Comment by taejavu
18 hours ago
Forgive my ignorance - at what point does electromagnetic radiation not count as light? Because it seems obvious to me that since our bodies are warm, and heat is a form of EMR, then of course we radiate "light". But also, things that wouldn't be described as warm still do this - all matter in the universe emits EMR, does it not?
Would someone be so kind as to clear up my long-held misconceptions?
> at what point does electromagnetic radiation not count as light?
At the point when its wavelength is outside of visible range, roughly 380 to 750 nm. (Some experts will call (parts of) IR and UV radiation “light”, but that’s neither here nor there.)
> Because it seems obvious to me that since our bodies are warm, and heat is a form of EMR, then of course we radiate "light".
Of course, everything radiates, and everything radiates light if you heat it up enough (> 500°C, > 1000°F).
> But also, things that wouldn't be described as warm still do this - all matter in the universe emits EMR, does it not?
Yep, only things at absolute zero temperature truly do not radiate, and it’s impossible to get there.
However, afaiu, the study describes chemiluminescence, i.e. specifically radiation above thermal.
In my most recent trip through academic astronomy, not only do they say "visible light" early and often, radio astronomers refer to "optics" and "photons" and VLBI images are called "images" and not "maps".
It's not that wildly different from the 1980s -- even then I never heard anyone say something like:
> Of course, everything radiates, and everything radiates light if you heat it up enough (> 500°C, > 1000°F).
Like, literally, in an undergraduate class that I taught, one of the short-answer questions on the midterm was to ask what kind of light the teacher's hair emitted. The answer is, of course, infra-red light.
Emitting heat is obvious, well-known, and thus uninteresting. Humans do not see in the IR range, so the interesting thing is emitting light in the visible spectrum range. It also has various mystical / magical / religious connotations in the traditional culture for millennia.