Question

Why metals emit light when heated to high temperature

Answer 1

The higher the temperature, the faster the atoms/
molecules in the object are (T ~ v2), thus more energetic
collisions
More energetic collisions cause more sudden
accelerations/decelerations of the electrons in the
matter, thus light with shorter wavelength (higher energy)

Answer 2

When an electron goes from a high energetic state to a lower one, it emits a photon that we see as light. Higher temperatures cause some electrons to move to a higher state due to the increase in their kinetic energy. These higher states are unstable and so the electron will quickly move back to a lower state, releasing a photon and thus "light is emitted."

Answer 3

Thermionic emission