oops hit the post before i had the chance to tell about what a gel is. a gel on a 3D light is a 2D map that you shine the light through. For example on the forest floor the sun doesn't just beam down and hit the ground. It filters through waving leaves. Your 2D map can act as the leaves. It can even be animated to move in front of the light. that'll give you a flavor for it. there are 4 lighting tutorials for Poser I believe it is the highest level one that tells about the light gels. good luck :)