Join 3,432 readers in helping fund MetaFilter (Hide)


Why is this lightbulb flickering?
December 5, 2011 11:46 AM   Subscribe

Why is this lightbulb flickering?

I have two ceiling lights in my hallway, with lightswitches at either end of the hall. Both lightswitches are the kind that light up when the lights are out. Both lights are just single bulbs, and I have compact florescent bulbs in them.

Recently one of the bulbs, which was new, started flickering. I figured the bulb was defective and replaced it, but after a few days the replacement bulb started doing the same thing.

The flickering is on/off/on/off, not dimming.

The other light is fine.

What does this flickering indicate? I've replaced lightswitches but nothing more complicated than that; is this something I can fix myself or do I need a professional? Is my house about to explode?
posted by The corpse in the library to Home & Garden (13 answers total) 1 user marked this as a favorite
 
Does the flickering bulb also flicker when you screw it into some other place? If so, then you lucked into a couple of bad bulbs.
posted by Chocolate Pickle at 11:55 AM on December 5, 2011


Both lightswitches are the kind that light up when the lights are out. Both lights are just single bulbs, and I have compact florescent bulbs in them.

CFLs are generally incompatible with light and motion sensors. The electronics will result in a flickering. You need to get bulbs that work with the sensors you have.
posted by dhartung at 12:04 PM on December 5, 2011


To expand on dhartung's almost-certainly-correct diagnosis, the reason that CFLs don't work with most sensors is that the sensor is confusing the light about whether it should be on or off.
The sensor itself requires a little bit of current to power the electronics that determine if there's light/motion and whether it should switch the lamp on, and in the early days of such devices it really didn't matter, just pull a little current through the circuit. In an incandescent bulb, that's no big deal, as it's a current so tiny that it doesn't heat the filament. With a CFL, the entire white base is a housing for a ballast, an electronics board that converts house power (120V AC) to the kind of power the fluorescent wants to see, including an ignition pulse. The CFL electronics are designed to detect when there's 120V power supplied to it, and throw out an ignition pulse in response. With the wrong combination of sensor (drawing a leak current to power itself) and a sensitive CFL ballast, you get the CFL trying to light up in response to the sensor current, but not having enough power to stay on. Ways around this are to use a special light/motion sensor that intentionally powers itself off a different loop of house power than it powers the load (lights), or to just use an incandescent. Some CFLs are more prone to this than others, but it's not a question of quality or "dimmable" or any really fixed characteristic, it's just how that manufacturer's electronics happen to behave under this unexpected circumstance.
I'd recommend the incandescent - CFLs work best when they switch on and stay that way, rather than turn on and off. Frequent switching means they don't last as long, so the energy savings gets eaten up by lamp replacement cost. So you may as well use an incandescent if you've got one. I heard a colleague say, but I've never tested it, that if you have a room full of fluorescents on one switch, then replacing only one of them with an incandescent creates a pathway for the leak current that keeps the current from bothering the fluorescents, but I'm not sure this makes sense to me. You can try it.
posted by aimedwander at 12:32 PM on December 5, 2011


Did you try replacing the switches with non-illuminating ones?
posted by lee at 12:44 PM on December 5, 2011


CFLs are generally incompatible with light and motion sensors. The electronics will result in a flickering.

Just a nitpick: I think the OP is talking about illuminated switches (which have a little light inside them that lights up when in the "off" position) rather than any kind of sensor. However, these switches can still have problems with CFLs, particularly flickering on and off when the switch is in the "off" position. See here for a description of what's going on.
posted by Johnny Assay at 12:52 PM on December 5, 2011 [1 favorite]


We had a couple of lights flicker for over a year or so and finally had someone come out to look at it. Our house is old and has older/inadequate wiring. Turns out that one of the wires in the ceiling in our basement was overloading (or something) and had started to burn the wooden beams. It's all charred and scary looking now. I didn't think it would be a big deal and wasn't going to call an electrician, but it was worth it. I'd say call a pro just to make sure nothing serious is going on. Good luck.
posted by notcreative at 1:12 PM on December 5, 2011


Compact fluorescents flicker on and off when the voltage is low.
You might have a wiring problem. Check the voltage in that socket.
Until then, replace the flickering bulb with a tungsten lamp.
posted by the Real Dan at 1:40 PM on December 5, 2011


Do the bulbs flicker when they're supposed to be on, or when they're supposed to be off?
posted by flabdablet at 3:02 PM on December 5, 2011


Yeah, just replace both switches with new ones that don't have the little glowing light in them. That should do it.
posted by exphysicist345 at 3:36 PM on December 5, 2011


I think the OP is talking about illuminated switches

Agreed. But the reasoning is the same as given by aimedwander. It's all because of the ballast reacting poorly to the wiring conditions.

If these are lights that remain on long enough, you could consider an LED bulb, but they're still pretty expensive this year. If you use an incandescent, you will probably find better prices on LEDs by the time it burns out next.

If you have an actual wiring problem, that would probably show up with an incandescent, too. If you're concerned you could try a voltage tester (every homeowner should have one).
posted by dhartung at 3:50 PM on December 5, 2011


> Just a nitpick: I think the OP is talking about illuminated switches (which have a little light inside them that lights up when in the "off" position) rather than any kind of sensor

Yup, exactly.
posted by The corpse in the library at 3:55 PM on December 5, 2011


> Do the bulbs flicker when they're supposed to be on, or when they're supposed to be off?

It's just one of the bulbs, and it's when it's on.

We've had these light switches for two or three years and it's been fine until now, if that's relevant.

I'll try switching that bulb for a standard one, and try the flickering bulb in another lamp.
posted by The corpse in the library at 3:57 PM on December 5, 2011


If they're flickering when they're on, the illumination in your switches is most unlikely to be the direct cause. When an illuminated switch is on, it just connects its terminals together the same way as an ordinary switch. The only difference between an illuminated switch and an ordinary one from the lamp's point of view is that the illuminated switch will draw a very small current through the lamp when the switch is off.

Also, if I understand your description correctly, you've got two lights controlled by the same switches and only one of them is flickering. That would pretty much rule out the switches as the cause of the problem, leaving wiring/receptacles or bulbs as the fault possibilities.

If you swap the two bulbs and the flickering follows the bulb, you've got a faulty bulb. If the flickering stays with the same receptacle, you've got a faulty receptacle or faulty wiring.

The most common receptacle faults are corrosion and loose wires. If you shine a strong torch into the receptacle and see anything other than bright metal on the contacts where the bulb goes in, try scouring those contacts with a small bit of sandpaper. You will want to turn your electricity off at the breaker before doing this, as your illuminated switches might not isolate you sufficiently to avoid a shock.

Checking a ceiling receptacle for loose wiring connections should be no more difficult than replacing a switch, though access will be more awkward.
posted by flabdablet at 6:21 PM on December 6, 2011


« Older Who is Buzzy Bus?...   |  What should I get my lego/star... Newer »
This thread is closed to new comments.