Spectral Luminous Efficiency

Synonyms

Eye sensitivity functions; Luminous efficiency function; Relative visibility function; V(λ), V′(λ)

Definition

Spectral luminous efficiency (of a monochromatic radiation of wavelength λ) [V(λ) for photopic vision; V′(λ) for scotopic vision] (see CIE e-ILV [1])

Ratio of the radiant flux at wavelength λ _m to that at wavelength λ such that both produce equally intense luminous sensations under specified photometric conditions and λ _m is chosen so that the maximum value of this ratio is equal to 1.

Unit: 1

Overview

By the end of the nineteenth century, photometry achieved a level where it became necessary to describe the light perception efficiency of radiation of different wavelengths. Several methods were used to determine the spectral luminous efficiency function (called also spectral visibility). The two most important ones were direct comparison and the flicker method (based on the fact that if two lights are seen alternatively with increasing frequency, first the sensation of...