LEDs have hot beam?

So far I have thought that leds have a "cold beam" i.e. they don't emit infrared. Now I sensed some heat coming from my (unmodified) P1D-CE (2 other crees also). Am I going crazy, or what is going on here? Sensation is definitely more faint than in incands, but its there.
:huh2:

Sorry if this is an old subject but I couldn't summon proper search words.

It might not be the LED that's 'emitting' IR; it might be waste heat from the led radiating out. It's a subtle distinction that doesn't mean much

I've also felt heat coming from the beam of my L1D-Ce, only faint but it's there..

I'm currently working on a four-Cree home-made, and when I power up those four Crees at 1000 ma each, I can definitely feel heat in that beam when I place my hand within four inches of the diodes. This is with just the LED's on the heatsink - no optics, and I can feel that heat immediately upon application of power - before the heatsink gets warm, so it's definitely coming from the LED's.

Edit: Four Crees at 1000 ma each are probably giving me not too far from 800 lumens, and there's only a wee bit of heat felt, and that only a few inches from the source. Now, try that with an incan bulb putting out 800 lumens, and you'll really feel some heat! If there's any IR in the output spectrum of the Crees, its certainly very, very small.

Edit: Four Crees at 1000 ma each are probably giving me not too far from 800 lumens, and there's only a wee bit of heat felt, and that only a few inches from the source. Now, try that with an incan bulb putting out 800 lumens, and you'll really feel some heat! If there's any IR in the output spectrum of the Crees, its certainly very, very small.

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That much heat is probably just from the visible light itself being absorbed by your hand and thus heating it up -- your multi-emitter combo is probably emitting a few watts just in the visible wavelengths. In order for an incandescent to produce as much visible light, it would need to be running at a much higher wattage -- and most of that excess waste will be thrown out the front, as opposed to building up inside the body.

I feel heat from my Amilite Neo T5 as well.

You dont really feel the IR radiation.
You feel your skin warming up.

Its just a matter of energy output.

Extreme example: get an argon-ion laser. Doesnt output any IR at all. Try aiming it at your hand...

And btw: "hot beam" and "cold beam" are really really ambigious classifiers. Because in my understanding, most leds have very hot beams (high colour temperature).

IMSabbel said:

You dont really feel the IR radiation.
You feel your skin warming up.

Its just a matter of energy output.

Extreme example: get an argon-ion laser. Doesnt output any IR at all. Try aiming it at your hand...

And btw: "hot beam" and "cold beam" are really really ambigious classifiers. Because in my understanding, most leds have very hot beams (high colour temperature).

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Well, you could always say "you don't really feel a propane flame, you just feel your skin heating up." The effect is the same, of course. But, yeah, enough energy in any part of the spectrum can burn a hole in you. The light from LED's can still warm your skin even without a high IR content. That's one reason why I love LED's so much - I like as much of my hard-won output to be in the visible spectrum as possible.

Nocturnicus said:

Well, you could always say "you don't really feel a propane flame, you just feel your skin heating up."[...]

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If I point my L2D at a Crookes radiometer, it will make it spin. Does that mean the Cree is throwing heat out the front? I dunno...

I know my Mag '74 makes it spin a whole lot faster.

Ty_Bower said:

If I point my L2D at a Crookes radiometer, it will make it spin. Does that mean the Cree is throwing heat out the front? I dunno...

I know my Mag '74 makes it spin a whole lot faster.

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It means that it's delivering enough energy to heat the black surface of the radiometer's armature more than the white surface, causing a tiny little movement of heated air, and thus the rotational reaction. A perfect analogy of what a previous poster said - radiation in any part of the spectrum can be converted to heat energy. Cool - that's something I never thought of: aiming my LED's at my radiometer. I'll try that, just for fun.