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    Using Light Efficiently

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    Here i will be talking about how to use light efficiently and other factors that need to be considered when trying to make the most efficient use of light. It is simply not best to use a single light source with a fixed output capacity, but instead multiple lights of varying photon flux for different stages of growth. Dimmable fixtures is also effective and to a lesser extent fixtures that have veg and bloom functions. This is because when lights do not match the plants stage of growth, fixtures must be hung relatively high. This wastes a lot of light through radiated and reflective losses. To capatilize on available light one must use a cascade of light sources with varying output capacities. So that the light footprint and intensity matches the stage of growth.

    The canopy intensity guidelines cannot be followed unless you have a light meter which can measure the illumance or flux density of your light source in umols or lux per square metre. Lux meters only work on white light and simply cannot be used for monochromatic light sources, such as the common red and blue LED fixtures. For these you must use quantum PAR meters for reliable measurments and referencing. Although using smartphones to measure illuminance is possible, the accuracy may not be reliable due to hardware variances and the lack of cosine correction systems required for accurate measurements.

    Seeds & Clones:

    Clones loose a functioning root system and so rely heavily on stored resources rather than photosynthesis. As such the only amount of light they require is the level to compensate for the energy used for simply staying alive. Seedling light requirements is almost identicle because the age of leaves directly effects the potential for photosynthesis. It can take two or three weeks before a plant has developed leaves that are mature enough for higher intensities. Seedlings or clones are best between 60-90umols (5000-7500 lux). This is because, the enzyme activity and other key functioning systems in leaves are still developing and cannot photosynthesize as well as older plants can with mature leaves.

    Whether you are germinating or cloning just a few plants or many, early vegetation starts off with a very small surface area of leaves. It is a big reason why it is not ideal to start off with high photon flux lights, as you cannot bring the light source too close as the intensity will be too high. As a result light is wasted through radiated losses. Instead for early growth and a smaller surface area of leaves, a low flux light source should be used such as fluorescents, low power gas discharge or dimmable fixtures on low. By using light with lower photon flux levels, this allows you to be able to bring your light source closer without providing damaging levels of light intensity and limit the amount of radiated losses by making the light footprint and intensity match the stage of growth.

    Early And Main Vegetation:

    As young plants get older you can progressively increase light intensity until you reach full maturity. This is because as leaves mature the enzyme activity responsible for key aspects in photosystems, increases and allows for maximal processing of light through photosynthesis.

    During early vegetation before a plant has reached full maturity, average light levels between 250-350umols (20,000-30,000 lux) is ideal.

    With mature vegetation, it is best to keep the average light intensity between 500-700umols (40,000-60,000 lux) as the photosynthetic efficiency is best in this range.

    As your plants grow and the surface area of leaves increases and begins outgrowing your light source, you can start to consider introducing more light. At this stage of growth, plants are still filling the canopy and is not the best time to use the full recommended photon flux for your grow space. Instead increase your photon flux levels by using more powerful luminaires or increasing the power on dimmable sources. While still making sure the light footprint and intensity matches the stage of growth.

    Flowering:

    During flowering it is best to keep the average light intensity between 500-700umols (40,000-60,000 lux). When the canopy is filled, there is no need to bring your light closer during flowering. As the plants photosynthetic efficiency is unchanged and bringing a light source closer does not provide more energy to plants. Read my article on Light Proximity to learn more.

    By the time you have reached the flower stage, you will want to have filled as much if not all of the entire canopy of your grow space, so virtually little or no light gets through to the bottom. This ensures that most light is being recieved by leaves, instead of having radiated losses that pass through or around the canopy unused. When the canopy is filled you can proceed with the full photon flux that is suited for your grow space. If by the time you have reached flowering or at the end of the flowering stretch, the canopy is not filled. Then plan for future grows to use training techniques, increased vegetation time or higher initial plant numbers to ensure that this space is filled better by the time you reach flowering.

    Conclusion:

    Ultimately you are wanting to match your light source to your plants or match your plants to your light source. By managing light sources or plant configurations you effectively limit the amount of wasted energy and increase the efficiency of light utilization. You will also want to maintain your light intensity at the canopy for each stage of growth as the photosynthetic efficiency is best when kept between the ideal range. Between 700-1000umols (60,000-80,000 lux) efficiency declines rapidly and fully saturates at around 1000umols (80,000 lux). With any further increase in light intensity adding little to photosynthesis and is wasted as heat.

