Green wavelenght penetration to Lower Leaves

[porrista]

Hi,

I've been reading a lot this past days regarding light penetration and ended up reading that since the upper leaves capture most of the blue and red light, the green light gets reflected and transmitted/transferred to the lower leaves.

Read elsewhere that a plant has 2 types of leaves normally, some are specialized in receiving direct light and others, the lower leaves also capture the rest of the wavelengths not captured initially by the top leaves.

I see a lot of people recommending adding CFLs to the LEDs for light penetration, but when I check the CLFs spectrum, even the hot spectrum ones have a peak in yellow and green, which are supposed to not be used for plants for photosynthesis, yet plants do use this energy. so I wonder, why not putting some green light in the LEDs? Is it a matter of efficiency? Are LEDs best suited for LST and SCROG?

Also read that calyxes are not crucial in photosynthesis. They are generally light green compared to dark green found in leaves, product of photosynthesis.

Finally, is the UV light in the LED lamps exclusively for making the plant produce more resin/trichomes, to protect the seeds DNA from UV?

Also wondering if a fan blowing wind directly to the buds will also make them produce more resin to avoid dehydration

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References and citations:

Photosynthesis and leaf adaptation: how sun and shade plants respond to light - See more at: http://www.saps.org.uk/secondary/teaching-resources/113-photosynthesis-and-leaf-adatptation-measuring-rate-in-leaf-discs-from-sun-and-shade-plants-to-green-light#sthash.hMHhHiBT.dpuf

Leaves typically transmit only a few percent of incident PAR in the green band at around 550 nm, and are otherwise efficiently opaque in the visible range. Transmittance of PAR is normally less than 10%, whereas transmittance of far-red light is substantial (Terashima & Hikosala, 1995).

Leaves like to other biological surfaces not only transmit light but reflect a proportion. The amount of reflection depends on morphological and physical properties of leaves such as, leaf shape, thickness and shininess of the cuticle. However, it should be noted that reflected light then may be absorbed or transmitted by the lower leaves similar to the radiation reaching the canopy surface.

http://cdn.intechopen.com/pdfs-wm/28377.pdf

The effect of heat and wind on leaf water loss is greatest at the top of the tree. A tree, or any other plant, has several strategies to reduce the inevitable loss of water. There is a waxy covering (cuticle) on the leaf to reduce desiccation.
http://www.na.fs.fed.us/spfo/pubs/uf/lab_exercises/comparing_sun_leaves.htm

 

[churchhaze]

All photons between 400-700nm are effective at generating photosynthesis, it's just that some are more likely to be absorbed than others.

The most important spec of any light is intensity in either uMol/s or PAR W (total light output) per input watt of electricity.

 

[SupraSPL]

I see a lot of people recommending adding CFLs to the LEDs for light penetration, but when I check the CLFs spectrum, even the hot spectrum ones have a peak in yellow and green, which are supposed to not be used for plants for photosynthesis, yet plants do use this energy. so I wonder, why not putting some green light in the LEDs? Is it a matter of efficiency? Are LEDs best suited for LST and SCROG?

Since CFLs shine in all directions and have their intensity spread over such a large surface area, it is hard to put the photons in the canopy where we want them. In other words they suffer a lot of reflector losses. So even if a CFL has the same lumens/W as a Home Depot LED, a spotlight style LED will put down a lot more photons/W. In other words, I would not recommend adding CFL unless you don't mind the extra heat.

 

[porrista]

Heat is not a problem, on the opposite, I think I could benefit from a couple of extra degrees and lower humidity caused by that heat. The problem for me is the electricity bill + the cabling for adding more lights. I would like to keep it as simple as possible and adding more lights = more connector and cables in my closet and I don't like the idea of leaving a bunch of stuff running in my closet while I'm not home. Have thought of putting a coffee cup heater inside to increase evaporation and water consumption but haven't done it because of my fear to run more stuff in the closet.

