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Lettuce & Leafy greens

PostPosted: Sat Oct 27, 2012 3:30 pm
by JoeB
I have read everything I could on the subject so far on this forum and others. I am new to this forum and wanted to see what some of you think.

I read about lights and HID versus LED and low wattage and high wattage LED's and have a couple of questions.

When you start the germination process and grow lettuce or leafy greens to a baby stage of growth or just for sprouts can a low wattage 14w LED panel do the job?
I am not looking for flowering, just vegetative growth in the start up phases of the plants and then harvesting them.

I have looked at 14w panels in the US and in China between $29.00 and $54.00 and mostly the red/blue or just blue LED's. I think they will work but just not sure how long they will last. Please comment on this.

Also I could build my own 14w panel using LED's on metal strips. The advantage is I can make the size and shape I want and if an LED burns out it can be replaced easily. Please comment of this.

The space I want to cover is a typical 10x20 tray setup with 9 trays in a row. So the coverage needs to be 20"x 90". I was thinking if it were Chinese made 14w panels I would need about 3 panels to cover this space. Do you think that would work?
If I made my own strips I was looking for some help on what I should be looking at?

I have seen setups where some people just use CFL's pretty far away as well as just having lights in the room work and no lights directly above the sprouting trays.

Re: Lettuce & Leafy greens

PostPosted: Sat Oct 27, 2012 7:09 pm
by SisterMaryElephant
Welcome to the forums...

The short answer is: no. Three low power, 14w, cheap, Chinese LED lights will not cover 1800 square inches.

The long answer:
Depending on crop and coverage desired; a 14w light *might* be enough for seedlings/germination or maybe even cloning but they'd be pretty useless beyond that.

1800 square inches = 12.5 square feet. That would be 3.4w per square feet. Even if you used 12 of them you'd be running less than 14w/sqft. With that little light you'd be better off using six 4foot fluorescent tubes. You'd have more even coverage and more w/sqf.

At those prices you'd be better off buying bigger/better lights that would be more useful. You don't need HID for lettuce seedlings but for 20"x90" you'll need more than 43w.

You could build your own small panels but don't bother with cheap, low power diodes, even for seedlings you'll want to use 1w diodes. With 14 1w diodes it should be easy to see why it won't cover much of a grow area effectively. LED lights are a big investment and, contrary to marketing hype, they usually don't cover nearly as much as most people think...


Hope that helps...

SME

Re: Lettuce & Leafy greens

PostPosted: Sat Oct 27, 2012 8:03 pm
by JoeB
I understand what your are saying in the long answer but if all you wanted was lights for sprouting then the lights would always be used fro sprouting and never used beyond their intention.

I saw a video from a guy interviewing someone from a sprouting company and they were doing wheatgrass and other sprouts and had no lights over the top of the trays at all. All they had was fluorescent lights on the ceiling in the room and these plants grew really well. So I thought that if they got such great results using no lights why not use cheap LED panels. I would post the video but they are selling sprout products not lights but do not want to have an issue with that unless I can.

Are you saying that the LED panels will not work and have experience growing sprouts?

Re: Lettuce & Leafy greens

PostPosted: Sat Oct 27, 2012 8:40 pm
by SisterMaryElephant
Sprouts and seedlings are different. Seeds do germinate in the dark but after that they need light. You can't have photosynthesis without light. ;)

It's your money and garden, try them and see if you like the results. If you do like the results then other opinions don't matter. :D

Re: Lettuce & Leafy greens

PostPosted: Sat Nov 10, 2012 9:37 am
by JoeB
I know it has been a while since I posted on this subject. In your post last you talked about having 14w per sq foot. I have purchased several 3w LED's and I am now thinking about using 12 of them on 5 panels. That would give me 36 per panel and a 180w total. With the 12.5 square feet that I need lit that would give me 14.4w per square foot. I was able to get each panel cost to $25 with LED's, Driver and aluminum heat-sinks. The driver can go up to 45v so that is why I can go up to about 12 maybe 13 if I use more red led's.

I am going to build the first 5 panels and give this a try.

My last question then is on aluminum plate size or heat sink size. I have aluminum sheets and can make this any size I need but want to get it as close as possible to work on the coverage. I will be able to have between 12 and 13 LED's depending on color choices. The LED's are 120 degree view angle.

How or what would be the best way to lay out a aluminum sheet to cover the 20" depth and make sure I am covering it. Is there a formula on this? With 120 degree view angle how can you determine the correct spacing and size of the plate. I will be about 11 inches away from the top of the plants or trays.
My thought was a 9x12 plate or sheet with 3 rows of 4 - 3w LED's. The 12" length will cover the 20" space below. With that figure I was thinking that 4" of light needs to cover the sides. So 5 times 9 = 45" and 4 x10 = 40" for a total of 95". I am wondering if this will work on the plate size and if the LED's will cover the sides.