[jwr]

Well, but you could use solar power to supply power to those LEDs… oh, wait…

[reportingsjr]

This can theoretically be more efficient than growing plants under sunlight. Chlorophyll mostly absorbs light in the 400nm to 700nm band which is about half of all the photons that hit lights. Even in that band ~24%[1] of the energy in them in lost due to the higher energy photons (closer to the 400nm side) being converted to lower energy photons.

So right there plants are only 25% efficient at collecting energy from photons. This is why you see indoor plants grown under red LEDs. Modern commercially available solar panels are about 21% efficient so that is actually getting close to plant can do (I'm not going to include inefficiencies in power conversion right now). Solar panels in the high 40% efficiency range exist, but they are crazy expensive and only used on things like satellites.

So using current (very advanced) technology we could actually get about double the plant output per area land by using the most advanced solar panels we have to collect light energy to power LEDs.

[1] https://en.wikipedia.org/wiki/Photosynthetic_efficiency

[placeybordeaux]

You are ignoring conversion, storage, transport, LED, and LED -> plant losses.

[chongli]

You're ignoring land use. You can't build a huge conventional farm in the middle of the city. You can, however, cover all the buildings with solar panels. This gives you land that supports a high population and grows food in the same place. Heck, since you're using LEDs you could put the vertical farms underground, giving every resident access to fresh vegetables right in their own building.

[placeybordeaux]

I was responding to

>This can theoretically be more efficient than growing plants under sunlight

Which doesn't seem to be talking about all of the other externalities, just about sunlight vs man made light.