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    Is two 300w light still 300w or is it 600w

    Sort of depends on how you use them. Two 300W lights angled to give coverage to a single area/plant would be about equivalent to a 600W over that same area/plant but if they're hung side by side then you have less light over a bigger light footprint than you would with just the 600W. Many light manufacturers provide coverage maps for their light's footprint. A lot of people opt for multiple smaller light as it gives them more flexibility to adjust height from the canopy.

    What sort of lights specifically?
    GWE proposes a sweet spot of about 150W per plant. So two plants under one 300W should get about the same amount of light each as 4 plants beneath a 600W.

    To get things exact you really need a light meter, ideally a PAR meter rather than a lux meter (but the latter will work depending on the spectrum of your lights.
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      Do u know if they are true 300watt draws as well all led company's wil tell u the full capablity of the lights but the lights don't actualy draw that power that being said I have 3 leds 1200w 1000w and 600w now the true draw wattage is 350w 200w 100w. So if ur 300watt leds are true watts that's a different story but u also gotta think that each fan will take about 10watts. Also leds are desighned to only point straight down just like beach said it depends on the angle and how they are used. Also my true 350wat led I also keep 6inchs away from my plants thro veg to flower seedlings I keep it at 10inch. I hope this helps


        With leds u need to find the par value that's how ur gunna find ur useable light for ur plants and this is the equalition to find that 60x60 equals 3600 times that by the numbert of hours ur lights on (for example 24h) 3600x24eql 86400times ur par value equals(_) then devide by 1000000 this number will equal ur usuable light par. U want between 100-200par 200par is roughly 1000watt hps


          Originally posted by tyler_ hobbyist View Post
          Also my true 350wat led I also keep 6inchs away from my plants thro veg to flower seedlings I keep it at 10inch.
          I find this very confusing. I have been keeping my 136 true watt LED much further away than this for fear of burning my plants. More like 18". This is what is recommended in the article here on GWE. Although NebulaHaze does in a spot or two mention 12 to 18", most everywhere else in the article, she says 18" to 24"

          Obviously, if you're having success as close as 6" away with an LED more than twice as powerful as mine, it may explain the lousy results I'm getting. My LED is using 5W 90 degree lights. Does that influence minimum distances?

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          • Marley
            Marley commented
            Editing a comment
            Just move it closer everyday until she tells you to stop. There's so many LED lights out there and none will be the same.

          Mine also uses 5w 90degree chips. But for leds u need to figure out ur true par value to find out how far/close to keep ur light. Not all leds are made the same and all have different par rateings. Distance on the form is a general guidline. Do u know how to find ur true par value? U want 100-200 true par per day on average 200 true par would be a 1000watt hps at 25inchs


            Haven't purchased a meter yet. It's on the list. For the time being, I'm trusting the manufacturer's specs to give me an approximate number. I'm using the specs they give here for the calculations.

            At 18" - they say 480 umol per sq metre per second I'm running 136 real watts 18 hours a day or 64,800 seconds . I thought I knew the formula. But, I'm not so sure now.

            I'm also using 2 to 3 (46 to 69 real watts) per plant of CFL's to get at the lower sections. But it is really just the LED I'm trying to do the math for.

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            • DrPhoton
              DrPhoton commented
              Editing a comment
              You know i read that article you linked and their cited anecdotal evidence mentions nothing about cannabis. Although it mentions other plant species, its not directly related. Many plants have different capacity for available light.
              Did i miss it ?

            • OzBud
              OzBud commented
              Editing a comment
              No Dan you didn't miss it, I mentioned in the comments on your post below that like your source theirs didn't specifically mention cannabis either which is why I'm trying to find a source that specifically mentions the DLI saturation point of cannabis, the closest thing I can find is HT's claim of 25 mol per sq m

            • DrPhoton
              DrPhoton commented
              Editing a comment
              OzBud I know this is old but i had obviously missed this reply. The HT reference is completely inaccurate with what they are claiming. They completely misunderstand the article they reference to. The article describes the Daily Light requirements for plants, not the saturation. You will find no article referencing about a maximum level of DLI a plant can tolerate. DLI was and is intended for the measurement of light over time to determine a plants daily photosynthetic quota in outdoors or greenhouse environments. Using this information they can determine whether or not it is required to provide supplemental lighting.

