LED Light for Plants

[Inkidu]

How is every deep red (660 nm) led that I can find so expensive but

the grow lights(UFO etc..), that say they contain 660 nm, so reasonable?

I understand that they buy in bulk but it can't be that different. Buyer beware.

I just bought, have yet to connect, LEDENGIN 5 watt warm white and 10 watt

deep red. I like the warm whites, if there specs are right, because they contain

some low blues and some high reds. I have not seen, with my limited

experience, leds that fit that criteria so well (usually mid blue and mid red).

I would like to use the 40 watt version of the warm whites but there

specs show a serial board but MOUSER sells might be a board with many

connections. (not always the same as picture)

It is not clear to me how to hook up. I have tried several

times to get a clear answer from LEDENGIN but I have not received one.

Understand why mouser can't give me one they sell 1000's of products

I seems simple enough ? where do you hook up the pos and neg wires?

Can anyone help?

 

[blasterman]

How is every deep red (660 nm) led that I can find so expensive but the grow lights(UFO etc..), that say they contain 660 nm, so reasonable?

Because lights like the UFO are primarily intended for dope growers, and corresponding I.Q. levels do apply.

Far red is likely not necessary with typical orange/red 620-630nm LEDs working just fine. For the jillionth time, HPS has been proven as a fantastic long spectrum source, and HPS doesn't go near 660nm. Connect the dots please.

Right now I have house plants / cornplants going nuts over seven 3-watt red being run at 1-watt. Growth is ridiculous.

 

[thepaan]

I've been doing a lot of research on this lately. I wrote a paper for notes if you guys want to read it, I can attach it after work. Some things I discovered:

Plants only require red light for oxygen evolution (turning light into energy). Blue light is only required for responses that shape the plant's growth such as stem growth inhibition and leaf shape and orientation. Some plants have responses based on input from ranges outside red and blue (read: cucumbers).

The wavelengths most people show for chlorophyll are in vivo. The in vitro wavelengths are actually higher, around 650 nm for chl b and 670 nm for chl a. Furthermore, one study I read showed that the normal a:b ratio of 3:1 can be altered up to 6:1 with more desirable effects using that much more a-stimulating light. That being said, exclusive 660 nm light seems to me the best available solution at this time due to the unavailability of 650 nm or 670 nm LEDs.

The PAR standard calls for 25 moles/m2 per day. This converts to about 440 W/m2 (this is my own math based on this document), though I suppose the 400 W/m2 stated previously in this thread is also adequate. Optimally, you want your red light split 3:1 (300W:100W) for a standard ratio (or 6:1 - 343W:57W - for a possibly enhanced ratio) between 670 nm and 650nm, respectively.

Blue light responses are maximized with 8-20% of the red light (so 400 W/m2 red would require maximally 80 W/m2 blue). These responses have a broad range with multiple peaks between 430 nm and 480 nm which means pretty much any blue LED will do fine. (I'm aiming for 460 nm).

There are some red/far-red (phytochrome) responses which can be induced with 660nm (r) and 730nm (fr) light but these mostly relate to flowering and only in certain plants. For example, with enough fr you can 'feed' a poinsettia with growth-stimulating r and still induce flowering. The effects of fr are useless in crop plants.

There is more but this post is long enough methinks. ;P

 

[blasterman]

That being said, exclusive 660 nm light seems to me the best available solution at this time due to the unavailability of 650 nm or 670 nm LEDs.

I appreciate the technical depth of your response, but you keep repeating the same statement without qualification. If far red spectrum isn't required for existing legacy artificial light sources, why do we have to keep hearing why it's required for LED?
Far red spectral energy is virtually zero with current artificial light sources used in agriculture. HPS doesn't have it, and fluorescent and metal halide soruces only have a trickle of far red. These light sources have been used for decades for all manner of plant growth.

+650nm LEDs are hard to obtain, under-powered, inefficient, and rather pricey. However, 620-630nm LEDs are cheap, efficient, and easy to obtain. So again, why are we creating an arguement for far red LEDs?

 

[thepaan]

So again, why are we creating an arguement for far red LEDs?

