Implementation of CIE 2006 Cone Fundamentals in Photometric and Colorimetric MeasurementsRF Number RF-05
Since its beginning, colorimetry and photometry were directly related through the CIE colour matching function Y of the CIE 1931 standard colorimetric system which was set to be identical with the spectral luminous efficiency function for photopic vision, V(lambda). It is also well known that V(lambda) is not a perfect match to human vision and in particular it underestimates the visual response in the blue region. The physiology-based function, known as the cone-fundamental-based spectral luminous efficiency function, V_F(lambda), is based on the latest research and again relates photometry to modern (i.e. cone-fundamental based) colorimetry.
The RF shall consider the impact of cone fundamentals on measurement of fundamental quantities, including:
• The replacement or supplementation of the spectral luminous efficiency function for photopic vision V(lambda) by a cone-fundamental-based spectral luminous efficiency function V_F(lambda) in photometric measurements, including the possible need to replace photometers with new devices that are either matched to the V_F(lambda) function instead of V(lambda) or which directly take spectrally resolved measurements and derive luminous quantities through software integration.
• The possible need for the definition of a new defining constant Kcd,F for cone-fundamental based photometry, the intention of which is to reduce the impacts of a change in photometrical scales.
• The replacement or supplementation of the existing colour matching functions used in colorimetry with new functions based on cone fundamentals, including the possible need to replace tristimulus colorimeters with new devices that are either matched to the new functions instead of the existing colour matching functions and to update software or firmware for instruments which directly take spectrally resolved measurements and derive colorimetric quantities through software integration.
• The corresponding effects on scotopic photometry (including the quantity “S/P ratio” used to characterise sources) and mesopic photometry.