Color
Thomas Weinacht, Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York.
Content
• Receptors
• HSL color scheme
Key Concepts
• In the context of vision, color is the perception of different
wavelengths of light.
• The human visual system is able to perceive wavelengths
of light between approximately 400 nanometers and 700
nanometers.
• Longer wavelengths (less energetic photons) correspond
to colors toward the red end of the visual spectrum, while
shorter wavelengths (more energetic photons) correspond
to colors toward the blue end of the visual spectrum.
• Three different receptors in the human eye, known as
cones, respond to three different ranges of wavelengths
corresponding to blue, green, and red light.
• The central wavelength of a light source is described by the
term hue; the range of wavelengths (or purity) is described
by saturation; and the overall intensity, or brightness, is
characterized by lightness.
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The visual perception of different
wavelengths of light.
Light can be understood both as electromagnetic waves
and as particles called photons. Photons can have different
energies. The energy of a photon determines the frequency
and wavelength of the wave. The full range of wavelengths is
known as the electromagnetic spectrum, which spans from
the longest wavelength (lowest frequency) radio waves to the
shortest wavelength (highest frequency) gamma rays. In com-
mon usage, "light" refers to the small sliver of the spectrum
that the human visual system is able to perceive—
wavelengths between approximately 400 nanometers and 700
nanometers (1 nm = one-billionth of a meter). Each wave-
length of visible light corresponds to a different color, which,
in combination with other wavelengths, produces the rich
palette of colors humans can distinguish (Fig. 1).
A wavelength represents the distance over which a wave re-
peats itself in space. Longer wavelengths of light (less energetic
photons) correspond to colors toward the red end of the visual
spectrum. Shorter wavelengths of light (more energetic pho-
tons) correspond to colors toward the blue end of the visual
spectrum (Fig. 2). The simplified set of colors usually used to
describe the rainbow of the visual spectrum, from longest to
shortest wavelength, is offered in the mnemonic ROY G BIV for
red, orange, yellow, green, blue, indigo, and violet. Accordingly,
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Fig. 1: A wall of colored tiles offers a small sampling of the range of colors humans can
differentially perceive. (Credit: sarkelin/Shutterstock)
