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Old 15th April 2011, 12:53 AM   #1
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Default LED lighting - what's with the huge heatsinks?

As someone who has always been interested in lighting, I've been following the evolution of LED-based home lighting for several years now and am considering buying a couple bulbs (if they can be called that) to see how they compare to the incandescent and CFL lights we have here.

Several great advantages for LEDs: run very cool; use even less power than CFLs; no mercury; and last a looooooong time.

But I am rather put off by one aspect that looks like it will interfere with the dispersion pattern of the light they produce: their heatsinks.....large heatsinks in many cases.

Couple of examples:

40 watt equivalent indoor bulb

Not worried about dispersion with this one, but read on.....

Outdoor flood - the outerbody is all heatsink! And, these types are heavy too, heavy enough I worry about them possibly damaging the socket or mounting hardware.

Why would something touting itself as being so energy efficient use something to get rid of what seems to be a lot(?) of heat, which is obviously waste energy?

Btw check out this beautiful skyscraper in Malmo, Sweden lit by white LEDs: Turning Torso
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Old 15th April 2011, 01:26 AM   #2
tomchr is offline tomchr  United States
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Well... If you figure the energy consumption of a 50 W equivalent LED bulb is roughly 7~9 W, even at 90~95 % efficiency, upward of 1 W of heat will be produced. Of course, that's nothing compared to the 45~47 W of heat produced by a conventional 50 W bulb, but still. It's an amount of heat that needs to be gotten rid of. So the LED bulbs have some heat sinks. For spotlights it's not much of an issue. For globe-style lights, it may be... That would depend on your application.

Funny you should bring up Turning Torso. A friend of mine lives there and I got to visit a couple of years ago. That's a very nicely designed building. Especially the lighting design impressed me. They've also done a lot of stuff to reduce the energy footprint -- for example motion detectors in the parking garage so the light is only on when you need it to be. That's certainly something I wish they'd bother to do in the US.

With LED bulbs, I suggest buying a name brand bulb. I've had really bad luck with the eBay cheapos. You get what you pay for (DUH!). The Philips one I got for my reading lamp 2~3 years ago set me back about $30 (it replaces a $5 GU-10, 50 W bulb) or at least 6x the cost of the eBay cheapos. But the light is actually of a reasonable color temperature (warm-ish) and not the 9000 K you get from the cheapo bulbs. I have noticed that the prices have come down quite a bit. Now I can get the same bulb for $10~15.

~Tom

Last edited by tomchr; 15th April 2011 at 01:29 AM.
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Old 15th April 2011, 01:43 AM   #3
djQUAN is offline djQUAN  Philippines
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Quote:
Originally Posted by tomchr View Post
With LED bulbs, I suggest buying a name brand bulb. I've had really bad luck with the eBay cheapos. You get what you pay for (DUH!). The Philips one I got for my reading lamp 2~3 years ago set me back about $30 (it replaces a $5 GU-10, 50 W bulb) or at least 6x the cost of the eBay cheapos. But the light is actually of a reasonable color temperature (warm-ish) and not the 9000 K you get from the cheapo bulbs. I have noticed that the prices have come down quite a bit. Now I can get the same bulb for $10~15.

~Tom
Yes. And with cheap white LED's, the Phospor deteriorates rather quickly and the bright white light will turn into dim bluish light after a few 1000 hrs run time based on experience. Better LED's show little to no deterioration after prolonged use.
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Old 15th April 2011, 01:46 AM   #4
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I think it's also an issue of area. The actual emitter is very, very small, and frequently covered with a silicone lens. Now if you mount it on a circuit board (insulating fiberglass) you really don't give the heat anywhere to go.

...Which is why high power LEDs are frequently mounted on thick metal core boards, which then need to be put on some sort of sink just to get the heat away. Also, that sink is probably also dropping heat from the ac/dc converter and regulator, which on replacement lamps is on board.

Here's my bike light--obviously diy (ugly!). It uses 2x Cree MC-E (emitter has 4 dies per chip, so the light is effectively 8 LEDs) attached to a 22v LiPo hobby battery. On the "medium" setting I sometimes get cars flashing their high beams at me. I used thermal epoxy to attach the boards to copper pipe ends and then mounted RC motor sinks around the assembly. Stays cool at all but the highest setting.
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Old 15th April 2011, 01:56 AM   #5
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Default led dazzlers

hi
greetings read SILICON CHIP AUSTRALIA schematic can be downloaded even though its online payment just double click on image and slide show starts then
download
thanking you
andrew lebon
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Old 15th April 2011, 02:02 AM   #6
djQUAN is offline djQUAN  Philippines
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Quote:
Originally Posted by spopepro View Post
Here's my bike light--obviously diy (ugly!). It uses 2x Cree MC-E (emitter has 4 dies per chip, so the light is effectively 8 LEDs) attached to a 22v LiPo hobby battery. On the "medium" setting I sometimes get cars flashing their high beams at me. I used thermal epoxy to attach the boards to copper pipe ends and then mounted RC motor sinks around the assembly. Stays cool at all but the highest setting.
you should try running HID
HID Bicycle Light
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Old 15th April 2011, 02:20 AM   #7
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I believe the efficiency is now just about 50% which means the high power ones
need a lot of heat sinking.
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Old 15th April 2011, 11:11 AM   #8
marce is offline marce  United Kingdom
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The reason is to limit deteriation at the PN junction, when you do LED strip lights they are generaly done on an aluminium clad PCB to remove the heat. Without removing the heat you would not get anywhere near the 50000 hours they advertise for LED lighting.
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Old 15th April 2011, 11:29 AM   #9
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The LED itself is dereated at temperatures above 25C. Modern drivers are small 3mm IC's with minimal heat tolerance, maybe 600 odd mW unless its one of those with the copper bottom. The rest of the circuit is a mosfet (the cause of most of the driver's heat, normally aproaching 70C), an inductor dissipating heat etc... The current design I'm working on wastes about 1.7W between the wall socket and the LED. Outputing 12W, and doing well over 1000 lumens. It is twice as bright as a 15W CFL I have for comparison

Now when you deal with the small formfactor of a retrofit bulb, you have a 2W heater stuck in a sealed 1" diameter tube.... This alone requires quite a heatsink, as the temperature is added to the temperature caused by the LED. On a sink of about 4"x4" with 6, 1 inch high fins the LED (isolated from the driver) easily adds 25C above ambient. At 75C on the current LED I'm useing, you throw away at least 10% of light output due to derating.

Also the little sealed tube contains electrolytics which have lifespans reduced faster the hotter they run by quite a factor. So you on the one hand want to promise guarantee long life, as is expected from an LED, but the driver would be an achiles heel in terms of life expectancy.

Efficiency on the driver I'm working on is in the low 80% region.

Bicycle ligting tend to use more efficient step up dirvers, but have lenses with about 25 degrees diffusion. The LED I talked about has a 120 degree dispersion. Soure you don;t have as much light "wasted" on walls but working surfaces etc receive more light.

Here is the driver the big one is the previous prototype, the small one the current, the inductor and mosfet is on the other side of the board.
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Last edited by digits; 15th April 2011 at 11:38 AM.
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Old 15th April 2011, 03:24 PM   #10
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Default led dazzlers

schematic
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