[zsellera]

As someone working in the greenhouse lighting industry, I might have some insight on this:

1. there is an existing technology called energy screen/curtain, with the primary function of retaining heat, but can also reduce light pollution by an order of magnitude.

2. light that escapes is essentially money lost, however it alone does not justify the use of energy screens.

3. as long as farmers have access to (relatively) cheap heat and electricity, they won't invest into this technology.

4. for the time being, it's a regulatory issue, just like water use (a single plant use 2-2.5 l/day), supplemental co2 use and nitrate recirculation from runoff water.

[hedora]

In addition to wasting energy, light pollution at night is killing off insects, which (along with other factors, like neonicotinoids and habitat loss) is leading to ecosystem collapse.

For instance, North America’s bird population has dropped by 25% since 1970. Insects fared significantly worse over that period, but exact numbers are harder to come by.

[bjelkeman-again]

Water use and nutrient recirculating can be lowered dramatically with aquaponics, even CO2 use can be lowered in some configurations. It comes with added complexity and capex, but should be financially sustainable.

[mrmuagi]

> 4. for the time being, it's a regulatory issue, just like water use (a single plant use 2-2.5 l/day)

Is the 'plant' there a, say, tree or is it referring to the whole building?

[zsellera]

that's per a single tomato plant, summer time. I guess it's the same for any greenhouse crop, see the reasoning here:

water use is necessary to manage internal climate. the greenhouse was designed to keep heat inside. the plants have to cool themselves (hence the environment) by evaporation. the farmer manages evaporation rate by watering, temperature and humidity. there are many feedback loops, both negative and positive, balancing it is a non-trivial task.

btw. there's an average of 1.2-1.3 plant/m2 in most tomato greenhouses I've seen.

[mrmuagi]

Ah, thanks for the clarification. I was shocked at how large a number it seemed, but I only factored in how much water the plant itself displaces in its structure, not the maintenance water to maintain humidity, temperature, etc.