Why You Should NEVER Use Non-Dimmable CFLs with Dimmer Switches. | Energy Circle, LLC

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

Peter Troast

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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