Everyone here is saying there's not enough light. That's not actually true. The sun produces more than enough energy to grow all the plants. The issue is one of distribution. You have to distribute very particular wave lengths of light to the entirety of the structure and all the plants. This is a hard problem. Mirrors are inefficient. Fiber optics don't do exactly what you want, and plus, a lot of the light energy is unusable, because it's the wrong wavelength. Most modeling done in the space indicates that -- with current technology -- it's more efficient to capture the sunlight, convert it to electricity, and then use the electricity to produce light at the correct wavelengths.

As a whole, this means there's less energy available to irradiate the plants, but there's more energy in the wavelengths the plants can respond to, so it's more efficient.

I mean... think about it. Every time you look at a tree and see green, that is light that the plant has wasted. Hydroponic lighting is typically that deep purple, red, and blue, that plants can absorb. The goal is to make the plant leaves black, indicating that all light is being absorbed. Otherwise, you're just wasting light.

But even then it's not that simple. You need different wavelengths at different phenological stages, and what wavelengths you need depend on the crop (and variety, but you can at least control that for crops you can multiply vegetatively) you're growing, and then still you need to distribute that light to all leaves and not just the top ones. So now you need either LED's that can emit many different wave lengths, or you need many LED's that are only in use part of the time (killing your capital expenditure efficiency), or you need to move plants around to be under the right lights. And you need to move the light source to places where they can hit the leaves as much as possible, but you also need to keep the excess heat away from the plants (which is a problem even with today's highly efficient LED's - I mean, these are not like that IKEA nightlight you bought last week for $5.)

You’re right that they’re not like the ikea lamp I bought last week... they’re like the hydroponic lamps I bought two years ago for a shit ton of money.

Everything you said is right. It’s still more efficient to use the suns energy and then distribute the leds than to directly try to use the suns light. Modern hydroponic grow led controllers can adjust the wavelengths as the plants grow

The black leaf thing is interesting. Is that an oversimplification or do plants really only absorb visible light?

Plants only absorb very particular aspects of light. As far as I remember, it's only visible light, yes.

More information here: http://www.webexhibits.org/causesofcolor/7A.html

Hydroponic lighting is optimized for those particular wavelengths in the ~450 nm and ~650 nm peeks. Some plants absorb additional wavelengths, and could likely be targeted with other lights. The key though is that chlorophyll are like mitochondria -- highly preserved between species -- and they evolved to only absorb particular frequencies.

That’s really interesting, thanks for the explanation. Makes me think of tuning LED lighting the same way a mechanic might set spark timing. Obviously in reality the right lighting for a plant is known but it’s neat to be able to see the effect.

It may be well known but there are many practical considerations. It certainly requires a lot of tuning. For example, if you want to target all four peaks of absorption by cholorphyll a and b, that’s four wavelengths, but many people settle for just two due to cost. It’s all a giant optimization problem!

Research is inconclusive, but there are indications that UV light (although not required for photosynthesis) can have effects on yields and either on resistance against pests (insects/molds/fungi) or directly attack/kill/weaken those pests. So basically 'it depends', and people do their own tests and then determine if, in their specific circumstances, it is a net positive (economically) to add UV lights to their setups.

I think this is the main message. People in this thread are talking in absolutes about 'agriculture', but the reality is that there are many, many things that we don't understand well enough at the above-micro-level scale to be able to say 'you need to measure x, y and z and then we can calculate/model the optimal setup to grow something'. People are basically relying on (informed) trial and error, with feedback cycles measures in months or years, so it just takes a long long time for progress to be made - and even then, we usually don't know exactly why something works in a specific case. It's not like 'oh let's run an A/B test for the best color of our 'buy' button for a few days'.

1. Clean room farming means no need for pesticides

2. LED lights are pretty efficient, and they provide another avenue for optimization (e.g. color, intensity, timing, etc.). Whether or not those optimizations are financially effective is probably situationally dependent.

3. LED lights provide latitude independence. No idea if this is a serious reason, but I could see it being of interest to Iceland.

1. is a common misconception/myth. even if you manage to keep the bugs out, which is really hard and expensive, you still have to deal with fungii. good luck with trying to filter out those.

2. LEDs are not more efficient than double ended sodium light lamps. max efficiency seems to be around 50%. So the other half goes to heat waste which has to be managed. climate control and especially temperature control is an issue in indoor farming.

LEDs are simpler to cool, and at this scale it might be possible to use the heat for community heating.

Yes, agreed.

But also: Frontal heat radiation from HPS is working against condensation on plant tissue, helping to achieve good phytosanitary conditions.

Everything has its pros and cons.

1. OTOH, it also means there's now a need for manual pollination.

1. Leafy greens don't need pollination. It's in your best interest to avoid flowering if you want product anyone will eat.

2. Very few food plants are dioecious, and the ones that are (like asparagus and dates) are either ones where the fruit don't matter or are not likely to be grown indoors

While #1 (and your general point) is correct monoecious crops still have to be pollinated if the product is a fruit or seed. The stone fruits for instance are monoecious with male and female parts of flower on same plant unlike marijuana or dates where plants are either male of female. But this isn't leaf crops as you mention.

In some species pollination occurs generally just with wind or movement (rather than insects), for example corn where the pollen falls down from flowers above onto the silks which are the female portion (sort of a vaginal canal if you will, i.e for every corn seed there is an attached silk). Or tomatoes which have closed flower and generally always self pollinate as the flower is blown or shaken with a very small amount of cross pollination on occasion. Pretty cools setup with these type of plants, massive reproductive efficiency through mostly self pollination but a little bit of crossing occurs as the occasional foreign grain of pollen gets from another plant so there is genetic variation.

You're right.. It's not some kind of laborious process though. Having grown all these things (except corn) hydroponically, the problem is heavily overstated. For personal production, you basically have to do nothing. For commercial production, you could turn on a fan.

Yes, you seem to be missing the light supply. Plants need a lot of light to grow. In a multi-storey greenhouse, the incoming solar radiation per unit floor area is smaller than in a normal (one-storey) greenhouse. Thus the need for artificial lighting and associated costs, both for hardware and electric power.

This is very back of the napkin guesswork, but here goes:

If part of the pitch is that, more than just "vertical" farming, it is "vertical urban" farming (e.g. for logistical advantage of proximity to demand), that would imply potential proximity to other tall structures in a city. Probably taller structures. You would have concerns for consistency of sunlight. Also only the edges of the building would get it, so you would want your farm to only occupy the tiniest edge footprint of the building, but across multiple floors. That is an odd sort of lease to get from a building.

Even a new building built nearby after a year or two could destroy the efficiency of your once-carefully-selected site.

Another under-educated guess that I would be happy to hear about from someone more knowledge: I would guess that glass facades costs more than other materials.

Yes, you're missing light. The top layer of plants would get enough light, but the lower levels will only get some trickle-through, and that's assuming the hydro equipment doesn't block the light entirely. Either way, you won't have nearly enough to grow productive plants.