Lightmapping is the process of pre-calculating the brightness of surfaces in a Scene, and storing the result in a Texture called a lightmap for later use.
Lightmaps can include both direct and indirect light. This lighting texture can be used together with surface information like color (albedo) and relief (normals) by the Shader associated with an object’s material.
The data baked into lightmaps cannot change at runtime. Realtime lights can be overlaid and used additively on top of a lightmapped scene, but cannot interactively change the lightmaps themselves.
With this approach, we trade the ability to move our lights at gameplay for a potential increase in performance, suiting less powerful hardware such as mobile platforms.
Unity provides the following lightmappers for generating lightmaps:
For advice on setting up a lightmapper, see Lightmapping: Getting started.