# LED Light for Plants



## shpongled (Nov 15, 2009)

Hello, I have been without a electronics project for a while and have decided to build a small LED light unit to provide light for plant growth. The first unit I plan on building will be small, mostly for proof of concept and starting seedlings. Eventually I would like to scale up to something that might be able to keep a few small plants alive. Overall it going to be a cool project.

I am still working on the actual electronics design but have some knowledge and am getting help from the friendly folks at allaboutcircuits.com. 

I come to you knowledgeable and hopefully friendly folks to help with my LED selection. I am hoping to use 1W LED's for their high output. The problem I am having sourcing parts with the right output wavelengths. It seems that many of the high output LED makers are focusing on the damn LED flashlight people .

Here is a quick excerpt about the best wavelengths for photosynthesis:


> *Maximum chlorophyll A production occurs at 662nm (for red) and 430nm (for blue), while maximum chlorophyll B production occurs at 642nm (for red) and 453nm (for blue).*


 
I find most commercial grow lights say they use 1W 660nm and 450nm LEDS. The issue is I cant find any? There are a few other ranges that are important but if anyone can help me with these it would be a big step. 

I am going to use some cool and warm white lights also to fill out the gaps in the spectrum but there are a ton of options for those.


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## shpongled (Nov 15, 2009)

Does anyone know anything about http://www.roithner-laser.com/LED_HP_single_chip.html

They seem to have many different LED's with 660nm output.


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## joeparker54 (Nov 20, 2009)

I understand the potential value of having separate sources for blue and red light - blue generally contributes to vegetative and seed growth while red light is important for flowering. However, I'd think that just for proof of concept, that simply finding the warmest and coolest cree (or any other brand for that matter) emitters you can would suffice. Of course it all depends on what you're growing, which could be anything from alfalfa sprouts to cannabis.

check out the graph on page 3 here. While not optimal, i'd say the levels of light in the ranges you require may at the very least be sufficient for 'proof of concept'

BTW, have you emailed any LED growlight manufacturers to ask what type emitters they use? It's worth a shot.


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## Illum (Nov 20, 2009)

gee...I don't think any of those wavelengths exist in the literature of any high powered LEDs :thinking:



> *Maximum chlorophyll A production occurs at 662nm (for red) and 430nm (for blue), while maximum chlorophyll B production occurs at 642nm (for red) and 453nm (for blue).*


Osram golden dragons blue only goes up to 470nm but with an optical efficiency of 6 lm/W

For Luxeons...

```
Luxeons Colors    Min    Typ    Max
Blue              460    470    490
Royal Blue        440    455    460
Red               620.5  625    645
Red Orange        612.5  617    620.5
```
For CREEs...
Dominant wavelength range

```
CREE Color    Min    Max
Royal Blue    450    465
Blue          465    485
Red           600    620
```

As far as I am aware of, 660nm +/- is only available in T1-3/4 variants, classed as "deep red." Blue 5mm LEDs are only in 470nm +/- variants only.

your better off looking for studio lighting filters and safelight filters to achieve those wavelengths. I'm pressed to believe that they've been limited because of too many irresponsible individuals growing cash crops in their basements


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## Yoda4561 (Nov 20, 2009)

But using filters defeats the purpose, maximum vegitative growth and minimum power usage.


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## Illum (Nov 20, 2009)

Yoda4561 said:


> But using filters defeats the purpose, maximum vegitative growth and minimum power usage.



well, its not like we have many choices


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## asdalton (Nov 20, 2009)

Filters can only exclude light, not create any more colored light than the light source already contains. There would be no point in using a filter.


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## Illum (Nov 21, 2009)

so what do you suggest?


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## znomit (Nov 21, 2009)

asdalton said:


> Filters can only exclude light, not create any more colored light than the light source already contains. There would be no point in using a filter.



The only reason a filter would be useful is if the other wavelengths degraded growth somehow. 

Anyhooo, speaking of filters...
So how much of the sunlight do plants actually use? Would it be theoretically beneficial to convert sunlight to electricity and then power LEDs to grow the tomatoes?


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## Ekke (Nov 21, 2009)

Here's Deep Red for you:
http://www.ledengin.com/led_products.htm
10W is better pricewise, if I remember right..

Plants may need many more wavelengths than just 450nm & 660nm (depends what plant and what you want it to do etc.), so you have been warned..


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## Ekke (Nov 21, 2009)

shpongled said:


> I find most commercial grow lights say they use 1W 660nm and 450nm LEDS. The issue is I cant find any?



It might be that they are just saying that they use 660nm leds.. And if specs are in lumens, it's pretty likely that they LEDs are ~620-630nm. Six times more lumens than 660nm for same radiant power.


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## purduephotog (Nov 22, 2009)

shpongled said:


> Hello, I have been without a electronics project for a while and have decided to build a small LED light unit to provide light for plant growth. The first unit I plan on building will be small, mostly for proof of concept and starting seedlings. Eventually I would like to scale up to something that might be able to keep a few small plants alive. Overall it going to be a cool project.
> 
> I am still working on the actual electronics design but have some knowledge and am getting help from the friendly folks at allaboutcircuits.com.
> 
> ...



Ledengin Makes a 10W, 5W, and a 15w (I think) 660nm LED.

http://www.newark.com/ledengin/lz4-40r210/power-led/dp/16P3167

I own 5 of them.


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## Ekke (Nov 23, 2009)

purduephotog said:


> Ledengin Makes a 10W, 5W, and a 15w (I think) 660nm LED.







15W is quite useless (10W on the left, those are RED because there isn't 15W Deep Red datasheet), if you know how to successfully cool a LED.


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## Illum (Nov 23, 2009)

I oftened wonder how well these 10W/20W/30Ws contend in efficiency. and I've wondered of the possibility of using a narrow copper pipe with flat planes on both sides and have water flowing through the middle. A medium sized sump pump and a 5 gallon reserve oughts cool a pipe the length of length the table with no issues. water has high heat capacity and the warm water can be used for other things, especially for sanitary wash/flushing


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## kaichu dento (Nov 23, 2009)

My friend from University of Alaska Fairbanks is here in Japan right now for some conferences on lighting and last week he got a frantic message that our lettuce is just not growing since the sun went away and we've been running with nothing but 1,300 watts from LED's since August. Previous to the change we'd been giving the lettuce 18,000 watts from the Incans.

The big Incans are back on again and according to some of the Dutch growers we need to use a mixture of LED and Incan with the main point being lots of light, especially for the tomatoes.


