I have been working on a building lately and I recently discovered the environment lighting which is awesome because it's useful when working on a project.
However, recently reloading the .blend file, everything gets rendered black. I never used a light source in the first place, so I don't know what's going on. I thought I might have touched some setting without noticing it, but everything seems in order. Also changing the settings doesn't yield any visible different result.
I'm using Blender Render (2.71 rc2), Ambient Occlusion of 0.30, and Environment Lighting of 1 (white). This is the difference between what it used to be and what it renders now: