Lightmaps

Lightmaps are textures that store precomputed lighting information for 3D scenes. They are used to achieve realistic shading, soft shadows, and ambient lighting effects while keeping runtime rendering costs low. A lightmap typically contains color data representing the amount of light that reaches each surface point, and may be combined with other shading data during rendering.

Creation and application involve a baking process. The 3D geometry is unwrapped into a separate lightmap UV channel that lays out surfaces in a texture space without overlap. A global illumination calculation—historically radiosity, and more recently ray tracing, path tracing, or photon-based methods—computes the indirect lighting and shadows for each texel. The resulting color values are saved into a lightmap texture. At render time, the engine samples the lightmap using the surface’s lightmap UVs and multiplies or combines the result with the surface albedo to produce the final shaded color.

Lightmaps excel for static or largely static scenes, where lighting does not change over time. They reduce per-frame computation by transferring complex lighting into a precomputed texture. However, they impose limitations: dynamic objects may appear inconsistently lit, re-baking is required when geometry or lighting changes, and lightmap resolution must be managed to avoid visible tiling or blurring. Also, seams between lightmap texels and compression artifacts can affect image quality.

Modern pipelines often combine lightmaps with other techniques such as dynamic lighting, ambient occlusion maps, and global illumination caches. They are widely used in games and architectural visualization to deliver high-quality lighting with controllable performance.