Typically, which cones are least numerous and what color do they respond to?

• A. Long wavelength cones respond to red
• B. Medium wavelength cones respond to green
• C. Short wavelength cones respond to blue
• D. All cone types are equally numerous

Answer: (C)

Three kinds of cones in the retina are tuned to different parts of the spectrum, and their numbers aren’t equal. The short-wavelength cones, which detect blue light, are typically the least numerous. They respond best to blue light, around the short end of the spectrum (roughly 420–450 nm). In contrast, the long-wavelength cones (red) are the most numerous, and the mid-wavelength cones (green) are intermediate in number. So the statement that the least numerous cones respond to blue fits both the abundance pattern and the color they detect. The other possibilities don’t match because long- and medium-wavelength cones are not the rarest, and the three cone types are not equally numerous.