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## asdalton (Nov 23, 2009)

I'm surprised that they're using incandescent for growing, rather than the much more efficient metal halide or high pressure sodium.


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## kaichu dento (Nov 23, 2009)

asdalton said:


> I'm surprised that they're using incandescent for growing, rather than the much more efficient metal halide or high pressure sodium.


Metal halide and high pressure sodium are the incandescent lights we're using, for a grand total of 36,000 watts between the tomatoes and lettuce, not to mention another 6,000 watts in the little greenhouse.


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## asdalton (Nov 23, 2009)

Here on CPF, "incandescent" means tungsten filament. That was the source of my confusion.


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## Illum (Nov 23, 2009)

kaichu dento said:


> Metal halide and high pressure sodium are the incandescent lights we're using, for a grand total of 36,000 watts between the tomatoes and lettuce, not to mention another 6,000 watts in the little greenhouse.



Metal halide is effective in output, but you'd be surprised for small scale applications how effective incandescent lamps are in keeping a greenhouse toasty warm when its practically frozen over outside. 

Down here theres no weather of that sort for me to try it out myself


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## kaichu dento (Nov 23, 2009)

asdalton said:


> Here on CPF, "incandescent" means tungsten filament. That was the source of my confusion.


I may be the exception, but my usage of the term incandescent includes anything with a filament.


Illum said:


> Metal halide is effective in output, but you'd be surprised for small scale applications how effective incandescent lamps are in keeping a greenhouse toasty warm when its practically frozen over outside.
> 
> Down here theres no weather of that sort for me to try it out myself


We've been through five winters with the little greenhouse and three for the big one. For the last three winters (this is the start of our fourth) we've been pulling fresh lettuce and tomatoes out every day of the year, even at -60 below. It definitely makes a big difference having all those lights on!


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## Ekke (Nov 26, 2009)

shpongled said:


> I am hoping to use 1W LED's for their high output. The problem I am having sourcing parts with the right output wavelengths.



Ok, here you go:

http://www.edison-opto.com.tw/products_detail.asp?category=1&cno=251

Just damn expensive in small quantities..


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## Illum (Nov 26, 2009)

Edisons now look like rebels?:thinking:

huh...the federal series is quite distinct from rebels
the thermal pads tied to the anode, uses a TVS diode...

deep red 650-670nm
blue 455-475nm
dental blue 450-470nm

430nm is approaching UV...

I'm surprised about this "Cherry Red" in the Federal series
730-750nm, 750nm is the lower limit of our eyes capability to detect it. 700nm is where infrared light starts


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## blasterman (Nov 29, 2009)

Guys, I'll save you some time. The past several months I've been using LEDs over my reef tank and also for testing over terrestrial house plants.

For terrestrial houseplants use 3 or 4:1 red to blue works the best. Terrestrial plants want a lot more red light than blue...if you want size that is. Blue light tends to cause denser leaves and compact size. Red better overall growth. Note that NASA and the Japanese are all over red for fruiting and laughing at HID sources.

Or, use cool white instead of blue for better aethestic look. 

Also, I didn't bother with 660-670nm LEDs because they are a pain to find. I used typical 620-630nm 3-watt LEDs. 4 red 3-watt LEDs on an alu bar like all our other builds plus two blue or white. I found that if I suspended this over plants next to a south window that houseplants would ignore the direct sun and grow towards the LEDs. That's rather astounding if you ask me.


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## blasterman (Nov 29, 2009)

kaichu dento said:


> Metal halide and high pressure sodium are the incandescent lights we're using,


 
I really think you need some segmented trials to determine what type of light works best rather than just using that many overlapping sources. I would guess that lettuce would be amongst the exceptions that prefer a higher ratio of blue to red.

Also, I've seen pictures of high powered LED arrays mounted so high above plant beds in commercial greenhouses I'm shocked anything is growing.


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## kaichu dento (Nov 29, 2009)

blasterman said:


> I really think you need some segmented trials to determine what type of light works best rather than just using that many overlapping sources. I would guess that lettuce would be amongst the exceptions that prefer a higher ratio of blue to red.


We've got two parties pushing the agenda at the hot springs. One is a specialist from the University and the other is the owner, and more often than not they're on different pages. That said, we've been growing lettuce and tomatoes year round, in a greenhouse in Alaska for over three years, this being the start of our fourth winter, so no speculation needed as to whether we can do it or not, as we harvest fresh lettuce and tomatoes every day of the year. 


> Also, I've seen pictures of high powered LED arrays mounted so high above plant beds in commercial greenhouses I'm shocked anything is growing.


Oh, you've been to our greenhouse! I couldn't believe it when the owner told me how many fixtures he wanted in and how high to put them, but that was what the manufacturer told him. Things went fine into the fall... until we lost the majority of our natural light source!


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## Ken_McE (Nov 29, 2009)

kaichu dento said:


> We've got two parties pushing the agenda at the hot springs. One is a specialist from the University and the other is the owner, and more often than not they're on different pages.




What if you ran a sheet down the middle and tried one way on one side and the other way on the other? 



> I couldn't believe it when the owner told me how many fixtures he wanted in and how high to put them, but that was what the manufacturer told him.


Any chance of pictures? Are thes commercial LED grow lights or custom?


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## blasterman (Nov 29, 2009)

> Things went fine into the fall... until we lost the majority of our natural light source!


 
Ah, so you pulled the other light sources and are just using the LEDs now.....

It would be really helpful if the vendor in this case used a PAR meter beforehand. That way they could verify that enough photosynthetic light was reaching the plant beds.

I'm guessing these are those panel type LED arrays using 1watt emitters. Most common format being sold to greenhouses because they are made cheaply in Asia. What I don't get is most greehouses are set up in rows, so ideally you'd want to emitters arranged like we do on alu bars, and then drop them right over the plants.


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## kaichu dento (Nov 29, 2009)

Ken_McE said:


> What if you ran a sheet down the middle and tried one way on one side and the other way on the other?
> 
> Any chance of pictures? Are thes commercial LED grow lights or custom?


All the lights we're using are for commercial usage but I believe that the spectrum is a bit suspect for the LED fixtures, and that seems to have been borne out by testing at the university and the lack of growth we experienced once the natural light source ceased to be of much help.

Here's a thread I started some time back that has a few pics in it. I'll try to do an update later as there is only one of the fixtures shown in the pictures still in the greenhouse, while the majority of the LED lighting is coming from some that I installed back in August.