I think you misunderstand me. I am making an argument AGAINST far red light sources. At all. Legacy artificial source or not. Far red (any wavelength greater than 700) is only usefull for triggering specific plant responses. It doesn't drive oxygen evolution well (it adds some production if you only use < 650nm light concurrently - see Emmerson enhancement effect) and any energy it does provide would be better provided by a more visible wavelength. Far red can also trigger certain undesirable responses such as stem elongation.

Red around 650 and red around 670 are still both red and, in a living plant, are the peaks for stimulating chl a and chl b. The problem with using something lower than 650 nm (such as the 630 nm reds) is you are mostly only stimulating chl b. This causes an imbalance in the chl a:b ratio when compared to plants grown in sunlight. Also, because there is more chl b in PSII than PSI, the rate at which PSI can process electrons falls behind the rate at which PSII can supply them. What does PSII do with this energy that it can't give to PSI? It begins non-photochemical quenching in the xanthophyll cycle in which the carotenoids take the excess energy and dissipate it as heat. During this process one carotenoid (such as violaxanthin) is changed into another (such as zeaxanthin). Eventually you run out of carotenoids to convert and dissipate energy and once that mechanism is saturated the plant begins experiencing photoinhibition. The charge caused by the light exposure has no where to go so eventually causes irreparable damage to the D1 protein in PSII and the whole system stops working. Thus, you have a plant with unbalanced systems and a bunch of broken PSII floating around.

I'm not sure what scale you are using to measure efficiency of red LEDs. The 630 nm are more efficient when measured in lumens because the weighting for that wavelength is greater on the lumen scale than 660 nm. Take these LedEngin LZ-010 Family The red and the deep red have identical output in watts. While the red may seem brighter to your eye, the deep red (don't confuse this with far red) is much more efficient at driving oxygen evolution in a plant. The red is $21.75 and the deep red is $26.10 - thats an increase of 20% which is a little bit but not bad. If you were talking about something tiny like a Rebel (cost: $3.13) that would only amount to $.63 each. You would also need 4-5 rebels to equal the output of the previous LEDs so even those are only slightly cheaper at $16-20 compared to $21.75 for the same output.

Now, if only I could get a rebel in 670 and 650 nm....

 

[Inkidu]

Thanks for the reply thepaan. Your points explain to me why some led setups

don't work well for growing. A combination of not hitting the right wavelength,

especially considering the narrow wavelengths of todays colored leds, and not

getting the right proportion of wavelengths used. I am using my setup for of all

things to grow algae, which filters my freshwater fish tank. I just yesterday

connected (6) 10 watt deep reds and today I want to connect my (6) 5 watt

warm white leds. Do you have a opinion on the ratio? I have often wondered

if emphasizing one type of chlorophyll over another would have certain

benefits. Would your ratios also apply to the "lower" plants i.e. algae?

Any good links to help explain led grow lights?

Please attach any papers. Thanks for any help.

 

[jtr1962]

I'm reasonably sure that despite their low lm/W numbers deep red ( 660 nm ) LEDs are more efficient at converting power to radiant energy compared to 620-630 nm LEDs. The ones LEDEngin sells are as high as 25% efficient ( they actually give radiant flux in the data sheets ). I haven't seen a 620 nm LED do much better than approximately ~55 lm/W. 620 nm light has an eye response of roughly 260 lm/W, so that translates to about 21% efficiency. Moreover, it's in a range which is used by plants, but less efficiently than 660 nm. So cost and availability aside, I'd say it's a lot more efficient in terms of power usage if you go with 660 nm.

 

[thepaan]

Here is the paper I wrote all my notes in. All my sources are at the end of it.

As long as your algae is green it is generally grouped with land plants when discussing photosynthetic response. It has been shown, especially in cucumbers, that certain plants absolutely require wavelengths outside the red and blue. Because it isn't known what photoreceptor cucumbers use, it may be present in many plants but in a redundant form or it may play such a minor role that it's effects were not measured. In this regard, I believe using a white LED is beneficial in that it still has a large blue output due to it actually being a blue LED with a phosphor which converts some of the blue energy to a range. This range would fill in any gaps which may be missing in your spectrum however, I would stick with the cool whites and still use pure blue as well. This is because in a cool blue about 2/3 of the underlying LED's light is converted to other wavelengths where in warm white it's more than that.

