Hello.

I manage an apartment building and I have a photocell front door light that is flickering on an off every quarter of a second.

It has a photocell that points down from the fixture. It is happening when it is night time and there is no natural light.

It is using a CFL bulb.

I have the same light in front of 20+ other apartments in the same building configuration and reflective light situation and none of the others have ever had this problem.

I have swapped the light fixture out with another identical fixture and get the same flickering problem.

I have tested the voltage coming to the light and it is a constant 120v (no flickering of the voltage).

If I put black electrical tape over the photocell, the flickering stops and it stays on.

If I take the tape off and shield the photocell with my hands (to block any light reflection) the flickering starts again.

By the way, when I first install the new fixture, it does not flicker right away but starts after a few minutes.

Any suggestions on how to fix the problem other than keeping the tape on there and therefore having the light on 24/7?

Thanks for your help.

I suspect the photocell ckt. had a cap open up. Check it in daylight. Block it with something opaque, not your hand, and time how long it takes for the light to come on. Remove the cover and observe how long it takes for the light to turn back off. They should both be substantial time delays. But you say you swapped with an identical fixture (known good???) and got the same results? You should still do the timing test on a non-flickering fixture as a basis for comparison.
Secondly, the CdS might be reacting to a non-visible light source. I don't know the spectral response off hand, just that the resistance varies from hundreds of ohms in strong light, to millions of ohms in darkness. A filter film over the window might fix that.
Photocell ckts are designed with hysteresis, also called positive feedback, snap action, differential, deadband, schmitt trigger action, and some I'm forgetting. If some of the light from the fixture that you're controlling, can reflect back to the photocell, you might be exceeding the switching threshold. Or could this light be interacting with another fixture controlled by a photocell??? I had to troubleshoot a complaint about the lights going off at a bus vaulting island a few years ago. I climbed the ladder and eyeballed the viewing window for the photocell. I could see the pretty new street light that the city installed across the street. The fix involved an empty pop can, tin snips and a couple cable ties. I blocked the sight line between the photocell and street light, while still allowing ambient light to enter the window.
Joe

Any new tenants with car alarms that flash super bright LEDs when the system is armed?
Joe

Here is some additional information after my initial post.

When I said it flickers every quarter of a second… To better describe the flicker, it is a constant and consistent on/off/on/off with it pausing just a fraction of a second before it changes (like someone is moving the light switch up and down as fast as they can).

It is hard wired (I bypassed the light switch).

It is actually the third, identical fixture (all from different orders) to do the same flickering.

It is mounted in a very dark place (the other lights don’t shine into the area it is at).

Thanks

A CFL does not have enough load when off to turn off the PC. You can prove that to yourself by putting in a regular lamp.

I had the same problem with an occupancy sensor.

This Photocell fixture is designed for a CFL (it has a GU24 base) and all of the other identical fixtures on the property are working correctly with CFL’s.

Thanks.

Are you saying that the fixture used to work in this location, and now it doesn't, or has this location always had a problem?
Joe

Is there a white or light colored wall/floor across from this light that is reflecting back at the PC?

Three identical fixtures over the past year have never worked at this location.

I think years ago the same model fixture used to work there but I am not sure on that.

Thanks.

Whatever the exact reason for the problem is you have proved that the photocell is incompatible with that particular application or location. I would suggest a different type or make of photocell, or moving it to a different location, depending on what's most practical.

Geoff has nailed it ... not every photocell, motion sensor, timer, or other control works with every kind of light. CFL's have really brought this issue into focus.

The fast flicker is almost a guarantee that there are components fighting each other.

The only other thing to check is your grounding. Many controls and ballasts use the ground wire as a 'neutral,' and a poor ground path can cause problems like this.

It almost sounds as if someone installed one of those 911 flasher switches in place of a standard on/off switch, but since you say their on a photocell, I assume this is common area lighting, so there probably isn't even an inside wall switch that the tenant or anyone else could access.
If that somehow turned out to be the case though, they usually have a bypass position so switch will operate on/off normally. I know at least the ones that Leviton makes have that feature anyway.

This sounds more like an Available Voltage / Circuit issue, as opposed to a False Triggering Photocell (P/C false triggered by reflected light from the Fixture's Lamp).

If the issue was from False Triggering, there should be at least 2-3 Seconds delay for the "OFF" Cycle, and at least 2-3 Seconds delay for the "ON" Cycle.

Apparently the P/C's Relay is closing upon Energizing the Fixture (as it would do normally); however, the Voltage drops rapidly and excessively under the Load of the Lamp, Ballast & Relay Coil (during inrush).

