All COB Users - Lettuce Grow Challenge!!

Lighting Uniform light distribution is required in the Pond Growing Area. A supplemental light intensity within the range of 100-200 µmol/m2/s (for a total of 17 mol/m2/d1 of both natural and supplemental lighting) at the plant level is recommended. It should be noted that 17 mol/m2/d is the light integral that worked best for the particular cultivar of boston bibb lettuce that we used. For some cultivars, 15 or mol/m2/d is the maximum amount of light that can be used before the physiological condition called tipburn occurs.

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ilam said:

Anyone has any ideas of what the ideal PPFD should be for lettuce?

Edit: Found this: http://www.cornellcea.com/resourcesPublications/growersHandbooks/index.html

That's the Cornell Lettuce Handbook, they did some badass science on a massive hidroponic facility.

I also, found this within that document:


Notice what they say about the lettuce they grew being sun hardy (up to 17 mol), and less hardy lettuces burning @ over 15 mol. They also state that some varieties can tolerate up to 30 mol/m2/d.

Now, i didn't know what mol meant so i did some reading, and also found this:
http://www.apogeeinstruments.com/conversion-instantaneous-ppf-to-integrated-ppf/

They have a table where they state that 17 mol (@ 24h photoperiod which is what they used)
is basically 200 μmol m-2 s-1.

Does this mean that as some have guessed, some people in this thread are burning the crap out of their lettuces by blasting them with values up to 3 times higher?

Honestly, i'm not sure, it's 3 am, i'm tired and my head hurts and i'm also clenching my jaw. So i guess It's time i go to sleep. Let's try to figure out this lettuce stuff guys, it can't be that complicated. Love you all <3

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• Light intensity is maintained at no less than 50 µmol/m2/s of PAR (Basically this is 50 PPFD) during the first 24 hours the seeds are kept in the germination area. (This level of illumination prevented stretching of the seedlings while minimizing the tendency of supplemental lighting to dry out the surface of the medium.)
  
  
• For the remaining 10 days, the light intensity is maintained at 250 µmol/m2/s. The photoperiod (or day length) is 24 hours. Shorter photoperiods are acceptable if the light intensity is increased to provide the same total daily accumulated light (~22 mol/m2/d). Anecdotal evidence shows that some lettuce seedlings can tolerate 30 mol/m2/d.
  
  PD:
  ~22 mol/m2/d = ~254.63 PPFD
  30 mol/m2/d = 347.22 PPFD

ilam said:

So yeah... I've slept a little bit, so let the horses run wild.

This is how their lettuce looked:

According to them, this is "Boston Bibb Lettuce" (the one in the left and in the back at least).

If we trust Cornell's Science (at least i do), they provide this information:

Seedlings:

(The first 11 days of lettuce production takes place in the seedling production area. Seedlings develop best under constant lighting conditions with specific, closely controlled temperature, relative humidity, carbon dioxide, and irrigation.)

• Light intensity is maintained at no less than 50 µmol/m2/s of PAR (Basically this is 50 PPFD) during the first 24 hours the seeds are kept in the germination area. (This level of illumination prevented stretching of the seedlings while minimizing the tendency of supplemental lighting to dry out the surface of the medium.)
  
  
• For the remaining 10 days, the light intensity is maintained at 250 µmol/m2/s. The photoperiod (or day length) is 24 hours. Shorter photoperiods are acceptable if the light intensity is increased to provide the same total daily accumulated light (~22 mol/m2/d). Anecdotal evidence shows that some lettuce seedlings can tolerate 30 mol/m2/d.
  
  PD:
  ~22 mol/m2/d = ~254.63 PPFD
  30 mol/m2/d = 347.22 PPFD

Normal Growth Phase:

They never provide any hints of changing the light intensity after the initial 11 days were done. So it should be safe to assume that lighting levels remained constant until harvest.

Pics:

Love you all <3 Back to sleep

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muleface said:

so what do you suppose would be needed to grow lettuce in a 2x4 spot? what would be ideal? 6500k lights? something else? how many watts? Im looking to scale this out pretty big. say maybe 25 bins.

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RyGon said:

I don't think there is any

I don't think there is any reason to doubt the research. I follow most of their recommendations. My seeds in rockwool germinate over about 3 days in a dome with no direct light on a warm surface. They spend the remainder of 2 weeks in another dome under a standard CFL with a 24 hour light period. Then I move them upstairs to the DWC under the conditions I described above.

We should consider that the spectrum will be different under different light sources and there is quite a bit of research showing that red to blue ratio and red to far red ratio have a significant impact on lettuce. I have linked some videos earlier in the thread. Since red pigmentation seems to increase as you approach the maximum DLI and higher proportions of far red have shown to both increase chlorophyll activity as well as decrease pigmentation, I think far red supplementation is at least worth looking into for lettuce growers. I will be adding a "full spectrum" COB in a few weeks which should provide some additional far red but I'm not sure how much of an effect it will show since I am already getting whatever far red is not being blocked by my windows from the sun.

