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  1. L

    Five technical questions about LEDs in general

    Thanks for that tip. I always knew about lm/w but it never occurred to me to compare it to theoretical efficacy limit to calculate thermal efficiency - but now that I think about it it makes perfect sense. So, if I were to look at an XM-L at max current (3A), we have 100lm/w (as per cree...
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    Five technical questions about LEDs in general

    Thanks to everyone for the replies so far. This one was particularly useful because of the answers to question #5 - I checked all the LEDs listed and although they do indeed make arrays with up to ~9000 lumens, none of them are better than the cree in terms of lumens per unit cost, at least...
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    Five technical questions about LEDs in general

    Hope this is the right subforum. I have some generic questions about LEDs in general. Here they are in no particular order: 1. How much of the input power to an LED is lost as heat? For example, take a Cree XM-L running with 10W input power (3.2V x 3.0A). How many watts are actually dissipated...
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    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    Ahh, you seem to be familiar with Malta... Been here before on holiday by any chance :wave:? There is no cree distributor, and no one who sells the kind of high-power flashlights CPF thrives on. In fact the only reason I actually learnt cree exists was because I saw some flashlights on eBay...
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    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    Shoot. It'd cost $15 for one LED and another $30 to ship it to Malta from digikey... though shipping comes free for orders of over $100 apparently.
  6. L

    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    Ahh, now we're talking. 4000 lumens for a unit price of about €13... the problem, like you said, is that there are none for sale on ebay or DX or KD. I found some on another site with a unit price of €12.60, but to get one, the shipping would cost an additional €20! :sick2: But to order a lot...
  7. L

    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    LED drivers are really not a problem for me hehe. I have a couple of combination buck/boost and adjustable constant current supplies. I've also got an inverter so if it runs on 240VAC it would be good too! The only things I can't run are those 50 watt LED arrays that need a 35V forward voltage...
  8. L

    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    Thanks for the replies so far. I don't have any particular application in mind. At most I would be using the LED as an emergency backup to light up the room when there's a powercut. I've found that for high power emitters it's hard to beat HID / metal halide based on price per lumen. But then...
  9. L

    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    I checked the prices and they're not much better than the XM-Ls. An XM-L on ebay costs about €7 and gives 1000 lumens. A 15W bridgelux is almost €30 and only gives 850 lumens. However your post reminded me that there are cheap (ish) no-name LED arrays. Something like 5000 lumens for €25 or so.
  10. L

    What ar the most efficient and (separately) cheapest LEDs available at the moment?

    By efficiency, I mean lumens per watt for a high power LED (the kind used for flashlights) Last time I checked itwas the CREE XM-L U2 - but has anything better been released into the market? Secondly, which is the most cost-efficient high-power LED in terms of lumens per dollar (or euro)? I...
  11. L

    No real benefits to overdriving XML

    Walterk - interesting theory. I've tested an XM-L stuck to a heatsink designed for an Intel Core i7 CPU (130 Watts) that barely got warm, and using my eyes to judge, I noticed an obvious increase in brightness from 3A to 4A but no significant increase on going from 4A to 5A so the absolute...
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    Odd XM-L failure upon startup when overdriven to 4A (in-rush current?)

    So it looks like the cure could be to first turn on the supply, and then connect the LED (or set the supply to 3.5V voltage limit and 3A current limit). P.S. Can someone please answer my questions about LEDs turning "blue"? Thanks!
  13. L

    Odd XM-L failure upon startup when overdriven to 4A (in-rush current?)

    When you say "went pop", what kind of failure mode are you referring to? Blown wires, burnt die? In reply to another poster, I did notice the yellow die had darkened considerably in the vicinity of the place where two of the three bond wires connect to it. P.S. Sometimes on CPF you hear people...
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    Odd XM-L failure upon startup when overdriven to 4A (in-rush current?)

    LED was purchased pre-soldered to the PCB. I have a cheap ebay-bought infrared thermometer. I basically lined up the measuring hole of the IR thermometer directly above the LED dome, about 1cm away from the LED, and pulled the trigger. Putting my fingers on the LED board seemed to suggest no...
  15. L

    Odd XM-L failure upon startup when overdriven to 4A (in-rush current?)

    I recently bought a CREE XM-L T6 with the intention being to do some maximum power testing (i.e. see how much it could take before something broke). Setup: The LED came pre-soldered to a 16mm round board and I stuck the board to a Xigmatek Dark Knight (pics of heatsink here) with thermal...
  16. L

    No real benefits to overdriving XML

    Regarding running LEDs at very cold temperatures - there's a very easy way to do it. Very very easy in fact. All you need is a thermoelectric cooler (T.E.C.), also known as a Peltier cooler. If you've never seen one in action, you'll be amazed. I have two of them. It's basically a flat plate...

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