hmmmmm....odd question but none the less......an exact figure would be pretty hard to give as there are many factors thatll affect the temps.......i would say that in a 1m2 grow tent in a room with avg. temps ul be sitting around the acceptable region 24-26 degrees C......but if ur going to all that trouble to get only 200w then why not get a 250w mh/hps ballest? soo much better light. more penatrative and more lumes at better spectrums......little cost £30 from screwfix?