# Talk:Dimmer

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## Proof a rehostat will be dissipating 25% of the loads rating at maximum

(i think the statement above is right but i need to go through the proof to convince myself before i add it)

find turning point to find point of maximum power

${\displaystyle P_{dimmer}=V_{dimmer}I}$

${\displaystyle I={\frac {V_{supply}}{R_{dimmer}+R_{load}}}}$

${\displaystyle V_{dimmer}=V_{supply}{\frac {R_{dimmer}}{R_{dimmer}+R_{load}}}}$

${\displaystyle P_{dimmer}=V_{supply}{\frac {R_{dimmer}}{R_{dimmer}+R_{load}}}{\frac {V_{supply}}{R_{dimmer}+R_{load}}}}$

${\displaystyle P_{dimmer}=V_{supply}^{2}{\frac {R_{dimmer}}{({R_{dimmer}+R_{load})}^{2}}}}$

${\displaystyle P_{dimmer}=V_{supply}^{2}\left({\frac {R_{dimmer}+R_{load}}{({R_{dimmer}+R_{load})}^{2}}}-{\frac {R_{load}}{({R_{dimmer}+R_{load})}^{2}}}\right)}$

${\displaystyle P_{dimmer}=V_{supply}^{2}\left({\frac {1}{R_{dimmer}+R_{load}}}-{\frac {R_{load}}{({R_{dimmer}+R_{load})}^{2}}}\right)}$

${\displaystyle {\frac {dP_{dimmer}}{dR_{dimmer}}}=V_{supply}^{2}\left(-{\frac {1}{(R_{dimmer}+R_{load})^{2}}}--2{\frac {R_{load}}{({R_{dimmer}+R_{load})}^{3}}}\right)=0}$

${\displaystyle {\frac {1}{(R_{dimmer}+R_{load})^{2}}}=2{\frac {R_{load}}{({R_{dimmer}+R_{load})}^{3}}}}$

${\displaystyle R_{dimmer}+R_{load}=2R_{load}}$

${\displaystyle R_{dimmer}=R_{load}}$

therefore both loads are running at half the supply voltage therefore the load is running at 25% of its rated power and the rehostat is also running at 25% of the loads rated power.

The equations don't exactly hold for real-world incandescent light bulbs, though, because the tungsten filament radically changes its electrical resistance as it heats (over a sometime 10:1 ratio!).
Atlant 12:55, 29 January 2007 (UTC)

## Rheostat dimmer?

That alleged "rheostat dimmer" in the photograph looks a lot more like a motor-driven, two pole variable autotransformer dimmer to me. Those windings look like copper, not nichrome.

Atlant 17:54, 7 August 2006 (UTC)

Sorry, I was always told by my teacher that this was a rheostat, but I guess he could be wrong. I believe the image could still be used somewhere in this article. JWGreen 00:48, 8 August 2006 (UTC)
Oh, no problem with using the image -- it's perfectly valid for what we're trying to illustrate. I was just quibling about the nomenclature. I just looked at the high-resolution version of the image and there's no doubt that those are autotransformers; thanks for making the change in the article!
Atlant 13:52, 8 August 2006 (UTC)

Variable autotransformers are generally known as variacs.

Rheostat dimmers which looked somewhat similar may have been used a _very_ long time ago. Tabby 22:33, 15 September 2007 (UTC)

## Something in ?Spainish?

I removed the following from the start of the article. I don't think it's relevant, and even if it is, it's in the wrong language: "HOLA SOY PAPAS NATAS DE ELCTRONICA 2006 "4 AÑO c" Bryson430 13:01, 23 August 2006 (UTC)

Iknow a small amout of spanish, it means word for for word literaly "Hello this is potatoes notes of electronics" KeepOnTruckin 21:36, 29 January 2007 (UTC)

## Mistake

There is a mistake on the dimmer's schematic. I build it and you have to add a 20k resistor between the scr's gate and the negative to stop the sinking current from the zener diode. —The preceding unsigned comment was added by 24.37.33.106 (talkcontribs).

