Veggy Seedlings-LED watts per square foot? DIY LED recommendations?

I am building a grow light for some vegetable seedlings. We start them from seed in "flats" that are 11 x 22 and have 36 plants in each. We grow the seedlings until they are about 8 inches tall and then plant them if our timing is right for the spring.
We usually have 8 to 10 flats each year.

I need to know the following information:
A) How many watts per square foot is adequate to grow seedlings in this manor using LED lights?
B) What color (wavelength) LEDS will I need?

I just finished building some custom fixtures for my garage out of 10W cool white power leds. I used a single ATX computer power supply and some resistors and have them set at around 8 watts each. My garage is bright now and I love it!

Time to apply the technology to my seedlings.. I just need some guidance.

You could get away with 1W-2W per sq ft if you use Cree XM-L2. You could use 4500K or something along those lines. You can get very cheap and very efficient (80%) 350mA driver so you could link 2 or 3 XM-L2 in series and each will dissipate about 1W. With a setup like that each LED will dissiapte about 1W and emit 160lumens at an efficiency of nearly 50%. Once the plants get larger if you think they need more light just swap in an 600mA driver or bigger.

The LEDs and drivers are very cheap on fasttech or aliexpress. Fasttech has decent prices on small heatsinks. If you build something like this you will have a more efficient growing lamp than anything on the market. Good luck!

What about all those special colors like red and blue that everyone uses to grow with?

What am I missing?

Murphyball said:

What about all those special colors like red and blue that everyone uses to grow with?

What am I missing?

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White is the new purple!...again.

(anybody remember the iSunlight panels? All white Eshines?)
http://www.amazon.com/iSunlight-Full-Spectrum-White-1200/dp/B005YKSRPQ/ref=cm_cr_pr_product_top

Anyway, what your missing is everything in between the r/b peaks that the whites can provide.
Follow Supra and all the other DIYers in the led section...good stuff.

ellydee said:

White is the new purple!...again.

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I'm sorry but I don't understand what that means.

(anybody remember the iSunlight panels? All white Eshines?)
http://www.amazon.com/iSunlight-Full-Spectrum-White-1200/dp/B005YKSRPQ/ref=cm_cr_pr_product_top

Click to expand...

A quick google search showed reviews on Amazon saying those were an over priced scam.. But did they work??

Anyway, what your missing is everything in between the r/b peaks that the whites can provide.
Follow Supra and all the other DIYers in the led section...good stuff.

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Now this I understand. Should I add some reds and blues to go with the whites? Looks like this Supra person knows his stuff..

To be Honest you can get away with one LED. Your looking for something for seedlings and tested so I would go with the cree CXA3050. I made my own led light per sqft for flowering in the 2700k spectrum and as the thread bbspills made shows they work. They plants love the light. I have recently bought 4 of the 5000k from digikey and I am waiting on drivers. The drivers I use are the meanwell LPC-60-1400 and a 12v 2A driver for my fans from amazon.

I was able to get the whole setup together shipping for a day of work and $76.38

I think you can easily get one of the lowes cloner sizes 20inx10in(which easily fits 50 clones) of coverage for seedlings and 1 sqft for veg

Here is a picture of my setup but I have 4 lights on each setup over 4 plants in a 2x2 for my own uses. I have looked and designed panels over and over but this setup triumphs. Isolate each led and you will prosper!

Part number for LED: CXA3050-0000-000N0HX250F-ND

for veg you can get an aquarium led for plant life. they are cheaper and work great. i find a good mix of white with a few blue is best form all the posts research. or you can use several 23/26 watt cfl 6500k and make a hood.

SupraSPL said:

You could get away with 1W-2W per sq ft if you use Cree XM-L2. You could use 4500K or something along those lines. You can get very cheap and very efficient (80%) 350mA driver so you could link 2 or 3 XM-L2 in series and each will dissipate about 1W. With a setup like that each LED will dissiapte about 1W and emit 160lumens at an efficiency of nearly 50%. Once the plants get larger if you think they need more light just swap in an 600mA driver or bigger.

The LEDs and drivers are very cheap on fasttech or aliexpress. Fasttech has decent prices on small heatsinks. If you build something like this you will have a more efficient growing lamp than anything on the market. Good luck!

