CFL bulbs and Dimmer Switches (& not the obvious question!)

lee676September 13, 2008

I recently bought a floor lamp that is designed to take 3 incandescent light bulbs, but with which I plan to use compact fluorescent (CFL) bulbs instead for their substantial energy savings.

The problem is: the lamp has a dimmer switch. I don't intend to use it, that is, it will be left full bright all the time. My question is, can I use standard, non-dimmable CFLs in this lamp? I am aware that even when set to full brightness, most dimmers are actually only letting about 95% of the voltage through. So I have several choices:

a) Use the cheap CFLs I already own and hope nothing bad happens;

b) Buy new dimmable CFLs which are expensive and not sold at most local stores;

c) Replace the dimmer switch with a simple on-off switch, assuming I can find a suitable part (or I can open up the lamp and rewire to bypass the existing dimmer switch, and add a new on/off cord switch), or

d) Keep the dimmer and use 40w halogen/infrared bulbs that are dimmable and as bright as 60w incandescents, although not nearly as efficient as the 14w CFLs that are just as bright.

I have had trouble with dimmable CFLs the one time I bought them - they buzzed noticeably whenever dimmed. And CFLs don't take on that nice, characteristic orangish dimmed-light color when dimmed.

Any ideas?

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Replace the dimmers with a switch. The dimmers have a voltage drop across them even when set for full intensity, your 95% may be correct. That means the 5% loss must be dissapated as heat.

    Bookmark   September 13, 2008 at 7:55PM
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Even when 'full on' the regular dimmer still distorts the AC waveform.
Triacs (the device used to create dimming) only turn on when there are a few volts across them.

This has the effect of trimming the AC waveform slightly.
In many cases it is fine since there is some margin in most devices for the extra heat this distortion produces.

    Bookmark   September 14, 2008 at 11:36AM
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Well, I settled on using Philips Energy Saver halogen bulbs, which are 40w but give off the same light (800 lumens) as a standard 60w incandescent and have incandescent-like dimming characteristics. Unfortunately, they're slightly larger than standard light bulbs and won't fit through the hole in the glass globes my floor lamp uses. So it's back to the store to return those, and I need to use something else.

I'm not aware of any other manufacturer selling similar bulbs (except Osram in foreign markets, but they run on 240V). Regular halogen bulbs are only slightly more energy efficient than incandescents, so I guess I'm back to using CFLs. I tried a cheap non-dimmable 14w CFL just to see what would happen if I leave the dimmer on full. It does seem to light up fine. I heard a faint buzz sound, but I often hear this from CFLs in non-dimmed lamps too. If I dim the lamp, the CFL starts flickering and then goes out completely.

Is there any safety risk in using a non-dimmable CFL if I leave the dimmer on full bright all the time? Or do I need to buy $50 worth of dimmable CFLs? (btw, changing the dimmer to an on/off switch or bypassing it would require more disassembly of the lamp than I have time for).

    Bookmark   September 23, 2008 at 4:31PM
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Yes, there is a safety risk in using a non-dimmable CFL with a dimmer, even at full brightness.

Your options - your sane ones, anyway - are to replace the dimmer with a switch (shouldn't take more time than you've spent in this forum already), find and purchase dimmable CFLs, or use normal light bulbs, like the lamp manufacturer intended.

Perhaps you could save energy by dimming the bulbs instead?

If you absolutely insist on using CFLs in that lamp with the dimmer still in place, pay close attention to this quote from another site (which I'll link to shortly): Warning! ... If one decides to test what happens if a CFL is used with a dimmer, at some settings (with possibly most CFLs) it may actually appear to work perfectly normally. One could easily be excused to imagining that there is no problem, as long as the dimmer is set to the maximum and left there. There's no visual clue, with normal light output and no nasty noises. Certainly, the lamp can't be dimmed, but that may not seem a major concern. I have seen this done - the dimmer knob was taped to hold it at the maximum setting.

Don't do it! While it may appear to work normally, the current drawn by a typical CFL used this way increases up to 5-fold, to the point where it is potentially very dangerous. The current spikes are very narrow, but can exceed 8A with an 18W CFL. The RMS current drawn can be as high as 0.5A - over 5 times that drawn with no dimmer in the circuit (and that's with dimmer set to maximum!).

Where the CFL has a fusible resistor at the mains input, this is present to limit the maximum (peak) current, and prevent internal short-circuit failures from blowing the main circuit breaker or fuse. Fusible resistors do not react (fuse) with excessive dissipation, so if the lamp is used with a dimmer (even if set to maximum), there is a very real chance that the fusible resistor (and/or other parts) will overheat due to the massively increased current, possibly leading to a (hopefully) small fire. The fusible resistor value can vary widely. Some have a very low resistance, so the chance of serious overheating is small. Others can use values ranging from 10 ohms up to 22 ohms. Some don't use one at all, but you don't know from the outside.

