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 spect

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.