HID Question

Thundercat said:

Will the lights be in an air cooled hood is the first question that is important. If the hood is air cooled you could keep a 400w 8 inches inches below with no problem. I had a 400mh That the plants almost touched the glass multiple times, I had to raise it up as they grew. If it's not air cooled I would think you'd want to be closer to 12-14 inches.

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tstick said:

When I was using 400 watt MH, I kept the lights about ~18" above the plants with new bulbs. You should take a reading with some kind of photography meter or something that can give you a number to base from and then keep tabs on the light level as the bulb ages....and move the light accordingly. As a general "old school" rule of thumb....If the light is casting a very sharp shadow under the plants, then the light is probably adequate. I'll probably catch Hell for advising such an inaccurate method...but, what can I say? This is what I was taught!

Also, I did not have any kind of lens or glass between the bulb and the plants, so the plants were getting the FULL spectrum of the MH, as well as full heat. I have been told that this is a very unsafe method to use due to hot bulbs getting a drop of cold water on them and BANG!!!....but...that's....what....I did back then!

You will likely have to play it by ear as far as adjusting the height of the light, because there is no universal formula that all plants will respond to the same. In general, when the plants are young, start the light farther away (~24") and then watch the plant response as they get older and larger and stronger and able to take more intense light. This will also apply to switching to a flowering spectrum.

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Thundercat said:

I was specifically referring to flowering with it FYI. Obviously young plants should be a little father away. I don't remember how high I had the 400 when I was vegging with it. Once I started flowering though I only needed to have one plant under it so I got the light nice and close and ONLY had awesome results. There is zero reason you can't get a 400w closer then 12 inches unless you are having heat issues at the leaf surface. 8 inches is totally doable if you cool the light and will maximize the useage of the light output. The close you get the deeper it can penetrate too.

You can definitely get good results in a 3x3 with only 400w, glad it worked well for you. I'm tying to clue in on things that might help him get the MAX results he wants. I could flower a 5x5 or 6x6 with my 1k instead of a 4x4 but I would get way lower intensity on my plants and less penetration into my canopy if I raised I high enough to do that.

As far as spectrum and stretch, he said he has a MH which would be the optimal spectrum for veg. Which leads me back to him potentially having the light to high if he has stretch issues.

I don't use HID for my small seedlings and clones. I built a custom 200w cfl fixture years ago for that. It works great while they are little and as soon as they have a few leaves and some roots they go into my veg tray under a T5. Then 1-2 weeks later they go straight under my 1k hps.

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