My lights aren't compiling, for whatever reason. When I compile the map, no matter which compilation method I use (from the BSP menu), the lights I have placed in the map have no effect on the actual lighting. Basically, I can run around on the map, but everything is 100% lit and has no effect from the lights I've put in. It's like there's some kind of ambient light I don't know about. Strangely though, when I try to put ambient light in, it has no effect either. I'm using GTK Radiant 1.4.0 (I might have to switch to 1.5.0 if I can't fix this, and I'll see if that works). The problem either has to do with GTK Radiant (before now, I've used JK2Radiant) or some change in the JK3 mapping (I've only done JK2 before) that I don't know about. Help is appreciated!
My guess is that your map is leaked, and therefore the VIS and lighting stages arent completing.
I actually solved the problem, thanks to help from another thread.
I had BSP Monitoring enabled, but my firewall wasn't allowing a connection to wherever the program was connecting, so it stopped compiling before the light was finished.
I unchecked the box in the Preferences menu, and it works just fine now.