For a blue light at 400 nm, under Purkinje effect, under which lighting condition will it appear brighter?

For a blue light at 400 nm, under Purkinje effect, under which lighting condition will it appear brighter?

• A. Photopic
• B. Both
• C. Neither
• D. Scotopic

Answer: (D)

Purkinje effect describes how our eye’s sensitivity shifts with lighting. In bright, cone-dominated (photopic) vision, we’re most sensitive around greenish light near 555 nm, so a very short-wavelength blue light around 400 nm doesn’t look very bright. In dim, rod-dominated (scotopic) vision, the sensitivity curve moves toward shorter wavelengths, with rods peaking around blue-green and overall short wavelengths taking on more brightness. So a blue/short-wavelength light at 400 nm will appear brighter under scotopic conditions than under photopic conditions.

Purkinje effect describes how our eye’s sensitivity shifts with lighting. In bright, cone-dominated (photopic) vision, we’re most sensitive around greenish light near 555 nm, so a very short-wavelength blue light around 400 nm doesn’t look very bright. In dim, rod-dominated (scotopic) vision, the sensitivity curve moves toward shorter wavelengths, with rods peaking around blue-green and overall short wavelengths taking on more brightness. So a blue/short-wavelength light at 400 nm will appear brighter under scotopic conditions than under photopic conditions.