Light and Foliage density theory Maximizing g/watt

Intro

These are my thoughts on how to maximize yield per watt.
I know it is long, but if you read the entire post, I have broken down every piece of math and theory on plant growth to amount of light and light density that I can think of and even if you don’t understand all of it you should be able to get a general gist and this may help immensely in gaining g/watt. I have broken it down into sections also so you can easily reference back.

Background

So I have been doing scrog for a few years now. My space is only five feet high and I have 600 watt lights, so scrog is a necessity. I have thought a lot about efficiency in terms of g/watt, g/sq. foot, g/gallon soil, etc. There are many different ways to quantify efficiency. Most people look at g/watt. This is what I strive for as well. I am not limited on space, but I only have so many lights and so many outlets to run them on, so maximizing g/watt is my goal.
First let me say that if you are not limited on light and need to maximize g/sq. foot, this does not really apply to you. Some of it may be partially relevant though and I would recommend to read this anyway.
About two years ago I saw this guys thread.
https://www.icmag.com/ic/showthread.php?t=174163 Im sure a lot of you have looked at this already. I had never really plucked leaves before, a few here and there but nothing like this guy was suggesting, but decided to give it a try since our setups were pretty similar. Before this I had only been getting about 8 zones per light, not that great. So I did a control test where I literally plucked every leaf longer than about an inch every day all through flower. The plants did pretty good, but bulbs were old and sq footage was small, so yields were about the same. The second round I plucked a little less and waited longer into flower to start plucking heavily. These guys still had a small footprint per light but I did get about 10 zones a light. The biggest success for me though was the g/gallon of soil and g/sq foot. One of them finished at just over 5 zones in a 3.5 gallon bucket, about twice what I was getting before I started plucking, and the zones/sq foot was around 1-1.5. Anyway, that’s just some background on my theory. Heres the interesting stuff.

I made this thread about a year ago on light distance, the first post is relevant for this thread although not absolutely necessary to read if you don’t feel like it.
http://www.gardenscure.com/420/lighting/136337-myth-inverse-square.html#post1360760

My theory is, its not about using all of the light, what matters most is the efficient use of the light. So even if some light hits the ground, this may not be a bad thing.

Leaf Theory

Leaf Efficiency With Respect to the Plant(nugs)

Lets start with the leaves. Each leaf needs energy to stay alive, and each leaf produces energy as well. The efficiency of a single leaf with respect to the plant is equal to Eout/Ein. Eout is energy produced by the leaf, and Ein is energy used by the leaf. This means if more energy is produced by the leaf than is used by the leaf the efficiency is greater than one. So anything over one means a net gain of energy for the plant(nugs).

Leaf Efficiency With Respect to Light

Now we get into a lot of speculation. The assumptions I am making are necessary to develop this theory and are generally correct, but will vary depending on setup, strain, etc.
Depending on light density (watts/sq foot), each leaf will have a different efficiency of converting that light to energy for the plant. This is efficiency with respect to light, not to the plant as I was explaining earlier. Here the efficiency is Eout/Ein also, except Ein is amount of light that hits the leaf. Eout is still energy the leaf produces. This efficiency will be less than one, and depends on the light density. Say you have 100 watts per sq ft. This is way more than this leaf can actually use. Lets assume it can convert 50% of this light to energy for the plant. This means the leaf creates 50 watts per square foot. Still a lot of light. Now lets pretend we are supplying 50 watts/sq foot. The leaf will be able to use a higher percentage of this light, say 75%. This means the leaf creates 37.5 watts. This is a 50% increase in efficiency. Of course, these numbers are pure speculation, but the idea is right. The more light that hits a leaf, the less efficiently it can use this light. This is the law of diminishing returns, which holds true for everything except geodesic domes. Sidenote: Geodesic domes are the only structures that gets stronger as you scale them up in size(I am an engineering nerd, as you can probably guess by this post already).

Once the light density is below a certain amount the leaf can no longer produce more energy than it needs to stay alive. Say the leaf needs 10 watts per square foot to break even on Eout/Ein with respect to the plant. If you supply 10 watts/sq foot, then even if this leaf is using 100% of the light, it still isn’t worth having the leaf because it only creates enough energy to support itself.

I hope everyone is still with me here, this is a lot of info to read. Even I am getting lost as I reread it. And there is a lot more coming.

The Sweet Spot

So there will be a sweet spot of watts/sq foot where the leaf is most efficient with respect to light and amount of energy it supplies to the plant. There is the initial 10 watts it needs to survive, and then anything additional goes to the plant(nugs). But the more light you supply above this sweet spot of watts/sq foot the less the plant gains per watt because of the loss in efficiency. This is where the largest assumptions and greatest variation between setups and strains will be. I think anything over 50 watts per square foot is too much. The guy in the thread I referenced had 40 watts/sq foot, and he was hitting over 1g/watt.

Low Light Density and Leaf Plucking

Overall Efficiency With Respect to Light

Say you are running 40 watts per square foot. Each leaf needs 10 watts/sq foot to support itself. Say the leaf is 80% efficient at converting the light to energy at this light density. Then the Eout/Ein of leaf to plant is ((.8*40watts)(energy the leaf creates))-((10watts)(energy the leaf uses))=22 watt gain for the plant(nugs).
Now we can look at net gain of energy by the plant versus energy supplied by the light. In the example above the plant gained 22 watts per 40 watts of light. This is an efficiency of 22/40=55%. Now lets pretend we are using 100 watts/sq foot. The leaf is 50% efficient at this light density. Therefore the leaf gains 50 watts and uses 10. The plant gains 40 watts and the efficiency of plant(nugs) to light is 40/100=40%. Therefore the better g/watt efficiency will be at 40 watts/sq foot. Now pretend we have 20 watts/sq foot at 90% efficiency. The leaf gains 18 watts, uses ten and the plant gets 8 for an overall nug to light efficiency of 8/20=40%. Therefore the “sweet spot” is around 40 watts/sq foot.

