I just finished making my cool tube. I am not sure what the temp difference is but I know that the 400w hps ran for a hour and I could touch the glass and not get burned . I made mine for less than 80 bucks, I bought a aero-flo 6"duct fan on ebay for 35 bucks at 240 cfm, and bought a glass tube from michaels for about 5 bucks and spent 35 at home depot to wire and duct everything up. I am anxious to see how the skunk reacts under its new 400 hps rather than the 175mh that i had on it, but I couldnt install the hps because of the temp prob. Anyway hope this helps....