A lightmap is a pre-calculated texture used in computer graphics to simulate realistic lighting on surfaces and objects within a scene. The idea comes from 2 tenets:

  • Computing realistic lighting can be too expensive to be performed at runtime, especially when including light bounces
  • Most objects in a scene are “static” which means they won’t move and don’t need to have their illumination levels recomputed every frame

A lightmap is therefore an alternative to realtime lighting: highly expensive lighting computations can be performed ahead of time and stored in a texture. It is a common optimization as, instead of computing power, the resource used is computer memory which makes it a valuable alternative for CPU-bound games.