CFLs, voltage and dimmer switches

Over the course of 2 weeks, all 7 of the CFL floodlights in my kitchen burned out. They were purchased at different times and so I don’t think it is a cluster phenomenon. The lights are tied to a dimmer and I know that CFLs don’t play nice with dimmers - these in particular do not dim. The landlord had an electrician/handyman (so I don’t think a real electrician) over and he said the problem was that I need CFLs that work with a dimmer switch. I suggested that they get rid of the dimmer but the landlord wants to leave it. I tend to be an empiricist so all of them burning out over 2 weeks but at different ages (some on this switch for over a year), the incandescent bulbs burning out in the bathroom around the same time (which I told the landlord) and the incandescent bulb they left on to show me the kitchen lights worked burning out the next time I turned it on tell me this ain’t no wrong CFL on a dimmer switch issue.

Will having non-dimmer CFLs on a dimmer switch burn them out?
Does their dimmer theory even make sense given the different ages of the bulbs?
My theory is the voltage is too high - maybe 130V. I have to hunt up my voltmeter but in the meanwhile, would that cause premature bulb burn out? If so how quickly?
Does my “high voltage theory” make sense if the bathroom and kitchen are different circuits? If so does that imply the whole house is over-voltaged?
Can a household circuit even be over-voltaged?


Either get dimmable CFLs (or better, LEDs), or get rid of the dimmer.

Dimmer switches will significantly shorten the lives of CFL bulbs that aren’t designed for dimmer use, even if you leave the dimmer in the full on position.

There’s no transformer inside of a house, so there’s really only two ways that a house can end up with an overvoltage. Either the incoming voltage from the power company is too high, or there’s a problem with the neutral connection. In a typical U.S. residential service, two or three homes are all fed from a single center tapped transformer (aka a single split phase). The two connections at either end of the transformer are 240 volts apart, and the tap in the center is exactly in the middle, so what you have is 120 volts from the center tap to either line and 240 volts from line to line. The center tap becomes your home’s neutral. 240 volt appliances are connected to both lines, and all of the 120 volt circuits are connected from one line to neutral, usually alternating so that the house will be roughly balanced between the two lines.

If there’s a bad connection between the breaker box and the transformer on the neutral wire, what happens is that you still get 240 volts from line to line, but the center may not be in the center because it’s not tied to the transformer any more. So you may get 140 volts on half of your circuits and only 100 on the other half, but they’ll add to 240. This type of problem can be verified with a voltmeter measuring the voltages at the top of the breaker box. ETA: To be clear, the voltages you’ll get when you have a bad neutral connection will depend on how much current is flowing through each circuit. If the currents are perfectly balanced then each phase will measure 120. If one is drawing more current then its voltage will go down and the other phase’s voltage will go up.

An overvoltage from the power company can also be verified by measuring the incoming voltages at the top of the breaker box.

When you make measurements, note that it’s probably not going to be exactly 120 volts. It used to be that the power company would guarantee something like +/- 10 percent. Many of them now guarantee +/- 5 percent. The power company’s web site will often tell you what they guarantee.

Your landlord and handyman are definitely 100 percent correct in that you have a problem using non-dimmer CFLs on a dimmer circuit, and that alone could easily be responsible for all of your short bulb life problems. Whether or not you have additional voltage issues would require some poking around with a voltmeter to determine.

going into a breaker box is not something for the inexperienced. there is all kinds of places to extremely easily come in contact with lethal electricity.

you can with care get a measurement of total voltage at something like a dryer receptacle, assumes wiring in good condition.

yeah a non-dimable CFL will be killed by a dimmer.


We bought a house about ten years ago, and thought “Gee, that light seems so much brighter here” just about the same time the UPS on my computer started squawking about over voltage, reporting 145. We called the utility, they confirmed in excess of 140 on both legs, and (probably) changed the tap on the local transformer as 145/290 is excessive.

It’s worth noting that a “loose” neutral can also cause over or under voltage, but in that case, the voltage on both legs will still add up to 240. One leg may be 100 and the other 140, for example.

In addition to dimmable CFL (or LED) bulbs, you probably need a new dimmer switch. I assume your existing switch is for incandescents, and it won’t work well (and maybe not at all) with a CFL. You need a dimmer that is specifically designed for CFLs/LEDs.

Also worth noting is that the short lifetime of non-dimmable CFLs with a dimmer switch isn’t the only risk. It can also be a fire hazard.

Checking voltage is a good idea, a floating ground is not your friend, but if you can’t get a on-off switch, nor a modern dimmer that is made for CFL or LED, your best choice may be IC or IC-halogen as they are OK with a dimmer, a IC blub should last longer - offsetting the eletric costs, though I am unsure about the halogen as they are designed to run hot as part of their long life preservation method and a dimmer may be counter to that, but it should last OK, and fine if you use it ‘full on’

Remove the dimmer and put it in a baggie. Pin baggie to wall or otherwise keep AND remember dimmer.
Replace dimmer with switch (big box acceptable here).

When leave, swap backwards.

You happy, landlord happy. CFL happy.

I don’t know if it’s all OK for a tenant to do their own electrical work and I’m not sure that is something that leads to a happy landlord, the order maybe more more like:
:smiley: :mad: :cool:

A few years ago I was using a light dimmer at work to vary the power to a light in a test apparatus. I monitored the voltage to the light bulb using an oscilloscope. As expected, the voltage looked pretty distorted throughout the range. (This is due to the phase-fired proportional controller in the light dimmer. The turn-on of the built-in triac is delayed during each half-cycle.) Here’s the strange thing: when I adjusted the dimmer to 100% brightness, I was expecting the voltage across the bulb to be a nice sine wave. But it wasn’t; it was wacky & distorted looking.

So… with some dimmers at least, turning the knob to full brightness will not provide a nice sine wave to the bulb. I am thinking the higher frequency components in the distorted voltage signal may cause damage to certain CFLs.