TL;DR - do all dimmers reduce maximum brightness of LED lamps?

So I had a recently bought a dimmer switch (Lutron Diva DVCL-153P) for an LED light, and I immediately noticed that the light was dimmer than before, even at full brightness. I grabbed a multimeter and tested the live wires (121v), and then the load end of the dimmer against common, with the light on (106v). I know that these new dimmers do fancy AC signal chopping (phase cut?), so my multimeter may just be confused..

Anyway, so I grabbed some other dimmers at Costco (FIET 72309) and tried one out. It was noticeably brighter than the Lutron, and the Fiet read 115v on live load with the light.

I emailed Lutron about it, and they told me that I can always expect 5-10% brightness cut whenever I put a dimmer in. This seems crazy to me - I spend good money to get brighter lights, and lose some because there's a dimmer? Why don't dimmers have full bypass at the top end? Or can I find a switch where I can toggle between dimmer and bypass?

Or am I missing something?


  • Hello, and welcome to Home Improvement. You (and Lutron) may be right on the brightness, but there's no way you can get an accurate measurement with a random multimeter. They just measure the average voltage, and the shape of the curve (as you guessed) does matter. Mar 30, 2019 at 20:58

1 Answer 1


Yes, some dimmers have a bypass at the top. And the bottom.

The game is really about wave-shaping, and nothing prevents a dimmer from giving 100% top voltage via a switch, or 99% top voltage via silicon. However in practice, the wave-shaping is done to make the dimmer as cheap as possible while not hopelessly incompatible with LED. Peak performance is not a priority.

Speaking of "cheap", CostCo and Feit Electric are not "spending good money"... unless we're talking "throwing good money after bad". Big-box is a sea of junk, it's basically the Alibaba crud but with the safety hazards fixed. You have to buy much more carefully if you want performance.

On the other hand, pro grade equipment is more accessible than ever.

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