Amount of light?

[Delps8]

Personally I would do some defoliation, lst, etc along with adding fill lights to boost what the lower portions get.

Yup. I've ended up with a couple of spare lights and, I'm trying to think of ways to use them for my next grow.

An unused grow light really is a sad thing when you think about!

 

[Talonxracer]

Yup. I've ended up with a couple of spare lights and, I'm trying to think of ways to use them for my next grow.

An unused grow light really is a sad thing when you think about!

If I do no lst to a plant and I get a typical phallic appearing plant I always add fill lights in the vertical corners of the tent in this pic I already harvested the top 8" (1.4oz dry). With the fill lights the rest of the plant was done at the same time

 

[Delps8]

If I do no lst to a plant and I get a typical phallic appearing plant I always add fill lights in the vertical corners of the tent in this pic I already harvested the top 8" (1.4oz dry). With the fill lights the rest of the plant was done at the same time
View attachment 1479976

Thanks for that info. That's a really solid, KISS approach.

I've always (all three grows <insert smiley face> ) topped my plants so I've never thought through how to harvest a plant grown that way.

 

[Butrod]

The DLI is more of a starting point(some plants want a little more, some less), the DLI is how much light the plant can use in photosynthesis, bigger does not change the amount of light the plant receives at individual leaves .

True, but doesn't the plant consequently need more light the bigger it gets? From the light it will get energy which will be used to grow. Each day the plant builds a few thousand more cells, nodes, internodes all which can process more sugar to grow even more. So, from a physiological standpoint out, it should be able to use up a greater net amount of sugar as each day passes so it consequently would need to intercept more light, too. Outdoors that's happening.

 

[Butrod]

If you measure the PAR at the surface of a cannabis leaf and then measure the PAR directly below the leaf, the reading below the leaf will be a tiny fraction of the reading that was taken above the leaf. I checked into this a few months ago and, even though the leaf was narrower than the 1" sensor on the Apogee, the reading below that leaf was below the light accommodation point, meaning is the amount of light needed to be a net photosynthetic contributor to the plant (63 µmols in cannabis)

Thanks for that number. I tried googling where that come from but only found this:

An Update on Plant Photobiology and Implications for Cannabis Production - PMC

This review presents recent developments in plant photobiology and lighting systems for horticultural crops, as well as potential applications for cannabis (Cannabis sativa and C. indica) plant production. The legal and commercial production of the ...

www.ncbi.nlm.nih.gov

Light Compensation and Saturation Points
Increased PPFD increases with plant growth and photosynthetic rate, and this linear increase occurs between the light compensation point and the light saturation point. The light compensation point is the point at which the photosynthetic activity of the plant equals its respiration activity, and the resulting CO2 release from respiration is equivalent to that used during photosynthesis. The light compensation point is used as a base to select an appropriate light intensity. If light intensity is below the light compensation point, there is a net loss of sugars (Noodén and Schneider, 2004).

Does that mean now all my lower leafs about 2-3 inch below the canopy are loosing energy instead of creating them?

 

[Delps8]

Thanks for that number. I tried googling where that come from but only found this:

An Update on Plant Photobiology and Implications for Cannabis Production - PMC

This review presents recent developments in plant photobiology and lighting systems for horticultural crops, as well as potential applications for cannabis (Cannabis sativa and C. indica) plant production. The legal and commercial production of the ...

www.ncbi.nlm.nih.gov

I appreciate you sharing that link. I've googled it a few times and the only link that I was able to come up with is here. Bugbee sorta mentions it in passing in one of his videos. Besides those two references, I've seen nothing else except for your link.

One of the reasons I've looked into that is because, well, I'm curious by nature but, more importantly, I'm interested in finding out more about defoliation.

Does that mean now all my lower leafs about 2-3 inch below the canopy are loosing energy instead of creating them?

Any leaf that receives less than the light compensation point is a net loss in terms of photosynthesis meaning that they burn more carbs than they create. That's, obviously, not a major issue because cannabis has been a round 6 times longer than we've been walking upright (28 MM years vs ≈ 4.3 MM) so that would imply that those leaves are doing something valuable for the plant other than just acting as sugar factories and, yup, they are. They're valuable for transpiration, defense, and as nutrient stores. I'm sure there are other functions - that's just off the top of my head recalling my high school bio classes from half a century ago.

One of the things I want to do this summer is start learning about plant biology so if anyone has a recommendation for a good intro text, please let me know.

