...try googling "hps mh light distance chart" or similar keywords...I found one once online. has inverse graphs that show the distance from plants and the equivalent sunlight intensity.

As far as temps...is it really 65 degrees under the light. Probably higher. 65 degrees farenheit doesn't sound cold to me. When I used to garden delicate plants other than cannabis, I never worried unless the temperatures got below 50F.
notanotherteensmoker Reviewed by notanotherteensmoker on . hps 250 distance? how far above the plants would a 250w hps need to be?. It is quite a cold area, about 18 degrees celcius which is about 65 degrees farenheit. I have just changed from fluoros and cfls to hps. anyone know? Rating: 5