To which light is the eye most sensitive?

Correct answer: c green

In the middle of the visible window, near 550 nm, the eye's sensitivity curve peaks (1.0); the light there is green.

Why the other options are wrong

• a blue: This is not the answer: Blue is toward the short end of the window. The eye is most sensitive in the middle, near 550 nm.
• b violet: This is not the answer: Violet is near 400 nm, right at the edge, where the sensitivity curve is low. The eye is most sensitive in the middle, near 550 nm.
• d red: This is not the answer: Red is near 700 nm, the long end, where the sensitivity curve is low. The eye is most sensitive in the middle, near 550 nm.