            How well your lights are made makes a huge difference in the quality of the light that your plants receive. You can not apply the information from one manfacturer to another. Weak LED lights can be much closer then a stronger one. If I took my lights any closer then 15 inches, I got burnt plants. You need to play with your lights to see where the sweet spot is.


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                As already said, manufacturers provide different quality and design that are mostly incomparable to eachother.
                What tyler is referring to is called the daily light integral, its the total daily amount of photon energy over the PAR range. PAR is not a metric unit but a unit set. PPFD is the metric system measured in umols that uses PAR to define its testing parameters.
                With cannabis, the max DLI a plant can receive before co2 supplementation, is around 40-45 mols a day. This is about 1000umols @ 12h light schedule.
                In nature plants will typically not receive more than 60 mols.

                When supplementing with co2, plants can be pushed to their genetic potential of about 65 max DLI.
                If a plant receives more light than it can handle, a plant will go into what is called photoprotection. This is where a plants photosynthesis rate is slowed to protect itself. If too much light is provided, a plant will eventually result in photodamage where dangerous reactive oxygen species occur, causing cascade damage to the photosystem centers. This is called photoinhibition.
                Even when all limiting factors such as co2, light and water are adequate, the plant still has a limit on its photosynthetic rate.
                Even if a plant can receive more light, it may not be utilizing it efficiently and could cause a plant to use photoprotection.
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                • Gears
                  Gears commented
                  Editing a comment
                  There's a lot of info in the chart an PDF. If I've read it right, with the added PAR of my 2 to 3 CFL's per plant, I'm likely providing a good amout of daily light.

                  Of course, I haven't allowed for all the CO2 I keep exhaling on my plants while sitting in front of them for hours a day.

                • OzBud
                  OzBud commented
                  Editing a comment
                  I think there must be some sort of confusion.

                  Yes, I know DLI can be calculated from PPFD, it's actually pretty simple to do.

                  That still doesn't help me with the answers I'm looking for which is: What is the DLI saturation point of cannabis?

                  How does one know the plant has absorbed as much light as it possibly can within its photoperiod?
                  The light intensity might be low enough that the plant doesn't get light burn, but over the course of the lights on period it may receive more light than it can process, therefore wasting light and power.

                  I wasn't interested in this topic until I saw Tyler claim 100-200 moles per day is good which I thought to be outrageous since intense sunlight doesn't really go above a 60 DLI but there seems to be no evidence (that I can find anyway) to either confirm or disprove his claim.
                  Just got me to thinking, I run my autos on 24/0 which lots of people seem to agree with autos more light is better but then there's those that think that after about 20 hours of light per day you get little to no return for that extra 4 hours of light which to me says plants are approaching, possibly even passing their DLI saturation point.

                  Anyway, this is going well above and beyond the original topic of this thread so I'll leave it at that for now and continue to search for the answers I am looking for. I appreciate your time and the intellectual conversation, none of my mates would have even the slightest clue about these sort of things. If I come across some conclusive evidence I will be sure to let you know. Knowledge is power.

                • DrPhoton
                  DrPhoton commented
                  Editing a comment
                  No theres no confusion, i know exactly what you mean. But it runs under the assumption that cannabis has a daily limit and then just suddenly stop or slow down, as if they have a counter.
                  Most green plants are classified as either C3 or C4 which represents how carbon(C) is used during photosynthesis. Cannabis is a C3 type, meaning that it doesnt store carbon at night and use it during the day. Carbon is sourced exclusively from the air and so it does not depreciate at the end of the day like C4 type trees do. This is why carbon supplementing works with cannabis, which would not if it were a C4 type.
                  In order for photosynthesis to slow down, there needs to be a limiting factor in the photocenter to prevent the ongoing process.
                  I will be going over my books on this heavily tonight, if you wish to discuss or talk further about this let me know. You have peaked my interest.
                  Regarding longer photoperiods, yes i believe it is beneficial. I think this contradicts a statement i made on a forum a while back with someone asking the same question. But my understanding has changed.

                As BuddMarsh said find the sweet spot ,it's really not that hard if you can check your plants often.
                Cfls for a week or two
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                  Hey Dano if u find anymore info on this topid I am very interested in this as well I would love to hear about ur findings


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