what kind of light are you using? you only said its 150w... but of what type?

if its incadescent... at least replace the bulb with a CFL, incadescent is basically worthless for cannabis.

if its already a CFL, 2'4" is WAAAY too far, it should be like 1-4" away depending on how much heat it puts out.

if its a HPS/MH, thats probably still a little on the far side... with HPS/MH you use the 'hand test' put your hand at the top of the plant and move the light close enough that your hand is still comfortable (heat wise), and then back off a couple inches