My post: "in a north-south row orientation they receive more red light when the sun is lower in the sky."

DA: Your assumption is incorrect...The fact that the light seems redder does not mean there is more red light than in the noon day sun. It means there is a lot less yellow, green, blue, and violet."

Nothing wrong with my assumption, only my ambiguous wording. Let me rephrase to make my meaning clear. My meaning is that, due to the north-south row orientation, each plant receives increased exposure to light during the early and late hours of daylight, and that the extra light, although of lower energy due Rayleigh scattering/filtration, retains the longer wavelengths by which photosynthesis is most efficient.

Better? <g>

"Time is what prevents everything from happening at once" - John Wheeler