However, I obviously want the other walls of the trench to be lit by the light bouncing off the first wall. I am assuming (perhaps incorrectly) that I require radiosity to do this.
Following some tutorials, I enabled radiosity, subdivided the trench, set the emit and ambient properties of my material to 0.1 (I also flipped the normals after some head scratching), This is what I get:
This sort of looks ok other than being way too light, but after some fiddling to try and a darken it, I realised that by setting the “emit” to 0.1, the entire trench is emitting light.
This is not what I want, I want only the light reflected from the top half of the wall to light the trench, not the entire trench itself to be an emitter!
Am I going about this the wrong way? Should I be doing a raytrace or something instead?
There are many ways to light something like that. You could for example duplicate a number of regular lamps set to a low energy value with a low distance value as well and place them in a row on top of the trench. (ray tracing for shadows enabled).
Or you could use the Ambient Occlusion feature set to Approximate and a falloff of maybe 2 (depending on the scale of your trench). the picture that i uploaded used the Ambient Occlusion feature. This calculates light/darkness values based on how close some pieces of geometry are to one another.
In both cases a sun light from one side gives the right space-feeling.
Btw, in the Scripts-Window you find a script called ‘discombobulator’ (under Mesh), which will generate some random detail to the inside of the trench. Just search for a tutorial on that.
Hope this helps,
Sloane
ps
The Blender Internal renderer cannot calculate light bouncing off some pieces of geometry (this is called Global Illumination). In order to achieve that you have to fake it by using methods like the ones in the top. Some free external renderers (Yafaray/Luxrender) are designed to render physically correct pictures. I.E. for those render-engines one sun light from the side would be enough to light a star-wars scene like that.
