Lightmap
A lightmap is all the lighting data of each face. This light data is then applied additively to each face to produce the final lit effect. Especially common in BSP based engines, it's the method used for most lighting effects within the source engine.
Determined during the vrad compile proccess lightmaps are only applied to brush faces as models are lit differently. The lightmap's scale refers to the number of texture pixels per light pixel (luxel). Smaller values means more luxels, thus a better quality but larger BSP size and compile times. The lightmap resolution can be viewed within Hammer by altering the viewmode in the top right to lightmap. It can also be viewed and edited from the Face Edit Dialog on any normal face. Faces such as displacement maps calculate and use thier own lightmap scale, different values will often get reset by Hammer to match the displacements lightmap size.
