| quotient of the luminous flux Φv by the corresponding radiant flux Φe|
unit: lm · W -1
NOTE – When applied to monochromatic radiations, the maximum value of K(λ) is denoted by the symbol Km.
Km = 683 lm • W -1 for vm = 540 x 1012 Hz (λm ≈ 555 nm) for photopic vision.
K′m = 1700 lm • W -1 for λ′m = 507 nm for scotopic vision.
For other wavelengths : K(λ) = Km V(λ) and K′(λ) = K′m V′(λ).