LED's radiate heat, you can feel heat when you shine the BEAM on your cheek or upper lip from 100 lumens and over LED lights, because visible light contains a bit of heat energy, and LED's do emit a small amount of infrared. Am I correct?
LED's radiating heat
- Thread starter L.E.D.
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Oddjob
Flashlight Enthusiast
Yes indeed. That's why you hear modders talking about heatsinks, thermal conduction, etc. You'll feel the heat when holding certain lights on their highest settings as your hand helps conduct heat away from the light.
Totally different things here, I'm not talking about thermal conduction. I know how heatsinks work, that's besides the point. The point is the photons THEMSELVES, the light BEAM ---contains ENERGY, and that energy can transfer HEAT to objects regardless of wavelength,--- and is why you can feel heat from the BEAM of brighter LED flashlights, not talking about from the BODY of the flashlight. The LED is still radiating heat, just not as much in infrared as an incandescent. Let's say, theoretically, you took away all of the infrared being generated by a 1000 lumen incandescent, leaving absolutely no infrared in the spectrum, only visible remaining. You would still feel heat coming from the beam, due to the heat energy in visible light.
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Marduke
Flashaholic
Check your physics. By definition, light heat energy is infrared. Other frequencies are NOT heat. That is separate from certain frequencies which are able to interact with certain compounds to produce heat during interaction, but the electromagnetic energy itself is not heat.
Case in point: microwave radiation is not "heat", but it can react with water molecules causing them to vibrate rapidly, which in turns does emit heat. However the microwave radiation itself is not "hot".
The "heat" radiated from LED's is from a VERY small amount of IR in the beam. This is over a full order of magnitude smaller amount of IR than in an equivalent brightness incan beam. This is also very different than the heat conducted out the back of an LED.
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MrGman
Flashlight Enthusiast
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+1. The actual "light" output that is being radiated is not heat it is photonic energy waves. Enough of them when they hit a surface can cause that surface to get warm, but they are not warm themselves.
The sun which is 93 million miles away sends lots of photons across the energy spectrum at us. Those photons being absorbed into all the surfaces they hit cause things to warm up but they carry no heat with them through the vacuum of space from the sun. they are not hot.
But as we all know energy can be converted from a wave to heat.
Yes, I wasn't saying the photons themselves are "hot", but that when they interact wth a molecule, cause the molecule to heat. Back to the other question though, about the 1000 lumen incandescent with all infrared somehow filtered out. Would you feel no heat at all from the beam? Does visible light cause no heat at all?
Most pedantically, heat refers to thermal energy flowing from a warmer substance to a colder substance -- under this definition, EM waves of any wavelength are not heat, but are one mechanism for transferring heat. IR is no exception.
Heat is frequently used in a looser sense to refer to any non-flowing thermal energy, or to any means of heat flow. Under these looser meanings, IR may certainly be considered heat radiation, but visible light is equally heat, because visible light is equally effective for "heat" (pedantic sense) transfer.
I think the conventional association of IR as "heat waves" is probably because hot, but not incandescent, materials radiate heat only as IR, and even the hottest objects commonly experienced still radiate the vast majority of their heat in IR. But there's no physics basis for considering IR as "heat" and other wavelengths as "non-heat", and the effectiveness of visible light for heat transfer should be obvious with the prevalence of monochromatic and narrow-band sources today; think about burning things with (visible!) lasers.
Any wavelength that's absorbed by skin (including everything emitted by a white LED) will transfer heat, and since the LED emits almost entirely in the visible range, the heat sensed when you shine an LED light on your face is almost entirely due to the visible light; L.E.D.'s conclusion is completely correct.
Jarl
Flashlight Enthusiast
"Back to the other question though, about the 1000 lumen incandescent with all infrared somehow filtered out. Would you feel no heat at all from the beam? Does visible light cause no heat at all?"
Yes, you would feel some heat. Visible light carries energy, which can and will warm the surface it is absorbed by. IR simply carries more energy (E=HF, IR is a higher frequency than visible light)
Yes, you would feel some heat. Visible light carries energy, which can and will warm the surface it is absorbed by. IR simply carries more energy (E=HF, IR is a higher frequency than visible light)
Actually, IR is higher wavelength, lower frequency.
