The term for hot objects production of light is “black body radiation”
Anything above absolute zero will radiate some energy in the form of electromagnetic radiation. For very cold objects, it is very long wavelength and low intensity, barely detectable by even instruments. Things do this because of entropy, energy always seeks to be at the lowest energy level possible.
As atoms get hotter, the energy they release gets more intense and of a shorter wavelength. At a certain temperature (starting around 400C) that wavelength starts to get into the visible spectrum and we see it as light.
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