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Ok.. so I ordered 4 of the Cree XM-L2 that you linked to just to get me started. Why do you suggest to drive these 3 amp leds at such low current? I understand the lower power when the seedlings just start to sprout, but whey only 600ma for growing?

I sure hope that Fasttech reputable! LOL..

You certainly can run them harder and hotter than I do. I just chose 700mA as a good value point for my preference, based on the charts below. 600mA-700mA has plenty of reach for vegging up some pretty tall bushes in 5 gal buckets. If I ran them harder they would be vegging too fast for my system and I would run out of vertical height in the flowering rooms.

The last column is the number that interests me most, output efficiency (par watts/dissipation watts). You can see how it drops as you increase the current and of course it would drop more if the junction temps was allowed to rise past 50C. Of course this number doesn't tell the whole story because one spectrum may be more photosynthetically efficient or desirable than another spectrum but it does give us some idea of how the LED stacks up.

SupraSPL said:

You certainly can run them harder and hotter than I do. I just chose 700mA as a good value point for my preference, based on the charts below. 600mA-700mA has plenty of reach for vegging up some pretty tall bushes in 5 gal buckets. If I ran them harder they would be vegging too fast for my system and I would run out of vertical height in the flowering rooms.

The last column is the number that interests me most, output efficiency (par watts/dissipation watts). You can see how it drops as you increase the current and of course it would drop more if the junction temps was allowed to rise past 50C.

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Ah.. Got it. So you're just running them at the point where you get the most bang for your electrical dollars. Makes sense.

So like I said, I ordered four of the Cree XM-L2 T6-4D 1200LM 4300-4500K you linked.

I'm wondering if I should mix in a few of the 620-630nm reds too? They have these on ebay: http://www.ebay.com/itm/5PCS-Cree-XLamp-XP-E-Red-620-630NM-1W-3W-LED-Light-Emitter-w-20mm-Star-Base-/321100795689

Or do you think its not needed?

Thanks again for your help..

Adding reds and or deep reds will likely somewhat improve the efficiency of your spectrum. The XPE and XPE2 630nm are awesome but it is dependent on the bin, which is not specified in the auction. The P3 bin is the best available and in order to actually improve the SPD of an XML2 T6 I figure we probably need the top bin. Cutter and ledgroupbuy have the P3 bin available on stars. I think digikey or mouser has them loose. Steves LEDs has the Luxeon ES deep red EX6 on stars.

I use XML2 neutrals for vegging all-white and they seem to work just as well as the R/W/B vegging areas so there is probably no need to introduce complexity unless you are experimenting or if you are planning on running off the grid.

Thank you..
I think I'll just stick with the XML2 then since adding the XP variety means more money and using a separate driver because the voltages are different.. I can always add them later.

I take it you guys prefer using dedicated constant current drivers for these? Probably more efficient than dumping energy through resistors with a constant voltage source yes?

Yep you guessed it CC drivers seem to be the best way to get the job done. They are cheap, efficient and readily available. With a CC driver you can add reds or blues to your white string with no problem, as long as you stay within the vF range of that particular driver.

Nice spread sheet Supe. Nothing like organized notes. OP is getting some good advice. I'd do a nice full spectrum like Area 51. Rapid LED has some nice clean kit bundles. So many possibilities.

RedCarpetMatches said:

Nice spread sheet Supe. Nothing like organized notes. OP is getting some good advice. I'd do a nice full spectrum like Area 51. Rapid LED has some nice clean kit bundles. So many possibilities.

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Those pre-built led fixtures are ridiculously expensive.. I can't get over the price these suppliers charge for those things. I guess if I was growing a cash crop it wouldn't be a big issue, but for crying-out-loud, its some LED lights, a power supply and some aluminum. Is there some patented nano-technology involved I'm not aware of? Does it cure cancer?

I ordered an LPC-60-1050 meanwell driver for another project from reefledlights.com as they are having a closeout special.. $20 + $4 to ship.. Couldn't beat that deal anywhere.

My first project was to light up my welding table in my work shop.. I mounted four 10w china import led chips to a 3x3x48 piece of aluminum tube.. Wow.. I love leds!

Thanks for all the advice.. I'll probably be looking for more soon!

I like the driver deal (thanks for the heads up) and DIY mentality...but China? I so feel your passion for saving money and building your own panel...just can't cheap out on the LEDs IMO Good luck on your journey and keep us posted!