Flourescent bulbs on a dimmer switch

[Pitt123]

I recently bought new CFL (flourescent) light bulbs only to find out that they will not work with a dimmer switch. From what I have read it seems to be because these bulbs have a ballast in them that may not work with a dimmer switch.

I was hoping to see if anyone could give me a more in depth explanation?

 

[RobbieR]

Sounds like you need a dimmable electronic ballast in your fixtures.

 

[suemarkp]

You can get dimmable CFL's, you just need to look for them (and they cost more). Usually, there is a large "Dimmable" label on the package. If not, you have to read the small print around the base of the electronics portion of the lamp. Most will say "not for use in dimmers".

Even if you get dimmable ones, they don't dim as nicely as incandescents. You can probably go from 100% to 50% brightness, then they abruptly cutoff. They also don't dim as easily when they are cold. So if you've dimmed them down as far as they go and have a dimmer with a separate on/off control which "remembers" the dimmed level, they may not come on when you turn them back on if they are cold. You'll need to go to full brightness, wait a minute for them to warm, and them dim them back down again.

LED based lamps also come in dimmable and not, but the LED ones don't have as many issues. Costco has some dimmable LED A19 40W equivalent bulbs for $10 each which I like better than CFLs, except the color temperature of the LED was not as nice as the CFLs. But at least they have more dimming range and come on to full brightness right away.

 

[steve66]

I recently bought new CFL (flourescent) light bulbs only to find out that they will not work with a dimmer switch. From what I have read it seems to be because these bulbs have a ballast in them that may not work with a dimmer switch.

I was hoping to see if anyone could give me a more in depth explanation?

Yes, they have their own ballasts. Ballasts are normally made to keep a steady light output in spite of varrying input voltages. That gives the best combination of long lamp life, light output, and energy efficency.

It also helps keep all the fixtures at a nice steady brightness - the light at the end of a run is just as bright as the first light in a run. And there is less flicker and change in light output when other heavy loads start (for example, when the air conditioning kicks on.)

But all that works against exactly what a dimmer is expected to do - which is to make the light output vary.

 

[Dennis Alwon]

You cannot just use any dimmer with any CFL. The dimmer needs to match the cfl design. Lutron makes special dimmers for CFL's but they only guarantee their success with certain brand CFL bulbs. I believe Philips is one of them but the dimmable kind.

 

[Pitt123]

You cannot just use any dimmer with any CFL. The dimmer needs to match the cfl design. Lutron makes special dimmers for CFL's but they only guarantee their success with certain brand CFL bulbs. I believe Philips is one of them but the dimmable kind.

What are the differences between the different types of dimmers that would allow one type of dimmer to work with CFL's while another type may not?

 

[Dennis Alwon]

What are the differences between the different types of dimmers that would allow one type of dimmer to work with CFL's while another type may not?

I do not know that answer. Perhaps some of our more technical minded members know. I do know that there is no standard for designing CFL's or LED's. This creates unique problems for each different design when trying to manufacturer a dimmer to work with all of them.

Call Lutron and they will tell you which CFL's their Led and CFL's work with. It may very well work with other brands but there is no guarantee.

 

[steve066]

It seems like the term "CFL" is being used to describe both:

1. Compact flourescent lamps like triple twin tubes, and twin tubes. These typically go in a commercial light fixture, and the ballast is always part of the light fixture.

2. Fluorescent replacements for A19 lamps. These have ballasts as part of the lamp, and they have standard screw bases so they fit into typical residential lamps.

Not just in this thread, but in most threads about CFL, I'm never sure which type of lamp we are talking about.