Cones have peak sensitivity around which wavelength?

• A. 420 nm
• B. 600 nm
• C. 700 nm
• D. 555 nm

Answer: (D)

Cones drive daylight, color, and high-brightness vision, and their sensitivity isn’t tied to a single wavelength. There are three cone types with different peaks, and when their responses are combined under bright conditions, the overall photopic sensitivity peaks around 555 nanometers, in the green part of the spectrum. That’s when cone-driven brightness perception is strongest. Individual cones respond best at their own peaks (roughly blue ~420 nm, and green-yellow ~530–565 nm for the others), but the brain’s integrated signal yields the maximum at about 555 nm. The other options lie farther from this peak, so cone sensitivity is lower there.