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## kaichu dento (Nov 29, 2009)

blasterman said:


> Ah, so you pulled the other light sources and are just using the LEDs now.....
> 
> It would be really helpful if the vendor in this case used a PAR meter beforehand. That way they could verify that enough photosynthetic light was reaching the plant beds.
> 
> I'm guessing these are those panel type LED arrays using 1watt emitters. Most common format being sold to greenhouses because they are made cheaply in Asia. What I don't get is most greehouses are set up in rows, so ideally you'd want to emitters arranged like we do on alu bars, and then drop them right over the plants.


Actually I just pushed the other lights around as I had a strong feeling that it wasn't going to work out exactly as it was presented to me. Fortunately they were still in place so all they had to do while I'm gone was to rearrange them a bit.

The university took some readings on them and found that they did not appear to be at as ideal of wavelength points as the older pair shown in this thread, also linked in the above post.

Sounds like you know a bit about this sort of thing and could help us out getting things right! How about coming to Alaska for a winter break at the hot springs!


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## blasterman (Nov 30, 2009)

Hey Kaichu, lets try this from a different direction.

Lets assume you weren't running any LEDs at all. How much wattage total of metal halide would you figure you'd need (assuming no sun) to get good growth over the floor?


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## kaichu dento (Nov 30, 2009)

blasterman said:


> Hey Kaichu, lets try this from a different direction.
> 
> Lets assume you weren't running any LEDs at all. How much wattage total of metal halide would you figure you'd need (assuming no sun) to get good growth over the floor?


What we've been running in there from the start has been 18 1,000 watt fixtures per side, which I think has been good enough for the lettuce, but due to penetration problems a bit lacking for the tomatoes which do fairly well on the side facing the lettuce, but really poorly on the outside wall. 

From what I understand there will be more lights on the tomatoes when I get back, but how much I'm not sure. I'll be back there in a couple more weeks.


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## blasterman (Nov 30, 2009)

The problem here is that even with the inconsistent nature of HID out-put (no two bulbs are alike), there is some un-official concensus in the agriculture industry about watts per foot for platn growth. It's like, 25-50 watts per foot depending of what you are growing (tomatoes requiring the most amount of light). Does that seem about right for your floor?

Even though LEDs are far easier to establish foot candles or just plain lumens per foot, there doesn't seem to be as much info out there regarding this. I've actually offered to set some tests up for local green houses or colleges and establish this base-mark, but my responses have been luke-warm. People either don't get the science, or have been duped by cheap LED appliances and gun shy. I'm just in it for the knowledge and initial green science, but that base-mark is key.

What we *do* know is that HID / metal halide is weak in far red / orange. That's why high pressure sodium is often used to promote fruiting / flowering, and even HPS doesn't go beyond 600nm, if at all. That's why I'm just not taking those far red LED specs very seriously because it's just not there under current light light sources.

So, from what we do know, I'm guessing that lettuce is suffering the worst without HID, correct? That would establish the need for more blue/white with lettuce. Tomatoes are almost certainly a red light plant, at least when it gets into it's main growth phase.

If it were my call I'd try to lower the LED lights, and given their red dominance concentrate the fixtures over the tomatoes / fruiting plants rather than have them spread out and see if it helps.


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## Christexan (Nov 30, 2009)

Something else to keep in mind, kind of in concert with Blasterman's notes, the average of sunlight striking the earth through a daylight period per day is roughly 400W/m^2 (if I remember correctly from my reading on solar panels, looking briefly online I've found that the "high" is around 1000watts/m^2 at noon in tropical latitudes, so that number seems reasonable). 

High Pressure Sodium (HPS) give a decent broadband output, unlike LEDs which are either very narrow band (per color type), or broad with varying peaks and valleys (white-phosphor LEDs). 
So basically, to reproduce sunlight with a similar broad-spectrum source, you need 400W of light energy per m^2. If you can narrow the spectrum to, for example, 3 10% bands of the total spectrum and still achieve 90% effective growth (I don't think a narrowed band output is ever going to equal natural sunlight in efficiency), then you are looking at maybe 40% of sunlight's watts/meter, or 160 watts of light output to achieve natural growth rates. 

HPS and LED are in the same ballpark on electrical efficiency, roughly 20% right now, and roughly 100lm/watt each (peak efficiency cool-white LEDS are better, but commercially, 100lm/w is actually generous to LEDs with a good broad spectrum, or mixed RGB sources... 80lm/w is more realistic if reproducing a broad spectrum)....

Given all that, you'll need at LEAST as much electrical power as HP sodium lights for a broad-spectrum LED solution. You'll need at least 40% give-or-take if you can narrow it down to 3 10% spectral ranges. So if trying to match the results of the 18000 watts of sodium lights, you'll need at least 7200 watts of LED lighting in the same distribution. If trying to match the Sodium lights overall broad spectrum output, you'll need basically equivalent wattage for LEDs, fixture dispersion being equal.

Of course if you can more optimally place the LED fixtures (closer and better distributed to the plants), you might be able to improve things a lot, but that's more "ifs" and a lot more planning and work. 

LEDs are not ready to replace HPS lights today, the net output efficiency of each are roughly equal at this time, and the fixturing challenges of LEDs make the already well-developed HPS the clear general purpose winner. As broad-spectrum (special white-phosphor, or mixed-RGB arrays, not cool-white phosphors like most are today) LEDs cross the 100lm/watt mark at operating fixture conditions (meaning maybe 150lm/watt in the lab at room temps), they may become more competitive, but right now it's simply a technical experiment, it won't gain any electrical efficiency over HPS (unless again, it can be narrowed to certain bands effectively, AND/OR the actual LED fixturing results in better light application to improve the effectiveness). 

Feel free to correct any errors I may have made in my assertions (doesn't have my full attention), but hopefully I'm in the ballpark on all of it.


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## blasterman (Nov 30, 2009)

Only thing I would disagree with is calling HPS 'broadband'. Or, at least my understanding of the term which is broad spectrum?

Typical HPS lights, unless they are contaminated with other metals like mercury, have an emission spike around 580-590nm, and drop off rapidly at either end. This is kind of at the edge of the long wavelength photosynthesis line, but not ideal. However, HPS being so common and a readily available technology it's become popular to get the job done.

Certainly HPS throws more energy at the far wavelength than metal halide / HID per watt. HPS also has very good conversion factors in terms of raw light out-put per watt consumed compared to even LED. Just look at the debates regarding solid state street lighting -vs- HPS. However, LEDs can go much deeper in the red range than HPS, and if they are otherwise close in terms of raw lumen efficiency woulnd't this given an advantage to the red LEDs? 

Lettuce, as I've learned via search engines seems to be a rather difficult plant to adapt to LED growth because it has rather finicky spectral requirements.


