Author Topic: Dimly glowing CFL in light fixture  (Read 760 times)

secondcor521

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Dimly glowing CFL in light fixture
« on: January 25, 2022, 10:12:07 PM »
Hi all.

I have a ceiling light fixture that has a CFL that glows dimly when the light is switched off.  I don't know much about electric stuff, but I'm guessing that means that there is a little bit of current flowing that shouldn't be.

It's so dim that the only time I notice it is when all the lights in the house are off and it's dark outside.  So just barely glowing.

I figure the problem is either in the fixture or the wall switch.  (Duh.)

No other electrical problems that I know of.  House was built in 2004, standard contractor grade spec home.

What do I do first?  What should I be looking for?  How do I fix this?

Thanks!

SailingOnASmallSailboat

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Re: Dimly glowing CFL in light fixture
« Reply #1 on: January 26, 2022, 01:55:13 PM »
I'd probably swap out the bulb into a fixture that has a bright CFL bulb in it now - this will test the bulb. And then try that CFL in the fixture you're wondering about.

TLDR: check the bulb first.

secondcor521

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Re: Dimly glowing CFL in light fixture
« Reply #2 on: January 26, 2022, 02:06:17 PM »
Thanks, will try that.

bacchi

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Re: Dimly glowing CFL in light fixture
« Reply #3 on: January 26, 2022, 02:14:18 PM »
Turn off the switch, remove the plate, and put a voltmeter across the terminals.

It takes a lot of juice for a CFL to start. Does the light stay dim for hours or for a few minutes? If it's only briefly on, it could be the residual power in the capacitor. I've seen that in LED headlamps.

secondcor521

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Re: Dimly glowing CFL in light fixture
« Reply #4 on: January 26, 2022, 02:17:58 PM »
Turn off the switch, remove the plate, and put a voltmeter across the terminals.

It takes a lot of juice for a CFL to start. Does the light stay dim for hours or for a few minutes? If it's only briefly on, it could be the residual power in the capacitor. I've seen that in LED headlamps.

Don't have a voltmeter.  May buy one.

Hours.

GuitarStv

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Re: Dimly glowing CFL in light fixture
« Reply #5 on: January 26, 2022, 04:38:16 PM »
CFLs will often glow for a while after they're turned off.  I've actually noticed this before and checked my socket with a voltmeter.  Usually after 5-10 minutes you'll notice that they go completely dark.

BudgetSlasher

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Re: Dimly glowing CFL in light fixture
« Reply #6 on: January 26, 2022, 04:41:12 PM »
Since it goes for hours ...

What kind of switch?

There are several types of switches that are labeled as not for use with CFL/LED. The reason being something in the switch draws a small about out power; what comes to mind are motion sensor, but there are also switches that have a small light built into them ... some dimmer switches or perhaps smart switches without a neutral connection might have the same results. Since most normal switches are inline on the hot wire the only way to the neutral is across the lights. These low amounts of power are not enough to light up a standard in incandescent bulb but the lower power needs of high efficiency bulbs are a different story ... it could be enough to light (or keep lit) a LED/CFL.

What happens if you take out the bulb while it is dimly glowing and wait a few minutes and put it back in? Does it glow again or stay dark? Either way there is current flowing, but it takes more current to get a CFL glowing than it does to keep it glowing dimly.

I would not suspect the fixture. For power to get the fixture and thus the bulb is has to get past the switch. Without buying additional tools, if you are handy and comfortable with doing it replacing the switch is pretty quick and cheap (a budget grade single pole switch is less than a buck and a 3-way switch is less than 3 bucks). That would be a quick and cheap diagnosis.

If it isn't the switch and current is somehow getting to the light ... something odd is going is going on.

If you turn of the circuit breaker the bulb is on does the light go out?
« Last Edit: January 26, 2022, 04:43:27 PM by BudgetSlasher »

secondcor521

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Re: Dimly glowing CFL in light fixture
« Reply #7 on: January 26, 2022, 05:39:39 PM »
Bingo, we have a winner!  The switch in that location is a dimmer switch.

It's hard to tell, because it has a big flat rocker switch like all the other light switches in the house, but it also has a little tiny horizontal slider at the bottom (that is sort of hidden when the light switch is turned on because the bottom of the rocker switch blocks it from view).

It's also silly because the light fixture it controls is in an interior hallway area between the kitchen, master bath, laundry, living room, and garage.  There's no reason I can see to have a dimmer switch there.  It's utilitarian light, not mood light.

I suspect what happened was that the builder for some reason ran out of regular rocker switches but needed a switch for that location and just said what the heck, I'll put this dimmer switch in that I have on hand.  NBD, especially since the house was built in 2004 when incandescent light bulbs were all the rage.

I turned the dimmer slider all the way down and with it that way the CFL no longer flickers.

Thanks all!

GuitarStv

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Re: Dimly glowing CFL in light fixture
« Reply #8 on: January 26, 2022, 08:08:35 PM »
Since it goes for hours ...

Whoop, missed that.

BudgetSlasher

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Re: Dimly glowing CFL in light fixture
« Reply #9 on: January 27, 2022, 05:28:03 AM »
It is not a sure bet that it is the switch, but I would say it raises the odds. And it is as good a place as any to start.

Let us know if it works or even if it doesn't.

Since it goes for hours ...

Whoop, missed that.

That was not actually aimed at you. You were the little red warning that a new post had occured while I was typing, which I chose not to read.

I had the same thought as you initially, when I had CFLs I  would go into a dark room a few minutes after turning the light out and be a bit confused by the glowing pigtails.

 

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