The Voltage Drop is high enough to cause the P/C's Relay Coil to "Drop Out" -

• which then opens the Circuit to the Ballast -
• which then reduces the Load on the Circuit at the Fixture -
• which results in the Voltage rising to "Normal" again -
• which causes the P/C to close the Relay -
• which connects the Ballast / Lamp to the Circuit -
• which places the Circuit under Load + Inrush -
• which causes the Circuit's Voltage to drop excessively -
• which causes the P/C's Relay Coil to "Drop Out" -
• which opens the Circuit to the Ballast -
• (repeat rapidly and endlessly)

Then again, the area of the affected Fixture might be possessed by a Practical Joking Poltergeist, which will require the services of an Electrical Exorcist...

--Scott (EE)

Have you tried to swap out with a fixture at a different spot? I.e., take the flickering light and swap it with a similar light at a different location known to work good. If the first flickering light still flickers at a "known" good spot, it's the light. If a known good light flickers in the location. It's most likely an environment issue. Light from some where subtle enough to piss you off without you noticing it.

Here's a long shot though. Can you take a voltage reading with a solenoid based volt meter? Perhaps there's a weak connection. Only time I use a DMM to measure voltage is whin I know I nave a good solid connection to the source.

Times like this is when you just want an edison base with a 100 watt bulb in it. We would not be talking about low voltage and bad connections. Take out the PC and watch the bulb.

I do agree, swap it with a known good one. Maybe hook up a keyless with an A19 in it and then look at the voltage, flicker or whatever.
If the power is good and a known good unit still fails, that type will not work there. Try something else. Maybe use a remote photo cell.

The TOP suspect is a marginal neutral return.

This return leg/ or grounding conductor will read 'fine' on a DMM, even a small analog meter.

Once loaded the voltage differential will collapse...

Then see Scott35, above.

The poor neutral can exist MERELY by being too far from the panel -- resulting in excessive impedance.

While the neutral is the TOP suspect, even the 'hot' (120V) may have too much impedance or too much of a parallel load. ( much more uncommon: 'make-up' on neutrals is very commonly much more sloppy than the 'hot' conductor.)

In your case, I would not be surprised if the load was wired off a 'house' panel. (on the landlord's dime) This will usually be a dinky panel back near the Service entrance -- with just perhaps ONE circuit dedicated to this lighting run. (count up the fixtures on this circuit -- too many and you're into 'multi-vibrator land.')

&&&&

I've seen this 'multi-vibrator' effect on every manner of electronic 'ballast' or power conversion logic -- especially in site lighting where the distances are LONG.

Upsizing the conductors -- especially the neutral solves the problem, nothing else.

The very size of your building is suspect: this particular fixture 'smells' like it's very far from your distribution panel.

It's as common as dust for the installation crew to NOT spot the voltage drop because of impedance on such long neutral runs -- which will, obviously, never be line of sight.

I've seen this defeat countless foremen and j-men.

Multi-vibrators are worth studying on Wiki just for an understanding of engineered flip-flops.

By the way, your computer utterly depends upon multi-vibrator logic, they always have.

As intelligent devices pervade our lives, you'll encounter this frustrating tick more than once.

And, with this, you're the 'smartest wire-man' in your complex!

Is it just me? I could've sworn that our O/P stated that the lamp stayed on solid when he placed opaque electrical tape over the photocell. Don't you think that all the various line anomalies,(Love that word!), would still be there with tape on the sensor? So I still want to know how long it takes for a normal fixture in a normal location to switch on with the photocell blocked, and turn back off when unblocked, in broad daylight. I don't think that any photocell ckt used in a lighting application, should react as quickly as he described, so knowing the normal response time is important. He could be getting RFI in a higher impedance part of the circuit, causing it to act like a relaxation oscillator. But I would only suspect something like that if the normal response is slower than what he's seeing. If a normal fixture can really switch on and off that quickly, I would use the pop can trick, to block light coming from different angles.
Joe

Joe, when I test photocells, it typically takes about three minutes for the lights to come on, after I have covered the sensor with black tape.

When I first apply power to the photocell, it takes about half a minute for the photocell to activate the lights - and another minute or two to shut off the lights if it's sunny out.

If a photocell is being fooled by reflected light, the light can cycle fairly quickly; any HID light will take a bit to come up to full brightness and trip the sensor. By "quickly" I mean maybe 15 seconds on followed by three minutes off. Reflected light will not cause the extremely fast cycling described by the OP.

I keep coming back to my original guess. The PC is not compatible with a CFL and I bet it works fine if he put an A19 in the circuit.

