venting your lights seperatly is great for heat reduction,it does not eliminate all the heat problems though.yes u have air moving most of the heat,but the bulb especially in a cool tube will eventually heat up the glass and head into your grow room,a lot of people dont run a.c,but its personal preference.the people that do want ideal conditions or just dont have the cash to fork out for a huge exhaust and a perfectly mated intake.personally i believe its because they want ideal conditions.but the fact still remains,its like being in a car in 100 plus temp. the inside is nice bith the a.c on but put your hand on the window and its hot as shit,and if your sitting on the sunny side of sed car your going to feel the warmth on your legs,a vented fans works the same way.as far as using your lights for a heat source,thats a great way 2 cut down on heating costs but u dont have the controll like u would with a thermostat.