Light not being blocked by back of faces

[osiris231]

I have a light that is sitting high in my level, above where a player would be able to get to so I have removed faces on my buildings that are facing up. When I calculate lightmas the buildings don't cast shadows for the sections of the buildings where there are no faces facing up and hence shadows are being calculated as if light is coming through those walls.
It would be a waste to just set the material to double sided and I would like to not add geometry.

How do I fix this?

[Graylord]

Tick the "Use Two Sided Lighting" box in the properties of the asset in the level.

[osiris231]

Thanks Graylord,
I've tried that but it doesn't seem to work, the effect is still happening, do you recommend anything else?

[osiris231]

I don't know if it's related but the meshes have multiple materials, do I need to handle the lightmaps differently when you have multiple materials?
I have two material groups and two unwraps (uv and lightmaps), the uv unwrap has overlapping maps because there are different materials but the second unwrap, the lightmap unwrap has each individual face separated with room to avoid bleeding.
Could this affect lighting?

[JessieG]

I recommend using light blockers. Import a cube static mesh into UDK then, to make things easier, click the "levels" tab at the top of the content browser and go to "Level -> New Level..." and name it "LightBlockers" or something like that so you know what it is and save it in the same location as your map. When the option for streaming method shows up, choose "Kismet". This way this level can only show up while you're playing if you set it up in kismet to show up.

From here, you can right click the level in the level tab and choose "Make current". Now just add the cube meshes (as many as you need to block the light) inside of the missing portions of the building, kind of like if the building was a wrapper around the cubes. Add as many as you need to get the correct shadows and bake the lighting. When you play it, the cubes wont show up because they have to be loaded in via kismet, but the shadows they cast will still be there.


The UV mapping isn't the issue. With no backfaces to catch the light, it'll pass right through. Turning on two sided materials or something like that isn't as optimal as just using light blockers to get the shadows you want. Also, for your lightmaps, you want to avoid having every single face separated. You want as few separate UV islands as possible. The UV maps you use for textures will have no impact on the lightmaps, and the UVs of an object do not effect the shadows they cast onto other objects in any way.