I've been revisiting the watt requirement because I keep thinking it's way too high. After some toiling I think you need less than 100W/m2 deep red light (as opposed to 400W/m2) and still 8-20% of that in blue. This still means about 50 Cree XP-E or 67 Luxeon Rebels per square meter for the blue alone.

 

[moonfish]

I've learned more from one of the dope growers pages. He actually grew stuff. With fish tanks they are measuring PAR and saying it is the golden ruler. I'm not sure watts/m2 really applies because you're leaving out one dimension, height.

It isn't hard to grow algae, just have a nutrient N/P/K imbalance and leave the lights on for 10-16 hours a day. Too much and you can get green water.

 

[Inkidu]

Thanks for the info thepaan. The paper was an easy read considering the

complexity of the subject. Couple ?'s I have read that the usual spectrum posted for

chlorophyll absorption is skewed because of the process of separation. But how

was it determined that the chlorophyll a and b are 670 and 650 respectively in

vivo?(in million words or less) Not that I don't believe it and I might not need

to know just curious. How much do these values differ from plant to plant?

Your paper mentions the use of far red in some instances. Would a possible

use of a single far red(this is for algae) for an hour at the end of the night,

once the other lights turn off, have any benefit? Wouldn't be that hard to diy.

I also notice that unfortunately the deep red led , that I am using and which falls short of 670,

falls off so sharply at approx 660 but gradually works up to that level. The

use of an already "red" warm

white might not have been a good idea on my part for the 650/670 ratio

I did use a 5 watt warm white

with 10 watt deep red but the ratio (red to deep red) might be better with

something cooler. Thoughts? I am having a hard time getting my head around how

much(red) the white adds in comparison with what the deep red puts out.

Once I look over all the links at the end of your paper I might get the

answers but I do appreciate any help I can get.

 

[thepaan]

Dope growers do know a lot (I actually learned a lot from reading various forums on that) but most are still using the UFOs with 5mm LEDs or HPSs. The UFOs are a joke because they put out very little light and the HPSs put out the wrong spectrum and the growers measure adequate lighting with lumens.

I've been wrestling with the height requirement too lately and in an aquarium it might matter but for air I don't think the loss is going to ammount to much as long as your growing container has highly reflective walls. For a non-enclosed growing space you will want to calculate the watts per steradians then use the invierse square law to calculate diminished intensity based on distance. I believe water also blocks more light than air so there might be even more loss than distance squared... maybe cubed? BTW, the reef aquarium growers also know a lot.

For exactly where I got the in vivo numbers for chlorophyll (and other pigments) see this site. Specifically, look at chapter 5 (page 106). There are many factors that contribute to the test-tube absorption spectra of plant pigments. They can be damaged during extraction, they may be separated from other components which alter their absorption, and the structure of the leaf itself can interfere with light before it arrives at the pigments. As for how it was discovered, I imagine it went something like this. They first found the absorption in solution. They then used a live plant and measured incident light on the surface of a leaf. Then they measured the light which was reflected and the light which passed through the leaf. Subtract reflectance and transmission from incident light and you get absorption. It was likely noticed that the living plant had no peak at 643 but instead a shoulder in the absorption at 650 and so on.

As I said before, I don't believe far red (>700 nm) is of any use unless you wish to induce (or avoid such) a specific response like flowering. Read here for a bit about photoperiodism which is likely the reason you'd want far red and here for more about phytochrome specifically.

I don't think the 660 nm reds are optimal but I don't think there is anything better for artificial lighting at this point. The output spectrum for either side of the peak wavelength for an LED should be exactly mirrored across the center. If it isn't then I'm not sure why. The white LEDs don't add much red at all. It would involve a lot of math but to find it exactly you would use the spectral output chart that shows the intensity as a function of wavelength and write down the relative intensity for each wavelength. Last time I did it, I used every 10 nm but the more sample wavelengths you include the more accurate your result will be. You would then have to set up an equation based on the total lumen output to discover the actuall percentage of lumens each wavelength contributes. Then convert the lumens of each wavelength to watts to remove the lumen weighting (which is why I used 10 nm increments). I suggest using a spreadsheet to do all the math for you.

