hi all i have a 400 watt hps bulb in my grow press what should the distance between the top of the plants and the light be?? thanks
12-18" from the top of the plants, personally i love to use a infared temp gun for r/c car engines to check the temps at the top and bottom of the plants. a general rule of thumb is if you can place your hand on the top of the plant and be able to keep it there for 30+ seconds you should be good.
my small plant is 20 " away and large plant it 15" do u reckon this is okay should i higher up the smaller plant so there bot at 20" i read that its best to do this
Yes raising plant pots to equalise distance is always good. That way you can even out the light better and stop the more vigorous ones shading the others.