light bulbs and dimmers

[Scoot]

I just put in some can lights (aka. pot lights) in my basement. I put them on a dimmer switch. I put in my bulbs that I use in the upstairs cans. They work just fine.

I went to buy more lights and a salesman mentioned that "those lights won't work if they're on a dimmer switch". Funny, they seemed to work just fine when I checked them out before... Of couse the onese he wanted me to buy were twice the price of the regular lights.

Can somebody give me the scoop on this?

[Walleye Guy]

Flourescent lights generally do not work well on dimmers. I am not a sparky so somebody who is can correct me if I am wrong.

I believe a dimmer is just a voltage regulator so to speak. Flourescent lamps require near the entire 110 volts to light up. Incandescent bulbs will light up with less than 110 volts.

[riverrat56]

Recessed Cans should work just fine on a dimmer, as long as they do not have a compact flourescent light in them (although they are now making dimable flourescent lights).

Salesmen are just that, they are trying to turn the greatest profit, especially if they work on comission. I'm to the point that I just tell them to go away.

[polarsusd81]

Halogens and incandescent lights work well on dimmers. I am not too sure about LED's but would be interested to find out. Flourescent lights as stated, will not work well on dimmers. I use flourescents in hall lights, kitchen, and bathroom. The rest are a mix of incandescent and halogens. When I finish off the rest of my basement though, I am interested in doing some accent lighting with some LEDs.

[JohnMickish]

Not exactly true that flourescent lights don't work on dimmers. Obviously if you have a dimmable ballast that works but if you don't what can you do? You see there are electronic dimmers and resistive dimmers. One being relatively cheap and one not. You can run anything on a good electronic dimmer as it (at the risk of oversimplification) cuts out parts of the sine wave yet still gives full voltage and 60 Hz. Basically it's a wall mount VFD (variable frequency drive). Ever seen a light dimming panel in a restaurant, theater or stage?

[riverrat56]

mnfishinguy by cutting down the sine wave, what would change causing the lights to dim? I didn't completly understand all the theory we learned in lab classes last year, and some AC stuff went right over my head. Just trying to gain some knowledge.

[JohnMickish]

It's all in the magic, and you have to believe in magic.

Not to be a smart A** here, but it's pretty deep, and you might want to revisit the AC theory a bit.

Basically you are tricking the load into thinking it's getting the full voltage and frequency it needs but in reality it isn't, but at the same time it is. Like I said, it's magic. OK, it's really in the magic smoke they pack into those little boxes and once you let the smoke out they don't work anymore.

[JohnMickish]

Sorry, that was kind of a smart answer. Maybe Lmitout or somebody else can try to add to it.

When I say part of the sine this is what I mean. Now we all know that if you block the upper or lower sine you get a pulsed DC, right? Now we all know that if we did that with our dimmer we would smoke the ballast. Now imagine what would happen if you took half the sine away, but this time you took part of the upper and part of the lower sine. Still with me? The ballast still "see's" full voltage and 60 Hz but dosen't get the full current.

With your el'cheapo resistive dimmer you cut down the voltage going to the fixture (you don't save any electricity, the watts that are no longer going to the fixture are now turned into heat by the resistors) and we all know that electronic ballast need full voltage or they overheat. That is why you can't use these on fixtures with a ballast. See, this electricity stuff is easy, just ask anyone here.

[riverrat56]

Right, it makes sense now, I had to pull out a textbook out of that book bag I packed away till next fall, and do some reading. They really shouldn't have put that class that early in the morning....

Thanks