PrideofCucamong said:Whats up Kat. I have my 400w HPS about a foot away from my plants, and i have a fan right next to it filtering the air out of the grow room. It keeps the room a nice temp. Do you think i could get it a little closer to my plants? I am not sure where exactly to keep it. My plants have been under all fluorescent light for a month. Should i keep the light pretty far so they can get used to it, or just blast em? Thanks for any help!
Well the rcommended distance for optimal growth for HIDs is:
400W - 12 Inches
600W - 18 Inches
1000W - 24 Inches
So if you're one foot away with a 400W you're right where you should be. Now if you just moved clones over from fluoro's today, then the suggested procedure would be to start it about 6" further away or 18" in your case. Then adjust the light an inch closer each day until it's a 12" and then maintain that. Although that's really more for clones or seedlings that have just barely established and are then moved to a stronger light. Having been there for a month (under fluoros) the plants are probably strong enough to just start at 12" and not worry about getting them used to it. I just did that myself with some clones about a month old except I have a 1000W so the distance is 2 feet. They're doing just fine and have already grown at least an inch in 24 hours.
In theory you can get the light as close as you can as long as you're still maintaining good temps at the canopy. However, even if the temps are good you can still have harmful effects to the plant from a light that's too close. Namely what they call bleaching aka light stress. That's why the recommended distance is said to be optimal. You can potentially get closer but it's not as good for the plant as the recommended distance. Another factor to consider is the closer the light the smaller the footprint, if you have the maximum number of plants a light can handle the plants on the outer edge of your space will not get as much light as they should because there is not enough distance for it to radiate out that far before traveling past the plants.