[sbierwagen]

Plants are actually pretty miserably inefficient at turning sunlight into stored energy: http://en.wikipedia.org/wiki/Photosynthetic_efficiency (not only do they reflect away most of the light, but photosynthesis isn't linear at all graphed against light intensity: most of the noonday sun is wasted)

There's no real consensus on why. (There's some wild guessing that green photons might be too hot to handle: smashing fragile biomolecules apart rather than powering them... (http://scienceline.ucsb.edu/getkey.php?key=500) but then why does chlorophyll run fine on purple light?) You'd figure that there would be incredible selection pressure on increasing photosynthesis efficiency, but maybe they're stuck on a local maxima: it's not like a single mutation can turn a C3 plant into a C4 plant: http://en.wikipedia.org/wiki/C4_photosynthesis