I bake lightmap in blender and follow the instructions from blender to create a gltf node to save the light map texture as ambient occlusion texture. By doing this I don’t have to load light map externally in three js when loading gltf file since gltf file don’t save lightmap data internally. In threejs I assign aomap to lightmap and then set aomap to null for each mesh’s. The lighting result looks OK, but I don’t know whether there is any lighting information loss when I save it in blender as ao map? Can somebody enlighten me thanks!
If it looks the way you expect, then I think it should be fine. Just be aware that aoMap is a single-channel texture (red channel), where lightMap is a three-channel RGB texture. It’s possible that an exporter might try to merge your aoMap with other textures (e.g. it’s common to merge AO + Roughness + Metalness into a single texture) so if that happened it would overwrite the blue and green channels of the AO map.
I think I got a wrong concept about lightmap thought it only have single component which is black and white.