 

[Inkidu]

Thanks for the reply thepaan. You guided me to quite a lot to read will take

some time to absorb it all. Some more ?'s for anyone. I noticed on the data

sheet for the ledengin 10 watt deep reds there is a peak color shift that

happens with the increase in the case temp. (page 8)


http://www.ledengin.com/products/10wLZ/LZ4-00R210.pdf


Is this peak color shift toward 670 nm or in the other direction?

Understandably to some extent you are playing with fire but, could you

adjust a variable fan to keep the led in zone where a more ideal

peak color could be obtained? Also might use max. current.(will decrease life)

Side note While what I am doing, growing algae, lends itself nicely to leds

1 very directional light

2 the ability to put the light very close to where I am trying to grow the algae

I do not need to be so concerned with the absorption of light because it least

in my present case the light is not required to penetrate much water.

There is quite a disproportionate absorption of red compared to blue.

An interesting thought experiment. Since land plants evolved from algae

was chlorophyll a, mainly driven by red and which seems to me used because

it's so effective, a driving evolutionary force for plants to "escape" the water?

Thanks for any help or corrections.

 

[thepaan]

You're beginning to ask questions I've not studied in depth :P

IIRC the wavelength of a hotter-than-normal LED is higher in number. The higher number is actually a lower energy where the difference is lost to heat. So yes, a 660nm LED would tend towards 670nm when overheating. I wouldn't try it though, because it reduces the life of the LED and (again, IIRC) the difference is only a couple nanometers at best. The variance in binning is greater than the variance you get from overheating.

I've burned plants with the LedEngin minus a lense. I suggest getting a diffuse lense/cover/something if you plan to put them very close.

On the evolution of algea into land plants: I'm not sure. But, evolution occurs because it can, not because it has to. I don't think the color of absorption had much to do with plants comming about. That may be true with all the different forms of algae but not land plants. Instead I think it more likely that some ocean plant was able to live on land and, having no competition for a space to exist, thrived and gave way to all the plants we have today.

 

[blasterman]

I don't think the 660 nm reds are optimal but I don't think there is anything better for artificial lighting at this point.

Again, I point out that:

(1) 660nm LEDs AREN'T used wholesale in greenhouses yet. Their most popular commercial implementation is flowering and dope plants, and that mostly for augmentation.
(2) Current artificial light sources used in green houses don't have significant red beyond 620nm or so. I can happily supply spectral graphs to prove this for both Metal Halide and HPS.

(3) Green house owners I've contacted that have tried LED fixtures are about 70% in agreement that 'they suck', have been 'ripped off' and went back to legacy light sources. Most of the LED fixtures that failed are using 660nm LEDs.

I would have to agree with the green house owners and take their word over a couple guys here trying to sell under-powered LED fixtures. Wouldnt' you?

I appreciate your research, but the big question is why there is a discrepency between your claimed requirements and existing light sources.

Also, marine Zooxanthellae algae is mostly blue dominated because water absorbs red light rapidly at depth. So, the evolutionary requirement has adopted to a more blue-cyan- requirement. Red light will actually shut off growth in some corals because it's a signal they are growing above water.

As I said before, I don't believe far red (>700 nm) is of any use unless you wish to induce (or avoid such) a specific response like flowering

I don't believe anything beyond 600nm is really required, and the success of current non-LED sources that are deficient in much beyond orange light would tend to support my claim.

 

[blasterman]

I'm not sure watts/m2 really applies because you're leaving out one dimension, height.

Watts/m2 already takes height into account. You can't calculate area (m2) until you know the area the lights are being projected into.

Otherwise, watts doesn't work well because it doesn't take spectral output into account. A 20k metal halide is a different beast than a 5600k metal halide and will deliver radically difference amounts of PAR. These light sources are also horribly fixture dependant.

By and large cool white LEDs are more consistent in this respect than MH or fluorescent because they are more directional.

 

[thepaan]

Again, I point out that:

(1) 660nm LEDs AREN'T used wholesale in greenhouses yet. Their most popular commercial implementation is flowering and dope plants, and that mostly for augmentation.
(2) Current artificial light sources used in green houses don't have significant red beyond 620nm or so. I can happily supply spectral graphs to prove this for both Metal Halide and HPS.

