Under equal luminance, which color would appear brighter under scotopic conditions?

Under equal luminance, which color would appear brighter under scotopic conditions?

• A. Red
• B. Green
• C. Blue
• D. Yellow

Answer: (C)

In dim light, vision is dominated by rod photoreceptors. Rods are most sensitive to blue-green light, with peak sensitivity near 498 nm. When you hold luminance equal across colors, the color whose wavelength is closest to that rod peak will stimulate the rods more and look brighter. Blue light is closest to 498 nm among the options, so it activates the rods more effectively than red, green, or yellow and thus appears brighter under scotopic conditions. Red and yellow lie further from the peak and are perceived dimmer, while green is also less optimal than blue for rod sensitivity.

In dim light, vision is dominated by rod photoreceptors. Rods are most sensitive to blue-green light, with peak sensitivity near 498 nm. When you hold luminance equal across colors, the color whose wavelength is closest to that rod peak will stimulate the rods more and look brighter. Blue light is closest to 498 nm among the options, so it activates the rods more effectively than red, green, or yellow and thus appears brighter under scotopic conditions. Red and yellow lie further from the peak and are perceived dimmer, while green is also less optimal than blue for rod sensitivity.