Why guess the temperature and take a chance?
http://boards.cannabis.com/showthread.php?t=40868
That will help you
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Why guess the temperature and take a chance?
http://boards.cannabis.com/showthread.php?t=40868
That will help you
...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.