A way to bake lighting into textures for the meshes that are in your scene. If you want to lightmap your scene, each mesh must have a light map channel. A light map channel is a uniquely unwrapped UV texture coordinates for a mesh. No two surfaces can overlap or share UV space because the light map determines what faces are lit/unlit. If they were to overlap or share space, then a face that may not be lit could appear lit accidentally. The light map channel in Unreal Engine is UV channel 1. Channel 0 is used for all other uses.
All UV’s for light maps are placed into an atlas texture together and brought in over top of the world. You can see this atlas texture under Lightmass → Lightmaps in World Settings.
Light map resolution determines the lighting/shading quality given to each mesh. Go to details panel → Lighting → Override Light Maps to enter a new value. Use power of 2 values. Different objects can have different light map resolutions.
View lightmap density by going to Lightmap Density in view modes:
Higher resolutions appear yellow → red, lower resolutions are closer to blue/green.
The statistics window is another method to look at optimization and performance. You may use it to quickly determine which lights/meshes are the most expensive and make alterations as necessary to achieve your performance goals.
