Four Pigments of Sight

Plate 98 speaks for itself: “Colour is a vote among three cone pigments.”

The Physics

The human retina has four visual pigments: rhodopsin in rods and three cone opsins. Each cell's response is its pigment's sensitivity weighted by the incoming spectrum.

R = ∫ S(λ) s(λ) dλ

• R: photoreceptor response, arbitrary units
• S(λ): spectral power of the light, W m⁻³
• s(λ): pigment spectral sensitivity, dimensionless
• λ: wavelength, m

Measured by microspectrophotometry. Bowmaker & Dartnall, 1980.

Sources

• J. K. Bowmaker, H. J. A. Dartnall, J. Physiol. 298, 501 (1980).

On the poster

Plate 098, “Four Pigments of Sight”: the pixel-art plate with its slogan “Colour is a vote among three cone pigments.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.