That's exactly what I thought, visible light will still heat objects. Thanks all, got what I needed to know. Looks like my choice of pyrex for the lance base was a good decision...
W00t. EXACTLY. Thanks for that as well.
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oldpal
Enlightened
Benson is pretty much correct here... it's the absorption of energy from the radiation whether its gamma rays, visible light, micro-waves or IR that sometimes gives rise to the heating of an object.
Marduke is the one who needs to check his physics here. Electromagnetic waves are not heat, even IR.
Hugh
Marduke is the one who needs to check his physics here. Electromagnetic waves are not heat, even IR.
Hugh
Marduke
Flashaholic
Except visible light is a couple of orders of magnitude less when it comes to transmitting thermal radiation. The VAST majority is in the IR wavelengths.
Easy experiment:
Take a P61 lamp and hold it 1/2" away from your bottom lip for 20 minutes. Repeat with the LD20 on turbo for approximately 20 minutes. Let me know what happens...
Easy experiment:
Take a P61 lamp and hold it 1/2" away from your bottom lip for 20 minutes. Repeat with the LD20 on turbo for approximately 20 minutes. Let me know what happens...
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Negative. Did some researching. The P61 just emits massive amounts of infrared. Even the encyclopedia says you're wrong: "That infrared radiation is a form of heat and other electromagnetic radiation is not, is a widespread misconception in physics. Any electromagnetic radiation can heat a material when it is absorbed."
A visible laser will actually burn an object quicker than an equivalently powered infrared laser, since the higher frequency, lower wavelength photons from visible light have more energy per quantum, a "magnitude" more in fact, in terms of "electron volts". Gamma rays are a little over a million electron volts... sexy...
darknessemitter
Enlightened
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Yeah, it looks like there are a lot of misunderstandings in this thread related to the term "infrared".
I'm not an expert on this, but I'll try to explain the little bits of it that I do understand.
Yes, any type of electromagnetic radiation can can be absorbed by matter, converted to heat.
[EDIT: It sounds like I got this paragraph pretty mixed up. Disregard it for now] Remember, heat is the movement of electrons as they orbit the nucleus. Faster orbit= more heat. The speed of electrons orbiting is obviously not the same as electromagnetic radiation, which is the the weird photon/particle-and-a-wave thing. Does that make sense?
[EDIT: The rest of this should be accurate]
Mid-range or Mid-wavelength infrared is the frequency range that we often associate with "heat", even though it is not literally heat. Increased heat generally causes matter to release energy in the form of mid-range IR, which is why mid-range IR can be used to detect differences in temperature (think "Predator" vision).
Near IR or Short wavelength IR is the closest to visible light and behaves somewhat similarly to visible light. This is the kind of IR that is often used to assist nightvision equipment, and the kind of IR that most remote controls use.
There's also Long wavelength IR, but I don't remember much about it... sorry, you'll have to google it or something
On incans: I think the reason incan beams feel hotter isn't necessarily because they give off more IR specifically (remember, not all IR wavelengths are the ones we associate with heat), but because they give off more overall electromagnetic radiation over a wide range of wavelengths, much of which we can't see, but we can feel.
Hopefully someone else who understands this better than me will post something soon...
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oldpal
Enlightened
This is clearly wrong. The heating of a substance has absolutely no effect on the presumed motion of "orbital electrons". You are confusing this with the increased motion/vibration of atoms in a lattice or molecules of a gas.
Marduke
Flashaholic
And they could shine the equivalant incan light on their arm and they would say "I have second degree burns"
Seriously, shine a ROP high and a P7 light on each arm, see what happens.
Marduke
Flashaholic
Approximately the same OTF lumens, so not really. Since the "visible" lumens are in the same ballpark, any differences can only be attributed to the difference in IR.
According to you, the visible light lower wavelength and with higher energy (which is correct) should be hotter, which is the P7. However, the energy level is only part of the story. Absorption is the other.
Back to conventional definition, thermal radiation is defined as .1-100mm wavelength. Hint hint, that's IR....
oldpal
Enlightened
Is it now?
Thermal radiation spectrum range: 0.1 to 100 mm. This is the radiation emitted by a hot body.
It includes some ultraviolet (UV) radiation and all visible (0.4-0.76 mm) and infrared radiation (IR).
From your own ref url.
Hugh
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