(It was on for an hour)
In: 2
Light bulbs produce light because you feed it electricity and the stuff inside them gets really hot and starts glowing. When you turn it off, it may not be getting electricity anymore but it still needs a minute to cool down.
A fancier version of what /u/mysticpolka said:
Everything in the universe emits “light” (electromagnetic energy) and the amount of light it emits depends on many factors including its temperature per the Stefan-Boltzmann Law:
https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law
Note the amount of light emitted depends on the 4th power of temperature, but this only applies if you use an absolute temperature scale like Kelvin or Rankine.
Most things we see in everyday life emit too little light for us to see, unless we heat them up so they generate more light (iron gets “red hot”, copper glows green, and so on)
As mysticpolka notes, tungsten, the material inside traditional light bulbs, takes a few seconds to cool down to where the quantity of light it emits becomes too small for us to see.
If it is a LED bulb, it may receive enough energy to glow dimly continuously through capacitive coupling when its wire is in proximity to another energized wire, similarly how an electrician’s screwdriver works only touching one end. This is more likely to happen if the switch is wired incorrectly to interrupt the ground wire. If you see bare LEDs, their phoshor may glow for couple dozen seconds because its purpose is to re-emit recieved light in another color, and it continues to do so very faintly.
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