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## hank (Nov 30, 2009)

http://www.google.com/search?q=NASA+LED+plant+growth


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## Ekke (Dec 1, 2009)

Christexan said:


> Feel free to correct any errors I may have made in my assertions (doesn't have my full attention), but hopefully I'm in the ballpark on all of it.



If you measure efficiency in lm/W with plant lighting, you don't know what you are talking about. Sorry. :ironic:

Here's HPS spectrum in red and photosynthesis rate:






Lumens are relative to human eye response peaking in green color that plants mainly reflects. ~620nm red light has over six (*6*) times more lumens than ~660nm deep red with same *radiant power*. ~720nm are important to phytochromes.


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## Christexan (Dec 1, 2009)

Nope, I don't measure growing efficiency in lumen/watt, and so I do know what I'm talking about, I'm not talking about "growing" at all, but referring to electrical input efficiency to power output(both in watt units) of light output. 

The current radiant efficiency of HPS is around 258mw/watt according to one "grow study". 
http://www.actahort.org/books/128/128_10.htm

The current radiant efficiency of a white phosphor LED is around 22-25% (220-250mw/watt). That's pretty much the long and short of my post, what wavelengths are "best" is the challenging issue that I don't touch other than to say that if HPS is wasting power on wavelengths plants don't care for, and you can use LEDs targeting the bands that plants really want, then you can certainly improve efficiency a LOT. But your total light (radiant output) will be less (and less power loss, which is a good thing). 

I'm definitely no expert on what plants need to grow however, not a clue, just comparing light sources total output (in radiant power measured in watts) to total electrical input (in watts). 

The power of sunlight striking the earth is approximately 400w/meter on average during daylight hours. Since white LEDs are roughly 20-25% efficient at converting electrical power to radiant power (across the total spectrum, not in lm/watt or anything to do with human eye response), then if you have LEDs illuminating 1sq meter with an equivalent energy to that received by sunlight, you need 4-5x the power (so 2000w+ electrical input to reproduce sunlight conditions on a per-meter basis). 

I thought I'd made it pretty clear (given the complexity), but apparently not. 

If you can isolate certain bands of say 10% wavelengths that match up to LEDs, and only need 3 or 4 of those bands to get nearly equal growth to HPS, THEN you can save substantial amounts of power (requiring only 30-40% of the electrical input). 

I did mix in lm/watt as a secondary item (luminous flux), but the primary principle involved was electrical power to radiant power conversion (measured in watts, not lumens), the lm/watt that I mentioned was only a generality applied to HPS and white LEDs for comparison sake of the "state of the system" today. All else being equal, HPS produce more total light (radiant), than LEDs today, my point was that as the more well-known lm/watt figure increases for typical white LEDs (radiant efficiency and luminous efficacy are closely linked if the method (white phosphor from blue LED) doesn't change, they'll need to be in the neighborhood of 150lm/watt luminous intensity in "ideal" specifications before their total radiant intensity exceeds HPS given the same electrical input in "real-world" (warm temps) conditions. Getting close to that already, but fixture challenges remain an expensive challenge as well. 

Until then, only a "banded" solution will make LEDs more desirable for growing than HPS, if an ideal wavelength mix is found that is equally effective.

Also, not sure where you got your HPS graph from, I'm sure it matches at least one HPS light (a poor one for growing purposes), but many models and mixes of HPS are out there and that isn't even close to an ideal HPS "growing" light (per looking at sites that sell them and feature the spectra). The spectral emissions vary widely by composition, here is a different curve (plotted against the "plant sensitivity curve" from eye hortilux (an HPS "plant" light maker (I didn't plot it, they did))

http://www.eyehortilux.com/images/lu1000bHTLen-sd-r.jpg


Regarding Blasterman's post, I agree, I may not have mentioned it clearly enough

HPS isn't "broad spectrum" in the sense of sunlight or incandescent, but much more so than other arc solutions such as mercury or LPS. 
(A VW Jetta is faster than a Hyundai Excel, but that doesn't make it a racecar, kind of thing).


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## Ekke (Dec 2, 2009)

Thanks for the clarification, I just think that lumens and plants should be discussed in different topics. That HPS was some random street ligth, if I remember right, but I found similar graph in some study that involved HPS & LEDs, assumed that would be suitable spectrum, but apparently it isn't. I'm not a big fan of HPS, and haven't put so much (any) time on researching those. 

I'm currently "building" a LED growing light with ~450nm, ~470nm, ~620nm, ~660nm, ~730nm & (cool) white leds. Just have to decide the rations first, and what leds to use. I'm mainly concerned about 500-600nm wavelengths because there won't be so much light in that region. 

~450nm blue led can but >500mW light with ~1.1W power in ideal conditions and it's photosynthesis efficiency should be >90%. Surely with higher current (and temp) efficiency will drop, but I should still be quite good.

There really isn't ideal light for all plants, they need different light, and also depending what you want them to do. I'm planning to grow chilipeppers, and I'm hoping that I can control flowering with light. But there are lots of research to be done with different wavelenghts, and there are so many of them. Too much lack of info, too little time and money. Interesting topic all in all.


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## X_Marine (Dec 7, 2009)

Very interesting thread and as I read I see there is no clear solution. It would seem as efficient as leds are that there would be much more information available. 
I wanted to subscribe so I could keep up with the progress being made.

Not much to offer other than I have seen HPS mentioned many times and I have been using them for area lighting for years vs mv, or mh. But just prior to parting with my x some years ago I remembered buying some HPS for the greenhouse I had built her. That after reading they had at that time come out with a new bulb which had added some blue to the HPS which made it much more suitable for green house use.

The name of the bulb is Phillips SON AGRO 430W 4/4.
This may be old info and please disregard if this is the case as I have not kept up with the tecnology.

Good luck with your endevor.
X/BillyD..


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## T0RN4D0 (Dec 7, 2009)

Some comments about the plants problem. The "incans" are by no means incans, but very efficient light source (OK OK, crees go higher, but try assembling a 1000W cree and see how much that efficency costs you), and replacing them with 15 timess less Watts of (lets be optimistic) twice the efficiency of LEDs, you were way underfeeding your plants with light. 

If i remember correctly, HPS and MH do abou 90lm/w. A decent emitter will do lets say 120lm/w. But thats white leds, red LED should put out less lumens, but thats really not the point, because the plant should be able to absorb all of that. And i think you need to combine many different LEDs, so a few types of RED, and a few types of BLUE, to cover different wawelengths. Also, if designing a LED grow light, you should take advantage of the level of control LEDs give you, and design a specific mixture for the type of plant you are growing with it. Adding more blue ones for letuce, adding more red ones for flowers... 

