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Thread: why does IR LED become hot to the touch

  1. #1
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    Default why does IR LED become hot to the touch

    I bought a 3V IR led and when I tested it the LED becomes hot to the touch and i thought it was my hand that was hot but it wasn't. Is it normal for it to become hot to the touch?

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    Default Re: why does IR LED become hot to the touch

    Just because we can't see IR doesn't mean it's not emitting light/heat. Point a video camera at it and you will see it.

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    Default Re: why does IR LED become hot to the touch

    IR is more heat than visable light, that is why your supposed to be carefull with exposing your eyes to it.

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    Default Re: why does IR LED become hot to the touch

    Quote Originally Posted by VidPro
    IR is more heat than visable light, that is why your supposed to be carefull with exposing your eyes to it.
    Well, both IR and visible light can heat things up -- take a bright enough visible LED, and focus the light from it on your skin and you'll feel the heat just from the visible rays being absorbed.

    The reason IR is potentially bad when talking about lasers or IR LEDs is that your eyes may be exposed to intense levels but you won't be able to tell -- no sensitivity to IR means there's no blink reflex.

    I bought a 3V IR led and when I tested it the LED becomes hot to the touch and i thought it was my hand that was hot but it wasn't. Is it normal for it to become hot to the touch?
    Do you mean you feel the heat radiating from it, or that the LED itself is hot to the touch? Keep in mind that in any LED there will be some inefficiency, meaning some of the electricity you put in will go into heating the LED itself, rather than radiating out. Higher-powered LEDs require heatsinks for this reason.
    Last edited by 2xTrinity; 04-13-2007 at 02:27 AM.

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    Default Re: why does IR LED become hot to the touch

    I guess your LED gets hot because you are overdriving it, which means that it's carrying too much current and dissipating a lot of power. What kind of driver are you using? You mention that it's a 3V IR LED, but LEDs require a current, not a voltage, to avoid being overdriven.

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    Default Re: why does IR LED become hot to the touch

    bandwidth of light

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    Default Re: why does IR LED become hot to the touch

    Quote Originally Posted by Bertrik
    I guess your LED gets hot because you are overdriving it, which means that it's carrying too much current and dissipating a lot of power. What kind of driver are you using? You mention that it's a 3V IR LED, but LEDs require a current, not a voltage, to avoid being overdriven.
    I'm using 3V from 2 AA then 2 AAA and both of them caused the LED to be hot to the touch. Would there be a resistor in the LED?

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    Default Re: why does IR LED become hot to the touch

    Quote Originally Posted by rivethead147
    bandwidth of light
    Do you mean wavelength? If so, then I believe that is why IR light creates significant (comparitively) amounts of heat.

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    Default Re: why does IR LED become hot to the touch

    *
    Last edited by macforsale; 08-28-2007 at 09:58 AM.

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    Flashaholic* 2xTrinity's Avatar
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    Default Re: why does IR LED become hot to the touch

    Do you mean wavelength? If so, then I believe that is why IR light creates significant (comparitively) amounts of heat.
    The heating is only dependent on the power/amplitude, not on the wavelength. One watt of IR will heat up a black object as much as one watt of visible light. Then there's the issue of waste heating of the LED itself (rather than heat projected in the beam), that has to do how efficient your LED is, and how hard you're driving it. Greater efficiency means less waste heat. I believe IR are usually the most efficient LEDs, followed by blue.

    However, driving an LED harder than recommended specs causes efficiency to go down, and temperature to go way up -- potentially damaging the LED, especially if it isn't heatsinked. Also, if an LED heats up, its resistance starts to go down, and it will draw more and more current until it burns out -- this is called thermal runaway. One thing to keep in mind is that with LEDs, small changes in voltage lead to big changes in current. Supplying an LED with a certain voltage is not sufficient -- instead, test out the current going to an LED with a multimeter, and wire in a resistor to reduce to the current as needed (do a google search for LED resistor caculators to find out which value is needed). Also, I'm not sure what sort of LED this is, but I'd also recommend attaching this to some sort of copper/aluminum heatsink if possible.
    Last edited by 2xTrinity; 04-14-2007 at 12:07 PM.

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