You could try using the same pattern I used in Halls Of Horror, with very slim logic zone lines, each going from on-off-on-off-on. Unless that's the predictable thing you're talking about.

The other option, you could use the timer prop and make the time it takes to flicker really short. There's not too many ways you can make flickering lights, but for horror maps, it mostly depends on how you can fluctuate the logic stuff and enemy spawning around, while also maintaining a spooky environment. Flickering lights are a smaller part, but don't wear yourself out trying to perfect it.