The reduction in the luminosity of a red light relative to that of a blue light when the luminances are reduced in the same proportion without changing the respective spectral distributions.
Note: In passing from photopic to scotopic vision, the spectral luminous efficiencies change, the wavelength of maximum efficiency being displaced towards the shorter wavelengths.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
Celsius (previously Centigrade)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM