Just my :twocents: but thinking maybe we should think in terms of the seasonal patterns where the strain your working with are like.
Like: Fall light because of the angle it hits atmosphere, changes it color a little. Mid-summer(veg) more straight in, more uv and blue.
Time length varies of course, as does temp, and maybe moisture. I think we can optimize everything but if we get to far off base, mother nature will pick us off.

Of course maybe I'm all wet, and global warming and the hole in the ozone layer are good things.