Lower your intake temperature, or get a more powerful fan, or both. I have a 4" 170 CFM fan connected to a 1k light in an air-cooled hood, and that's not really enough fan power to cool the light, so what I did to compensate was lower the temperature in the room itself to like 60 degrees, which keeps it around 77 degrees near the light. I too need a more powerful fan, just lack the money for it at the moment. Looks like a 6" centrifugal is the way to go with a 1k light.