Luminous fractional reflectance

Specular gloss n. The luminous fractional reflectance of a specimen in the specular direction. It is sometimes measured at 60°... 

Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectro-photometric method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results. 

Light reflectance (reflectance, reflectivity). The fraction of the total luminous flux incident upon a surface that is reflected, generally a function of the color (wavelength) of the light. Johnson SF (2001) History of hght and colour measurement a science in the shadows. Taylor and Francis, London, UK. Saleh BEA, Teich MC (1991) Fundamentals of photonics. John Wiley and Sons, New York. 

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