I don't think "cold spots" like PC
is comparable to halide. But I do know that Metal Halide, sodium, and halogen bulbs must run at a higher temperature to reach optimum output. I don't think there will be any "adverse" effects of fans blowing in on halides, but the idea is to remove the heat that is generated, not cool off the bulb so heat isn't produced. I think you are going to find most proof to be up in the air. Find what works for you and stick with it. Heck, try it both ways and see which reduces temp more, or is quieter, or you like better. For my opinion, however, I'll stick with the "out"