Anyways, i think growing with leds is not as easy as it is with HIDs or fluoros. And they are not that much more efficient, and are simply not suitable (at least economically) for every project. For the enormous powers that plant growth requires, LEDs are way to expensive, they are harder to cool, wawelengs might give you trouble... 

The only nice thing about them (the way i see it) is, that you could put them really up close to the plants, spread them under them, in between... Thats something you can not do with a 1000W HPS. But again, thats way too complicated for a big grow, thats usefull if youre growing something in a big shoebox lol.


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## Inkidu (Feb 22, 2010)

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?


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## blasterman (Feb 23, 2010)

> 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.


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## thepaan (Feb 24, 2010)

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


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## blasterman (Feb 25, 2010)

> 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?


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## thepaan (Feb 25, 2010)

blasterman said:


> 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....


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## Inkidu (Feb 25, 2010)

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.


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## jtr1962 (Feb 25, 2010)

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.


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## thepaan (Feb 26, 2010)

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.


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## moonfish (Feb 26, 2010)

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.


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## Inkidu (Feb 26, 2010)

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.


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## thepaan (Feb 27, 2010)

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.


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## Inkidu (Feb 27, 2010)

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.


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## thepaan (Feb 28, 2010)

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

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.


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## blasterman (Feb 28, 2010)

> 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.


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## blasterman (Feb 28, 2010)

moonfish said:


> 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.


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## thepaan (Feb 28, 2010)

blasterman said:


> 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.
> ...


 
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.


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## Inkidu (Feb 28, 2010)

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.


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## thepaan (Feb 28, 2010)

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.


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## Inkidu (Mar 6, 2010)

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.


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## X_Marine (Jul 5, 2010)

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..


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## blasterman (Jul 5, 2010)

What I've researched in the meantime only confirms what I've stated before. In terms of terrestrial plants, particularly fruiting and vegetative plants, orange/red light plays a very significant role. The problem is that LED's *aren't *a very efficient source of orange/red light compared to HPS, which is the dominant commercial light source for this kind of light, and this disparity isn't going to change on the near horizon. Because Cree is getting better at making hyper efficient low CRI cool-white emitters is meaningless to a plant or symbiotic algae because white light doesn't matter. Also, because this forum is weighted heavily towards LED technology doesn't change this fact. Another problem is you have several posters here that are selling low powered LED fixtures and not being very genuine in their responses.

LEDs can generate specific amounts of 660-670nm light that other sources can't do well, but evidence that this is critical for commercial plant growth is sporadic and tends to be mentioned when it's in the *commercial advantage* of the proponent. 

In regrads to corals, it's a different story. I've tested different colored LED lights on Acropora, Montipora, and several LPS species, and the only color that matters is blue. The closer to 440nm, the better. This is an obvious evolutionary response to the rapid absorption of red light in water. The good thing about LEDs in this respect is they are very efficient sources of far blue, so this is why LEDs are enjoying such success in reefing along with the fact they scale so well. 

The real frustration is that rather than talking about this, simply order some generic 3watt LEDs and test it for yourself. Using C-channel, super glue, generic blue/red LEDs and cheap drivers you can easily build solid state light panels equal to any commercial source for a fraction the price.


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## slebans (Jul 6, 2010)

blasterman said:


> What I've researched in the meantime only confirms what I've stated before. In terms of terrestrial plants, particularly fruiting and vegetative plants, orange/red light plays a very significant role.


Blue, green and many other colors(wavelengths) play equally significant roles in the process of photosynthesis.



> The problem is that LED's *aren't *a very efficient source of orange/red light compared to HPS, which is the dominant commercial light source for this kind of light, and this disparity isn't going to change on the near horizon.


12 months ago I would have agreed with your statement. Leds producing red wavelengths could not come close to an existing HPS bulb's 40% efficiency in converting electricity to light. Once you place the bulb within a refector though - you would lose an additional 15-20% of the output. By late last year, providing you did not drive the leds too hard - you could find a red led that would match an HPS for output electrical to light efficiency. Recently, Osram released a Red 660nm led with a claimed efficiency of 40%.(Sorry for the linewrapping).
http://catalog.osram-os.com/catalog...Oid=0000000300018fab056f0023&act=showBookmark

I agree that HPS will remain the dominant source of lighting for greenhouse growers. Two things have to happen to change this outcome.
1) Led's must become efficient enough that you can pack the required watts into the same space as existing HPS fixtures and be able to economically/reliably remove the waste heat.
2) The operational cost savings of running LED versus HPS must be able to finance the capital cost for the new led light fixtures. 



> Because Cree is getting better at making hyper efficient low CRI cool-white emitters is meaningless to a plant or symbiotic algae because white light doesn't matter.


Not sure why you state that white light does not matter.What if the white light is 2700K at a CRI of 90? Regardless, I believe that even CREE cool-white emitters produce light that is useful to plants.



> Also, because this forum is weighted heavily towards LED technology doesn't change this fact. Another problem is you have several posters here that are selling low powered LED fixtures and not being very genuine in their responses.


You sure hit the nail on the head that with that statement. 




> LEDs can generate specific amounts of 660-670nm light that other sources can't do well, but evidence that this is critical for commercial plant growth is sporadic and tends to be mentioned when it's in the *commercial advantage* of the proponent.


As you have mentioned in previous posts - plants grow just fine under HPS. I think the issue here is the relative importance led grow light suppliers attach to wavelengths between 660-680nm. Technically, they are correct in their assumption that 680nm is important for the process of photosynthesis. What many of them do not seem to understand is that 680nm is the most efficient wavelength absorbed by Chlorophyl A. This is because the energy of a photon at 680nm contains the exact energy required to raise the dimer chlorophyl A molecule at the center of an antennae complex to the necessary excited state that will allow the process to liberate an electron. Basically, allowing for variances in specific wavelength absorption rates, all absorbed photons from 380nm to 680nm will have exactly the same effect in the process to free up electrons. The difference is that the photons of shorter wavelengths than 680nm contain excess energy that the plant must then dissipate as waste heat. And since a photon is a photon is a photon - for a given amount of output watts - you will generate a lot more photons at 680nm than 380nm. 

This document really helped me to understand this issue.
16.3 Photosynthetic Stages and Light-Absorbing Pigments
(hint - if you print the page to PDF all of the side bar diagrams are reproduced within the resultant document at full size/resolution)
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mcb&part=A4434

Finally, I would state that the majority of my research on these topics has been centered around the production of lettuce/spinach.

