There was some talk about this over on the forum, thought I'd make an example map. Hit the button and the door opens, pouring wonderful yellow light into the room, a la c0a0c. The light moves with the door, and it looks pretty darn good, although it's a door so it's solid. Same setup non-solid can be done with a func_train. A relatively simple trick, BSP and RMF included.
As for the effect, nicely recreated.