Well, yes, effectively. By turning all the incoming light (including red, green and blue, and the non-visible spectrum, given a solar cell that's sensitive to i

Well, yes, effectively. By turning all the incoming light (including red, green and blue, and the non-visible spectrum, given a solar cell that's sensitive to it) into electricity and using that electricity to power a grow light. I'm not saying that it's a feasible way to get more energy flux into the plants this way; I think it's unlikely. But that's theoretically a way to do it. If on the other hand you emit light on the same spectrum as you receive it, then it's impossible to generate more flux, even in theory.