Why are second UVs important for lightmaps?

• A. They prevent lightmap texture overlapping and ensure proper light baking.
• B. They store color data for textures.
• C. They determine the object's physics material.
• D. They control the object's animation timeline.

Answer: (A)

Second UVs are the coordinates the lightmapper uses to lay out baked lighting on a mesh. They’re a separate UV channel from the one used for color textures, so the light data can be packed into its own atlas without distorting albedo or detail textures.

Providing a dedicated, non-overlapping UV layout lets the lightmapper map each surface correctly to the lightmap texture. This prevents different parts of the model from sharing the same texel in the lightmap, which would cause incorrect lighting, seams, or bleeding after bake. Proper texel density and island separation ensure accurate, artifact-free baked illumination across the entire model.

In short, second UVs give the lightmapper a clean, independent layout to bake lighting into a texture, which is essential for correct and artifact-free lightmap results.