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1. Lighting
   
   Uniform light distribution is required in the Pond Growing Area. A supplemental light intensity within the range of 100-200 μmol/m2/s (for a total of 17 mol/m2/d1 of both natural and supplemental lighting) at the plant level is recommended. It should be noted that 17 mol/m2/d is the light integral that worked best for the particular cultivar of boston bibb lettuce that we used. For some cultivars, 15 or mol/m2/d is the maximum amount of light that can be used before the physiological condition called tipburn occurs. High pressure sodium (HPS) lamps are a type of High Intensity Discharge (HID) lamp, and are used to supply light. These lamps are relatively efficient, have a long life (~25,000 hours, generally these lamps lose 1% output for every 1000 hours), and slowly decay in output over time. There is a recent development in the manufacturing process for metal halide lamps that gives them a lifetime similar to high pressure sodium lamps. Metal halide lamps have a spectrum that is slightly more efficient for plant growth than high pressure sodium lamps. A new bulb produced by the Philips corporation has exaggerated the benefits of metal halide lamps including shifting more light production to the blue and red portions of the spectrum and decreasing the heat output of the luminare. Independent lighting consultants have specialized software to determine proper number and placement of lamps needed for a specific and uniform light intensity. It is critical to have the correct lighting system installation.
   

OneHitDone said:

You may well be on to something with the Far Red. If I'm not mistaken most all COB's drop off short of the Far Red Range. Would definitely make for some interesting testing. COB's with some Far Red mono supplementation

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OneHitDone said:

They outlined the lighting in the Pond area in that article. Combined sun and supplemental

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muleface said:

OK, here it is, my Lettuce setup. Ill keep posting with pics until no one cares anymore.

Here is the setup, They are in 3 inch net pots, in 55 gallon tubs, the tubs are about 46 inches long and 20 inches wide. There are 4 cobs running the length of the tub, right down the middle. the plants sit right in the middle of 2 cobs which are 3000k and 4000k. This is an aeroponic step up.

The other are under a standard 8 bulb 6400k t5 fixture, the bulbs are 54 watts each.

I will put clear domes over the pots for the first week or so.

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ilam said:

How are your other crops doing, like the basil and tomatoes, i bet they can take up the higher PPFD values easily? Did only the lettuce die? How did that even happen?

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RyGon said:

Yep, I think that is what I am seeing. I am lighting an area around 32" x 20" with sunlight from about 7AM - 3PM and then with 4000k COBs 68.5v x .81A = 50.5W @ 17" above the deck which works out to around 20000lux from 3PM - 9PM. Daylight intensity varies but generally has a higher value than 20000lux. I don't have a PAR meter, but the advice I was given was based off of the 17 mol per day recommendation and was 20000lux for 18 hours per day. At this point, I am using a 14 hour lighting period.

I don't know if that simplifies things at all but yeah, I think DLI is the most important factor.

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muleface said:

so lets suppose i have 4 vero 29 gen 7 cobs running at 80 watts each, how would you determine mol from that?

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muleface said:

so I picked up a case of Integrated T5 LED Tube Lights. They are 6500k and 22 watts each. I have no idea if they are actually 22watts from the wall, we shall see. I am thinking they might bridge the gap between led and lettuce. Or perhaps i just dropped a bunch of money on useless crap. Time will tell.

The lights are 4 feet long, so i am thinking i might do a NFT setup with them, perhaps in 4 inch pvc pipe. run 1 light above each run of pipe, so i could do 200 feet of lettuce.

Any idea on spacing for lettuce? i have been doing like 9 inches apart in 2 inch net pots. Could they be closer? should they be further?

I may go back to trying the cobs too, but i think they are dumping out too much light, or at least overkill, i probably could raise them up and get a lot more coverage.

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OneHitDone said:

Very curious to see how these work out.

I believe I have my greenhouse NFT on 8" centers for lettuce. Will confirm that tomorrow if it helps

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muleface said:

i actually just ordered NFT channels from somewhere (farmtech?) I think they are on 8 inch centers, but they have 1 inch holes in them, which seems weird. am i suppose to use net pots there? do they even sell 1 inch net pots? Hell, i may just drill them out with a hole saw and use 2 inch pots.

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OneHitDone said:

You don't use netpots for commercial lettuce production
Start seeds in Oasis Cubes or Rockwool and drop them right into the hole sitting on the bottom of the channel

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ilam said:

Have you used Oasis cubes yourself? I've seen them but haven't actually found anybody with actual experience. They look like a legit rockwool alternative.

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