It would depend on how electrically leaky your zener diode is versus how easily-triggered your SCR is.
Atlant 12:59, 29 January 2007 (UTC)

## Efficiency

Article might benefit from an explanation of the effect of dimmers on lighting energy efficiency, or efficacy. I'll add a link to an article that explains this and more Tabby 01:42, 30 March 2007 (UTC)

## Circuit mistake

The dimmer circuit is a short circuit result in instant damage to the SCR —Preceding unsigned comment added by 209.202.68.187 (talk) 17:39, 25 November 2008 (UTC)

## Architectural/civilian usage

It is probably appropriate to add a section dealing with the use of dimmers in "regular" uses like homes, architectural uses and other non-theater uses...

--Keeper of the Keys (talk) 16:15, 20 April 2009 (UTC)

yes i agree, i came here looking for info on why a domestic dimmer switches make bulbs 'sing', it took a while to wade through with no headings indicating 'domestic use', -a common term ? 79.76.235.17 (talk) 16:56, 6 July 2009 (UTC)
me too. Much still assumes theater/event use rather than domestic/residential - just needs clearer headings. - Rod57 (talk) 14:17, 15 November 2016 (UTC)

## Rheostat Dimmer Efficiency

The article gives the rheostat efficiency as "as low as 0.5". I think that the efficiency would approach 0. Consider a time when the rheostat is very high impedance compared to the bulb. Almost all of the power would dissipated in the rheostat. (Both componants see current I, but the power is proportional to their individual impedance 'R' from P = I^2 * R.) If the rheostat was 10x the impedance of the bulb then the efficiency is 1/(10 + 1) ~= .09. For what it's worth: My math (incorrectly) assumes that the impedance of the bulb is constant with changes in current. Heating will increase the bulb impedance, so the impedance will decrease as rehostat impedance increases. This will further undermine efficiency, but the decrease is dependent on the type bulb and other variables.K Mlnarik--206.197.156.11 (talk) 15:36, 18 September 2009 (UTC)

## Schematic bridge rectifier

The dimmer schematic image's bridge rectifier makes everything more confusing. Can we make it a normal bridge rectifier symbol? — Preceding unsigned comment added by 71.237.188.199 (talk) 23:03, 6 September 2011 (UTC)

Ok, just did it. It's better to have it later than never. DesbWit 09:42, 4 May 2012 (UTC) — Preceding unsigned comment added by DesbWit (talkcontribs)

## Circuit Symbol

What is the correct symbol to use to represent a dimmer in an electrical circuit schematic diagram? Thanks --Lbeaumont (talk) 02:51, 14 October 2011 (UTC)

No dimmer symbol shown in IEEE Std. 315 (aka ANSI Y32.2, or CSA Z99). I suspect as a rather complex device internally it would be shown as a box labelled "dimmer". There's almost certainly an architectural symbol for lighting layouts, but finding it means getting out of my chair. --Wtshymanski (talk) 14:15, 14 October 2011 (UTC)

## No mention of TRIACs?

Are TRIAC dimmers not widely used? TRIACS are related to SCR's but different. For exmaple, they don't require the bridge rectifier because they conduct AC.192.139.122.42 (talk) 20:20, 24 October 2012 (UTC)

They are in there - a triac is just another thyristor. --Wtshymanski (talk) 20:55, 24 October 2012 (UTC)

## Leading and trailing edge dimmers

Some eg [1] can be 'programmed' either way. Could use this as an inline ref or an external link ? - Rod57 (talk) 14:13, 15 November 2016 (UTC)

## Leading and trailing edge terminology confusing

This may be industry standard terminology, but it seems confusing as the description of 'leading edge dimmer' would have it turning on during the trailing edge to achieve dimming greater than 50% ? I guess the name refers to dimming starting from (or being off during at least some of) the leading edge (rather than when the dimmer turns on). It might also help to have a detailed description of how a 'trailing edge dimmer' works ? - Rod57 (talk) 14:39, 15 November 2016 (UTC)

## Could explain restrictions eg re CFLs and LEDs

Could refer here to why some domestic dimmers are not suitable for CFLs or LEDs, and why some have a calibration to adjust minimum output (maximum dimming) ? Some domestic dimmers have small inductors too. - Rod57 (talk) 14:46, 15 November 2016 (UTC)

## Separate AC and DC

Rheostats will work on DC as well. The SCR type (illustrated) will only work on AC. Not sure about the other types. Maybe we need a DC dimmer section ? - Rod57 (talk) 14:55, 15 November 2016 (UTC)

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