For this crop I will wait and see. I was just wondering if my plants would benefit from having the green spectrum in there as well and my wondering began when I saw the CFLs had this high green peak of light and very low levels of the wavelengths the LED outputs.

In fact, if the CFL produces unused wavelengths, how comes it works pretty decent for flowering? I had a crop with 138w of CFL, 69w 6500k and 69w 2700K and a single auto yielded 62g dry. If the CFL has a lower PAR than LED ( green peak is not absorbed for example ), it means LED HAS to be better than CFL just because of the PAR.

e.g.

From the peaks, I estimate 25% blues, 35% green and 40% red on a CFL, the rough PAR could be like 60% of the wattage, while with LED is is 100% PAR. So, if I use the same amount of watts, the LED will be more effective, right?

Also, if green light is not absorbed and the tent interior reflects 100% of the light, what happens to those photons?

I will leave my current grow with extra light, just to measure the outcome of the 150w LED I have. It's PAR is equivalent to a 250wHPS and it should yield accordingly. I will keep testing my yields this year with the LED only.

So far, I'm not convinced that CFL adds any benefit except for adding more PAR in the correct spectrums.

I would also like to see how lower bud development results with LED vs CFL. My current theory is that the green light photons of the CFL are used by the lower leaves to produce more bud in the lower zones and that LED may work better for LST and SCROG since the light it emits seems to be captured in the majority by the leaves at the top of the plant.

My other questions is: If the LED light is absorbed in its majority by the top layer, why does the plant still has a lot of healthy dark green leaves below the top canopy? Reflected light from the tent walls?

 

[Devildenis69]

Hey,

I'm pretty stoned right now and English isn't my native, so I haven't understood every stuff you said, I'll read it again
just wanted to notice that green wavelenght was useful in case of high light intensity, something about carotenoids ...

"[...] carotenoids participate in photoinduced electron transfer processes – they cannot transfer sunlight energy directly to the photosynthetic pathway, but pass their absorbed energy to (bacterio)chlorophylls. Carotenoids also protect against excessive light by quenching both singlet and triplet states of (bacterio)chlorophylls. The carotenoids are brightly colored in the portion of the visible spectrum where their absorbency is low and wavelengths are transmitted or reflected (red to yellow)"

I let people knowing better all this biological stuff better than me, speak about it

 

[porrista]

Hey,

I'm pretty stoned right now and English isn't my native, so I haven't understood every stuff you said, I'll read it again
just wanted to notice that green wavelenght was useful in case of high light intensity, something about carotenoids ...

"[...] carotenoids participate in photoinduced electron transfer processes – they cannot transfer sunlight energy directly to the photosynthetic pathway, but pass their absorbed energy to (bacterio)chlorophylls. Carotenoids also protect against excessive light by quenching both singlet and triplet states of (bacterio)chlorophylls. The carotenoids are brightly colored in the portion of the visible spectrum where their absorbency is low and wavelengths are transmitted or reflected (red to yellow)"

I let people knowing better all this biological stuff better than me, speak about it

Exactly, that's why leaves turn yellow when not getting enough direct lights.

 

[alesh]

Modern white LEDs - probably best LEDs for growing purposes right now - generally have about 40% of green light (500-599nm). They also produce more* light per dissipated energy while having less losses, too. I can't see how would you benefit from adding CFL's unless the purpose is to heat the canopy.

*LEDs - unlike CFLs - vary greatly in efficiency. Various cheap generic LEDs might be less efficient than CFLs while high quality ones could a lot more efficient.

 

[Devildenis69]

Exactly, that's why leaves turn yellow when not getting enough direct lights.

Interesting thing, I've already thought about it, and came to the conclusion that "our vision" is a very bad basis for thinking about leaf absorbtion ...
if you have some infos about the evolution of the leaf absorbance spectrum during flowering, I'll be very interested to hear about it

a studie that I found, let me think that the photosynthetic efficiency in 710~750nm was increasing at the end, while the 630~660nm was decreasing ... however there was one species among 4, that was behaving in an opposite way ... damn can't find this paper again