Bulb

A bulb is a round object that is filled with electricity and can produce light when it's turned on. Inside a bulb is a metal filament and when electricity is passed through it, the filament heats up and produces light. Bulbs are shaped this way so that it does two things: it spreads the light in all directions, making it brighter in the areas close to the bulb, and focuses the light, making it brighter in one specific direction.