A Terrain Lighting file has no header and contains an array of zone lighting blocks. The zone map controls the layout of these blocks in world space but Battlezone uses row-major order starting at the southwest corner of the map.
When terrain is loaded without a LGT file, the game computes new terrain lighting based on the sun direction, terrain vertex normals, and terrain occlusion. External tools can modify the LGT file to improve quality and the game will use the modified version.
Each zone height block is a 128 by 128 array of lighting entries in row-major order starting at the southwest corner of the zone. Successive entries in a row are at increasing X positions (west to east). Successive rows are at increasing Z positions (south to north).
Each lighting entry is an unsigned 8-bit value representing the light level at that location. Zero represents minimum lighting (25% brightness due to ambient light) and 255 represents maximum lighting (100% brightness).