(3) Green house owners I've contacted that have tried LED fixtures are about 70% in agreement that 'they suck', have been 'ripped off' and went back to legacy light sources. Most of the LED fixtures that failed are using 660nm LEDs.

I would have to agree with the green house owners and take their word over a couple guys here trying to sell under-powered LED fixtures. Wouldnt' you?

I appreciate your research, but the big question is why there is a discrepency between your claimed requirements and existing light sources.

Also, marine Zooxanthellae algae is mostly blue dominated because water absorbs red light rapidly at depth. So, the evolutionary requirement has adopted to a more blue-cyan- requirement. Red light will actually shut off growth in some corals because it's a signal they are growing above water.



I don't believe anything beyond 600nm is really required, and the success of current non-LED sources that are deficient in much beyond orange light would tend to support my claim.

First, Let's not get carried away with this-type-of-light vs. that-type-of-light. This forum is specifically about LEDs so let us talk of the best LED solution for the purpose mentioned in the thread.

It is a misconception that red light induces flowering (especially in weed). Flowering is a phytochrome response and is wholly dependent on the length of the night period. Take the poinsettia as a perfect example. It will grow big green and bushy as long as you give it 12(?) hours or more/day of light - or even two 6 hour periods spaced evenly - or even 10 hours then a 10 minute interval midway through the dark period - or even any combination that keeps the consecutive hours of night short. However, once exposed to a continuous night of length 14-16ish (iirc) hours it begins changing color to red and flowering. The poinsettia is a perfect example because it absolutely requires a long night period (is obligate) to flower where some plants (weed) are only influenced by the night length (are facultative) and will eventually flower regardless of how long or short it is.

I surmise that the reason LEDs are not used in greenhouses has more to do with the buy-in cost then enything else. The cost of an adequate LED fixture in a greenhouse for even a few square meters will be in the several thousands of dollars range. I imagine a potential buyer opts for the cheaper UFOs or other solution using underpowered 5mm LEDs. The inadequate intensity of those types of LEDs (you would need around 500 5mm LEDs to have equivalent intensity of a single Cree XP-E at 350mA) then taints their impression of LED lighting as a whole. We are further presented with difficulty in comparing incompatible measurements and thus determining how much LED light is needed vs. (for example) HPS light. A 660nm LED output is measured in mW or W where an HPS output is measured in Lumens. Entirely too much math is required to get an exact radiometric conversion (though I've done approximations).


It is true that LEDs are probably not the best artificial lighting solution for growing plants on a commercial scale. But, especially for some onesie-twosies or for something like growing lettuce in your kitchen when it's -3C outside, I think they are more than optimal and the potential is incredible - which, as far as I know, is what we are talking about.

 

[Inkidu]

Thanks for the input.

"The first plants on earth evolved from shallow freshwater algae much like

Chara some 400 million years ago." If it is true thanks wikipedia

I mention this because it might stimulate some productive thoughts about

"led light for plants".

And obviously diverse topic including many different plants trying to be

grown in many different ways by an incredibly fast changing world of what

led light is available to grow plants.

Thepaan any suggestions on something to diffuse the led for my plants?

Any help is appreciated to grow a plant under my led.

 

[thepaan]

Right now I'm using a plastic dome cover you might find over your hallway ceiling light. For an aquarium though, you might want some kind of tube - possibly, one which you can seal the ends to keep water from getting in.

 

[Inkidu]

If anyone is interested I just added 4 rebel royal blues and 2 rebel blues

to my setup, which includes 6 (10 watt) deep red ledengin and 6 ( 5 watt)

warm whites. Seeing growth but I think I might need to dial it in i.e. seeing

better growth right outside of lights. Might be a ? of water flow, this is only

for growing algae, and proper diffission. I presently am only using some

decorative glass and wax paper to help breakup the light. Still pretty

early,only two days, to make much of a conclusion about effectiveness.

Hope this helps.

 

[X_Marine]

Wow, this is an awful interesting thread.
I hate to see it dry up.
After this amount of time I would think there is a lot that has been discovered. Please share..

Thanks
X/BillyD..