bio

Chlorophyll

The main pigment plants use to catch light. Chlorophyll absorbs strongly in two narrow bands — one blue band near 430 nm, one red band near 660 nm — and largely ignores the middle. That is why leaves are green: the green light bounces back to your eye, so the colour you see is precisely the light the leaf declined to eat. This is an inherited evolutionary habit rather than a physical necessity: under a different star a biosphere could settle on a different absorbing band, and its leaves would wear a different colour.