Idk guys, I think both of you all are right. PF is right in that the environment determines expression levels of genes(health of the plant), and this in turn affects future generations through survival or non survival in those conditions. But the future generations will not become more deficient, instead they will utilize the available environment better and eventually thrive. This is the nature of selection. But I think the other guys also have a point. The difference is mainly due to intensity, as the genetic effects will take too many generations to manifest themselves.
I think that over many many generations and subsequent selections, you could evolve a plant species to thrive on a more 'limited' spectrum of light. But, I think we're talking hundreds or thousands of generations, and not really anything that matters in our lifetimes(look at how we selected for modern corn, starting with maize). Maybe if you had the capability to select from thousands of plants in each generation, you could make it a little faster, but it's still going to take a lifetime(s).