Basically, it transforms electricity from the really dangerous high voltage energy generated in a power station to something you can safely use in your home.
Now, the conversion of food energy is part of the great balancing act that is maintaining homeostasis, and one of its greatest tricks is cellular respiration.
This light immediately smacks into a subatomic particle, which absorbs it, converts a little bit of the energy into motion, and re-emits the light with a little bit less energy.
Because, that equation shows the rate at which energy is converted from electricity into another form of energy, such as heat, light, or mechanical power.