 

[Death The Cultivator]

True, but doesn't the plant consequently need more light the bigger it gets? From the light it will get energy which will be used to grow. Each day the plant builds a few thousand more cells, nodes, internodes all which can process more sugar to grow even more. So, from a physiological standpoint out, it should be able to use up a greater net amount of sugar as each day passes so it consequently would need to intercept more light, too. Outdoors that's happening.

No, at least not in my experience. 1ft tall mother plant vs a 6ft tall plant still benefits from the same DLI. All the biomass deemed non productive, weak/thin branches get removed in veg and flower. In my previous example, light saturation occurred at just over 25 DLI with 800ppms of c02 despite it being a room full of 6-8ft tall plants.

From seed to harvest without c02, DLI goes between 3-40 or 70-900ppfd. Without the right conditions as ambient c02 is around 400ppms, only so much growth is achievable compared to running 1000ppms and having that DLI be 25-50(no extra c02 pre veg) or 300-1100ppfd.

Another consideration is the optics of the grow lights. Cobs/boards/hid have more intense but smaller light patterns compared to strips. The former suits large plants much better than the latter which works better in vertical close proximity situations.

Outdoors, plants only get so large and the intensity does not remain constant as the sun rises/sets. The equator reaches 2000ppfd with a lot of factors influencing the DLI, even in the tropics, the average DLI is between 20-40. Again, ambient c02 is only 400ppms.

Ultimately, we're playing a game of diminishing returns past a certain point.

Wavelengths of light and photosynthetic pigments (article) | Khan Academy

Properties of light. How chlorophylls and other pigments absorb light.

www.khanacademy.org

I think the only solution where "more" light would be a benefit in a large plant is by adding 20% more lighting to the sides of a plant - 480w+100w of side lighting that focuses on the areas where the light cannot penetrate as well from above.

I'm in a group that has been testing grow cabinets and with side lighting of 50w and top lighting of 250w - 13-18oz have been achieved in a 2x2 with only 20% more light filling the gaps that the top can't reach. Nearly double of what I see normally achievable(50-75g per sqft)

The way I imagine that is rain coming down but the edges being weak so the center of the plant and canopy receive more light than the sides and lower branches outside of the optimal range of the top lighting.

With strip lighting I typically saw between 12-18 inches of penetration vs 1000w DE getting ~36".

 

[Death The Cultivator]

I appreciate you sharing that link. I've googled it a few times and the only link that I was able to come up with is here. Bugbee sorta mentions it in passing in one of his videos. Besides those two references, I've seen nothing else except for your link.

One of the reasons I've looked into that is because, well, I'm curious by nature but, more importantly, I'm interested in finding out more about defoliation.



Any leaf that receives less than the light compensation point is a net loss in terms of photosynthesis meaning that they burn more carbs than they create. That's, obviously, not a major issue because cannabis has been a round 6 times longer than we've been walking upright (28 MM years vs ≈ 4.3 MM) so that would imply that those leaves are doing something valuable for the plant other than just acting as sugar factories and, yup, they are. They're valuable for transpiration, defense, and as nutrient stores. I'm sure there are other functions - that's just off the top of my head recalling my high school bio classes from half a century ago.

One of the things I want to do this summer is start learning about plant biology so if anyone has a recommendation for a good intro text, please let me know.

Raven Biology of Plants, Eighth Edition (9781429219617) | Macmillan Learning

Request a sample or learn about ordering options for Raven Biology of Plants, 8th Edition by Ray F. Evert from the Macmillan Learning Instructor Catalog.

www.macmillanlearning.com

This has been favorite so far.

 

[Delps8]

True, but doesn't the plant consequently need more light the bigger it gets? From the light it will get energy which will be used to grow. Each day the plant builds a few thousand more cells, nodes, internodes all which can process more sugar to grow even more. So, from a physiological standpoint out, it should be able to use up a greater net amount of sugar as each day passes so it consequently would need to intercept more light, too. Outdoors that's happening.

You're on the right track but switch it around just a bit.

As a plant grows more leaves and as those leaves mature, the plant can take process more light - there's more "solar panels". And, the plant will be able to photosynthesize more (generate more carbohydrates) as it gets bigger because there's more leaf area. That, in turn, will require additional sugars for the plant to survive.

 

[Delps8]

Raven Biology of Plants, Eighth Edition (9781429219617) | Macmillan Learning

Request a sample or learn about ordering options for Raven Biology of Plants, 8th Edition by Ray F. Evert from the Macmillan Learning Instructor Catalog.

www.macmillanlearning.com

This has been favorite so far.

Thank you. I'll definitely check it out.