I have a Lutron Diva dimmer, gray color, that was installed by a manufacturer in 2016 to operate some [fancy expensive] LED ceiling lights.

this dimmer is not a smart dimmer, has no light to it, but has a white neutral wire connection to it. Any other non-smart dimmer on depot/lowes shelves (lutron/leviton) does not have a neutral wire connection. what's its purpose here on this gray lutron diva dimmer I have? I don't know if the switch got thrown out yet so i don't have the model # of it.

someone explain forward-phase and reverse-phase dimming...


  • 1
    Is it a neutral wire or a white wire being used as a hot(it should be marked black or red)? Neutral must be white, but white does not mean it is neutral. I think by 2016 code required a neutral to be in the switch box, usually capped and wasted, but you should also have a black and red wire in the box also. Black and red connected to the switch.
    – crip659
    Oct 31, 2023 at 19:48
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    @crip659 but even in 2016, if it was an old box it could have a switch loop. Another possibility is a 3-way switch - at least some of the current Lutron Diva dimmers have the same SKU for single and 3-way applications. Oct 31, 2023 at 19:49
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    @manassehkatz-Moving2Codidact I took manufacturer as the builder of the house. It could be the manufacturer of the lights but seems odd.
    – crip659
    Oct 31, 2023 at 19:54
  • manufacturer of a mobile office, it is definitely neutral; black hot, red to light, many whites tied together and one coming off to dimmer, green ground not connected to dimmer. If I remember there was no provision on the dimmer to connect the ground. I came across something about "forward phase dimming" ?
    – ron
    Oct 31, 2023 at 20:40
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    Can you post the Lutron model number, or a photo of the dimmer's labeling, please? The Lutron dimmers come in various models within a given product line to accommodate various types of lights, and some of them require a neutral... Nov 1, 2023 at 0:01

1 Answer 1


so what i had was a reverse-phase dimmer, this pdf from Leviton explains it


The most common technology used to produce forward phase controls is Triac based dimming. In this type of dimming, a semiconductor acts as a switch, controlling both positive and negative half cycles. Due to the nature of how the triac works in forward phase, it is not interrupting current at the end of the cycle, but rather letting the signal go to zero.

Reverse Phase (Electronic Low Voltage) Controls Reverse phase controls modulate the input power by turning ON in the beginning of the cycle and turning OFF in the middle of the cycle. In order to increase the light output, the power would be turned OFF later; and to decrease the light output, the power would be turned OFF earlier. The most common technology used to produce reverse phase controls are MOSFETS. In this type of dimming, two MOSFETS act as switches, one on each of the positive and negative half cycles. Due to the use of MOSFETS in the design, reverse phase dimmers generally require a neutral wire for operation.

  • Yeah, that's the kind of thing I was suspecting myself Nov 2, 2023 at 0:02

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