600W HPS Bulb Temps

I'm wondering which 600W HPS bulb will run the coolest temperature wise, while not impacting yield too much. I will be running a 600W digi ballast and likely a 6" air-cooled hood WITHOUT any fans for the first grow. I will obviously have fans in the room venting off the hot air, but nothing running through the light tube itself. this is why I want to know which bulbs burn the coolest.

the room is about 6'x6'x8'

Buy a $70 fan to cool your hood. Although depending on the outside temps you might be able to get away without it. I had my 600 in a 5x2x8 closet with the door opened for a little while with no fan and it never got above 83 tops. It was pretty cool outside at the time though.

Skipping on ventilation will cause all kinds of problems. Properly venting out the heat is what lets you control your environment.
Find a way to get a quality inline fan, if not dont expect much of a harvest

The heat is an unavoidable problem that you have to face. You need a fan anyway you look at it. You can use a large exhaust fan for the room or get a fan for the hood and vent it out. You could just AC the hell out of the room but it's more expensive than a fan. The coolest 600 watt light would be an led. Have fun with the price on those.