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  1. #1
    Slothful dirt hippie
    Reputation: verslowrdr's Avatar
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    Mar 2004
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    Thanks- and stupid Q on Cree Q5 bulb

    Just wanted to thank everyone for recommending the Fenix L2D-Q5. I used it on my helmet as a backup last night while out running my 3 dogs on a sled, and it works SUPER. Always nice to see if that's a deer, elk, or a cougar ahead of us while out in the middle of absolute nowhere....

    I've posted on a sled dog board about the flashlight and the bulb itself since this may be an item of interest to other mushers. Someone asked about heat sinking these Q5s: do they generate more heat than the Luxeon bulbs, less, or about the same? He was referencing the huge heat sink in the Princeton Tec Apex headlamp as comparison.

    I had no idea about the relative heat generation between these bulbs so I volunteered to ask you fine mtbr experts and report back.
    "...Some local fiend had built it with his own three hands..."

  2. #2
    GMF
    GMF is offline
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    Quote Originally Posted by verslowrdr
    I had no idea about the relative heat generation between these bulbs so I volunteered to ask you fine mtbr experts and report back.
    The short answer is that the better the LED, the less heat it generates. For a given amount of power that you put into it (say, 3 watts), more of that input power is turned into light, and less is wasted as inefficient heat.

    So specifically for your examples, a Q5 Cree will generate less heat than a first generation Luxeon LED both consuming 3W (or whatever) of electricity. I don't know the real numbers, but ballpark would be that a luxeon might convert 10% of that 3W into light (~100 lumens), leaving 2.7W as heat, while the Q5 Cree might turn 20% of that 3W into light (~200 lumens), leaving 2.4W as heat. So you can see that twice as much light does not equal half the heat.

    Having said that, you can run a bright LED really hard and obviously make it hotter that a poor quality LED run very easily.

    I hope that made sense and helped...

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