Led Temperature

Discussion in 'General Electronics Chat' started by BrainFog, Jul 16, 2012.

  1. BrainFog

    Thread Starter Member

    Jan 24, 2011
    Hello everyone, sorry for not being around much but I have been busy studying and haven't managed to get involved in my electronics hobby much.

    Recently I have been playing around with a high power LED I know a fair amount about LEDs but have no experience with high power ones. I have gotten myself a simple 10w 9-11v LED on ebay. Seeing as I wish to build a light which will last, a small grow light for my aquarium, I know I will need to keep it cool. I was actually surprised at how much heat it gave off at only 300ma It is rated for 900ma. Still the light it gives off is very high so I am happy. For my experiments I have been using an LM317T as a current limiter from a 12v SMPS power source. I only plan to use the LED at about half current to extend its lifespan.

    Currently for my tests I am using a heat sink taken from a pc power supply which works well but after about half an hour at only 300ma the heat sink gets too hot to touch for more than about 5 seconds.

    I have found no clear answer to this using google. What sort of temperature should I be aiming for in order to gain maximum lifespan from my LED?

    Thank you
  2. bertus


    Apr 5, 2008

    In the datasheet of the led there should be a derating curve that shows the expected lifetime at certain temperatures.

  3. #12


    Nov 30, 2010
    The heat sinks in computers are usually made for forced air flow. Perhaps the fins are too close together for convection to work properly. The same size heat sink with wider spacing might work a lot better without a fan.
    strantor likes this.
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    You must use a bigger heatsink.. Its insufficient. Plain and simple..

    Rule is.."cooler the better" to maintain is lifespan/luminous flux..
    In general keep junction temp below 80 deg C.
  5. takao21203

    Distinguished Member

    Apr 28, 2012
    Use a VGA cooler. Costs $3, runs from 12V.

    Use a Diode to drop 1V. Or a small resistor (10 Ohms or 22 Ohms for less brightness). These will also get hot. And experts on the forums here don't like diode as voltage dropper. So, use a power resistor...

    And you have to screw it tight to one corner of the VGA cooler. But no problem!

    Small electronic 12V transformers can often be adjusted. So, you would not need current limiting elements.

    I have my 10W LED running for months now, as reading light and for computer keyboard. No detoriation.
  6. Markd77

    Senior Member

    Sep 7, 2009
    The cooler the better, but from the description I would say it is running at 60-70 C which is probably not too bad. Of course, if we ever have a warm summer, the LED temperature would be higher.