Photopic

Photopic refers to vision under bright illumination in which the eye's cone photoreceptors mediate perception. Under photopic conditions, humans exhibit high-acuity vision and color discrimination, because the three cone types—short-, middle-, and long-wavelength sensitive cones—are active, enabling trichromatic color vision.

The photopic luminous efficiency function V(λ) describes the eye's relative sensitivity to different wavelengths in this regime. It peaks at about 555 nanometers, near the green part of the spectrum, and is used to convert spectral power distributions to luminance and to weight colors in colorimetry and lighting design.

Photopic vision is contrasted with scotopic vision, which operates in low light and is dominated by rods with limited or no color vision, and with mesopic vision, which occurs in intermediate lighting when both rods and cones contribute.

Anatomically, cones are concentrated in the fovea, providing high spatial resolution. Color perception arises from the relative stimulation of the three cone types, and daylight color appearance is largely determined by this cone mechanism and surrounding adaptation.

In practice, photopic concepts underpin lighting standards, display engineering, photography, and color science, guiding how luminance, color rendering, and brightness are modeled under daylight and well-lit conditions.