Chlorophyll's Gap

Plate 97 speaks for itself: “Leaves are green because they throw green away.”

The Physics

Chlorophyll a absorbs strongly in the blue and the red. Green light falls in the gap between those bands, so it is reflected and transmitted, and leaves look green.

E = h c / λ

• E: photon energy, J
• h: Planck constant, J s
• c: speed of light, m s⁻¹
• λ: wavelength, m

Chlorophyll a in solvent: peaks ≈ 430 and 662 nm. Green between them is mostly not absorbed.

Honest caveat: In a real leaf much green light is still absorbed after many scatterings; 'mostly' is the honest word.

Sources

• R. J. Porra, W. A. Thompson, P. E. Kriedemann, Biochim. Biophys. Acta 975, 384 (1989).

On the poster

Plate 097, “Chlorophyll's Gap”: the pixel-art plate with its slogan “Leaves are green because they throw green away.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.