What is the peak sensitivity of the photopic luminous efficiency function?

The photopic luminous efficiency function describes the sensitivity of the human visual system under well-lit conditions, reflecting how well different wavelengths of light are perceived. The peak sensitivity of this function occurs at approximately 555 nm, which falls within the green region of the visible spectrum. This peak indicates that light at this wavelength is perceived as the brightest by the human eye, making it a critical reference point for understanding vision under photopic (daylight) conditions.

In addition, the 555 nm peak is significant for various applications, including lighting design and color vision assessments, since it correlates closely with the sensitivity of cone cells in the retina. The human eye utilizes three types of cone cells that are sensitive to different parts of the spectrum, and 555 nm is where the combined responses of these cones generate maximum luminance perception.

Other wavelengths such as 507 nm, 680 nm, and 400 nm represent different degrees of sensitivity that are not at the maximum perceived brightness. Therefore, understanding the peak at 555 nm helps clarify how we perceive brightness and color under standard lighting conditions.