE IN THE GROUND
lmao, I just got that same one and it was broken just a few days ago, same spot
ive seen cases where a timer and photocell are working together...one backed up the other...
❤
Are you gonna record explanation video on how you - master electrician fucked up on Current and Amps topic? Asking for a friend
im paying 1000$ to attend a school where teachers are reading off the book for us....
They have them built into bulbs … those are a pain in the ass, most times they are useless
How would I disable mine? I want my light on all day. Should I cover it with electric tape ?