Zamieszczone przez knna
Thanks, guys. I hope we can work improving our setups by eliminating the wrong concepts that lead us to work on wrong directions.
In this sense, lets examine Penetration (BTW, if you want to find thousands of excelent botanists articles about this topic, search for "extinction coefficient k" (add "canopy" to eliminate results of other areas apart of botany).
The main thing I would like to dispell about Penetration is that the light source caracteristics, although affect on some degree, dont rule out it, but is one of the factors that affect less penetration. At least, if we consider just top lighting.
Penetration is mainly ruled out by how crowded is the grow area (how many leaves) and the angle of leaves. Light density achieved at bottom areas mainly depends of them, and just minimally of the caracteristics of the lighting, especially if its a fixed one.
Some botanist concepts are usefull in this context. Leaf Area Index (LAI) is an adimensional figure that informs of how many leaves there are for surface unit area. It sums the area of upper part of all leaves and divide it by the surface area of the grow. Thus a LAI=1 means that on a 1 sq meter of grow area, there is 1 sq meter of leaves (counting only upper part).
In general LAI is over 1, mostly between 2-4, but it may reach 6. Notice that growing techniques often are intended to strongly affect this parameter, thus the impact of SOG, SCROG, LST, defoliating, etc on "penetration".
Extinction coefficient (k) describes the attenuation of light density with vertical height. It depends strongly on the orientation of leaves. Planophile plants (most leaves are horizontal) have way lower K than erectophile plants (most leaves vertical). Especially when incident light comes from the zenit (the vertical).
The higher the LAI and k, the less light that reach the bottom areas.
In general, when using indoor just top lighting, it dont worth to have a LAI over 3. Usually a little over 2 is the max optimally useable indoors.
An ideal lighting must be designed according to LAI and k of plants being grown. And given the lighting setup is done, we must adapt LAI and k to the best values to get the best of the grow. Tyeing and pruning are great tools that allows us to strongly affect those parameters. Of course, LAI itself is very affected by how large is the plant, thus choosing the right vegetative time is critical to obtain the best results, as any mynimally experienced grower knows.
Therefore, its very difficult to generalize. What is good for 5ft plants probably isnt for 1ft ones. Different strains have different leaf angles, and more yet, plants have some ability to adapt it to the lighting environment. At the end, growers sharing their experience on their own conditions is the only key to improve on the long term.
There is no rules valid for all situations in this sense. Possible combinations of LAI and K are too many to fit a solution optimal for all. Aditionally, we can strongly affect them using growing techniques. Recently many people has discovered how defoliating plants may improve yields.
So we should forget to find an universal valid solution, but concentrate on understanding factors that affect on each situation and try to get the best for that concrete situation, either by manipulating the light setup, either by using general growing techniques.
But the main thing we must have in mind is that is not lighting that rules penetration, but plant's caracteristics.
Only understanding the given plant caracteristics we can design a lighting that works better for them. And on a opposite way, we can train our plants to use better a given lighting setup. Improvements on LED growing involve those two factors. Lighting and plants pattern must be considered together.