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Optimal PAR readings for determining LED light height placement

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  • Optimal PAR readings for determining LED light height placement

    Noobie here setting up for my first grow. I have a Hydrofarms PAR quantum meter and Advanced Platinum P600 Veg/Bloom LED light and a 2x4x7 tent for two bubble buckets. I am trying to find out what the optimal micromole reading should be at the plant leaves in order to set the height distance of my light during seedling, veg, and flower stages. Is there a chart or data anywhere that gives the best PAR values during a plant's life cycle? I don't want to burn the seedlings by setting the light too close or have it too far away from the canopy and not providing an optimal PAR level. Any advice is appreciated.

  • #2
    PAR is the range of light the plant use. So there is no par level. There are only micromoles (photons) within the range the plants use (PAR) and that's what your meter reads. Anything north of 500 and up to 1200 micromoles per square meter per second is ok I think
    current grow

    granddaddy purple journal


    • kjones6160
      kjones6160 commented
      Editing a comment
      Thanks for the info. Yeah, that's what I was looking for...what should the optimal micromoles reading on the PAR meter be at the leaves for best growth? With a PAR meter I should be able to adjust the height of the LED light up or down to dial in an optimal PAR level for the plants, at least in my theory, but hey...I'm brand new at this. Although, I do have a scientific background and am trying to get it right on my first grow. I've also read that a total of 18 moles per day is the optimal amount of light for these plants. And I'm going to be starting a white widow autoflower from seeds using rockwool and then placing the starter cube in a 6 inch net pot with hydroton into a 5 gallon DWC bucket.

    • 9fingerleafs
      9fingerleafs commented
      Editing a comment
      Great. I don't even own a light meter but I'm familiar with the theory. Lights are always going to be brighter at the center so those are the plants in risk of light burn. Start at the manufacturers recommended distance for the light and take measurements. Depending on the strain and mostly the age of your plants you will have to adjust based on the plants reaction. Stretchy too far. Burnt too close. You know what I mean. Some scientific method in order to get it right. Another thing to consider is the footprint. You may need to sacrifice some intensity in the center in order to provide enough light to the edges. That sort of things

  • #3
    A couple of rough guides to use, but ultimately the amount of heat at the canopy will dictate what you are able to use:

    PAR values
    cuttings 60-90 umoles-
    veg -300-425 u moles
    flowering 700- 1,200 umoles

    Seedlings/clones 200 umol per m2/s
    Vegetative 500 umol per m2/s
    Flowering 1000 umol per m2/s

    i follow the first set, based on height since I don't have a meter- generally with autos, I set the height and let the plant grow into it and adjust in flower.
    Roots Organic Original (amended) - Tents (16"x16"x48"), (20"x36"x63") and ( 2'x4'x6'), space bucket and window sill.LED's, Marshydro300w, Reflector series 48 & 96-150w UFOs

    grow journals-




    • 9fingerleafs
      9fingerleafs commented
      Editing a comment
      Excellent info my friend. I think those are the numbers kjones needs to base on

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