Why You Should NEVER Use Non-Dimmable CFLs with Dimmer Switches.

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By Will - September 21st, 2011

CFL dimmer warningToday’s CFL light bulbs are a real improvement over early manifestations. Buzzing has largely been eradicated, many are now instant-on (or very close), and don’t take the time to warm up that earlier CFLs did. Dimmable CFLs are now available, too, and some of them are pretty good. The mercury content of CFLs, too, has been a concern for some; but most high quality new compact fluorescent bulbs have so little mercury that it’s not really a concern. (Many have a mercury content equivalent to that of a can of tuna, and less than would be released into the environment as a consequence of the extra fossil fuels burned to power an incandescent bulb.)

But there’s one issue with CFLs that’s a pretty big deal, and that needs to receive a lot more attention if we’re going to see a peaceful transition to energy efficient light sources: non-dimmable CFLs cannot and should not ever be used with dimmer switches.

This isn’t so much because they won’t perform well (they won’t, although some may appear fine, at least for a while), but because it actually presents a pretty serious fire hazard. Here’s why:

How dimmer switches work:

To put it in layman's terms, most modern dimmer switches essentially function the same way as if you were to turn a light on and off really, really fast (about 100 times per second). They're designed to work with incandescent bulbs, and they work with incandescent bulbs really well. Dimming an incandescent bulb reduces the bulb's energy consumption, makes it look really nice, and the transition from 0-100% light output is pretty smooth.

What happens when you screw a CFL into a dimmer switch:

CFLs are a more complicated piece of technology than incandescent bulbs, which presents a problem when they're connected to a dimmer switch. There's some really good info about the science of CFLs and dimmers here, but basically the problem is this: CFLs have less resistance than incandescent bulbs, which means that the floodgates are opened when they are exposed to the electrical fluctuations that a dimmer sends, and they actually can consume up to 5x the current as when they're not connected to a dimmer (and that's when the dimmer is set to max). This overheats the bulb and can actually cause it to light on fire. Bad news.  

This is a pretty serious problem; while there aren't a ton of documented cases of fires being started by CFLs being connected to dimmer switches, there are some. 

So be sure to tell all your friends: non-dimmable CFLs shouldn't be plugged into dimmer switches. Not everybody takes the time to read the warning labels on everything they buy, but this is something we should all be aware of. 

On a final note, for clarity, dimmable CFLs are fine. You'll want to pair them with the right type of dimmer to get the best performance, but you don't have to worry about them catching on fire. 

Happy Wednesday!


Comments

Is it still a fire hazzard to plug a non-dimmable CFL into a CFL specific dimming circuit? What I mean is, according to your blog the fire hazzard exists if you plug a CFL into a circuit with a dimmer designed for an incandescant bulb. What if the dimmer switch you're using is specifically for CFLs? I know your non-dimmable CFL still won't dim, but does the fire hazzard still exist? How do those dimmers differ from the ones designed specifically for CFL dimming? Posted by Squash Josh on Mar 27, 2012 8:15pm

Dimmable-CFLs are dimmable because of the special electronics in the ballast (housed in the plastic part at the base of the bulb) which steps up the current to be extremely high frequency to create a circuit through the gas in the tube and ignite the bulb.  The modern CFL-compliant dimmers work with this, but they also work with other types of bulbs, by reducing the current flow. 

A normal/non-dimmable CFL will still have a problem and would not work correctly. I'd say its more likly to simply not function at all than it is to cause a fire, but depending on the quality of the bulb and what kind of ballast it has its concievable that it could still overheat.  Fire is probably a remote risk, but it could happen, more likely it could damage the bulb or substantially reduce its lifespan. 

Posted by SageFriedman on Apr 3, 2012 2:22pm
Thanks for the reply. My house was built almost entirely with non-dimmable CFLs. I am going to change the light switches out for Z-Wave switches, but they are almost exclusively dimmers. I've decided to just change the bulbs at the same time to dimmable CFLs to alleviate the problem. I wonder how much 1xx non-dimmable CFLs would sell for on ebay :). They'd probably all break in shipping. Thanks, Josh Posted by Squash Josh on Apr 3, 2012 2:40pm
On rare occasion some dimmers, such as the toggle dimmer in my dining room, have a shorting switch that shorts across the triac circuit at the 'max' setting, which applies full, unaltered 60 cycle AC current to the lighting circuit. Using such a dimmer with non-dimmable CFLs is perfectly fine as long as it is immediately turned to the full-on position or off position, and nowhere between. Posted by Anonymous on Jul 23, 2012 10:24pm

How do I determine if my dimmer has a switch that shorts across the triac circuit at the max setting? I have Lutron Diva DV 600P. On single.

