I guess the devil is in the details but I can't see how mirrors will be positioned to support vertical farming. It's be interesting to see some viable ideas (if those exist).
It's beyond my pay grade. I have no idea if 'optical fibers' are an option here. I suspect 'not' only because it hasn't been done already and feels like it if worked for vertical farming, it would also work to supplement office lighting so there is some monetary incentive to get such a system implemented in some way.
The other problem is that you still have the same issue. That is, for every square cm of sunlight you collect the best you could do is direct that light to a square cm of a plant. That is, you can't just increase surface area of collected light so to provide sunlight for vertically stacked plants, you need the equivalent horizontal surface area to support those.
