How much Flux for wall sconces

jtr1962

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Nov 22, 2003
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Flushing, NY
I'm assuming here you're going for a mood light effect rather than trying to light the entire room. If so, then a few tens of lumens will be adequate. You can run superflux (pirahna) LEDs at 20 mA and still get long life (compared to 5-10 mA for indicator-type LEDs). At 20mA most commodity grade LEDs will put out 3-4 lumens. Maybe about 10 on a board with a driver circuit will be adequate. Use fat pcb traces to spread the heat evenly. The only downside is that it's harder to get consistent tints once you stop using power LEDs.

Another possibility is a power LED such as a Cree underdriven at perhaps 100 mA. You shouldn't need a heat sink. Again, use fat traces on the pcb to spread the heat evenly. At 100 mA you should get in the neighborhood of 30 to 35 lumens depending upon bin.
 

snarfer

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Feb 21, 2008
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Wow that looks really cool. I see why you wouldn't want heatsinks, but it does seem like that concept demands a fair amount of light.

If I had to implement that design as quickly as possible I would look at some of the products currently available for LED channel letter lighting. I believe they are designed to be run in enclosed areas with little ventilation.

Maybe something like this.
 

SemiMan

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Jan 13, 2005
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Do not use Piranha LEDS or any sort of 5mm LED. They are epoxy encapsulated and WILL degrade very quickly....the white ones at least.

I would suggest going with at a minimum something like a Nichia 1/2 watt, or moving up to a Luxeon REBEL or Cree equivalent. What color temp are you looking for? Nichia tends to have the tightest tolerance on bins even if they do not have the best efficiency and life. Luxeon tends to win in real world life, Cree on efficiency, Nichia on color control.

You will always need SOME kind of heatsinking with practically any LED, it is all in how you implement it. For a 1/2 watt Nichia, a double sided circuit board with 4 ounce copper and 1 square inch on both sides per LED should be enough as long as the board is not up flush against the fixture.

How much light is enough? Consider a 10 watt halogen directs (yes actually gets out of the fixture) about 150 lumens...that may be a good place to start. Even double that may be inline with what you are trying to achieve.

Semiman
 

blasterman

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Jul 17, 2008
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My vote is also for using a high powered LED such as the Cree or Luxeon and under-driving it.

The fixture here has it's aethestic appeal by nature of the light source bouncing off multiple flat white surfaces. This generally requires a brighter light source than you would think.

Orientation of the LED is also critical and require some fiddling for best effect. You probably want to use a bare/non-lensed emitter, and pointed more towards the front of the fixture.
 
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