Photosynthetically Active Radiation, LEDs, and you

[kinnza]

I suggest to avoid Luxeons now. Cree, Nichia and Osram has surpased Lumileds by far in efficiency terms, aswell as Toyoda Gosei and Seoul Semiconductor and Edixeon (2 last use Cree's dies in blue/white).

The new Cree XR-E 7090 deliver 85lm/watts in the top end binning. NIST measure more than 75 lm/w @350mA last month, in continous lighting mode and thermal stability, with just the MCPCB as heatsink. Taking into account the Stokes effect losses (at phosphor conversion), it mean a radiometric efficiency about 40% of the blue die, better than best of the best HIDs avalaible today, and without reflector losses. SSC has announced some days ago a new model, using the Cree's die, wich achieve 100lm/w, althout this month they only serve 80lm/w models. Its design is similar to Luxeons. Edixeon has announced a very similar device. Compared with the 28 lm/w of Luxeon V, or 40lm/w of LuxIII (at typ currents), no sense currently buy Luxeons. I suppose Lumileds will release some top end new led soon, or its future isnt clear.

Im currently building a system with 67 Cree 7090 3watt, 60 reds and 7 blues. They are directly attached to a 4m copper pipe (18mm diameter, to improve at max air forced cooling), wich end in a hermetically sealed box with a 8cm PC fan. The copper pipe spiral around the plant. I expect only a increase of 3-4ºC over ambient temp of the pipe, but ill measure it when running, and if its higher, ill water cool the pipe, instead of air cooling. As the Crees have the bottom slug electricaly isolated, i attach them directly to the copper pipe, reducing the thermal resistance at minimun, a very relevant issue when working with red leds, wich output degrades strongly with increased die's temperature.

If HB LEDs continue improving its perfomance at this rythm, in one or two years, leds will have surpassed HIDs in horticulture. SSC has launched the Ariche, a directly 110-220 VAC driven LEDs, wich currently emits 40 lm/w@350mA, but they expect 80lm/w at the end of 2007 and 120lm/w at the end of 2008.

The whole system materials cost me about 100$. Im building the driver to run them directly for the 220VAC plug, rectifing to DC and conmuting with feedback from a 1ohm resistor to limit current. I want to test it with PWM, too. All the leds will go in one single serie. Im using 635nm peaked red leds, due they was stocked when the new XR was launched, and i buyed it for cheap. Using this wl has its advantages, due to the reduced need of 730nm light and that at 640nm, excitation of photosystems I and II are balanced, thus providing the best quantum yield, although not the best photosyntetic action possible.

At first, im going to use them at 450mA, due to i calculated there the best ratio efficiecy/cost per mW emited. Taking into account thermal output degradation, at 700mA red leds im going to use just emits 9% more mW but consume 70% more energy, considering a junction ambient thermal resistance of 25ºC/W (thermal resistance junction board is 17ºC/W).

[LaserGecko]

Hi everyone,

(Woo hoo, the registration is unlocked!)

I've been reading this thread and lots of others related to photosynthesis for a few weeks now. Some friends of mine asked me to come up with an LED based replacement to their current HID system. Many hours of research later, I've found sources for 660nm, 640nm, 450nm, and some of the broader carotenoid wavelengths, but only found relatively expensive sources for the 430nm LEDs.

First, my research led me to believe that these were the primary wavelengths of light with which you need to be concerned (Chlorophyll A - 660/430, Chlorophyll B - 640/453, carotenoids - can't recall off the top of my head). However, I think I read a response somewhere (on here, I believe) that alluded to the fact that you actually want the LEDs to produce a slightly higher wavelength (~2-3nm higher than the target) instead of matching it exactly.

Does that ring a bell to anyone? I can no longer find that message. Of course, I could've been in overload from spending so much time reading, too. So, if that's offbase, please let me know, too.

Second, I actually found a company in China that could produce the 430nm LEDs for a much cheaper unit price...if I was willing to buy 5,000 of them. (IIRC, about a third of the best price I found from a US manufacturer for 1,000 quantities). Working through the math shows you that you can spend some more $$$ than the 1,000 and quite a few more diodes. Gee, I think there may be a market out there for them. (I can't recall the figures off the top of my head right now, though. That documentation is elsewhere.)

Anyway, do those figures agree with what you all have found or I have missed something significant?

Thanks!

[Rob]

Welcome to the boards.

You may be recalling one of kinnza's posts, perhaps this one:
http://forums.linear1.org/index.php/topic,891.msg5287.html#msg5287

There are several members here that have done more homework on this than I have.

