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Old 15th April 2011, 04:12 PM   #11
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High power LED driver running directly off universal mains voltage, i.e. 85 to 265VAC
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Old 16th April 2011, 03:19 AM   #12
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Originally Posted by tomchr View Post
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.
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The LED itself is dereated at temperatures above 25C. Modern drivers are small 3mm IC's......
Tom and Digits, thanks for the thorough explanations. I didn't realize these LEDs required such elaborate circuitry i.e. I figured they at most they would use some type of simple diode system to provide the LEDs with a DC power source so they wouldn't have a 30Hz flicker (which would be really irritating).
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Old 16th April 2011, 03:21 AM   #13
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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.
Didn't know this, but makes sense: around 2003 I bought an LED nightlight and after a year or so, realized it was rather blue instead of the icy white it started out with.
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Old 16th April 2011, 03:32 AM   #14
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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.
Nice! Coincidentally, last week I was checking out headlamps at an outdoor retailer for a new trail bike I'm considering buying and made the mistake of looking into the business end of the lamp while I quickly hit the power button on, then off. That was a really stupid thing to do - had spots in front of my eyes for five minutes after. I guess I'm still used to the "gentle" LEDs I experimented with back in my analog electronics college course back in '87 (in my microprocessor class the next semester, I was given one of the "fast" Heathkit/Zenith trainers to work with: the Motorola 8 bit processor was now working at a fiery 1 mHz! Yes, that's ONE megahertz ).
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Old 16th April 2011, 03:35 AM   #15
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Btw I realized several of you guys (and women?) seem to be building LEDs almost from scratch. How "stripped down" can you buy an LED?
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Old 16th April 2011, 03:56 AM   #16
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Fun factoid: not exactly related to this discussion - this is definitely old tech - but one of my favorite kits I ever made was Radio Shack's neon bulb "Goofy-lite" in their soldered P-Box series:

RadShak 1979 catalog - flip to page 136 (this was nearing the end of this series of kits, so earlier catalogs featured more kits and more detailed descriptions)

List of most P-Box kits, including the Goofy-Lite, along with schematics and manuals

Anyway, I wired my Lite using the random option - the manual wasn't kidding when it said it made for a mesmerising sight, especially at night. I'd say the flash rate for each bulb was about twice a second. Batteries lasted a long time, probably because of the high voltage nature of the circuit.

I would have kept this kit but during a move to a new house, most of my electronic kits, including all of my P-Box kits (nine IIRC) were accidently thrown away. I also built that 3 channel color organ pictured on the opposite page, along with the shortwave and AM radios on the other page. I still own the radios and both still work.
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Old 16th April 2011, 05:31 AM   #17
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Btw I realized several of you guys (and women?) seem to be building LEDs almost from scratch. How "stripped down" can you buy an LED?

You get them loose, here is my sample of the new Cree LED that was anounced at the end of Feb, not available commericialy yet. Absolutely stunning colour rendition, and very strong output.
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Old 16th April 2011, 06:43 AM   #18
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You get them loose, here is my sample of the new Cree LED that was anounced at the end of Feb, not available commericialy yet. Absolutely stunning colour rendition, and very strong output.
That is an AWESOME LED. 4000 lumens at 85oC that is just insane (especially since it is Cree (and not some no name Chinese company) which means it is likely a true 4000 lumens (or atleast close to it).

For white LEDs name brands are better (you can get specific color codes so they will always match), the last longer, are more efficient, etc. For example, for years chinese companies were releasing white superflux LEDs (also called Piranha LEDs) which were 5-chip 100mA white LEDs. This is a form factor that is square with four leads very commonly used in automotive lighting and what not because the legs allow for more efficient heat transfer. The white LEDs produced around 1-2 lumens (not bad at all for that time period), but color consistency was crap and they died easily. Then Cree comes along with their P4 piranha LEDs in white, bam 4-7 lumens at 35mA. More recently in comes Nichia with their new white superflux which puts out ~21Lumens at 50mA. These are still low power LEDs which mean NO heatsink at all and just a few is capable of lighting the inside of a car pretty well.

As for getting LEDs, yeah you can purchase them loose or in the case of high powered LEDs you can purchase them loose or mounted to a board/star. Such as like this: $9.80 - XMLAWT 1000-Lumen LED Emitter White Light Bulb (3.0~3.5V) - Flashlight Parts and Tools . To give you an idea of the output of that LED 1000 lumens is a rough equivalent to a low beam halogen headlight bulb (thought the halogen bulb outputs the light in all directions, this is very directional).

Lastly, why the huge heatsink? LEDs do NOT like high temps, most prefer the die to be kept below 125oC. Additionally, they produce a relatively large amount of heat (1W or more) from a die that is roughly 1mm or so on a side. That heat can cause a rapid T spike which causes thermal run away and then a dead LED.
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Old 16th April 2011, 01:48 PM   #19
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Stage lighting is using a lot of led fixtures nowadays.
Hard white or infinitely colour variable versions abound and it is quite amazing how much light these put out !.
A company I work for has a huge Barco modular led tv system... based on 4 colours of 1/8" leds spaced 10mm apart and this thing will still give a useful image with afternoon direct sunlight on it....at night time from a distance the overall brightness is dazzling.

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Old 16th April 2011, 05:06 PM   #20
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The LED I posted is rated to use about 42V at 270mA = 11.34W, although it can handle up to 1000mA with derating of lifespan. They are run from constant current drivers to extend lifetime. Aslo current is sensed to adjust for temperature increases.

They come in 4 flavours, a 3000k and a 5000k, and within those two you can choose between a higer output one (about 1300lm) or a higher colour rendering index which does about 950lm, I think as long as you get about 100lm/W you are in good company. I wouldn't trust any of the noname brands with this stuff though.
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