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Since we established a grow light influences photosynthesis rates not by par watt efficiency alone but also radiated heat ( see here and here ) let's tackle another important aspect that heavily influences net photosynthesis as well, the direction of the light.
Oh and no trolling please.
If the trolls want to participate, restrict your replies to "I agree/disagree, because <insert relevant valid arguments and logically true conclusions>" and you may get some attention.
This replacement 'bulb' can provide better uniformity and penetration and photosynthesis than a diy cob light:
Not suggesting anyone buy that bulb of course, their numbers are inflated.
Just as less heat, LED being directional is often presented as an advantage. Which is true in some ways, but the opposite of reality in others. The main advantage is being able to direct the light downwards (and the heat upwards). More specifically, the advantage is that you do 'not' have to direct the light upwards, away from the plants. Being forced to a limited direction is not actually an advantage. Intuition may make one believe so, but is not the same as reality.
See this article for the difference, you may learn something about container gardening in the process:
http://gardenprofessors.com/container-planting-intuition-vs-reality/
Cannabis' structure is evolved under the sun, and not optimized to receive light straight from above. Much of the sun light is scattered in the atmosphere and arrives as diffuse light on earth's plants.
A common problem led users run into is lack of penetration. Some lower the leds, others go as far as to defoliate the plant... Futile, and out of ignorance, and very ironic, as usual. A few quotes:
"Plants use diffuse light more efficiently than direct light, which is well established due to diffuse light penetrates deeper into the canopy and photosynthetic rate of a single leaf shows a non-linear response to the light flux density. Diffuse light also results in a more even horizontal and temporal light distribution in the canopy, which plays substantial role for crop photosynthesis enhancement as well as production improvement"
"Therefore, the direct light usually wastes photons by concentrating the light resource to only a fraction of all leaves, leading to a less efficient photosynthetic use of light by plant canopies (Gu et al., 2002). Diffuse light, however, effectively avoids the light saturation constraint by more evenly distributing light among all leaves in plant canopies, and leads to a more efficient use of light (Gu et al., 2002)."
"Diffuse light penetrates deeper into the canopy; thus, the lower positioned leaves receive on average a higher light intensity which leads to a higher total nitrogen and chlorophyll content in the canopy, and consequently results in a higher leaf photosynthetic capacity in the lower of the canopy (Li et al., 2014a)."
"Diffuse light improves spatial light distribution in the crop canopy, thereby stimulating crop photosynthesis; the more uniform horizontal light distribution within the canopy plays the most important role for this effect."
That same more even distribution applies to temperatures. The combination allows in case of cannabis allows for taller colas, donkey dicks, that are hard at the bottom too and healthier plant overall.
This is partly why comparing par readings on a flat surface, the foot print numbers at for example growershouse, isn't as reliable as it may seem. They do not equate directly to total photosynthesis in the plants and the angles can make a huge difference.
Greenhouses across the globe are changing to diffuse glazing because of the proven results, more photosynthesis and a significant increase in yield for a wide variety in crops from vegetables to house plants.
"The Wageningen University in the Netherlands showed that by using diffuse greenhouse covering materials, production of sweet pepper can increase 5 to 6 percent during the summer. Another experiment with cucumbers raised the number of crops by 7.8 percent, and showed a weight increase of 4.3 percent. If a material had been developed with the same haze but with 4 percent more light, then the production values would have raised to 11 percent and 7.8 percent, respectively. The list of trials conducted by Wageningen UR can easily be expanded with tomatoes on average being 8.5 grams heavier. With regard to potted plants, the cultivation period for chrysanthemum could be reduced by 25 percent."
"We will see a larger benefit from diffuse light in areas with more direct light. For example, Holland is already rather cloudy due to its geography, so the effect of diffusing light will not be as great"
Again, the difference is substantial there already, the potential much larger, especially with artificial lighting not scattered as much by the atmosphere.
