What sets off light?

Electrons are excited by something, such as heat from an electric current. They jump to a new orbit around the nucleus. When then fall back to their normal orbit, a photon is released. The energy of the photon is determined by the particular atom and orbits, and that determines the wavelength (color) of the light.

That explains why, e.g., mercury vapor lights have a combined orange, blue and purple color that only appears white. See https://en.wikipedia.org/wiki/Mercury-vapor_lamp#E...

Maybe a physics expert can explain if there are other processes at work. I'm not sure how incandescence can generate the whole spectrum.

"What sets off light?"

Light is emitted by accelerated charges.

A timer - or a motion sensor - or a switch - or, if you want to turn it off, breaking the lamp.

Is this colloquially worded? "...sets off..."? What does this mean?