I was reading something that quite impressed me, and I want to hear from our experts here about this subject. Everyone knows that 75-85 is supposed to be the optimal grow room temp. This guy, who is an industrial grower, said that this temperature was arrived at over time, because any higher than that, and your HID or HPS will burn the top of the canopy. It is approx. 10 degrees hotter under the light (say, 12-16 inches), thereby making the temp of the canopy 85-95. So, anyone who has their thermostat set at 75, and has been successful, was really maintaining an 85 degree canopy temp. He has gone to all LED’s, and he suggests that the most optimal temp for LED rooms is 85-95, as there is negligible heat coming down off the fixture. He reckons that the higher temp = more transpiration, ergo more movement of fluids through the girls, and so on. Like exercising, if you will. It would really be sweet to hear from Robert on this one, but please, anyone, share you thoughts on this idea.


That may very well be true for the canopy and higher temps at the canopy certainly work very well with CO2 rich environments, however you also need to worry about the temp of the root zone which ideally shouldn’t be much above 70F, especially in certain types of hydro like DWC.

how low can the root zone go

Obviously you don’t want the roots to freeze.

You do not want to get your hydroponic solution much below 60 degrees.

The best way to adjust the height of your lamp is to place your hand, palm down and lower light until it is hot; And you cannot leave it there. Raise lamp 2-3" Plants will not burn. Using this method; I have never had this issue, unless I let canopy get too high. ( I use this sign as a prompt to raise my light or use some method of lowering the canopy.