An introduction to lightmaps
Basically in source lightmaps control how detailed your shadows are, this short tutorial will just give you a quick explination as to how to change the lightmap scale
To change the lightmap scale you select the face of a brush with the face selector and you can see the lightmap box to the right of the texture shift tab.
In source a face usually defaults to a lightmap scale of 16, which is, to be honest, pretty poor, so to change the lightmap scale just use a different number, note that you can only use powers of 2, so thats 2, 4, 8, 16, 32 etc. if you dont you will get an error message when you try and play the compiled map.
You can check your lightmap grid in the 3d view, this just gives you a look at your lightmaps on your faces, for example in this picture the left grid has a lightmap scale of 32 (euch) and the right has a scale of 2...
so basically on the left half of the wall the shadows would look horrible and nasty, whilst on the right they would be very fine and precise
but heed warning, lowering lightmaps increases vrad times ALOT so its only best to play with lightmaps for the final compile of a map. on the same note you can increase lightmap scales to make vrad take less time, but of course, the shadows would look worse.
Ta for reading