    Matching light sources to plants is not possible for some, if you are limited to using single output lights, you can use a single light source for the entire grow by raising the fixture. However this is not making efficient use of your light and as such valuable resources are wasted through radiated and reflective losses. Ideally with fixed output sources you want to match your plants to your light source as you cannot control the photon flux. But because most are limited on how they can do this, you may have to bring your light source closer in order to utilize some otherwise wasted light. With wide and dense canopy, when you bring the light closer, and the inner hotspots increase. Much of this extra light goes unused, as you reach the limit of photosynthetic efficiency. But the light on the outer edges increases and does get utilized. So there most definitely is a benefit for bringing a light source closer when the canopy is not completely filled. As a rough guide, you dont want the inner hotspots to be any higher than 1000umols or 80,000 lux.

    As always please comment your thoughts or any questions on the subject.
    Last edited by DrPhoton; 11-02-2018, 06:30 AM.
    Written Articles:
    Light Metric Systems
    Using Light Efficiently
    The Light Cycle Debate
    Environment Conditions
    Grow Light Technologies
    How To Compare Grow Lights
    To Defoliate Or Not To Defoliate
    Having A Light Source Too Close

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    #2
    Great write up Dan. Happy 420! 😥
    Current Grow
    Power Plant | 2x2x4 Tent | FFOF Soil | BP Cal-Mag | FF Trio Nutes | 300 LED | Temp R/H Gauge | Humidifier | Fans | 2 Gallon Smart Pot | 4' 190 CFM/Speed Controller | 4' Carbon | Passive Intake

    Comment


    • DrPhoton
      DrPhoton commented
      Editing a comment
      I wrote it while i was watching the nba playoffs, had a great day

    #3
    Always good stuff Dangerdan, thanks.

    Comment


    • DrPhoton
      DrPhoton commented
      Editing a comment
      Thanks dutch.

    #4
    Thanks DANGERDAN !
    SO, why do LED manufacturers all seem to suggest lower heights above canopy during flowering? Is this just to protect very young plants?
    I don't have any light meters, so I more or less follow their guidelines. I run 21" above during Veg and at least 15" during flower. They do fine at 15" but I think I saw evidence that they don't like 14". So, does this mean that I can lower them closer to 15" in late veg?

    Comment


    • DrPhoton
      DrPhoton commented
      Editing a comment
      Yea i would say 15" is around 900umols.

      Ideally you want to match your plants to your light source as you cannot control the intensity. But because most are limited on how they can do this, you may have to bring your light source closer in order to utilize some otherwise wasted light. When you bring the light closer, and the inner hotspots increase. Much of this extra light goes unused, as you reach the limit of photosynthetic efficiency. But the light on the outer edges increases and does get utilized. So there most definitely is a benefit for bringing a light source closer when the canopy is not completely filled. As a rough guide, you dont want the inner hotspots to be any higher than 1000umols or 80,000 lux. 12" is around 1200umols which is fine if your plant can tolerate it. If however you can back your light off to get between 500-700umol then you maximize the efficiency of light utilization. But the canopy must be filled so most of the light is being received by leaves.
      Last edited by DrPhoton; 04-26-2018, 08:11 AM.

    • Campesino
      Campesino commented
      Editing a comment
      OK, Thanks.
      So, I'll go with 900 @15", because that seems to conform to everything. Plants that got closer than that seemed to start light burn (@<14" probably above 1000umol)
      My canopy is certainly full, but the lights really can't go higher so I'll have to stay up around 900umol on several tops

    • DrPhoton
      DrPhoton commented
      Editing a comment
      Sounds about right,

    #5
    Updated and changed title name.
    Written Articles:
    Light Metric Systems
    Using Light Efficiently
    The Light Cycle Debate
    Environment Conditions
    Grow Light Technologies
    How To Compare Grow Lights
    To Defoliate Or Not To Defoliate
    Having A Light Source Too Close

    Check Out Our Social Media Channels For More Resources:
    Facebook
    Twitter
    Instagram

    Comment


      #6
      Excellent read and very informative. Thank you.

      Comment


        #7
        Improved readibility and added further information.
        Written Articles:
        Light Metric Systems
        Using Light Efficiently
        The Light Cycle Debate
        Environment Conditions
        Grow Light Technologies
        How To Compare Grow Lights
        To Defoliate Or Not To Defoliate
        Having A Light Source Too Close

        Check Out Our Social Media Channels For More Resources:
        Facebook
        Twitter
        Instagram

        Comment

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