[antiRepublicrat]

Does he think that the "un-utilized" photons were just rolling around on the ground, waiting for plants with chlorophyll to scoop them up?

I think he's saying that since one class of life was all over the place and absorbing one set of the light spectrum, instead of competing another grew to absorb a different set of the spectrum.

Isn't there a reverse of this, a "green window" effect?

[Redcloak]

But that doesn't make any sense. If plant A is over here absorbing light between 600 and 700 nm, plant B in some other location, also absorbing light in that band, isn't affected at all. They don't compete. The plants that used retinal didn't suck up all the light in that particular spectrum.

Plants compete for light by growing taller and getting out of shade cast by other plants. Being short, but using a different spectrum of light doesn't help a plant; it's still in the dark.