Lightmaps Look Wrong in Unity
Black, dark or blotchy baked lighting
Also known as: Unity baked lighting black · Unity lightmap dark · Unity lightmap UV overlap · Unity generate lightmap UVs · Unity lightmap artifacts · Contribute GI
Quick answer
Unity lightmaps look black or blotchy when the mesh has no usable lightmap UVs or is not set to contribute to baked lighting. Turn on Generate Lightmap UVs in the model's import settings, enable Contribute GI on the object (Static), set the light's mode to Baked or Mixed and then run Generate Lighting from the Lighting window. Overlapping UVs and a low lightmap resolution cause the blotches.
How to fix it
Check the lightmap preview in the Lighting window and increase the scale in lightmap for large or important surfaces. Hand-made lightmap UVs avoid the seams that auto-generated ones can leave on hard-surface props. Light leaks at wall corners usually mean thin or open geometry. Remember that moving a baked object does not update its lighting, so bake once the layout is final.
