complications?

How would plants respond to limited height? Will the leaves burn if too close to a 400w hps? and how close is too close?

400w without an air cooled hood will burn your plants if you get it too close.
I keep my 1000W 1.5 feet away inside a 6" cool tube

Put your hand under the light, if it feels hot on the back of your hand, chances are its too hot for your plants

screaminsemen said:

Put your hand under the light, if it feels hot on the back of your hand, chances are its too hot for your plants

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This is the advice you are after.

Uncovered 400w bulbs need to be more than 6" from the plant, but no further than 24 inches. A properly covered and cooled system can be placed as close as a few inches from the plants, but I wouldn't go closer than 4 inches from the 400w.

I actually have a plant that has a flower which is within a few inches of my 1000w system which is Air Cooled. The leaves on that stem are not as green and lush but the plant is throwing out several new flowers and stacking very well.

You want the bulb as close as possible, but you want the plants outside of the "bubble" of heat. Using the back of your hand is the best way to determine the boundary of the bubble.

perfect advice thanks