I just replaced an old Pass and Seymour slide dimmer switch with a Lutron single pole switch with a side toggler. I'm using incandescent bulbs. The new switch dims the lights fine, but when I slide all the way to the top, the light is not as bright as it was with the previous dimmer in max position. I'd estimate it's 70-80% of previous max brightness. Any idea why this happening?

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    It is phantasmagorically difficult for human eyes to detect light levels in absolute measure, because they are so good at auto-adjusting to conditions. Hell, eyes automatically white-balance. So unless you are using competent test instruments in equal conditions (e.g. moonless night vs moonless night), this could be entirely in your head. Jul 7, 2019 at 19:35
  • My Fluke 115 true rms reads 109.0 V at the base of a kitchen light fixture on a Lutron dimmer on full brightness. Nearby receptacles give 118 V. I'm not going to try to read the input voltage at the dimmer, at least right now. Can this be right?! Jul 7, 2019 at 20:28
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    @JimStewart that is not wholly meaningful on a sine wave which is being misshapen by a triac. You need something smart enough to measure both voltage and current on the whole sine wave. Jul 7, 2019 at 21:45
  • Buy new LED BULBS with a higher lumen level and adjust as needed.
    – Alaska Man
    Jul 7, 2019 at 22:03
  • @Harper Why do you need to measure current? The voltage and current should have the same clipped sinusoidal waveform. Cut off voltage with a leading or trailing edge triac and you have no current during the periods where voltage is clipped to 0. Jul 7, 2019 at 23:25

1 Answer 1


Many new dimmers are designed to “save energy” by limiting the full brightness to 80 or 90% of actual full brightness. Some of them have a hidden slider to adjust the top end. You’ll have to either shop for a different dimmer or put up with it.

  • Our 4 year old Lutron dimmer in the kitchen has a single slider adjustment under the bezel for the minimum brightness. It has no adjustment for the maximum. The kitchen dimmer was put in at the same time as new ceiling light fixtures so I cannot tell if the lights are as bright as they would be with a simple switch. Jul 7, 2019 at 20:12
  • @DoxyLover Thanks for the answer. I didn't even consider that it was energy saving. Will see if I can adjust it. Otherwise will buy something else.
    – user69908
    Jul 7, 2019 at 22:56

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