Compute the scotopic (rod) luminance from spectral energy
lum = ieScotopicLuminanceFromEnergy(energy,wave)
Purpose:
The CIE scotopic luminance function describes wavelength sensitivity
of the rod system. This is the system we use under low light
conditions. The cone system is used under moderate to bright light
conditions and is called the photopic system.
The energy data format can be either XW or RGB. WAVE describes the
wavelength samples.
The CIE defines a formula to compute scotopic luminance from the spectral radiance
distribution (energy).
scotopicLuminance = Km * (xwData*Vprime) * deltaLambda;
xwData are the space-wavelength representation of the signal (energy).
Km is a scale factor, chosen so that a blackbody radiator at the
freezing temperature of platinum has 60 scotopic candelas per square
centimeter. (Wyszecki and Stiles pp. 377-378 and also p. 384, is 1745.
By comparison, the scale factor for photopic luminance is 683).
Vprime is the scotopic luminance function
deltaLambda is the wavelength sampling interval.
Examples:
wave = 400:10:700;
energy = vcReadSpectra('crtSPD',wave)';
energy = [1,1,1]*energy;
lum = ieScotopicLuminanceFromEnergy(energy,wave)
Copyright ImagEval Consultants, LLC, 2003.