Disclaimer

All of this hinges on the assumptions made about how much light is needed per leaf, and how efficient each leaf is at converting energy at different light densities. The assumptions above are only to demonstrate the theory, and may be quite different than real world numbers. I know plants are usually only about 5-20% efficient at converting light to usable energy, but for the purpose of this argument I just used easier numbers. So to the naysayers who will gripe about unrealistic figures, read the bold section, I know they are unrealistic but this is the math that needs to be considered when trying to increase g/watt.

Extensive testing would need to be done to find any real numbers. However, the guy in the above thread uses 40watts/sq foot and yields over 1g/watt, clearly something is working well. Conventional pot growing wisdom says a minimum of 50watts/sq foot should be used. This might be true if you are trying to get larger yields per sq foot but that is not the goal here.

Leaf Plucking

If half the leaf is covered by other leaves(assuming the light that penetrates these leaves is negligible) then the leaf is useless because it is only getting 20 watts. The 20 watts is used on half the leaf at an efficiency of 80%. Therefore the leaf creates 18 watts, uses 10, and overall efficiency is only 40%. Half the leaf is covered, therefore this half is not creating any usable energy, and is useless to the plant. But if you pluck the leaf above it, then this whole leaf is getting light and efficiency goes up 15%.

Example of Shaded leaf

This is my argument for low light density and a very thin canopy. The low light density means that the leaves have a high efficiency of converting light to energy. The thin canopy makes it so that there are very few leaves that are shaded and so every leaf is efficiently using the light. Suppose there is a spot 1 inch square that light doesn’t hit anything but goes to the ground, and this light is lost. Now suppose there used to be a leaf there. The leaf though is a large fan leaf and takes up 4 sq inches. Only 25% of this leaf is getting light. The rest is heavily shaded by other leaves, stems, and nugs. Lets scale up so I can use the same numbers as before and not confuse people more than I already have with this post. Say the hole is 1 sq foot, and the leaf is 4 sq feet. Same proportions only now I can use my 40 watts per square foot I used before. The leaf creates .8*40=32 watts total, not per sq foot of leaf, but for the one square foot that the light is hitting the leaf in. Therefore the leaf creates a total of 32 watts. But the leaf needs 10 watts per square foot to stay alive. Therefore the leaf uses (4 sq feet)*(10 watts/sq foot)=40 watts to stay alive and creates 32 watts of energy. Therefore there is a net loss of 8 watts. This leaf is taking energy from the plant instead of supplying it. I would pluck this leaf.

Leaf Plucking

I pluck leaves on top and on bottom. Top ones because they shade everything, bottom ones because everything shades them. I try to leave a 1-2 leaf thick canopy, but I do have spots where a little bit of light hits the floor. Of course some light penetrates the leaves, and at higher watts/sq foot more light will penetrate and a denser canopy may be desirable. I am still fine tuning this and don’t have all the answers, but the reasoning behind it is sound. The only problem is finding the “sweet spot”. Also, plucking the leaves stunts the branches that you pluck them from. So for my setup I can pluck leaves to slow growth of specific branches. As long as you don’t trim the whole plant from dense canopy to nothing in one day, the overall growth will not slow and flowering will not be delayed, if anything it speeds it up. Stretch is also minimized the more you pluck.

I don’t really know how to wrap this up, but luckily this is a forum and people can ask questions and comment, so I don’t really have to. Thanks for reading and please do ask questions/comment because I think this is an important topic.

Hmmmm, dissapointing that this got so little attention. I think this explains the use of light more in depth than anything I have ever seen. Just reread it since I wanted to post a follow up.

Update
Since posting this I have had more and more success with plucking leaves and low light density. My setup is still the same 4 feet by 4 feet under a 600 watt doing a scrog. The last harvest I had 4 chambers, 2 lights per chamber, with a few cfls in the corners for side lighting. Pots were 3.5-10 gallons. I had basically two harvests since I originally posted this thread. My average yield per chamber was around 930-950 grams. When factoring in the cfls, which I only used for the last month of flower, this comes to a yield of a little over 1 lb per 600 watt light. Just wanted to bold that for the people who skim through. The gram per watt was .75-.8 depending on the chamber. This is an increase of about 40% from anything I ever got with higher light densities and a thicker canopy. Same strains and relatively the same amount of experience.

I hope people read the first post and think about how this relates to their grows since, in my opinion, 90% of what I have read about maximizing yield and trimming plants is wrong.

Hi dudex

I have done this defoliation technique myself in the past with mandala satori & grapefruit.

I do not have any pictures from that grow or any record of it other than comments i made at the time on the icmag thread It was that thread which inspired me to try this technique and i yeilded my biggest harvest to date.

I found a long veg time combined with a little lst during early veg yeilded the greatest but i guess a lot is dependant on the strain you are working with & the environment etc

PEACE

I think its a great thread..everything makes sense.