Posted by Anonymous on Aug 24, 2014 2:01pm
Can I replace my dimmable light switches with non-dimmable switches and then used standard cfl bulbs? Posted by Anonymous on Aug 28, 2012 7:18pm
Of course. Posted by Anonymous on Aug 28, 2012 7:32pm
I did what I should not have done - used CFBs in a dimmable lamp. No fire, no burned bulbs, but the lamp just stopped working. Even when bulbs were replaced with incandescent , still doesn't work. did I kill my lamp for good? Posted by Anonymous on Oct 15, 2012 10:53pm

I have the same problem. My ceiling fan is working fine, but lamp is not working any more. Any help?

Posted by Anonymous on Apr 13, 2013 10:58am

I have a floor lamp. Used non-dimmable CFLs. Worked fine at first, then suddenly turned off by itself.

Left it off for 2 hours. Still didn't fully turn back on, just flickering lightbulbs. Replaced CFLs with incandescent bulbs...didn't turn on.

Put the CFLs back in and as a screwed them in, they flickered and eventually they all fully lit. I had to keep turning until they fully lit.

Lamp is back to normal. But if I turn off the lamp switch, it won't turn back on without finding that perfect dim setting (like finding a radio station by slowly turning a knob).

I'll just go back to incandescent bulbs.

Posted by Anonymous on Jun 9, 2013 11:07pm

I have this one switch that control BOTH the under the cabinet kitchen lights (fluorescent light, the short long tube ones, not CFL) AND a stripe of incandescent lights (like those one in the bathroom alongside a mirror). If I change this to a dimmer switch, will there be a problem? I am thinking if the dimmer is off (at max), BOTH lights will turn on like it is right now. But when the dimmer is on, just the kitchen fluorescent light will not turn on and I can still adjust the degree of the strip of incandescent lights -- which is my purpose of changing the switch. Thanks in advance

Posted by Anonymous on Aug 31, 2013 8:38pm

Yup----never realized that flourescents life span affected by dimmer switches.
First use of flour bulb lasted 2 weeks and bulb blew. Thought that flourescent would last for years!?

Posted by anonymous on Oct 12, 2013 7:33am

Quick question. I have recessed flood lights throughout many of my rooms, using 60 watt bulbs. I decided to replace them all w/ energy saving "dimmable" floods instead. However, I was told I need a special dimmer switch for them as well. Is that really necessary?

Posted by Anonymous on Oct 25, 2013 1:38pm

I have a 1950's house with dimmers that are controlled by a five inch (approx.) diameter disc. When it's rotated completely counter-clockwise the lights are off and they brighten to full capacity as it's rotated clockwise. There is no "click" to an off position. I have been told that this is type of system will not work with even dimmable CFL's. Is that the case? I'd like to add the efficiency of CFL's w/o having to remove by dimmer discs. Thoughts?

Posted by Max D. on Jan 8, 2014 11:45am

I had a ceiling fan recently installed that has 2 CFL bulbs. The fan is connected to a dimmer switch. Can those CFL bulbs be used if the light switch is kept on high when turned on, not using the dimmer function?

Posted by Anonymous on Mar 6, 2014 10:58am

Hello. I cannot seem to find a on/off non dimmable CFL light switch with a fan speed combo. Any help. My fans take CFL GU 24 bulbs which are not available as a dimmable bulb. Thanks

Posted by Moenshine on Jun 12, 2014 6:37pm

I'd also like to add that running a non-dimmable CFL or LED or even a remote controlled pedestal fan on a dimmer switch completely rapes the VLF radio spectrum. By that I mean everything from 60 hertz to 600 kilohertz is completely unusable. When the dimmer is turned on with the wrong load, you get pulses in the VLF radio spectrum that are really narrow and have a lot of spectral noise.

This also affects the HF radio spectrum so if you're a radio ham and the noise level is bad, take out the non-dimmable CFL from your dimmer swicth.

Posted by Brent Fisher on Jun 23, 2014 12:32am

Yesterday my kitchen's lighting fixture emitted muffled explosion noise and stopped working. I removed it and saw that the blue electrical box in the ceiling was completely melted, but there was no sign of fire, except by the old wiring next to the light bulb socket being blackened, probably the site of the short-circuit. The thing is, between the blue box and the apparent short-circuit location there's the light fixture and insulation, so it's a mystery how the blue box got melted so fast and when I removed the fixture right after the event there was no heat anywhere, so I'm wondering if the heated ceiling did that over the years. I replaced the sockets, the wiring (the wire insulation was all cracked) and the blue box, but now there is no power. I tested both three-way switches connected to it, one being a dimmer (the fixture uses two dimmable CFLs), and neither seems to be working; there's no power coming from both traveler terminals on the dimmer and from one of the travelers on the regular three-way switch. Is it possible that the short-circuit burned both switches and the circuit breaker didn't even turn off? I'm baffled by this, never saw something like it...

Posted by rgj on Aug 17, 2014 4:42pm

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