metal halide over heatingheating fluorescents?

[shabreeson]

I am making my own lighting system for my tank and I was wondering how close a metal halide can be with a fluorescent without any fan powered air flow? I also want to know how close can they be with a fan? cm or mm would be the greatest help.

My worry is that the metal halide will either overheat the floresant chamber to the point of explosion or simply crack the fluorescent bulbs.