Importance of 460nm red LEDs?

"Hypothetical: So if a monochromatic LED could convert 50% of its electrical energy to yellow light, it would outperform a monochromatic LED that could only convert 25% of its electrical energy to deep red light. Is this (more or less) correct?"

Only if the plant is capable of using the Emerson effect to downshift that yellow light to another energetic wavelength it can use. Very few plants have this capability, most of them that do have it are aquatic plants. Cannabis is not one of them, it is like most terrestrial plants in that it uses the Emerson effect for downshifting blue into other wavelengths they require since upconversion from red requires an active power input and frequency modulation - something plants just can't do (at least on this planet.)

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Originally Posted by RackitMan

Interesting. So if I am understanding you or the article properly, it is not so much that a plant specifically needs 660nm light, it is just that that wavelength gives the greatest photon->CO2 conversion rate.

Hypothetical: So if a monochromatic LED could convert 50% of its electrical energy to yellow light, it would outperform a monochromatic LED that could only convert 25% of its electrical energy to deep red light. Is this (more or less) correct?

Or does our fave plant require a SPECIFIC trigger at 660nm that cannot be compensated for by other spectra?

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so all of the above info is useless...i correct you in the beginning...you claim typo..ha....you are wrong on 660nm with your chloriphyl b statement..i explain with real world results that you can't wrap your ears around and it is the peak absorption rate for photosynhtesis...we explain the inefficiencies and you still don't get it...it takes some scientific jargon to get you to point and you still miss the peak creation of photosynthesis is 660nm and adding CO2 will substatially help with yield...that is real world language!

to Paan~thank you for your post:thumbsup:

Besides using light to drive photosynthesis, specific wavelengths are required for things like avoiding stem elongation (we want short fat plants, not tall skinny plants), proper leaf shape/size/orientation, stomatal opening (the pores underneath leaves that allow the plant to breathe), and flowering (in some plants). Some responses like flowering vary widely from plant to plant while others like stem elongation and stomatal opening are almost universal. Most of those responses can be had with minimal amounts of blue light (again, it depends on the plant)

Besides all that, I believe you have the right idea: A yellow LED of a high enough efficiency could be more efficient at driving photosynthesis than a deep red. Unfortunately, there is no such thing as a yellow LED - only red or blue LEDs with phosphors to convert a portion of the light. As such they will never be as efficient as the base LED.

If we look at our bean plant data from before (if someone has this data for cannabis I'd love you forever) we can see that 700 nm light causes the plant to consume about 34 molecules of CO2 for every 1000 photons and 650 nm light causes the plant to consume about 103 molecules of CO2 for every 1000 photons. From this, one might guess that given 1000 photons of 700 nm light and 1000 photons of 650 nm light then the plant would consume 137 molecules of CO2, but actually it consumes a bit more. This effect was discovered in 1957 by Robert Emerson. This effect exists because all higher plants have two photosystems and a full photosynthetic cycle (not sure if I'm saying that correctly) can not proceed unless both systems are stimulated. photosystem I, containing more chlorophyll a, uses the 700 nm light more efficiently while photosystem II, containing more chlorophyll b, uses the 650 nm light more efficiently.

Anyway, I'm using about 20% 460 nm blue LED and the rest 660 nm red.

Oh wow you just set an alarm off in my brain.

I was reading some article the other day about greenhouse growing of spinach and strawberries and some other things. In all cases they were able to significantly reduce the amount of light required by increasing the concentration of CO2 in the air. This is because the last part of photosynthesis, which takes CO2 from the air and converts it to sugars will also take in Oxygen and use it for photorespiration. Photorespiration allows the plant to sustain itself but doesn't really let it grow. In normal air a molecule of oxygen is used for every molecule of CO2 but the rate of CO2 can be increased by increasing its concentration in the air. This is important because as of now, it is more expensive to provide supplemental lighting (both the initial and electrical) than it is to fill a growing chamber with additional CO2.

Again...thank you for your input! it is well explained!:thumbsup:

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Originally Posted by thepaan

Anyway, I'm using about 20% 460 nm blue LED and the rest 660 nm red.

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For the whole grow or just for flowering? I used strictly a 50w blue LED panel last year for veg, no red or white, and it worked very well for my two medium small plants which I found surprising.

How many watts of LED do you find necessary per square foot (I realize it depends greatly on the output and wattage of the LED) for a decent grow and which manufacturer/emitter wattage did you choose?

I see E-Bay has some 20w 630nm LEDs for $16 to $25 or I can buy some 10w 660-670nm emitters for $30 at Mouser. As this is strictly for my own small (2' X 2') grow, intital cash outlay is more important than optimal efficiency. Your thoughts on this?

"Unfortunately, there is no such thing as a yellow LED"

I manufacture 570-580nm diodes.

"This is because the last part of photosynthesis, which takes CO2 from the air and converts it to sugars will also take in Oxygen and use it for photorespiration."

Atmospheric CO2 will not have an effect on the O2 concentration in the soil or medium - roots import oxygen, leaves export oxygen. They were able to reduce the light required with the CO2 increase due to the current effectiveness of LEDs, and the fact you don't have yellow or green light inhibiting other processes - you remove one limitation only to hit another one - they ran into the CO2 barrier and had to supplement.

Roughly 20 photons = 1 molecule of sugar. They didn't have enough CO2 for the consumption/sugar production part of the Krebs cycle.

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Originally Posted by RackitMan

For the whole grow or just for flowering? I used strictly a 50w blue LED panel last year for veg, no red or white, and it worked very well for my two medium small plants which I found surprising.

How many watts of LED do you find necessary per square foot (I realize it depends greatly on the output and wattage of the LED) for a decent grow and which manufacturer/emitter wattage did you choose?

I see E-Bay has some 20w 630nm LEDs for $16 to $25 or I can buy some 10w 660-670nm emitters for $30 at Mouser. As this is strictly for my own small (2' X 2') grow, intital cash outlay is more important than optimal efficiency. Your thoughts on this?

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For your 2x2 room a single 90w panel would well more than suffice.

Going over 5w for emitter power is pointless, you start hitting multi-chip emitters and they're fairly inefficient as it is.

eBay-found emitters are typically bottom-bin and way off-spec (you expect 460nm, you get 480nm instead.)

Mouser is overpriced, you're better off buying direct from LEDEngin if you're going that route.

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Originally Posted by RackitMan

Not even close. If the science as presented was complete and accurate, and 80% of HPS light was wasted then LEDs would be outperforming HPS by a huge factor.

Not happening.

I am not challenging you guys as you seem to think, but there is definitely a piece of knowledge missing.

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You need to read, and no I'm not saying I'm an LED expert or a lighting expert, but like DH said, the comparisons you are looking at don't seem to be of equal wattage. When LED's and HID's are matched by wattage, LED's destroy. Why not try and find a grow of 450W of HID and compare it to stra8's 450W of LED. No comparison. What you are saying pretty much is that HID's waste alot, and you keep saying that. And what you also keep saying is that LED's do not waste, because like you said, 1000w HPS lights not fail, but 450w LED's do the same work, so meaning, that the HPS light is LESS EFFICIENT......If I'm too high or not enough, someone tell me, but that's pretty much what I've been reading.

-C

Bingo!:thumbsup:
Give dat guy a beeg spliff!

Weeze