Reno, I agree with you on your typical lighting photocell observations. I would expect that to be how our OP's behave but I want to see his answer. They are designed with very long time constants.
Greg, he tells us that they are designed for CFLs and that they work fine elsewhere.
Todd, you said that you observed the voltage. Does that mean that you used a Fluke or similar meter with Min/Max Record? Have you contacted the mfg to see if they have reports of fixtures behaving this way? Are there any obvious RF sources in that location?
Joe

It certainly doesn't seem to be working where it is.
That just looks exactly like a solid state switch that is not able to shut off a CFL load. I see it all the time with 2 wire occupancy sensors. (quick flashing when they should be off).
My guess is it is on the edge of it's design envelope and there is something in the environment that tosses it over the edge. What does the manufacturer say?

The Manufacturer's response is: 愚蠢的美國人，你從中國買

(Guess this site doesn't support Chinese)

Thanks for all of your ideas and comments.

To answer some of your questions:

Yes, if I put black electrical tape over the problem PC it instantly stays on and does not flicker. Just a reminder that when I first hook up the fixture it does not flicker right away. But then 5-20 minutes later it starts to flicker and does not stop.

If I put black electrical tape over a properly working PC in the daylight it comes on within a few seconds and stays on. It then goes off within a few second once I remove the tape. It responds quickly but not as quickly as the flashing that I am experiencing with the problem PC.

The fixture is designed for a CFL and all of the other identical 25 fixtures on the property have CFLs and have never had the problem.

When I checked the voltage with my digital multimeter I remember it being a constant 120 or thereabouts. I will double this reading next time I am there.

The way the building wiring is set up is it a long single level building and this fixture is at the apartment that is the farthest from the mast head.

After the power comes down from the mast it goes into a service room with the meters. There is a main breaker for this apartment on our side of the meter and then the line travels about 50’ underground and then about 150’ through the attic past 5 apartments to this apartment on the end.

This apartment has its own panel in its apartment that controls the fixture.

The neighbor apartment (one apartment closer to the meters) is an identical apartment with an identical PC fixture that has always worked correctly.

Although, I don’t think we are leaning towards it being a problem with the fixture. Here is a link to the fixture so that you can visualize it. http://www.amazon.com/Nuvo-Lighting-60-3946-Photocell/dp/B0020S4VS2

Note the PC eye points down behind the bracket arm.

I have not contacted the manufacturer for any known problems.

I will be going back to the property in the next week or so and I will take another swing at resolving this. I will check to make sure all of the connections are tight and check for fluctuating hot, neutral or ground. Anything else you suggest I check?

Thanks,

Todd

FWIW, I would have a replacement $45 fixture with me, and do a swap after I checked the voltage, neutral & ground wiring.

Also, could the tenant have a 'timer' on the circuit???

A lot of the 'in wall' timers (electronic) do NOT like CFL/LED lamps/fixtures. I know this from personal experience.

Todd,
I just went to the link you posted and went straight to the reviews. They describe almost the exact problem as you have, just a lower flicker freq. They also describe a fix that's similar to the pop can trick I suggested. I agree with those who posted that it's a poor design because it switches at the rate of a motion sensor and not that of a lighting control. I would suggest that you put a good fixture in that location and keep that one as spare. Be thankful that the whole complex doesn't look like a disco revival community at night!
Joe

From Amazon

I wish I had the time to read the comments on Amazon. That's interesting, a bad batch of 'quality fixtures'!!

Todd,
If you were to place a straight edge on each side of the bracket arm and tangent to the glass, the extension of that line should NOT be able to point to any part of the photocell. If it does, a piece of wider opaque material should be placed on the back of the bracket, in front of the photocell. I'm not surprised that it takes several minutes to act up because garbage designers, don't need no stinkin' capacitors, or worry about temperature coefficients or Schmitt triggers. It would be fun to tear one apart to see just how many corners they cut.
Joe

The fixture is 'dimmable' -- which means TROUBLE.

THAT's where the multi-vibrator logic kicks in.

I suspect that the fixture's logic is 'hunting' for a stable state -- and is caught in an endless logical loop.

Look to see if you can 'lock out' its dimmable feature.

You don't want it, anyway.

This might be as simple as throwing a sliding switch in the fixture or pressing a 'pin-hole' adjustment tucked into the fixture.

Read the literature about the dimming feature.

You may have to poke around and fuss with it -- because of the terrible cut sheets enclosed by the factory.

[ The Chinese are masters of two great games: 'Go' and 'Guess.' ]