Uniformity is in this context how uniform the light is spread throughout the crop. Worst case scenario is light merely straight from the top. Heating up (if at all) and possible saturation and photoinhibition at the top layer of the canopy. Inherently not providing adequate penetration (hence intra/inter lighting in pro settings). Scattered light, penetrating the crop from many different angles, including reflecting more throughout and by the plants itself is what leads to the best uniformity of chlorophyll levels and photosynthetic efficiency throughout the plant. It makes a significant difference with directional light, up to negating that reflector loss %, but in real world photosynthesis.
The better uniformity led fans claim is one of those typical examples of how negatives are turned into positive (which, if realistic and practical is a very wise thing to do). The better uniformity really refers to spreading out a large led array uniformly over a surface, like some blurple monos setups, at the source. The cobs are not uniform by itself, even within the narrow beam there is a lack of uniformity with light intensity being higher at the center than the outer diameter.
Lenses can help there but it reduces efficiency, so do cob reflectors (10-15%). With many led diodes spread out there will be enough overlap and no hotspots. Spreading out the leds at the source is sort of making up for led being so directional. The light doesn't spread well when emitted, so you spread the light emitter itself. When you start using cobs you give up some of that advantage, especially if you keep them close to the canopy.
When cree starts offering larger packages with higher lumen output (lumen works fine for comparing bay lights) to replace the popular cree cobs, will the amount of light sources reduce further.... what happens when you can use only 1...
Led fans are always quick to link to the same icmag thread showing high reflector losses for hps fixtures but as I just pointed out in the thread ( https://www.icmag.com/ic/showthread.php?p=7401326#post7401326 ) there's more to a reflector than reflecting a certain % of light. That's relevant if, again, you only care about the par watt efficiency at the source, rather than the real purpose of using a grow light: photosynthesis in the plants
Sacrificing reflector efficiency for uniformity and better penetration and spread to effectively increase photosynthesis at the cost of efficiency at the source is an example of the difference between designing a grow light and pretengineering.
Good post from supraspl, especially the first sentence:
https://www.rollitup.org/t/diy-cob-reflectors.854312/
TLDR: subtract another 10-20% (in addition to subtracting up to 20% difference caused by the inherent leaf temp diff) of the par w efficiency numbers when converting to more realistic results on photosynthesis.
Discuss...
Oh and no trolling please.
If the trolls want to participate, restrict your replies to "I agree/disagree, because <insert relevant valid arguments and logically true conclusions>" and you may get some attention.This replacement 'bulb' can provide better uniformity and penetration and photosynthesis than a diy cob light:
Not suggesting anyone buy that bulb of course, their numbers are inflated.
Just as less heat, LED being directional is often presented as an advantage. Which is true in some ways, but the opposite of reality in others. The main advantage is being able to direct the light downwards (and the heat upwards). More specifically, the advantage is that you do 'not' have to direct the light upwards, away from the plants. Being forced to a limited direction is not actually an advantage. Intuition may make one believe so, but is not the same as reality.
See this article for the difference, you may learn something about container gardening in the process:
http://gardenprofessors.com/container-planting-intuition-vs-reality/
Cannabis' structure is evolved under the sun, and not optimized to receive light straight from above. Much of the sun light is scattered in the atmosphere and arrives as diffuse light on earth's plants.
A common problem led users run into is lack of penetration. Some lower the leds, others go as far as to defoliate the plant... Futile, and out of ignorance, and very ironic, as usual. A few quotes:
"Plants use diffuse light more efficiently than direct light, which is well established due to diffuse light penetrates deeper into the canopy and photosynthetic rate of a single leaf shows a non-linear response to the light flux density. Diffuse light also results in a more even horizontal and temporal light distribution in the canopy, which plays substantial role for crop photosynthesis enhancement as well as production improvement"
"Therefore, the direct light usually wastes photons by concentrating the light resource to only a fraction of all leaves, leading to a less efficient photosynthetic use of light by plant canopies (Gu et al., 2002). Diffuse light, however, effectively avoids the light saturation constraint by more evenly distributing light among all leaves in plant canopies, and leads to a more efficient use of light (Gu et al., 2002)."
