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#186514 - 05/17/09 10:37 AM Saving Electric with Dimming
Obsaleet Offline
Member

Registered: 04/05/03
Posts: 361
Loc: Pa
So I am reading the back of the Lutron dimmer & fan control selection guide and it tells me dimming the lights 10 percent saves, 10 percent electricity. I learned that that this is not true. Can you guys straighten me out? The chart continues with 25 saves 20 percent, 50 saves 40 percent and 75 save 60percent.

Ob
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#186515 - 05/17/09 10:49 AM Re: Saving Electric with Dimming [Re: Obsaleet]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
Ten percent of what?
10% of the pot range?, 10% of the current? 10% of the light output? I think it is a throwaway line.
If they mean you are letting 10% of the wave through that might be accurate. Get out your log tables and start up your slide rules. wink
Dimmers certainly reduce the watts used when they are "dimmed"
The real question is how much light you are getting for your lighting dollar
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#186518 - 05/17/09 12:47 PM Re: Saving Electric with Dimming [Re: Obsaleet]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8530
Loc: SI,New Zealand
Yay!,
Marketing hype. clap
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#186530 - 05/18/09 10:49 AM Re: Saving Electric with Dimming [Re: Trumpy]
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
It really depends how the dimmer works. As far as I know, most of the dimmers on the market now are of the switched type, which rapidly switches on and off a couple thousand times a second (I don't know the typical frequencies) to give you more of a duty-cycle type of dimming. This means the load still sees the same peak voltages, so W=V^2/R doesn't put us into exponential terroritory like rheostats would. On the surface looks like it would be linear- dim 50%, get 50% the light. However, at high switching frequencies, line conductors have considerable inductance, so currents while the switch is switched on are slightly higher than you'd get from looking at the resistance of the light bulb due to the building magnetic field, and the overall response curve isn't quite linear.

I'd imagine their claims are never exactly right since there are too many variables, but somewhere in the ballpark. Just don't plug in a CFL or LED bulb wink

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#186534 - 05/18/09 01:42 PM Re: Saving Electric with Dimming [Re: SteveFehr]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
I think the dimmers just gate the 60hz at given levels on the curve, selected by a pot and I believe a diac.


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#186536 - 05/18/09 05:19 PM Re: Saving Electric with Dimming [Re: gfretwell]
JoeTestingEngr Offline
Member

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
Greg,
I was thinking the same thing. They are usually just triacs with a variable hold off on the gate trigger. They add a snubber circuit to combat noise from the shatp leading edge at the trigger point. You'll always have some crossover distortion on them. I would guess that they all use sensitive gate triacs to allow the earliest triggering for maximum brightness.
Joe

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#186538 - 05/18/09 07:23 PM Re: Saving Electric with Dimming [Re: JoeTestingEngr]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
If it is a "full range" dimmer there is usually a switch that jumpers out the triac when you are all the way on.
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#186555 - 05/19/09 05:36 AM Re: Saving Electric with Dimming [Re: gfretwell]
SteveFehr Offline
Member

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
See... this is why there shouldn't be a timeout on the edit funtion. sleep

Triac makes way more sense. No idea where I picked up the idea that they were high-frequency switched.

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#186561 - 05/19/09 07:54 AM Re: Saving Electric with Dimming [Re: SteveFehr]
LarryC Offline
Member

Registered: 07/05/04
Posts: 775
Loc: Winchester, NH, US
"Triac makes way more sense. No idea where I picked up the idea that they were high-frequency switched."

Switch mode power supplies?

Larry C

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