Why can't you use dimmers with fluorescent or halogen lights?

Regular lightbulbs have metal (e.g. Tungsten) filaments in them. With a dimmer, you can alter the amount of electricity (trying to keep it simple) going through them. As much electricity goes through the filament, the hotter they get and become bright (give off light). You should be able to do this with a halogen light as well because I think they are filament based.

You cant do this with fluorescent lights because they are not filament based. They are gas-based. In other words, there is an inert gas (meaning it cant burn or react) in the tube. At a particular level of electricity, electrons (i.e. electricity) can “jump” from one end of the tube to the other. The “jump” causes the gas to give off light (glow).

So, if you want to think of this in simple terms. Think of a filament as a bridge. You could crawl across and still get to the other side. This would be a low level of electricity (using the dimmer) giving off less light.

Now, think of the two ends of the fluorescent tube as a trench. You have to run fast and jump over the thing. If you try and crawl, you wont get to the other side and fall in the ditch. This is basically that level of electricity where the light either turns off (electrons cant jump) or on (they can jump). Usually, its not very easy to dim such lights. Very few types are specially made for this type of thing—and they are sometimes noisy.

Hope this helps and that it was what you were looking for.

Thanks. Out of curiosity, what are the hypothetical repercussions of doing such? I’ve read “danger” warnings saying not to, but never explained exactly why.

Using a dimmer with a fluorescent tube? I didn’t realize that there was a warning label on there. Can you type out the text of the warning and anything else on there that might be relevant?

Since I am dealing with the dimmers in my house right now, I just learned about this—most dimmers work by rapidly turning on and off the circuit (which is why if you don’t have the correct type of dimmers for the ballast in the circuit, you can get vibration when the circuit resonates at a specific frequency). Flourescent lights don’t deal with turning on and off very well.

The concern for Halogen lights and consumer dimmers, is that the ratings on the dimmers are not large enough for the Halogen bulbs. It’s not unusual for one of these to exceed three hundred watts. They are, in fact, filament bulbs which can be dimmed with th proper dimmer.

You’ll rapidly burnout the ballast in a fluorescent light if you try to use a dimmer on it. For compact fluorescent bulbs, it means you’ll simply screw the bulb up. For tube fluorescent bulbs, the ballast is part of the fixture and would have to be replaced.

Mac is totally right about the rating for consumer dimmers. If you want to dim halogen bulbs, just get a properly rated dimmer.

@andrew – You can still get old-style resistance based dimmers, too, but they aren’t as energy efficient. It’s really freaking cool, though, how the new style dimmers work. They’re actually cutting the power every time the current alternates, then kicking back in at a certain point in the sine wave determined by the dimmer setting. My dimmer switch is smarter than me.

Good news! They actually make dimmers now for flourescent bulbs! You can get them in some stores now (and if you live in the bay area from the guy who sells them across from the Temescal Farmers Market in Oakland on Sunday mornings). Sorry – not sure the science behind them.

@sarahclif: Seriously??? I can’t believe it… what’s the brand name?

Sorry not sure the brand name of the ones in the stores. I was at a house party and some folks who were remodeling showed me the already installed version in their bathroom… Quite the house party eh? But we all couldn’t believe it and had to see! As for the ones for sale at the farmers market, I can’t go this Sunday, but I will next week and get back to you! Or anyone else who lives in the bay area and wants to go to a great market can check it out for you. The guy has a huge display set up out of his truck across from the DMV parking lot at the market.

How low can you dim fluorescent lights?

I’ve seen the CFL (compact fluorescent light) bulbs marked “dimmable” but they are more expensive; I’d rather use the cheaper, non-dimmable ones if possible. After reading through this thread, I’d still like to know the following: If you use regular CFL bulbs in a fixture controlled by a dimmer, but only use the switch to turn the fixture on and off at the brightest setting (eg. don’t use the dimming function), do you still stress the ballast in the bulb? Secondly, what is the failure mode of the bulb if so? Just dies or something more drastic?
The dimmers we have are of two types: the up/down switch to turn on/off with a slider knob alongside it to dim, and the round dial that rotates for the dimming function and toggles on/off by punching the dial in like a button. Our house was built in the mid-eighties, and the round dial probably dates from then. The dimmer up/down switches may be from the 90’s, though. thanks! :-)

As long as you are striving to have the bulb either at 100% brightness or off, you should not have any problem with non-dimmable compact fluorescent bulbs on your incandescent dimmer. It is running the bulbs in dimmed mode on an incandescent dimmer that wears the bulbs out faster than normal. There are other things that also wear out CFLs faster than normal, such as putting them in enclosed ceiling fixtures (where they tend to heat up more, and therefore break down sooner).

Running non-dimmable CFLs on a dimmer switch doesn’t pose a health or safety risk, just makes the CFLs more costly overall than they would otherwise be because it shortens their life. You’ll still save money with CFLs if you use the light for at least an hour a day (depends on what you pay for electricity and what you paid for the bulbs – see CFL calculator below).

So you should be fine if you don’t replace anything.

When the bulbs do burn out – hopefully after their full expected life of 8,000 odd hours of light – please dispose of them safely as they contain a trace amount of mercury. More on recycling fluorescent light bulbs in the second link below.
Source(s):
http://www.green-energy-efficient-homes.…
http://www.green-energy-efficient-homes.…

I’m not sure why you think that Halogen lamps aren’t dimmable, but if that were true than many dimming track lighting and theatrical lighting fixtures would have a very big problem. You may be making a (common) mistake of confusing Halogen with an arc-lamp such as Metal Hydrate or Sodium-vapor lamp, especially considering that Tunbgsten Halogen lamps and its cousin the Halogeena Fillament have a higher lumen output per watt, despite heat output being greater.

I use a fluorescent bulb in our outside lamp post, with a photo cell (is that what they are called?) to turn it off during the day. The cell does not work anymore, and I have to replace it. The replacement units that I found stipulate that they must be used with incandescent bulbs only. Why?