Which wavelength is the scotopic visual system most sensitive to?

• A. 550 nm
• B. 450 nm
• C. 507 nm
• D. 600 nm

Answer: (C)

Scotopic vision relies on rod photoreceptors and operates best in very dim light. The rods’ photopigment, rhodopsin, is most sensitive to light around 507 nanometers, which sits in the blue-green part of the spectrum. Under low-light conditions, this peak sensitivity means our eyes respond most strongly to wavelengths near 507 nm. The other wavelengths listed are farther from the peak: 450 nm is blue but not at the maximum rod sensitivity, 550 nm is closer to the photopic peak that cones favor in bright light, and 600 nm is red where rods are much less responsive. The overall idea is that rod-based (scotopic) vision has its peak sensitivity around 507 nm, which is why that wavelength is the best match among the options.