You may be able to dump your excess LED inventory on a popular auction site if you find yourself with extras. They're so easy to ship and handle that I'd imagine it would be relatively simple, and yeah, you'd probably find a market, people like to grow things.

[LaserGecko]

Thanks, Rob. That's exactly the message to which I was referring. I couldn't find that for the life of me the other day.

[Rob]

We're here to help!

[BVnursery]

Id be interested in your excess depending on specs. 

[cadstarsucks]

An interesting link on aquarium plants ... http://www.sankey.ws/plantlumen.html

Dan

[BVnursery]

For anyone working in this area we do have a relatively new player and they are US based with parts already at Mouser for one.

http://ledengin.com/index.html

[motobroker]

BV,
Thanks for the info. The UV and 660 nm dark reds look interesting. I have been having a very hard time finding these in the US.

[motobroker]

Yikes,
 $9 to $10 each for the 5 watt reds.

[BVnursery]

660nm with a decent out put are never much fun to find... 
All their units are good output with wide angles....

[motobroker]

I am going to get some on the way. I guess I will run them close to full power. I usually try to run hi powers around 1/2 power to get the most energy efficiency.  Here I will need to have the most Lumens/$$$.
Do you know of another source for 660s?  The only one I am aware of is www.roither-laser.com. They are about the same price, but lower power and have to be sourced from Austria.

[kinnza]

660nm light has only a 5% more photosynthetic efficacy than 635nm light, and produce a more extreme spectrum, more difficult to compensate and easily saturating photosynthetic systems.

635nm leds have efficiencies higher than 5% against 660nm, so really i dont understand why using them, when they are pricey (compared to standard 635nm leds, easy to find at 2-3$) and less efficients: currently 635nm leds have better efficiency for plants, and better price.

For good relation light emited/cost, currently the best choice is the new Osram Diamond Dragon, with a 2 sq mm chip (double than the other HB leds), only 2,5 K/W of thermal resistance and 2A of max current (rated as 1,4A typical). Still running at 1A they have a very nice efficiency:

Bin flux  Lm/w  Efficiency

KZ  30  17,5%
LX  34   22%
LY 39,5  23%
LZ 46,5 27%
MX 55  32%

(for thermal resistance junction-ambient 10K/W, 25ºC ambient temp, typical 2.2Vf (@1A), LER=170 lm/w, very prudent, probably actual eff is higher and LER, lower).

The two top bins gives more optic watts than a reflectorized 600w HPS, and far better uE/w due its higher wl emission. Still the LY and LX bin should be able to compete with large HIDs. Unfortunately, Osram dont accept concrete flux bin orders.

Of course, Im talking only about the red model, white and blue ones has to improve its perfomance to compete with other leds in the market. Its on the red leds, with high degradation due to junction temp, where a chip with double size worth in order of far easier thermal management and the possibility of driving them harder, dropping the initial cost (less leds needed) without dropping perfomance.

[motobroker]

Kinnza,Thanks for the info. I am new to LEDs and am trying to learn as much as possible.  I will look over the specs. DigiKey is getting $13 a pop for the KZ binned which seems a little pricey. I couldn't find prices for the other bins. 

I have been using the R binned K2s since they seem to have the most bandwith and are available for about $2.60.

How do you calculate LM/w efficiency in percentages? I am only familiar with LM/w.
Trying to compare the R binned K2 with the KZ binned DD, I calculate the Osram to be about 50% more efficient, but at 5x the cost.

[kinnza]

I calculated lm/w ratings using the manufacturer specs, by derating output to 1A and derating by heating (is here where thermal resistance play a esential role).

Having the lm/w rating, what you need to convert it to energy efficiency (visible light emited (optical watts)/energy consuption) is the LER (Luminous Efficacy of Radiation= how many lm produce 1 optical watt of a given spectrum).

Specs of red Diamond Dragon says it typically peaks at 634nm plus 2-3nm for the higher junction temperature (Osram only gives the temperature coefficient of dominant wl, not the peak one). I dont have any spectographic diagram of Diamond's spectrum, so i dont know for sure its LER, but other leds peaking at 635nm range between 150 and 180 lm/w. Ive supposed a LER of 170lm/w to do the conversion. When i get a SPD from the Diamond, ill can do a more accurate conversion.

Probably im going to order a reel of Diamonds. I still havent asked a quote, but i think the red is going to be about 3€ or a bit less. Ill try to get one of the top bins paying a plus, although it isnt easy with Osram distributors. Distributors for general costumers, as Digikey, gets astounding profit margins, usually 300-400% of the price they pay, up to 1000% (10x). We, led fans, can order full reels joining to do a group buy, as usually 2 or 3 of us can get a full reel alone. If you are interested, ill give more details when i get a quote.