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2 Sided Material Issue

I’ve modeled some curtains in Max for a scene I’m working on and, as they’re just a plane, have had to use a two sided material. The mat is a creme colour and looks fine from the normal-facing side but blue from the rear side.

I’ve included the whole scene just to show there’s no blue light bouncing around from anywhere. Scene below:

Frontand back.

Thanks in advance.

Hi Olly,

Actually, looks like the blinds are the same color on both sides (minus any stationary lighting). The fact that it appears blue from the back is simply an optical illusion.

This is due to how the engine handles 2 sided materials for lightmass. Unfortunately it doesn’t actually store different lightmaps for both sides. It calculates lighting for both sides and stores the average between the two. For dynamic lighting it works as expected but for static lighting its just one value for both sides.

You will need to make the 2sided geometry using the model instead of the material flag if you want accurate static lightmaps.

Hi Ryan, thanks for the quick response. Great I didn’t know that was an option will change that setting before the next light rebuild. In similar situations where a mesh is one sided, is it better to change the geometry to two sided or the material? Or does it just depend on the situation?

Just depends on the situation. Static lighting is the only case I know of for sure where the 2-sided material option will cause some grief, if you need to have different lighting values for both sides.

For leaves etc people generally do not notice since the averaged lighting looks somewhat similar to how subsurface lighting is supposed to look, but you get shadows blended together from both sides.