The pages on GameDesign.net (you'll need an account, its free) can explain it all to you. Light entities can have different preset styles, like flashing on and off, flickering like candles, etc...
There are an awfully large number of styles, you'll just have to see which one works best, although how you could implement reasonable looking lightning, I've no idea. Certainly not if you can see a large portion of the skybox, it'd just look weird. Having said that, if you contrived to have the lightning flash on the floor through a window, that might look kind of cool.
The GameDesign.net page kind of hints that there are a range of modifiable styles, but I don't know how you might go about this.
- Dag
p.s. I didn't just copy and paste the page in full because I don't really want to step on the Rust guys toes.
