Do LED's use less power when you dim them?

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Old 02-03-13, 12:21 PM
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Do LED's use less power when you dim them?

OK I know this sounds like a dumb question and I'm sure the answer is obvious but I'm about to make a big investment in LED's and I realized I didn't have any solid information about this question.

As an experiment i just replaced one of our downlights with and LED insert. It looks great and I am thinking of replacing all of our lights. We have about 40 of these lights in the house. The thing is that in many places where we use the lights they might be dimmed 50% of the time.

I realize that even at full power the LED is only using 9.5 watts which is less than the 65 watt incandescent bulbs use even at half power so while there is an economic component to this question its really more academic. Because LED's work much differently than incandescence requiring built in electronics I was wondering how the savings of the two types of bulbs compare when you dim them.
 
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Old 02-03-13, 12:57 PM
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Yes....LED's do use less power when you dim them.

If that is your intention......make sure you buy dimable LED lamps and LED designated dimmers.
 
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Old 02-03-13, 02:20 PM
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Keep in mind the LED's cannot be dimmed as low as incandescent. In case you weren't already aware.
 
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Old 02-03-13, 02:37 PM
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The power savings will depend on how the dimming is done. Some controls simply convert the power not going to the light into heat so the LED is dimmed but there is no power savings since you are making heat with the excess.
 
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Old 02-03-13, 04:19 PM
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Is there some way to tell what method a given dimmer uses?
 
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Old 02-03-13, 04:22 PM
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I wasn't aware of that. Approximately how much can they be dimmed. We generally dont dim more than 50% but in the family room when we are watching TV we sometimes go lower just to keep some light in the room while minimizing glare on the screen.
 
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Old 02-03-13, 04:56 PM
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Is there some way to tell what method a given dimmer uses?
If the dimmer has a wide front plate with (usually) three tabs on each side, those are actually cooling fins. That dimmer will convert the diverted power to heat.

I can't remember seeing a dimmer that didn't do that.

Dimming lamps will usually increase their life span, though.
 
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Old 02-03-13, 04:59 PM
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I can't say with certainty how low they will go, but I am thinking the number was around 5%-10%. You shouldn't have a problem if you want to go 50%.
 
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Old 02-03-13, 10:10 PM
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The method that a dimmer uses to reduce the power (dim) the light is not really all that important with LED lamps.
I mean......c'mon we're only talking a watt or two.

Check out the link to Lutrons LED dimmers.
http://www.lutron.com/en-US/educatio...lsandleds.aspx
 
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Old 02-04-13, 03:09 AM
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Dimmers use a pulse width modulation so the power loss is quite small with light loads. If you thought they just convert power to heat, say it's rated for 600 watts, set at 90% dimming you would have 540 watts of heat in your switch box.
 
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Old 02-04-13, 08:52 AM
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OTOH if all dimmers were efficient pulse-width modulated and ran cool to the touch they would all cost the same. A good question is how to tell what you're buying since the technology is rarely mentioned on the box.

Also--Couple days ago I was reading a CFL & LED bulb review in Fine Homebuilding and the author found many LEDs don't dim below 50% or so, and others dim all the way to off. Again--how can you tell before bringing them home?
 
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Old 02-04-13, 09:00 AM
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Personally, I would be looking into separating lights onto different switches so you could turn off some but not all. May not work in your situation but I just have never been much into dimming lights.
 
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Old 02-04-13, 09:10 AM
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I believe all dimmers these days use some form of pulse modulation, basically turning on and off the power to the light many times per second. For a fully resistive dimmer, it would have to be much larger than what would fit in a single-gang box.

If I was outfitting a room or home with LED lamps, I would do exactly what I did when I decided to go with CFLs way back when. I purchased 4 or 5 different models, and tried each one. Brought back the ones that were way too green. Found the best one, and bought however many I needed.

I haven't seen any reviews online about dimmable LEDs and how dimmable they really are. I'll be curious if anyone has any experiences!
 
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Old 02-04-13, 10:16 AM
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Every dimmer I have seen uses a Triac that just varies where on the sine wave it fires on. If it were at the peak, you would get 50% power. So the PWM frequency is set to 120 Hz since most will fire the Triac on both the + and - side of the sine wave. The heat sink is only required when they are run at maximum rating. A triac switched on drops about one volt so at 5 amps you dissipate 5 watts.

Some LEDs will not dim because of the circuitry used to control the current. If a switching type current regulator is used they adjust to keep the current at a fixed value even if the input voltage is low or PWM. Some newer designs are looking for a PWM input and adjust the current to follow that PWM.
 
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