[spurr]

Hey all,

Here are two good articles by David R. Hershey that debunk many wrong ideas in plant science, I especially like the part about green light, etc. I have a few studies showing that green light, under bright (high irradiance) white light (ex. HID) can drive rate of photosynthesis more than blue and red light.

The claims that green light isn't useful is total BS, and based upon flawed 'chlorophyll A/B absorption spectrum' curve passed around the cannabis world for many years (found via. a leaf extract inside a "spectrophotometer"; see this example). That is one major reason I dislike most LED arrays: they lack sufficient green light.

The 'action spectrum of photosynthesis' gives a much better representation of quantum yield from blue, green and red range light than does the 'chlorophyll a/b absorption spectrum'. Albeit the quantum yield of green light from high irradiance white light is undervalued in Kieth McCree's 'action spectrum of photosynthesis' (which is why Keith McCree's work, re: Quantum Flux Density and Quantum Yield Curve, are a bit flawed).

"Avoid Misconceptions When Teaching About Plants"
David R. Hershey
https://www.actionbioscience.org/education/hershey.html


"More Misconceptions to Avoid When Teaching about Plants"
David R. Hershey
https://www.actionbioscience.org/education/hershey3.html

[budlover123]

I was thinking that LEDs might be cool as a low power supplement to HPS to balance out the light spectrum a bit, like a bunch of royal blues and a couple white to balance it out, maybe green would be a better choice, that would make a nice cyan color. I've seen 1350 mW of royal blue leds change the color of a 400 watt HPS pretty noticeably, I'd like to test some green leds. Those direct color LEDs are something

edit: its noticeable to the naked eye, but a camera with standard white balance doesn't show a big difference

[Azeotrope]

If you only knew how many times I have heard the "green light is worhtless to plants" myth while discussing the CMH bulbs I like......... Just drives me crazy! Yes they have a large spike in that area of the spectrum and I like it.

[foomar]

Good link spurr , these two examples could save a lot of arguments , well worth reading in full .

A widespread misconception states that leaves reflect all green light and do not use green light in photosynthesis. Leaves often absorb more than 50% of the green light and use it efficiently in photosynthesis.The origin of this misconception is probably the chlorophyll absorption spectrum in textbooks. The chlorophyll absorption spectrum is a graph of light absorption versus light color. It shows that chlorophyll absorbs much red and blue light but little green light. However, accessory pigments absorb green light and pass that energy on to chlorophyll.


Capillarity is not a factor in upward water movement in stems. Capillarity occurs in tubes of small diameter that are initially empty. Water spontaneously moves up such tubes. Functional xylem comprises small diameter tubes that are not empty to begin with.

[GreenintheThumb]

So do you think that green light can upset the night cycle?

[trichrider]

that was inevetible...

[mean mr.mustard]

Math-durbators will rise and follow him! The rest will need actual proof.

Here's a tent full of plants grown entirely with 300 watts of LEDs at day 42 of 12/12. They stand 36" tall and the central colas are 18" by 3 1/2 inches. In fact the only thing hold back their height was the top of the tent. It's nice to read and try to understand how things will affect growth and maturation, but in the end experimentation will prove theories right or wrong.



If you like HID's fine! But don't try and and BS others into following you in order to stroke your ego, it's just not right.

[Unclepeter]

Originally Posted by GreenintheThumb

So do you think that green light can upset the night cycle?

if on all night, but green by itself is bad IMO, when used alongside red/blue and purple as each pigment absorbs differently to each other its beneficial, chlorophyll a likes red/yellow to green, b likes red,green and blue c and d are green and bacteriochlorophylls a-d likes pale blue to purple in this case its fine. but both c and d are more for algae production. higher plants typically like red/blue to green.

[mean mr.mustard]

So where's all this red light useful?

What about phytochrome?