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I have a floor lamp with a three-stage turning switch: off->low->high. I use the lamp only on the high setting, but need to pass through the low setting to get there. It's rated at 150W and I've been using CFL 150W equivalent. The bulb life has been terrible. Do I need dimmable CFLs?

  • Three way bulbs have three voltage contacts so when you're using a non-three way bulb, it doesn't get power from the "low wattage" contact and will only work (as a normal bulb) in medium and high settings. – JPhi1618 Dec 7 '15 at 16:41
  • Do you turn this light on and off a lot? CFLs do not like to be turned on and off frequently, I think their "life" rating is based on leaving the bulb on for 3 hours at a time. If your usage is considerably shorter than that you might consider switching to an LED. High-output LEDs are a little less common but you shouldn't have much difficultly finding 1500+ lumen LEDs today. – Hank Dec 7 '15 at 17:07
  • I don't really turn it on/off frequently, it's usually in one state most of the day (either on or off, depending on the day). If it's off, I might turn it on for less than 3 hours during meal time, but it doesn't actually get switched more than maybe twice a day. – Ken Zein Dec 8 '15 at 15:59
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A 3-way lamp has 4 positions: off, low (filament 1), medium (filament 2) and high (filaments 1 and 2). If you are using a standard (non-3-way bulb) instead of being OFF-LOW-MED-HIGH the sequence is OFF-OFF-ON-ON with no ill effect. The bulb simply uses one of the contacts (filament 2) instead of both.

However you say your lamp only has 2 "on" positions, so it's not a standard 3-way lamp then. I think it's likely that there is in fact a built-in dimmer and so yes your CFL bulbs are being burned out by the dimmed fixture. (Some dimmers never actually reach full voltage at "high" so it's possible that the lamp is being dimmed slightly even when on full.)

I would try replacing the bulb with a dimmable CFL to see if that gets better results (or upgrading to a dimmable LED).

As I said in my comment to the original question, turning CFLs on and off frequently can significantly shorten their life so that may be another possible explanation. Again, upgrading to an LED would solve that problem as well since they are not bothered by being switched on and off.

  • The lamp does kind of work very dimly on the low setting, and I never leave it on that setting, just pass through it when switching to high. – Ken Zein Dec 9 '15 at 19:44
  • @KenZein: OK then you definitely do not have a standard 3-way lamp. There must be a dimmer in there and yes that is the problem. – Hank Dec 9 '15 at 21:14
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There should be no ill effect from using a standard CFL in a normal three-way lamp; it's just switching another contact, not acting as a dimmer.

Bulb orientation, or heat entrapment, might be concerns. Or there might be something else causing that lamp to run at lower than normal voltage.

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