Should you keep HPS as low as Possible or up High?

I have my 400w HPS two feet from the top of my plants and they don't burn, but I'm afraid I'm not allowing it to grow taller.
Should you keep HPS as low as possible or up high?

It all depends on your temperature control.

I can keep my 600w within 1inch of the tops of my plants if I wish too.

A 400w should be between 8"-18" above your plants. Unless you air cool which clearly you don't.



J

keep it as low as you can or youll be wasting light

I try to get my HPS within 1 inch of plant. I have a watercooled jacket that I designed for my turd 400 watter... I am next looking at a 100 watt LED chip, 1 chip, 100 watts in a reflector.

I used to run cooltubes without vents and couldn't get them any closer than 12 inches from the canopy without burning my plants. I had a box fan and small oscilating fan but without high speed vents the 1 inch mark everyone is talking about above is not going to work for you.

Hoss is correct

hold your hand (palm down) just over the canopy. if the heat on the back of your hand gets uncomfortable after a minute, the light is to close

mrmadcow said:

hold your hand (palm down) just over the canopy. if the heat on the back of your hand gets uncomfortable after a minute, the light is to close

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The only problem with that is that your plant can shoot up in one day and burn... I keep my two 400w HPS around 8" from the top of my plants. I check them the next day and sometimes some will shoot up a few inches over night. So I will back the plant off. All my plants are on various stands to make sure that all tops are at the same level.

DawgMountain said:

The only problem with that is that your plant can shoot up in one day and burn... I keep my two 400w HPS around 8" from the top of my plants. I check them the next day and sometimes some will shoot up a few inches over night. So I will back the plant off. All my plants are on various stands to make sure that all tops are at the same level.

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Hey mate, what do you mean by you will back the plant off to keep the tops same level? back it off as in give it no light? I surely would like to know what I could do to keep them at same level n maybe even bushier and shorter, since i am growing in a 7ft tall room with a 1000 watt light. Help would be appreciated thanks

CannaMedGrow said:

back it off as in give it no light? I surely would like to know what I could do to keep them at same level n maybe even bushier and shorter, since i am growing in a 7ft tall room with a 1000 watt light. Help would be appreciated thanks

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No, don't take away a growing plant's energy source. I assume he means keep the light further away from the plants, whether that means raising the light or lowering the plants(if they're on stands as in his situation). If you have height restrictions, train your plants. LST, ScroG, top, fim, etc. The closer the light is, the stronger it will be and the less likely your plants will be to stretch. Keep in mind though that as you move the light closer, your total footprint shrinks.

no one has really mentioned that light goes by the inverse law, meaning that the further away the light is, the faster the light fades..
being this is true, you simply want to keep them as close to the plants as possible without burning them...

shit with a 400w mh or hps bare bulb when i started growing i would get them mad close (4-8 in) but i have to say i was pretty inventive. all types of fans running lol with a cooltube they might be touching the cool tube but not often i still keep them the same distance away cuz i want a large area of coverage and im often not growing just one plant so i say about medium height above canopy (6-12 in) 400w (8-16 in) 600w (12-20) 1000w note this is from canopy. so 4'6" plantx4 might have 1 1000w at about a height of 5'10" this would sufficiently cover the main budding area and the lower area quite well. the same type of calculation could be used to grow 30 plants 18"s tall(all eights include pot) under a 400w mh.

Good call racerboy.