Got around to experiment more with this IL stuff in Blender. I had a bunch of problems until I noticed that Blender is horribly bugged with mesh lights. For example it is a common trick to set materials of a lamp mesh to “shadeless”. Doing so though (even with emit set to 0) IL uses this mesh to cast light breaking everything. And to add insult to injury blender totally fails to understand the principle of single-sided meshes. To put it simple the mesh is at the ceiling of a building. The building is open at the back since it’s straight at the wall. Although another layer of faces with a non-shadeless material is above it (the outside walls of the building) blender casts the light all over the place. On the other hand with another mesh with the exact same material just a different color no light is cast at all even if I turn off “shadeless” and set emit to 100 over more. I see only one way and this is to use blender lamps and no mesh lights. Now comes the problem though. Blender seems to cast lights form meshes even if emit is set to 0 just because “shadeless” is ticked on.
Is there a way I can prevent blender from using meshes in IL and just stick to lamps no matter if materials have “shadeless” ticked or not?
I think you might be getting mesh lights confused with indirect lighting. Indirect lighting is exactly what it sais. Lighting from an indirect source. In other words, anything that’s somewhat bright releases light. What you seem to be looking for is a mesh that acts as a point light source, which I don’t think blender has. I mean, indirect lighting would work, but if you have anything else in your scene it can give unwanted results. For example, a brightly lit red box in the scene will light the ground around it red (if the number of bounces is above 1). If you find that with only a single bounce isn’t bright enough, try increasing the factor above 1. Another all out solution would be to use hemi’s to light the scene, then use spot lamps to cast shadows and spec but not diffuse light. Just remember, if you use hemi’s, make sure you turn off indirect light. If the hemi lights the scene too much, the indirect lighting will amplify it.
That’s not the problem right now. I’ve got materials which are “shadeless” since I don’t want them to be lit (for example the light tube material) as they are like the light source. Yet with blender IL these illuminate the scene incorrectly (especially on the back site). It’s a common trick in games but blender seems to fail at it so I can not light using mesh illumination (due to double sided problem) nor using lamps only (IL picks up “shadeless”… also with double-sided problem). So I’m in a situation where nothing works.
I don’t think that blender does any shadowing of indirect lighting with approximate gather method(or at least my tests seemed to indicate that), so that may be part of your problem.I don’t quite understand exactly what sort of problem you’re having with indirect lighting, so I’m not sure if I can help, but I will try:
Turn off AO when using indirect illumination, it darkens the effect considerably, and seems to negate it entirely at a strength of 1. (Note that this only applies if AO is set to multiply, add works fine)
Very low-poly meshes may need to be subdivided once or twice to work right. Try subdividing your window planes.
This is a no-brainer, but make sure the normals of your window objects are facing in the right direction. If they’re facing away from the objects you want to light, they won’t work.
I don’t think there’s a quick fix for this. I don’t know much about the compositer but maybe you could avoid this with some compositing?