The index of the realtime lightmap applied to this renderer.
A value of -1 (0xFFFF) means no lightmap has been assigned, which is the default. A value of 0xFFFE is internally used for objects that have their scale in lightmap set to 0; they affect lightmaps, but don't have a lightmap assigned themselves.
The index is 16 bits internally and can't be larger than 65533 (0xFFFE).
A lightmap is a texture atlas and multiple Renderers can use different portions of the same lightmap.
See Also: LightmapSettings class, lightmapIndex, lightmapScaleOffset property, ShaderLab properties.