Just my $.02

Stephen Lebans


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## thepaan (Jul 7, 2010)

So Slebans is right on here and I'd like to add to it. Also, I concur on the ncbi link - that was one of my resources as well.

I think it is important for anyone interested in participating in the discussion about plant lighting to understand how a plant uses said light.

*Photosystems*

If you read the link in Slebans post you will find it explained that there are two photosystems: PSI and PSII. Everything begins in PSII where light excites the core of PSII, creating a proton gradient within the system with enough force to cleave water into it's component gases. The electrons from this action are passed through mobile proteins to PSI where carbon fixation occurs and energy is created and stored in the form of ATP (temporary) and sugars (long term). Each photosystem uses an array of pigments to collect enough light and focus it towards the core (primary acceptor in the image below) in much the same way a sattelite dish focuses a signal. Thus, to achieve action, it is more important to have enough light (a strong signal) than the exact wavelength.








*Absorption vs. Action*

There are a lot of graphs showing what wavelengths are for plants and I think they are tossed around too casually and most of the time out of context so let me explain. In a Google search you will come out with two very different looking graphs - one is action spectra the other is absorption.

Some people have dark skin so they appear dark and their skin absorbs more visible light while some people appear light so their skin absorbs less visible lght. However, everyone absorbs some light and thus our skin has color. If it did not absorb visible light then our skin would appear perfectly white like this plastic beverage cup I have on my desk. Each spectrum of light our skin absorbs is collectively called the absorption spectra. To get an idea of the difference between this and action I would like you to think of how we get a sunburn. Not all light causes sunburns. We know this because artificial lights cannot give sunburns and so it was determined that UV wavelengths must cause sunburns. From all this we can gather that the action spectra for sunburns is very different from the absorption spectra of our skin. Similarly, the action spectra for photosynthesis is very different from the absorption spectra of chlorphyll.

Another difference you will find is between in vitro (within the glass) and in vivo (within the living) results. In vitro results have isolated the specific parts the scientist wants to study so they do not include the whole system. There are many reasons why the in vitro results are invalid for determing lighting requirements but let us leave it at that.

Absorption spectra in vitro:





Action spectra in vivo from http://members.misty.com/don/photosyn.html:






*Action/Moles vs. Action/Watts*

So now, we understand why we look at action instead of absorption and we can see that the action spectra has a much broader response curve than expected (e.g. you can grow a plant in only green light). But lets look closer at what exactly the above image shows. The measurements show quanta of light (Remember light is a particle as well as a wave?) used to convert an number of CO2 consumed at each wavelength. Because the number of CO2 consumed directly translates to growth, we can assume that the best growth is had at the best ratio which is the highest point on the curve. The remainder of the curve is relative to the highest point such that where it drops to .5 the plant is only consuming 50% as much CO2 - growing half as much - as at 1.0. But when was the last time you saw a data sheet for an LED list the output intensity in moles? We want watts, or at least we can convert. This link:

http://envsupport.licor.com/docs/TechNote126.pdf

has a decent comparison of action/moles vs action/watt. When we convert to watts the blue light gets a penalty because lower wavelengths have more energy.


*Why LEDs?*

So now we have an idea of what wavelengths drive photosynthesis best. With LEDs we can get a very narrow band in that range (around 660 nm) and not waste any electricity on other wavelengths. Unfortunately there is more to growing plants than producing growth. Examples are shaping that growth and triggering certain plant responses like flowering and fruiting. Fortunately, for the majority of plants, these responses can all be taken care of with a minimal (8-20% of red) amount of blue light (around 450 nm) and altering the length of light exposure.


*Why not HPS?*

HPS is not bad but it isn't optimal either. HPS is widely accepted for the volume of light (remember, I said earlier the amount is more important than the exact spectrum). It is suboptimal because it causes unecessary damage to the photosystems by overloading PSII. If we use Slebans's link to ncbi above, we see that PSII has more chlorophyll b than a where PSI has more a than b. Because PSII starts the chain but processes electrons at a faster rate due to better stimulation, it damages itself. See:

http://www.plantphysiol.org/cgi/reprint/153/3/988.pdf

for reference.

I hope I answered all of your questions. Feel free to point out any errors I may have made as I'm not exactly an expert - this is more of a hobby of mine.


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## Oznog (Jul 8, 2010)

thepaan- there's an important note added:
_*One more note 5/3/2010:*The action curve is shown to be of a measure of photosynthetic action per photon, rather than per unit energy. To convert this to photosynthetic action per unit energy, this curve needs to be weighted by wavelength. That would make the blue peak having a value around 55-60% of that of the red peak.

_That's a major biasing factor. The red is much lower energy per photon, and what we really want is photosynthesis per watt of light energy. As such, the Action Spectrum chart is MUCH more favorable to red than it indicates. 

Now the Action Chart... I'm still a little confused on the method (and thus the meaning).  There are two options:
One is that I apply 1 mol of photons externally and measure the response. Some will be reflected and not absorbed at all, but that will not be counted. 
Two, we could apply 1 mol of photons, note that say... only 70% of a wavelength is absorbed, and scale the response up to ABSORBED photons, multiplying the response measurement by 1/0.7. This is not altogether irrational, because unused reflected light may illuminate other leaves. Esp in those grow operations where they install reflectors around the plants (but I expect this is not an extremely efficient process.

I have difficulty here because the ABSORPTION chart says 525-625nm just isn't absorbed by A,B, or carotenoids at all. If the wavelength isn't _absorbed_, how can it be _used_ as per the Action Spectra chart?

One theory is that the chart's only saying A,B,or carotenoids are capable of absorption, but other substances may block or reflect light before it reaches them. However, AFAIK, the green color of plants comes DIRECTLY from the chlorophyll at the surface, which reflects green & yellow, and thus does not utilize them.

That would indicate the Action Chart uses #2 and only factors in absorbed light, and is somewhat misleading because the 1 mol of applied photons in the green range will not have 50% of the "action" of light in the deep red range, because (as per the Absorption Chart) the rate of absorption is only ~5% that of the deep red!

I have difficulty believing that the Action Chart uses the #2 idea... because it's more complicated to factor in absorption. But if it doesn't then there's no way to reconcile it with the Absorption Chart, which shows absorption of greens and yellows are negligible and thus could not possibly have Action at the listed rate. And that one link http://www.general-cathexis.com/images/ActionSpectra001.png describes it as "per energy incident", which does suggest it is NOT #2, but the "note" added 5/3/2010 says it's kinda wrong about "energy" being incident, and was using mols, so I don't know how literally to read this.


