Brightness description using different metrics

In 1924 CIE defined the V(λ) function to describe the “relative visibility”. It was soon realised that this was not a right description for brightness. During the seven decades that passed by, several attempts were made to describe brightness for monochromatic, less saturated and near white lights. Among the near-white light descriptions the approach by Haubner [1] is the best-known. For monochromatic lights CIE TC 1-30 suggests spectral brightness efficiency functions [2] (and spectral luminous efficiency functions), an earlier CIE Research Note proposed for trial a brightness matching model [3] intended mainly for VDU colours. During the past decade Hunt [4] and Nayatani and coworkers [5] developed models to describe colour appearance with a brightness axis. The present work deals with the comparison of the different brightness descriptions and investigates whether the colour appearance model by Hunt could be used also to describe photometric brightness or not. Finally we point out a discrepancy when mesopic brightness descriptions [6] are derived from photopic and scotopic luminosity functions: the photopic luminosity function correlates with visual acuity, flicker and distinctness of boarder related perceptions well, while the V’(λ)-function is brightens related, leading to the amalgamation of two different phenomena. A real mesopic brightness description should start from one of the photopic brightness descriptions and the V’(λ) based “luminance”.