This is the documentation for Enlighten.

Mesh changes

When a mesh that was included in Enlighten radiosity computations is modified or removed during gameplay, the indirect lighting might look obviously incorrect. If the mesh doesn't reflect a lot of indirect light, we recommend to exclude it from the radiosity computation. 

When a mesh which blocks light is modified or removed, to make the lighting more believable, Enlighten can make indirect light appear to transmit through the mesh. The effect works best for a mesh with a short distance between opposite sides, such as a thin wall or curtains.

You can specify the proportion of light transmitted between 0 = none and 1 = all. For example, you might modify the transmittance at the same time as playing a destruction animation for the mesh.

When the transmittance value is greater than 0, a proportion of the indirect light arriving at one side of the mesh is emitted at the opposite side. This gives an illusion of indirect light passing through the space occupied by a mesh. When the value is 1, all the indirect light that arrives at one side of a mesh is emitted from the opposite side. When the value is less than 1, the light emitted from the opposite side takes on a proportion of the colour of the surface at the point of emission.