Rods have peak sensitivity around which wavelength?

• A. 390 nm
• B. 570 nm
• C. 620 nm
• D. 498 nm

Answer: (D)

Rods drive vision in dim light, and their photopigment, rhodopsin, absorbs light most strongly in the blue–green part of the spectrum. That peak is about 498 nanometers, so rods are most sensitive to light around that wavelength. Among the options, 498 nm is the closest to this peak, giving the strongest rod response. Wavelengths far from this peak—like violet near 390 nm or red around 620 nm—are absorbed less efficiently by rhodopsin, so rods respond less at those wavelengths.