how to cool MH bulb properly???

"However, do not blow cool air directly over the lamps, as bulb cooling will result in inefficient evaporation inside the arc tube and abnormal spectral variations of the bulb will result. It is important to remember that these bulbs are designed to operate at a pre-determined temperature."

I read this on the net, is it true? So how should I ventilate the bulb? From above drawing air out? Any body have sugestions on ventalation. Its a 150watt MH...
One more thing

If I make a reflector like this parabolic one for a fish tank will it be O.K.? Because someone said about the light hitting the bulb and it overheating? THis is basically 5 pieces of mirror and flat shaped I guess we wont curved the whole way around 50% bulb?


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