Which statement best describes the Purkinje shift?

• A. Shift toward shorter wavelengths under scotopic
• B. Shift toward longer wavelengths under scotopic
• C. No shift
• D. Shift in luminance

Answer: (A)

The main idea is how the eye’s sensitivity to colors changes as lighting drops. In bright conditions, vision is dominated by cones and the peak luminance sensitivity sits toward longer wavelengths (green-yellow). As light fades, rods take over and their spectral sensitivity peaks at shorter wavelengths (blue-green). This makes the eye relatively more sensitive to shorter wavelengths in dim light, so colors like blue-green appear brighter compared to red objects. That’s why the Purkinje shift describes a shift toward shorter wavelengths under scotopic (low-light) conditions. The other statements don’t fit because they’d imply a shift to longer wavelengths, no shift at all, or a vague change in brightness rather than a change in spectral sensitivity.