What is the perfect amount of light?

Discussion in 'Lighting' started by mrjimbodangles, Oct 4, 2013.

  1. #1 mrjimbodangles, Oct 4, 2013
    Last edited by a moderator: Oct 4, 2013
    Hello fellow cultivation enthusiasts,
     
    I am new to using HPS and want to know how much wattage I need for a 3 1/2' x 3 1/2' (42" x 42") area. 
     
    I am guessing a 400 watt HPS would work, but would I get better results with a 600 watt HPS, or is that an overkill?
     
    Thanks in advance.

     
  2. #2 For A Better LifE, Oct 4, 2013
    Last edited by a moderator: Oct 4, 2013
    I'm using a 400wHPS in a 4'x2' cab. It's certainly an effective amount of light. But I'm sure another 200w of light would do no harm.
    The extra 200w of heat however would be a real problem for me.
     
    Basically you want to apply the Inverse Square Law, and
    *Get as close as possible to 10,000 lumens at the plant's height (Sun equivalent)
    while
    *Staying as close to the 75-85*Fahrenheit range as possible (optimum grow temp)
     
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    As you can see on the lumen chart, it is safe to go quite a bit above the 10k, but there is an outside threshold where more light becomes damaging to the plant.
    While it is acceptable to go as low as 5k lumens, it's generally accepted that peak production falls off the farther you drop from 10k.
    Keep in mind if you are using a cooltube then while it allows you to reduce distance from the plant surface (due to heat control) some light is lost to refraction.
     
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    And if you are using reflective surfaces like matt white paint or mylar, this reduces the impact of the inverse square law by a factor correlating to the distance the light travels, the reflectivity of the surfaces , and the angles light is hitting those surfaces at.
     
    Then ofc there is the Light Footprint of your reflector hood to consider
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    If I've illuminated anything (pun totally intended) it's that lighting is a very complicated question!
     
     
    It's pretty unusual for people to have a problem with too much light. So what most people do is get as much light in there as possible while keeping safe temperatures at the highest surface of their plant when it is fully grown.
    75-85*Fahrenheit = perfect
    105*Fahrenheit = photosynthesis shuts down and you have a serious problem
    Anything in between constitutes a compromise. I'm reaching 93*F and they're doing just fine
     
  3. That is the answer that I was looking for.  Thanks a million. 
     

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