"Diffuse light penetrates deeper into the canopy; thus, the lower positioned leaves receive on average a higher light intensity which leads to a higher total nitrogen and chlorophyll content in the canopy, and consequently results in a higher leaf photosynthetic capacity in the lower of the canopy (Li et al., 2014a)."
"Diffuse light improves spatial light distribution in the crop canopy, thereby stimulating crop photosynthesis; the more uniform horizontal light distribution within the canopy plays the most important role for this effect."
That same more even distribution applies to temperatures. The combination allows in case of cannabis allows for taller colas, donkey dicks, that are hard at the bottom too and healthier plant overall.
This is partly why comparing par readings on a flat surface, the foot print numbers at for example growershouse, isn't as reliable as it may seem. They do not equate directly to total photosynthesis in the plants and the angles can make a huge difference.
Greenhouses across the globe are changing to diffuse glazing because of the proven results, more photosynthesis and a significant increase in yield for a wide variety in crops from vegetables to house plants.
"The Wageningen University in the Netherlands showed that by using diffuse greenhouse covering materials, production of sweet pepper can increase 5 to 6 percent during the summer. Another experiment with cucumbers raised the number of crops by 7.8 percent, and showed a weight increase of 4.3 percent. If a material had been developed with the same haze but with 4 percent more light, then the production values would have raised to 11 percent and 7.8 percent, respectively. The list of trials conducted by Wageningen UR can easily be expanded with tomatoes on average being 8.5 grams heavier. With regard to potted plants, the cultivation period for chrysanthemum could be reduced by 25 percent."
"We will see a larger benefit from diffuse light in areas with more direct light. For example, Holland is already rather cloudy due to its geography, so the effect of diffusing light will not be as great"
Again, the difference is substantial there already, the potential much larger, especially with artificial lighting not scattered as much by the atmosphere.
Uniformity is in this context how uniform the light is spread throughout the crop. Worst case scenario is light merely straight from the top. Heating up (if at all) and possible saturation and photoinhibition at the top layer of the canopy. Inherently not providing adequate penetration (hence intra/inter lighting in pro settings). Scattered light, penetrating the crop from many different angles, including reflecting more throughout and by the plants itself is what leads to the best uniformity of chlorophyll levels and photosynthetic efficiency throughout the plant. It makes a significant difference with directional light, up to negating that reflector loss %, but in real world photosynthesis.
The better uniformity led fans claim is one of those typical examples of how negatives are turned into positive (which, if realistic and practical is a very wise thing to do). The better uniformity really refers to spreading out a large led array uniformly over a surface, like some blurple monos setups, at the source. The cobs are not uniform by itself, even within the narrow beam there is a lack of uniformity with light intensity being higher at the center than the outer diameter.
Lenses can help there but it reduces efficiency, so do cob reflectors (10-15%). With many led diodes spread out there will be enough overlap and no hotspots. Spreading out the leds at the source is sort of making up for led being so directional. The light doesn't spread well when emitted, so you spread the light emitter itself. When you start using cobs you give up some of that advantage, especially if you keep them close to the canopy.
When cree starts offering larger packages with higher lumen output (lumen works fine for comparing bay lights) to replace the popular cree cobs, will the amount of light sources reduce further.... what happens when you can use only 1...
Led fans are always quick to link to the same icmag thread showing high reflector losses for hps fixtures but as I just pointed out in the thread ( https://www.icmag.com/ic/showthread.php?p=7401326#post7401326 ) there's more to a reflector than reflecting a certain % of light. That's relevant if, again, you only care about the par watt efficiency at the source, rather than the real purpose of using a grow light: photosynthesis in the plants
Sacrificing reflector efficiency for uniformity and better penetration and spread to effectively increase photosynthesis at the cost of efficiency at the source is an example of the difference between designing a grow light and pretengineering.
Good post from supraspl, especially the first sentence:
https://www.rollitup.org/t/diy-cob-reflectors.854312/
TLDR: subtract another 10-20% (in addition to subtracting up to 20% difference caused by the inherent leaf temp diff) of the par w efficiency numbers when converting to more realistic results on photosynthesis.
Discuss...
