Why does infrared EM radiation feel warm on my skin, but blue or green visible light from an LED, even a strong one, does not feel warm on my skin?
If a bunch of people jump into a pool one by one, they're going to significantly shake up the water. If you get them to all jump in at the same time, you're going to have a decent amount of water ejected from the pool, and then it's no longer shaking. Or if you drop a car into the pool, same thing happens.
There is such a thing as too much energy. With atoms and molecules, the energy that causes jiggling is easier to absorb than the energy that causes significant changes like the ejection of an electron, or the changing of electronic states. What you feel as temperature is caused by the kinetic jiggling of the atoms and molecules you are in contact with. Infrared causes jiggling more so than blue light.
ignore this guy. its flat out wrong.
my sense is its to do with intensity. a toaster/oven uses >300 watts but leds are <10 I think.
might also have something to do with biology but thats not my field. high intensity visible/ultraviolet causes sunburns/cancer but you dont feel it.
This is simplified so much that it is almost bullshit.
The energy of high energy photons is high enough to be absorbed by electrons (UV).
Low energy photons carry only enough energy to thermally excite atoms, so each photon excites your skin thermally. UV photon energy is absorbed by breaking bonds, which does not generate heat but does cause cancer.
Well I doubt OP would understand the resonance frequencies of vibrational modes of organic compounds, because I barely understand that shit. But I think the analogy is good.
You don't know what you're talking about. it has nothing to do with intensity. A 300 W LED still wouldn't be hot. They make lamps like that to grow plants; it stimulates chemical reactions with chlorophyll and shit.
>Well I doubt OP would understand the resonance frequencies of vibrational modes of organic compounds, because I barely understand that shit. But I think the analogy is good.
woah you so smat
op never mentioned equal intensity visible vs infrared light, so relax dude. I think a 300 W visible would feel just as hot if not hotter than a 300 W infrared, but ive never tried. You wouldnt feel a 300 W uv light because its scrambling your fucking dna retard.
now piss off.
> I think a 300 W visible would feel just as hot if not hotter than a 300 W infrared
Infrared output and heat generation are synonymous, and a 60 Watt LED is not going to generate heat on the same order as a 60 watt incandescent bulb.
but its because your body is reflecting a significant fraction, not absorbing.
That is literally the same thing as saying the radiation doesn't cause a resonance in the vibration of the molecules your skin is made of.
How would you explain microwave radiation at the same frequency that a microwave oven produces? It will cause a measurable degree of resonance with the water molecules in your flesh, and cook you alive. it will get very hot. It's not because you're less likely to reflect the incoming light.
if youre not reflecting any visible light how can your eyes pick up the light that lets you see people?
the body contains more than just water and it tends to resonate at most infrared frequencies and reflects visible. thats why we evolved to see visible, not infrared.
white people reflect more visible you racist piece of shit.
pic related is why we evolved to see visible light, not infrared
But you're beginning to shitpost, so I'm sure this doesn't matter.
pic related is exactly what i said, we reflect visible and absorb uv/infrared, good job finding it.
i think weve answered ops question. microwaves are a quirck in the infrared coinciding with a rotational resonant frequency of water molecules. not a lot to do with ops question tho.
That's not the reason. And it ignores the fact that the index of refraction, and thus the speed of light, is a function of frequency for any real medium.
It's more standardized to write it this way, otherwise you might as well include the refractory index of water on that graph as well, and that's information overload.
In QM it's proper to use wavenumber because wavenumber space and position space are related through a Fourier transform.
In special relativity the speed of light in a vacuum is constant. In different mediums the speed of the photons will change but that's not the same thing as relativity's "speed of light" .
In Special Relativity, a change of coordinate system will leave the observed velocity of light unchanged. In a vacuum, electromagnetic waves propagate at the speed known as "c."
In other mediums, waves don't necessarily propagate at the same speed, and due to wave interference and such, the group velocity and phase velocity of a wave are also not the same. This is an important distinction that is almost never brought up.
Nothing about this violates SR. It's literally all just wave mechanics in a different medium than a vacuum.
Not entirely true. In the photon picture, you have to also consider a number of paths and their different interference. This is a complicated problem to write down in terms of quantum mechanics.
Watch both explanations in this video: