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I've just moved into a new place, and the hood fan in the kitchen takes Par 20 bulbs. I had some left over LED Par 20s from my last place, so when one burned out, I installed it, and then I replaced the other one with an LED while I was at it.

Once I did that, the light would no longer turn off. There are three brightness settings on the switch, but when I turn it off, it just gets slightly dimmer.

I suppose I could just put back the regular Par 20 bulb, but I'd prefer to save the 56 watts if I can. Any ideas on how to resolve this?

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Because somewhere in your system is a powered switch that relies on leaking small amounts of current through the (incandescent) light bulb. When they are not lit, incandescent bulbs are effectively dead shorts. LEDs are not. The small amount of current being leaked is too little to glow an incandescent. However it's plenty enough to glow an LED.

This posting talks about the problem, and one solution, and links to a "gory details" discussion.

  • So I understand, if it's "leaking" power anyway, am I using any additional wattage to illuminate those bulbs, or would that power be consumed either way? Is it safe to have them dimly glowing at all times? – Ryan Anderson Mar 1 at 14:07
  • @RyanAnderson the incandescents, being unlit, had a very low impedance, so if the dimmer is even slightly linear, it would have flowed more power on the incandescent. The safety of the LEDs can only be answered by product testing, so you would need to investigate the product's UL listing and what conditions UL tested. That sounds daunting, but here's the trick: NEC 110.3b says you must obey the labeling and instructions, because, UL tests for the uses described in the labeling and instructions. Did UL approve labeling that says "dimmable"? – Harper Mar 1 at 14:16
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    Good point. They are UL listed as dimmable, so I'm not too worried there. I'm replacing that hood fan in a year or two so I think I'll just deal with it – Ryan Anderson Mar 1 at 18:30

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