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The CIE 1924 photopic V(λ) luminosity function, [cie 3] which is included in the CIE 1931 color-matching functions as the y (λ) function, has long been acknowledged to underestimate the contribution of the blue end of the spectrum to perceived luminance. There have been numerous attempts to improve the standard function, to make it more ...
In scientific literature, one occasionally encounters the term scotopic lux which corresponds to photopic lux, but uses instead the scotopic visibility weighting function. [10] The scotopic luminosity function is a standard function established by the Commission Internationale de l'Éclairage (CIE) and standardized in collaboration with the ISO ...
A comparison between a typical normalized M cone's spectral sensitivity and the CIE 1931 luminosity function for a standard observer in photopic vision. In the CIE 1931 model, Y is the luminance, Z is quasi-equal to blue (of CIE RGB), and X is a mix of the three CIE RGB curves chosen to be nonnegative (see § Definition of the CIE XYZ color space).
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 10 8 cd/m 2). In humans and many other animals, photopic vision allows color perception , mediated by cone cells , and a significantly higher visual acuity and temporal resolution than available with scotopic vision .
In modern photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this weighting function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way. The weightings are standardized by the CIE and ...
The luminous flux accounts for the sensitivity of the eye by weighting the power at each wavelength with the luminosity function, which represents the eye's response to different wavelengths. The luminous flux is a weighted sum of the power at all wavelengths in the visible band. Light outside the visible band does not contribute.
There are two luminous efficiency functions in common use. For everyday light levels, the photopic luminosity function best approximates the response of the human eye. For low light levels, the response of the human eye changes, and the scotopic curve applies. The photopic curve is the CIE standard curve used in the CIE 1931 color space.
However, the overall luminosity function (which in fact is a weighted sum of these three curves) is subjective, since it involves asking a test person whether two light sources have the same brightness, even if they are in completely different colors. Along the same lines, the relative magnitudes of the X, Y, and Z curves are arbitrarily chosen ...