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

Today’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!

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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?

Sage Friedman's picture

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. 

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.


You asked about a CFL dedicated circuit, I understand that would be a fixture or fixtures that have a ballast in them. In these fixtures the sockets are different and will not accept a self-ballasted CFL anyway (meaning the screw in type that have their own electronics onboard in the base of the bulb). Therefore, a screw in CFL dimmable or non-dimmable will not work in these fixtures.

Just had a nondimming CFL bulb start smoking connected to a CFL dimmer

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.

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.

Can I replace my dimmable light switches with non-dimmable switches and then used standard cfl bulbs?

Of course.

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?

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

If your dimmable socket stopped working after using a CFL bulb, you likely burned out the triac circuit. Replace the socket or the dimmer, if the dimmer is a separate device.

Dimmable LED bulbs are now available from Cree that look WAY better than CFLs. They are also made in the USA. Make the switch. Use your remaining CFLs in a utility area until they burn out, and then never look back again.

The color corrected Cree bulbs are even better. They are virtually identical to incandescents in color. The regular Cree bulbs are pretty good, and are way better in color than CFLs.

I still use incandescent bulbs in the winter time. When I turn on all of my 100 watt lamps, the furnace runs a lot less, so obviously this is balancing out. They act like radiators, and since most of my lamps are placed near windows or walls, they do a nice job of radiating in the cold parts of the room.

A dumb thing that the government did was ban 100 watt bulbs first. 100 watt bulbs are actually more efficient (and produce a usable amount of light) than lower wattage bulbs. Running the filament hotter increases its resistance, which makes for more lumens per watt.

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.

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

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!?

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?

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?

Buy a C/L dimmer and replace the one you have, and replace with CFL or LED bulbs.

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?

No you cannot use CFL's in a dimmer circuit even if you keep the dimmer on high. You may get away with it for a few hours, days, or even months but eventually you will have either a "burned out" (no longer working) CFL or worse. You will almost certainly immediately get an annoying buzzing noise from the CFL. USe incandescents and dim them (saves power and works great) OR get dimmable LED's

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

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.

I found that only one of the three-way switches was not working -- the one with the dimmer. I replaced it but found also that the connections were not right (the switches needed to be both in a determined position for the lights to turn on), so I fixed that and everything works now. No more problems since. I still have no idea why the blue box was totally melted.

UL and other testing organizations assert that there are no safety concerns with using non-dimmable CFLs on dimmer switches.

I had CFL bulbs connected incorrectly to the dimmer switch of my bedroom ceiling light for the past year or so. They worked for this time period however they never dimmed just flicked on when the nob was turned up far enough. Recently, all of them stopped working. I changed them out for regular dimmable light bulbs which also did not work. Every now and then when I mess with the nob they'll blink on and off but I won't be able to get sustained light or reproduce any light at all. I'm thinking I may have shorted something originally with the wrong bulbs. Any idea what this could be? Is it something I should try and handle myself or should I call an electrician?

I have a light fixture with a dimmer switch that has 4 CFLs. My dimmer switch is always on maximum. I had occasional flickering for a while and only today I decided to research the reason and found this site...

I will replace the light bulbs asap, in a meanwhile, is there a chance that I did any damage to the electrical wiring? Used the fixture this way for at least 6 months or so... Thank you for your help, I am glad I found this out.


What about a standard electrical outlet that’s controlled by a standard on/off wall mounted switch... the setup commonly used with a floor lamp. Any issues replacing the on/off switch with a CFL/LED/incandescent compatible dimmer? And what if the outlet is used for other electric devices? For example a three speed table top fan? OK to set fan to highest speed and then control speed via the dimmer switch? If OK with bulbs but not fan, is something available that would safely work for any electrical device? Like a variable speed controller or something else mounted on wall instead of the dimmer?

Could a short in a fixture render a dimmer switch ineffective.

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