Light distance...?

How far should my 400W HPS light be from my two pots? The seeds are germinated and planted but have not sprouted through the soil yet. Right now the light is 21inches away from the soil. Is that close enough to prevent stretch or should they be closer, and if so how close?

Thanks

There are two factors to consider. Temperature is first; monitor the temperature at the average height of your plants. To close and you burn the tips to far away and you give up luminance penetration (PAR). Second is Luminance loss. Most experts are in agreement that light intensity diminishes exponentially fast.
For example:
A 400-watt MH from 0â?� to 12â?� is about the same luminance say 55000
Same light at 24â?� the luminance is now about 30000

Still good

Same light at 36â?� the luminance is now about 1200
Fan leafs block most of the light so nothing below sees enough of the light of day to do any good.

Lumens is a mathematical formula that measures the bulbs intensity at 1 foot. The color or type of bulb is not calculated in the formula I=L/D² Lumens received are a measured in watts-per-square foot or foot-candles. Calculating foot-candles or lux is a more accurate way to estimate the amount of light plants receive. This still only measures how much light you plants have available but not how much your plants use.

Light diminishes exponentially fast!

So how close you can place the light is really determined by the temperature at the top of your plants. 12â?� or less is all the same. So itâ??s 12â?� to 48â?� we have control of and the closer to the 12â?� mark the better without burning the leaves. If there is too much heat coming from your light then add a glass heat shield and heat exhaust fans to either suck the heat our or inline to push the heat out. How long you vent tubs are will determine weather you push or pull the heat out. You are better off if you blow air through your hood. This will allow you to get the light as close as possible but watch the temperature!

Thanks, that helps... but my seeds have not even sprouted yet. I can't tell if it will burn the leaves cuz there are no leaves yet. Is 21" from a 400W HPS gonna be ok or should I move the light closer?

dude, usually u should germinate your seeds before planting it.

Quote:

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Originally Posted by mellow mood

dude, usually u should germinate your seeds before planting it.

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He did. He says he did in his first post.

Yea, I germinated them, planted them, and now I am waiting for them to sprout.

Thanks AdidasZ

The trouble with this hobby is if you make a mistake, you're usually f*ucked up back to square one!

So play it safe. Let the seeds sprout in darkness. once you see the hook emerge from the soil, then its time to introduce them to light.

Seedlings will die in as quick as 3 hours, if too close to the light to some degree. (First hand experience) :eek:

Start at 24" and inch your way down everyday. Remember, this is far more "ART" than it is "SCIENCE" so play it safe. Inch down each day until you have a feel for your plants, their appearance and growth rate.

Too close too fast and you will stunt their growth. If you were using cfl, you could make the jump faster, but with the 400HPS, play it safe and watch the plants.

I dont buy the place your hand where the plant is and 'feel' for heat. Seedlings are far more sensitive to light than my hands. Watch for stretching...if you get any, drop a couple of inches but no more...

You'll find the height.

Quote:

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Originally Posted by HARDDON

this is far more "ART" than it is "SCIENCE"

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:confused:

I assume you are kidding?

With new sprouts i use a 430 watt HPS Sun Agro. I keep it 20" to 24" from the tops of the sprouts.

Good Kannabis Growing!

zandor. u shoud know kannabis growin is a beautiful art.