If a light has a wavelength of about 700 nanometers, what color is perceived?

If a light has a wavelength of about 700 nanometers, what color is perceived?

• A. Red
• B. Blue
• C. Yellow
• D. Green

Answer: (A)

Wavelength determines color in the visible spectrum. Light at about 700 nanometers sits at the deep red end of that spectrum, so it is perceived as red. The eye’s long-wavelength (red) cones are most stimulated by this range, and the brain interprets that pattern as red. For comparison, blue is around 450 nm, green around 520–550 nm, and yellow around 580–590 nm, so they correspond to shorter wavelengths than 700 nm.

Wavelength determines color in the visible spectrum. Light at about 700 nanometers sits at the deep red end of that spectrum, so it is perceived as red. The eye’s long-wavelength (red) cones are most stimulated by this range, and the brain interprets that pattern as red. For comparison, blue is around 450 nm, green around 520–550 nm, and yellow around 580–590 nm, so they correspond to shorter wavelengths than 700 nm.