What is a Y Brightness? Beta Reflectance Factor? Reflection Coefficient?


FAQ: What is a Y Brightness/Luminance?

FAQ: What is a Beta (ß) Reflectance or Luminance Factor for Brightness?

FAQ: What is a Reflection Coefficient (0-1)?


ASTM E284 Standard Terminology of Appearance defines reflectance factor as:

Reflectance Factor, n – ratio of the flux reflected from the specimen relative to the flux reflected from the perfect reflecting diffuser under the same geometric and spectral conditions of measurement.

The most common metric used to measure the brightness of materials is CIE Y Brightness or Luminance. The CIE Y metric is scaled between 0 (representing a Perfect Black of 0% reflectance across the visible spectrum) and 100 (representing a Perfect White of 100% reflectance across the visible spectrum).

The “ß (beta) reflectance or luminance factor” is the same as Y Brightness or Luminance, expressed as a ratio relative to base 1 instead of 100.

Another metric called “Reflection Coefficient, Visible (0-1)” is the same as ß (beta) reflectance factor: scaling the reflectance of the material between 0 for a perfect black and 1 for a perfect white.

In all cases the illuminant/observer combination used for calculation has been C/2° historically, but measurements of typical white or neutral materials, made under D65/10° will be very close.

Here is a table comparing Y Brightness/Beta reflectance and Reflection coefficient for typical white colors.




CIE Y Brightness/



ß (beta)   reflectance or luminance factor


Reflection   Coefficient, Visible


Perfect White of 100%   reflectance




Perfect Black of 0% reflectance




White Instrument Tile Standard




11-0108-50 100 x 100 mm (4 x 4 in) White Porcelain-on Steel Tile




A minimum luminance factor is the minimum allowable ß (beta) value established for a product, indicating the minimum amount of light that should be reflected by the sample.

Industry Reference Methods

ASTM E991 Standard Practice for Color Measurement of Fluorescent Specimens Using the One-Monochromator Method references reporting in Y, x, y D65/2° or D65/10° and includes references to beta reflectance factor.

BS DIN EN 471 High-visibility warning clothing for professional use. Test methods and requirements describes performance specifications of high visibility garments and accessories or safety clothing, including new and in use color and retroreflection criteria.

FAQ: Beta Reflectance Factor and MSEZ

FAQ: “I have a MiniScan EZ but need to report beta reflectance factor. Can this be done on this sensor?”

The ColorFlex EZ firmware features reporting in Y, x, y color scale for any illuminant/observer combination as standard.

A modification of the firmware, CMR-3105 MSEZ Beta Reflectance Factor, allows for the display of ß, x, y as a color scale and ß as a single index for any illuminant observer combination in MiniScan EZ firmware.

Various CMR-3105 firmware displays on the MiniScan EZ that include Beta reflectance factor.

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