The warnings placed on CFLs are not there just to irritate you or discourage you. They are not nonsense. Do not use CFLs with dimmers, period.

If you're interested in some more detailed, geek-oriented reading, Try here.

Now, all of this said, they DO make "dimmable" CFLs. I haven't seen one, nor have I ever heard anyone claim that they work very well - but they are (relatively) SAFE for what you're trying to do.

    Bookmark   September 24, 2008 at 3:43AM
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Thanks - that's what I was looking for - someone who wasn't just relying on hearsay or guessing whether it was safe. I guess i'll have to choose some sort of dimmable bulb. Incidentally, the dimmer on this lamp is inset into a carved wood block, not readily accessible which is why i'm not removing the dimmer. Usually i'm quite adept at replacing switches but this one's hard to get to.

What I really would have liked to use is something like these energy-saving halogens (GE calls them halogen/infrared or halogen-IR or just HIR), but the only ones sold in the US are oversized and don't fit in my floor lamp, which has small round openings in the glass globes that surround each bulb.

    Bookmark   September 24, 2008 at 2:48PM
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There are dimmable CFL's now available at the big boxes, and on the internet.

As always, "Live Safe Electrically"

    Bookmark   September 26, 2008 at 2:19PM
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I wound up using good-ol'-fashioned incandescent bulbs in this lamp. Even regular 60w incandescent bulbs barely fit through the small holes in the glass globes - I'm not sure what the manufacturer was thinking. I used 25w incandescent bulbs that have a conventional shape but are smaller than usual. Total wattage is at most 75 watts from the three bulbs together, but I usually have it dimmed. It's primarily a decorative lamp fixture, with overhead CFLs providing most of the light.

Although not very energy efficient even by the low standards of regular incandescent lamps, dimmed incandescent light bulbs give a distinctive, warm glow that I've yet to see duplicated by fluorescent, HID, or LED lighting, dimmed or otherwise.

    Bookmark   March 14, 2010 at 4:58AM
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Wow; I had no idea that using a CFL on a circuit with a dimmer switch was dangerous. I'm bumping this thread for others' benefit.

BTW, I actually *bought* that $60 worth of the best-quality dimmable CFLs I could find (GE) and they still buzzed, and hardly dimmed at all. The lamp store guy promised me this was the case, but I just had to try it. I returned them. :( It can't be too long before someone invents a better one, can it?

    Bookmark   January 20, 2011 at 7:53PM
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Thanks for the warning, I just replaced the dimmer switches for two sets of CFLs I have. I do notice that with the new switches, the CFLs have an audible buzz I don't hear with other CFLs. Are they damaged?

    Bookmark   January 22, 2011 at 6:08PM
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If you don't mind the cost, most LED retrofits are dimmable and dim more smoothly than dimmable CFs.

I've been experimenting with the $20 LED retrofits from Home Depot lately. They seem to work well, but radiate most of their light upward (away from the base). Whether this works for you depends on how you use the particular fixture.

    Bookmark   January 23, 2011 at 11:09PM
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PS - those $20 LED retrofits are a bit less efficient than your typical $3 CF, but much more efficient than incandescents.

    Bookmark   January 23, 2011 at 11:10PM
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The 40W CFL uses 9 watts and the LED equivalent uses 8.6. Making the LED more efficient. Also it lasts 5 times as long with no mercury content, making it better for the environment.

    Bookmark   February 24, 2011 at 8:36AM
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Taylor sells LED's I'll bet. In my experience LED's have
an almost 50% failure rate and those that continue
to operate lose over half their output in a year or so.

    Bookmark   February 24, 2011 at 8:43AM
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The 40W CFL uses 9 watts and the LED equivalent uses 8.6.

Better check whether that LED "equivalent" actually produces the same lumen output as the 40w incandescent it allegedly replaces. As in the early days of CFs, LED retrofits are usually blatantly (and unethically) overrated for their equivalence to incandescent bulbs.

When the actual lumen output is considered, I have yet to see a commercially available LED retrofit that exceeds the best compact fluorescents in efficacy. Many of the cheap ones are far worse than CF. Some can't even meet CA Title 24 efficacy requirements.

That said, to be fair, LED retrofits in recessed cans produce more apparent output than their lumen rating would suggest, because they radiate light in only one direction. Thus no light is lost in the can's relatively inefficient reflector. I have not tried to measure whether this makes up for their lower efficacy, however.

Saltcedar's comments about the degradation in light output or failure rate are worth paying attention to. Because LED retrofits are relatively expensive to manufacture, and consumers are pretty darn resistant to high prices, many of the producers (usually based in China) cut corners ferociously. And you know what THAT causes.

LEDs may indeed have a "bright" future in room lighting, but that future is still some way off.

    Bookmark   February 25, 2011 at 5:26AM
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