This page describes the behavior of a Light component when you set its Mode property to Realtime. These are also known as Realtime Lights.
Unity performs the lighting calculations for Realtime Lights at runtime, once per frame. You can change the properties of Realtime Lights at runtime to create effects such as flickering light bulbs, or a torch being carried through a dark room.
Realtime Lights are useful for lighting and casting shadows on characters or moveable geometry.