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hey, i just got a 400w hps with reflector. it seems like it gives off a lot of heat, how long should i have the light on? currently Ive been using 24 hours of cfl, would the hps be need to be cut back to 18 or 16 hours? also, how much longer before i start flowering? the plants are 38 days old and about 15 to 20inches high.
Yes, 400w give off tons of heat. Look to air cooled reflectors or a DIY cool tube... mine cost like $20 in all. Brought temps from 99 degrees to 78...
P.S. Flower when you want. Just remember that they will double in size so make sure you dont wait to long... then you have to do some late LST... lol... or suffer damage!
Start flowering when the leaves just overlap when you evenly distribute your plants over the grow area. They will grow for another 2-3 weeks. This is a very general rule I use when I don't yet know the details of a strain.
Yep, HPS give off a lot more heat than compact fluorescents.
You will need to up extraction to keep temps down as already mentioned.
Also, check out your ballast and see if it is also compatible with MH (metal halide lamps) Some ballasts are compatible with both kinds and if yours is you could buy a MH bulb for vegetative growth.
They give off a whiter light which is better for veg (plants grow faster, shorter and thicker) but no good for flowering. They also give off less heat than HPS.
But practically all HPS give off the right wavelengths for both veg and flowering so all you actually need is the one you have.
18h or over for vegetative growth, then give the plants a single 36h darkness period (speeds up the switch from vegetative growth to flowering) and 12h light/ 12h dark for flowering.
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