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## thepaan (Jul 8, 2010)

> That's a major biasing factor. The red is much lower energy per photon, and what we really want is photosynthesis per watt of light energy. As such, the Action Spectrum chart is MUCH more favorable to red than it indicates.


 
Exactly! most charts you see will have either blue higher or the peaks nearly even but the red is actually higher and when you convert to W it becomes even more favorable for red. But lets not forget the efficiency of the LEDs themselves - where blue are used as a base for white so they have had a lot more time and energy put into them to make them more efficient.




> Now the Action Chart... I'm still a little confused on the method (and thus the meaning)


 
O.K. So, the way this works is you have some light of a specific wavelength shone upon a leaf which is enclosed in a bubble of sorts. Inside this bubble they measure how many molecules of carbon dioxide are used up. They also measure the light that hits the surface of the leaf, called incident light. Light incident on the surface (measured in moles) divided by the number of carbon dioxide gives you a ratio. This ratio is normalized to 1 at the highest point on the curve then the remaing wavelengths are relatively adjusted. The energy terminology comes from counting the photons - each photon of a specific wavelength has a specific amount of energy. In other words, quanta of light (as long as wavelength is specified) can be considered energy of light.




> I have difficulty here because the ABSORPTION chart says 525-625nm just isn't absorbed by A,B, or carotenoids at all. If the wavelength isn't _absorbed_, how can it be _used_ as per the Action Spectra chart?....


 
First, it is very small but, both chlorophyll a and b have a non-zero absorption all the way across the visible spectrum. That they are green is only due to that being the dominant wavelength reflected - not the only one and not 100%. This absorption chart only shows absorption of those pigments as they exist in a tube. There are other protein-pigements besides chlorophyll. For absorption of an actual (bean) leaf see page 4 of this document: http://www.plantphysiol.org/cgi/reprint/46/1/1.pdf .

Here is where you have to seperate the idea that absorption of known components will be similar to action. The way a living plant uses light is very different from how the known components, after being broken apart, absorb it. We need to let go of the absorption chart as being relevant because it isn't. Let us say we want to grow a plant as quickly as possible but are going to use only a single wavelength of light. Because carbon fixation directly correlates to growth, it only matters which wavelength produces the best result compared to other wavelengths. We are not trying to stimulate any one component of the system but the system as a whole. To this end, knowing the component parts is irrelevant and knowing each component's absorption spectra is also irrelevant.

I hope this helps.


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## Oznog (Jul 10, 2010)

thepaan said:


> Exactly! most charts you see will have either blue higher or the peaks nearly even but the red is actually higher and when you convert to W it becomes even more favorable for red. But lets not forget the efficiency of the LEDs themselves - where blue are used as a base for white so they have had a lot more time and energy put into them to make them more efficient.



Actually the "lumen" figure is so biased against deep red and blues, it's inappropriate to use (which is why dental blues are rated in mW).

"Lumen" is a measure based on units of "brightness" as seen by the human eye. Now exactly how they decided what 1 lumen of "brightness" of blue vs 1 lumen of green vs 1 lumen of red is, that's pretty odd, but they did it. Infrared and deep UV are 0 lumens regardless of output power. Deep red reports as a very poor lumen/photon ratio because of a poor eye response/photon ratio, but IIRC the actual efficiency- mW of light energy out vs mW of electrical energy in- calculated to about 20%, same as other LEDs. Just poor visibility, which is irrelevant because we care about plant response, not eye response.

I tried to find the Osram Golden Dragon "deep reds" mentioned above. I found them at Digikey, but the price was ludicrously high for the output. It wasn't competitive with LEDEngin. Wondering when the market will pick up on deep reds.
Bottom line, the "deep red"s are typically NOT bad for power output, even if the lumen output is very small. LEDEngin rates 525mw out at 1A @ 2.8V, efficiency of 18.75%. Well, that's if you maintain 25C, which you probably won't, but LEDs of any color suffer similar derating effects.

I tried to look up the Osram Golden Dragon "deep red" mentioned above. All I saw was Digikey, but the price was very high for the device output. It wasn't price-competitive with LEDEngin. I wonder when the market will see the value of making deep reds?


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## Oznog (Jul 10, 2010)

thepaan said:


> O.K. So, the way this works is you have some light of a specific wavelength shone upon a leaf which is enclosed in a bubble of sorts. Inside this bubble they measure how many molecules of carbon dioxide are used up. They also measure the light that hits the surface of the leaf, called incident light. Light incident on the surface (measured in moles) divided by the number of carbon dioxide gives you a ratio. This ratio is normalized to 1 at the highest point on the curve then the remaing wavelengths are relatively adjusted. The energy terminology comes from counting the photons - each photon of a specific wavelength has a specific amount of energy. In other words, quanta of light (as long as wavelength is specified) can be considered energy of light.


I do see that. In this case, there might be a slight bias against wavelengths which are reflected instead of ones which are absorbed but not used. In a reflective growing container, some portion of reflected light may hit another leaf and a certain % may be utilized. However, light blocked by non-photopigment substances and not reflected is a total loss.



thepaan said:


> First, it is very small but, both chlorophyll a and b have a non-zero absorption all the way across the visible spectrum. That they are green is only due to that being the dominant wavelength reflected - not the only one and not 100%. This absorption chart only shows absorption of those pigments as they exist in a tube. There are other protein-pigements besides chlorophyll. For absorption of an actual (bean) leaf see page 4 of this document: http://www.plantphysiol.org/cgi/reprint/46/1/1.pdf .
> 
> Here is where you have to seperate the idea that absorption of known components will be similar to action. The way a living plant uses light is very different from how the known components, after being broken apart, absorb it. We need to let go of the absorption chart as being relevant because it isn't. Let us say we want to grow a plant as quickly as possible but are going to use only a single wavelength of light. Because carbon fixation directly correlates to growth, it only matters which wavelength produces the best result compared to other wavelengths. We are not trying to stimulate any one component of the system but the system as a whole. To this end, knowing the component parts is irrelevant and knowing each component's absorption spectra is also irrelevant.
> 
> I hope this helps.


Sorry I'm not trying to be difficult, but I still have trouble. OK, the Absorption chart only shows what light will be absorbed, not utilized (which is basically similar to its visible appearance of reflected colors), and painting the plant black would give it 100% "absorption"; but pointless. 

But yet the Absorption chart still seems to present a limiting factor: if there is no absorption of a wavelength, it is physically impossible to utilize it. Light cannot be reflected AND used. And that's true regardless of whether it was measured on the leaf or the leave were thrown in a blender and Chloro A separated out and measured for absorption without any other structures of the leaf presenting absorption. 

