I have already spend lots of hours trying to recreate the lightbeams in Michael's picture. I always get those gaps. I included a better picture and marked the gaps, where the lightbeam doesn't show through. As you can see I did manage to get the beams, but with those gaps I can never get a realistic look. Coming to think of it, maybe I can overcome this problem if I put some terrains far away in the distance, to cover the entire background underwater. Cause in front of the terrain the beams are ok. About lightgels the manual says the following: 'You can load any simple material to use as a gel, but only the materials color will be taken into account'. I'm afraid I do not always understand English that well, but for me this seems to say that a light gel gives only a color to the volumetric light. I'm going to play with this a bit more now. Probably till later, and hopefully I got a bit further then. Thank you for your help Guitta. :) Rynn