6 ms·

Not sure what numbers you’re looking for. Lettuce with state of the art horticultural leds probably can be grown optimally with as little as 10 watts per square

Not sure what numbers you’re looking for. Lettuce with state of the art horticultural leds probably can be grown optimally with as little as 10 watts per square foot. Flowering plants need much more and more full spectrum.

kragen 7y ago
In non-medieval units, that's 110 W/m², 9 times less than direct sunlight. Couldn't you get those low-light conditions more cheaply by stacking lettuce trays in a sunlit greenhouse, with lightpipes to shade the upper levels and get the requisite amount of weak illumination to the lower levels? (Edited to correct the calculated values.)
- TaylorAlexander 7y ago
  10 W/sq ft is 107 W/sq m.
  - kragen 7y ago
    Thank you for the correction! My calculation error (I had written "11 W/m², 90 times less than direct sunlight"), though unintentional, is an excellent demonstration of why using medieval units is a bad idea.
    - Dylan16807 7y ago
      Being off by a factor of ten is very easy with SI units too. Centimeters vs. millimeters for example.
      - kragen 7y ago
        Yeah, and I've certainly made that mistake more than once. (I try to avoid using centimeters or centi-anything for that reason, as well as deci-, deka-, and hecto-.) In this case, though, the calculation I biffed was a unit conversion from medieval units to modern units. It's harder to get calculations wrong when you don't have to do them at all.
- rini17 7y ago
  Weather would then affect the production, making schedules unpredictable. Plus, I am no expert but I guess you can't make plants actually use much more than 100W/m2 for photosynthesis, the rest of sunlight consists of unsuitable wavelengths. It ends up as waste heat that you'd have to cool away. Perhaps if you could efficiently convert green and infrared parts of sunlight to red/blue, that could help.
  - kragen 7y ago
    You mean because sometimes it's cloudy? Couldn't you solve that problem by turning on LEDs just when it's cloudy? Plants are pretty inefficient, it's true, but I don't think they're very efficient even with optimal wavelengths. But, yes, solar cells and LEDs can indeed convert green and infrared sunlight to red and blue, with about 3% efficiency under normal circumstances.
    - infogulch 7y ago
      If your plan is "light pipes, but fall back to LEDs" that means you have to build two complete systems. You get double the installation costs, incur the combined complexity of both systems (plus overhead), and box yourself into the limitations of both systems.
      - kragen 7y ago
        That might be true, but I'm not sure it is. It seems to me that you escape the limitations of both systems. Also, I think lightpipe daylighting generally costs orders of magnitude less than sunlight-comparable LED illumination, although I don't have firm numbers on lightpipe costs; so I don't think the installation costs double, just increase slightly. If we're talking about a greenhouse, where a leaky roof is a minor annoyance comparable to a leaky faucet, rather than a life-destroying disaster, lightpipe costs should go down quite a bit compared to their use in office and residential daylighting. The big question for me is, if you're going to build a hothouse, why would you build it with an opaque roof? That just seems perverse, like writing an HTTP server in bash or assembly language or something: http://canonical.org/~kragen/sw/dev3/server.s http://canonical.org/~kragen/sw/dev3/server.s
- nkingsy 7y ago
  Building material units in the US are in feet and inches so it’s my point of reference for building projects eg indoor growing
  - kragen 7y ago
    I bet you don't know off the top of your head how many watts per square foot sunlight is, though --- and that's the most relevant point of comparison. (Or horsepower, or Btus per hour, or whatever crazy unit.)
bjelkeman-again 7y ago
That seems about right, based on our lighting plan for our pilot plant.

kragen 7y ago

In non-medieval units, that's 110 W/m², 9 times less than direct sunlight. Couldn't you get those low-light conditions more cheaply by stacking lettuce trays in a sunlit greenhouse, with lightpipes to shade the upper levels and get the requisite amount of weak illumination to the lower levels? (Edited to correct the calculated values.)

TaylorAlexander 7y ago
10 W/sq ft is 107 W/sq m.
- kragen 7y ago
  Thank you for the correction! My calculation error (I had written "11 W/m², 90 times less than direct sunlight"), though unintentional, is an excellent demonstration of why using medieval units is a bad idea.
  - Dylan16807 7y ago
    Being off by a factor of ten is very easy with SI units too. Centimeters vs. millimeters for example.
    - kragen 7y ago
      Yeah, and I've certainly made that mistake more than once. (I try to avoid using centimeters or centi-anything for that reason, as well as deci-, deka-, and hecto-.) In this case, though, the calculation I biffed was a unit conversion from medieval units to modern units. It's harder to get calculations wrong when you don't have to do them at all.
rini17 7y ago
Weather would then affect the production, making schedules unpredictable. Plus, I am no expert but I guess you can't make plants actually use much more than 100W/m2 for photosynthesis, the rest of sunlight consists of unsuitable wavelengths. It ends up as waste heat that you'd have to cool away. Perhaps if you could efficiently convert green and infrared parts of sunlight to red/blue, that could help.
- kragen 7y ago
  You mean because sometimes it's cloudy? Couldn't you solve that problem by turning on LEDs just when it's cloudy? Plants are pretty inefficient, it's true, but I don't think they're very efficient even with optimal wavelengths. But, yes, solar cells and LEDs can indeed convert green and infrared sunlight to red and blue, with about 3% efficiency under normal circumstances.
  - infogulch 7y ago
    If your plan is "light pipes, but fall back to LEDs" that means you have to build two complete systems. You get double the installation costs, incur the combined complexity of both systems (plus overhead), and box yourself into the limitations of both systems.
    - kragen 7y ago
      That might be true, but I'm not sure it is. It seems to me that you escape the limitations of both systems. Also, I think lightpipe daylighting generally costs orders of magnitude less than sunlight-comparable LED illumination, although I don't have firm numbers on lightpipe costs; so I don't think the installation costs double, just increase slightly. If we're talking about a greenhouse, where a leaky roof is a minor annoyance comparable to a leaky faucet, rather than a life-destroying disaster, lightpipe costs should go down quite a bit compared to their use in office and residential daylighting. The big question for me is, if you're going to build a hothouse, why would you build it with an opaque roof? That just seems perverse, like writing an HTTP server in bash or assembly language or something: http://canonical.org/~kragen/sw/dev3/server.s http://canonical.org/~kragen/sw/dev3/server.s
nkingsy 7y ago
Building material units in the US are in feet and inches so it’s my point of reference for building projects eg indoor growing
- kragen 7y ago
  I bet you don't know off the top of your head how many watts per square foot sunlight is, though --- and that's the most relevant point of comparison. (Or horsepower, or Btus per hour, or whatever crazy unit.)

bjelkeman-again 7y ago

That seems about right, based on our lighting plan for our pilot plant.