Just a quick one today to clear up something that possibly isn’t experimented with much when considering lighting, the spread angle from the light_environment. The entity itself recommends a value of 5 degrees to start with however, as my attention was drawn recently to, this is actually quite a large angle. You’ll see on a sunny day, the shadow from a tall building is incredibly crisp. The angular size of the sun, a non-point light source, is about 32 arcminutes in the sky, which is just over half a degree. So picking a sun spread angle smaller than 5 degrees is a good idea if there is little to no cloud cover in your skybox.
The images after the jump are examples of sun spread angles 0, 1, 3, 5, 10 and 20 degrees. 3 degrees is the limit of what you want for a sunny day or a full moon (which is usually only a 60th of a degree smaller than the sun in the sky). 0 degrees looks blotchy on the lightmap scale 16 because of the chainlink, just smoothing that by 1 degree gets rid of that. If a cloud covers up the sun then the light source gets smeared out to nearly the size of the cloud, for such a skybox a larger value like 10 would be more accurate and for an overcast day 20 degrees is almost not enough.
Left hand side is using a lightmap scale of 16 and right hand side is on 1.