> like two-state glass

That would be crazy-expensive. A lot of greenhouses use poly-film, to give you an idea of the budget. Replacement cost is a large factor.

There is research on whether solar arrays would be a net benefit. Those cells would catch most of the sun’s light, turn it into electricity to power the LEDs that have wave lengths that are better matched to what the plants need.

A variation of that only catches the sun’s green light and uses it to power pink/red LEDs (https://www.treehugger.com/solar-technology/solar-smart-gree...)

Probably expensive and still a waste of electricity, but why not automate it like the covers over pro-tennis courts?