Having now established a resolution and Lightmap Size, we should specify baking details to improve the quality and appearance of our lightmaps. To do this, enable Ambient Occlusion and tweak the Max Distance field until you get the volumetric effect desired. This requires rebaking. Ambient Occlusion is sometimes called Contact Shadows, because it generates shadows where two or more solid bodies meet, such as the floor meeting the wall, or crevices and cracks. This creates a volume effect, enhancing the 3D feel of a scene:
In addition, enable Final Gather. Set the Ray Count to 256. Final Gather reduces noise and improves the quality of lightmapping. Higher values result in smooth, higher quality output at the expense of the calculation time:
Finally, you can increase the resolution of specific objects...