So the Absorption chart doesn't state how much photosynthesis is performed per mol or mW, only that it's absorbed, so it doesn't tell us the growth potential. But the problem remains, unabsorbed light couldn't be utilized for sure. This conflicts with the photoactive response charts of others in the green/yellow regions, regardless of whether it used mols or mW, because there's NO absorption shown in this range.





I'm thinking the way to logically resolve this is to simply discredit the data shown in this particular chart! It shows neither dimension nor scale... I suspect perhaps the Y-axis is not absorption=0 at y=0. Because your "bean leaf" link has an absorption chart showing something similar, but the range is 60%-95%. I think they depicted 60% at y=0 here, an undisclosed offset which is _very_ misleading, and the whole thing is just drawn for aesthetics rather than depicting actual data like the bean leaf charts.

I guess this chart being bogus explains it. The "bean leaf" PDF shows it much better, and it all makes sense from that.


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## thepaan (Jul 10, 2010)

> Actually the "lumen" figure....


 
No where do I speak of lumens. Lumens are irrelevant here.



> I guess this chart being bogus explains it.


 
You can think of it like that for our purposes but it isn't actually bogus.

A plant cell contains within it many different pigments. Many are known but many of these pigments are also unknown. The above chart represents the absorption of only three pigments _after_ they have been removed from a living plant. Isolating each part allows scientists to study it without interference from the rest of the plant but without that interaction it is also impossible to determine how it would behave. So what we have are two different representations: the bean leaf being the whole plant and the above chart being a few components of the plant. I think the key point I'm trying to make here is that these few components are not all the components and their values are not necessarily additive. They could be multiplicative or one could offset the absorption spectra of another when everything is connected.

Take, for example, chlorophylls a and b. The difference between them is two hydrogen atoms and one oxygen atom. With such a minor variation the absorption of each changes noticeably - by adding just 3 atoms. Then you connect all these parts you know about back together and it still doesn't look like the original because there are parts you don't know about. It all becomes rather daunting when you look at from that perspective.

So we go back to the living plant. How well does a living plant use each wavelength? This is what we want to know because this is what we are dealing with.


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## Oznog (Jul 11, 2010)

thepaan said:


> No where do I speak of lumens. Lumens are irrelevant here.


That was in regards to the regret that these deep-red LEDs aren't efficient. Actually, they seem to have the similar efficiency to other LEDs, and a high power output. Just a very low LUMEN value, which is irrelevant.

I noted that when comparing the "red" and "red-orange" Luxeon Rebels for making signal lights. The red had a substantially lower lumen value, and I thought they were inferior efficiency than red-orange and wished they'd "fix" this and give me a stronger true red. But in looking at the human eye response, I realized I was wrong- the human eye response drops off sharply outside the orange region, and the true red was a very similar radiated power. The purpose in that project WAS visual, so the shortcoming was in the human eye, not the LED technology, and thus red-orange was preferred over a true red.



thepaan said:


> You can think of it like that for our purposes but it isn't actually bogus.
> 
> A plant cell contains within it many different pigments. Many are known but many of these pigments are also unknown. The above chart represents the absorption of only three pigments _after_ they have been removed from a living plant.


Did you note my point that if there's zero absorption at a particular wavelength, then Action would HAVE to be zero? That's critical. I did note your point that this is for separated pigments and the molar Action to create chemical energy from light does _not_ follow Absorption. I see that. But, Action cannot take place without Absorption.

Well, I'm looking at the link you provided:
http://www.plantphysiol.org/cgi/reprint/46/1/1.pdf Fig 7 on pg 4 of 5, the Absorption line. And the Action line, really.

That's not the blendered, separated, _ex vivo _pigment, but I think it hints at the problem with that colorful Absorption chart. I think the colorful chart MUST have offset the results down by a LOT, probably ~60%. Which makes it _look_ like the absorption of Chloro-A is like *100x* greater at 675nm than at 510 nm. With next to zero absorption within Chloro-A,B, or Carotenoids as it _appears_ in that chart, then Action would be impossible! 

But it's not the case, as the Bean Leaf PDF chart shows the Action's like 35% greater on a mol basis at 675 vs 510nm, which would be 80% better on an _energy_ basis. There's action, less, but not 100x less- so there must be a lot of absorption. So I think the big color Absorption chart just has so much wrong with it, it's "bogus". Chloro A/B/Carotenoids _don't_ have zero absorption (thus no action is even possible) through the green/yellow range. 

I'm still troubled and unsure of this conclusion, because EVERY chart that I get for Absorption shows NO absorption in the 500-600nm range. Nothing. Total zilch for A and almost zilch for B. So it's not this _one_ chart. I think it'd be unusual for everyone to have put out an offset chart.

The only other explanation I could see would be that Chlorophyll has such poor efficiency that only a tiny % of Absorption is used. In which case the Absorption chart is correct and peaks are all from nonproductive absorption (like being painted with green). So the Absorption could have those very low areas and yet only have modest drops in the actual Action. But it'd need to be much less efficiency than I'd understood.


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## Oznog (Jul 11, 2010)

OK, so I'm seeing some other stuff that says it's carotenoids and xanthophyll here which somehow absorb wavelengths that Chloro A&B don't, and somehow pass energy along to Chloro A&B indirectly, using a wavelength that Chloro A&B can't even absorb directly.

That kinda makes more sense now, but I wish I had a better explanation of the process. In particular the efficiency (as per the Action chart) seems unexpectedly high for an indirect path into Chlorophyll's energy.


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## thepaan (Jul 11, 2010)

There really is almost no absorption in the pigments chlorophyll a and b in the green and yellow range. There are several reasons why this could be different than a living plant. As I explained earlier, it could be when connected together each component's absorption blends together. It could be there are components we don't know about. It could be that lower wavelengths (higher energy) lose some of that energy when passing through the leaf and get absorbed as a higher wavelength (lower energy). The wavelengths are obviously being absorbed by the plant but, as far as is known, not by the chlorophyll (or not much). I'm not sure what else to write here because that is about as good as I can explain it.


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## Inkidu (Aug 30, 2010)

I never noticed these Osram deep reds before.

http://www.mouser.com/ProductDetail...-W5AM-1T3T-1-L-Z/?qs=dzkBnbp7AzQjkL7H45NWtQ==

They seem cheaper and more efficient than LedEngin deep reds.

Has anyone used them or have an opinion?

Thanks for any help.


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