Index

DEFININGCONSTANT: luminous efficacy

  • PID: si:definingconstant:luminous_efficacy:2019
  • Definition: The luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, is exactly 683 lm/W.
  • Source: SI Brochure 9th Ed. 2019, p 127
  • Formatted: 683 lm W-1
  • Numerical Value: 683
  • Unit: lm W-1
  • Unit in Base SI: cd s3 m^2 kg-1 m-4
  • Notes
    1. This value was fixed by the CGPM in 2018 (Resolution 1), with effect from 20 May 2019.
    2. The luminous efficacy of monochromatic radiation of frequency 540 x 1012 Hz is a technical constant that gives an exact numerical relationship between the purely physical characteristics of the radiant power stimulating the human eye (W) and its photobiological response defined by the luminous flux due to the spectral responsivity of a standard observer (lm) at a frequency of 540 x 1012 Hz.
  • Related Definitions
    • hasConstantSymbol -> K_cd