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Thread: What distance should my light be from my plants?

  1. #16
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    Re: What distance should my light be from my plants?

    Optimum temp @ top of plant closest to light is 70 degrees. Therefore, your room must be much cooler than 70 degrees in order for the temp to be 70 degrees at the top of your plants. Air cool your lights with turbo exhaust fans w/glass. Make sure your air cool system is sealed so you don't loose CO2 if you're using it. Have wall-mounted fans blowing across the plants inbetween your light and plants and lastly and most important, GET AN AIR CONDITIONING UNIT! lol There are also water cooled lights as well that emit no heat too!

    BOTTOM LINE:
    Get the lights as close to the plants as possible w/o the temp at the top of the plant exceeding an optimum 70 degrees. (max 80 degrees)

    Good Luck
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  2. #17
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    Re: What distance should my light be from my plants?

    You might find this chart useful


  3. #18
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    Re: What distance should my light be from my plants?

    Do you know if the MH numbers are similar? I am trying to get my light as close as possible and right now am at 18 inches for a 400W MH in a 4 x 8 closet. Temps are running at around 80 degrees. Thanks for the chart. I will be switching to a HPS bulb for flower cycle.

  4. #19
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    Re: What distance should my light be from my plants?

    good info guys, thanks!!!


    I know the MH runs hotter if that helps at all Hypo....

  5. #20
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    Re: What distance should my light be from my plants?

    Quote Originally Posted by hypo hippy View Post
    Do you know if the MH numbers are similar? I am trying to get my light as close as possible and right now am at 18 inches for a 400W MH in a 4 x 8 closet. Temps are running at around 80 degrees. Thanks for the chart. I will be switching to a HPS bulb for flower cycle.
    MH puts out slightly less lumens than HPS, that chart is really for lumens not heat as it tells you how close you can get without doing damage from too many lumens and how far you can get while still getting enough lumens to grow proper

    as for heat, if you use air cooling then heat would not really be an issue and you could get as close as this chart states

    if you do not have an active fan air cooling system then back of the hand test will probably be good enough to tell you how close you can get, my friend has a 400w hps in a 3x2 space and his plants are growing up into the reflector hood and almost to the bulb without any damage but his bulb is old, i had a 400w in same size space years ago and got some slight heat damage on plants centered under light, mostly just leaves...

    in my opinion, a 400w MH or HPS is good for like 3x3 maybe 4x4 or a little more if done vertical, 4x8 is 32sq ft... you could do 400w for veg but for flower I would think you'd be better off doing 4x4... like half the plants and maybe more yield, def bigger nugs...

  6. #21
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    Re: What distance should my light be from my plants?

    according to the chart, a 400w light 18" from the plants would produce 7074 lumens, 4 inches lower the light is producing 4735 which is below the threshold for what they consider acceptable

    this means the top 3 or 4 inches would get just enough while the lower stuff would really struggle to thrive...

    also for reference I think the minimum lumens needed for growth are about 2000, mind you this is exluding LED's...

  7. #22
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    Re: What distance should my light be from my plants?

    hey 420 magazine world!

    i am totally new to this stuff. i just got my first clone about a week ago. it started off healthy and is turning yellow at the tips and around the edges of the leaves.

    i.d.k. if it is a light problem with it being too close (using a florescent light that is equivalent to 100 watts) its about 5-6 inches above the plant or if it is a nutrition problem.

    any kind of help would be appreciated. if it helps to add some pics, i shall do so
    Genesis 1:29

  8. #23
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    Re: What distance should my light be from my plants?

    Keep in mind that you should use some type of reflective material, such as mylar, in your grow space so the that the light doesn't just affect the tops of the plants.

  9. #24
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    Re: What distance should my light be from my plants?

    i just put my clones that are about 1 ft tall, under my 1000w hps at about 2 ft for a couple of hours and they started wilting. so i doubled the height, what do u guys say?

  10. #25
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    Re: What distance should my light be from my plants?

    Quote Originally Posted by pez4life View Post
    i just put my clones that are about 1 ft tall, under my 1000w hps at about 2 ft for a couple of hours and they started wilting. so i doubled the height, what do u guys say?
    what are your temps? do you have active air cooling on light?

    If you had them under something like flouro's then you need to raise your light to top position and gradually lower from top position to lowest position in a week or so...

    I had the glass of the hood for my 1000HPS as close as 6" from tops of plants without any heat damage. Its active air cooled and I didnt keep it that close for too long but mature plants should be able to withstand 24" from 1000HPS

  11. #26
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    Re: What distance should my light be from my plants?

    Quote Originally Posted by pakalolo408 View Post
    hey 420 magazine world!

    i am totally new to this stuff. i just got my first clone about a week ago. it started off healthy and is turning yellow at the tips and around the edges of the leaves.

    i.d.k. if it is a light problem with it being too close (using a florescent light that is equivalent to 100 watts) its about 5-6 inches above the plant or if it is a nutrition problem.

    any kind of help would be appreciated. if it helps to add some pics, i shall do so
    5-6 inches from a 23w cfl is prob not enough light to keep plant alive... you need that bulb much closer, you could have the bulb pretty much touching the plant and it would barely be getting enough light...

    but you might have nut problem as well or be over water/ph too hi/low... why dont you start a new thread with pictures of your plant and people can help diagnose...

  12. #27
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    Re: What distance should my light be from my plants?

    Quote Originally Posted by bizz View Post
    5-6 inches from a 23w cfl is prob not enough light to keep plant alive... you need that bulb much closer, you could have the bulb pretty much touching the plant and it would barely be getting enough light...

    but you might have nut problem as well or be over water/ph too hi/low... why dont you start a new thread with pictures of your plant and people can help diagnose...
    thanks man i'll get started with a new thread with photos in a few days (need time to prep stuff for my first child, expecting him to pop out soon)

    for now i moved the light really really close, its literally right on top of the plant. if anything, i will change the lighting system. this is my first grow ever and i hope it comes out great, but it is going thru tons of stress with the over water, trimming, and i dont even know. everything is turning yellow and i might just throw it away and start a new one, but we'll see1
    Genesis 1:29

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    Re: What distance should my light be from my plants?

    Hey smokey, what's this you say about the position of the reflector? you mean if I have a 2x4 space, the 18x36 reflector should be hanging with the 18" side parallel to the 4' side? let us know!

    Thanks

  14. #29
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    Re: What distance should my light be from my plants?

    Quote Originally Posted by anthonyps33 View Post
    Hey smokey, what's this you say about the position of the reflector? you mean if I have a 2x4 space, the 18x36 reflector should be hanging with the 18" side parallel to the 4' side? let us know!

    Thanks
    its not so much reflector as it is bulb, think about it

    the filament goes from top of bulb to bottom, so the bulb doesnt put out much light above its top or below its bottom compared to how the sides get lots of light

  15. #30
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    Question Re: What distance should my light be from my plants?

    hey i am using a 400w mh and a 400w hps does this equal 800w or should be used the same as a single 400w at 1 foot?

    heres my journal any other help much appreciated.

    http://www.420magazine.com/forums/jo...canada420.html

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