a - absorption coefficient - where,
                         
CRI - Color Rendering Index - a unit of measure that defines how well colors are   
         rendered by different illumination conditions in comparison to a standard (i.e. a
         thermal radiator or daylight).
d - physical thickness of a film layer
HWOT - halfwave optical thickness of a film layer (index=nf) where,
                         
k - extinction coefficient - unit of measurement for film absorption
l - wavelength (in nanometers, unless specified)
n - index of refraction
QWOT - quarterwave optical thickness of a film layer (index=nf) where,
                         
x, y - 1931 CIE chromaticity coordinates
X, Y, Z - tristimulus values