Qu'est-ce qu'un brillancemètre? (document en anglais)

A glossmeter measures specular reflection. The light intensity is registered over a small range of the reflection angle. The intensity is dependent on the material and the angle of illumination. In case of non-metals the amount of reflected light increases with the increase of the illumination angle. The remaining illuminated light penetrates the material and is absorbed or diffusely scattered dependent on the color. Metals have a much higher reflection and are less angle dependent than non-metals.

A glossmeter gives the amount of reflected light from a sample, compared to that reflected from a black glass calibration standard with a defined refractive index. The result is independent of the amount of incident light. The gloss value of the reference standard is defined to be 100 gloss units. Materials with a higher refractive index can have a measurement value above 100 gloss units. For transparent materials, the gloss can be increased by multiple reflections in the bulk of the material. Due to the high reflectivity of metals, values as high as 3500 gloss units can be obtained. For these applications it is common to use percent reflection of incident light rather than gloss units.

Glossmeters usage procedures. As well as their defined angles of measurement, are internationally standardized to allow comparison of measurement values. Angle of illumination is the most important criterion. To clearly differentiate between high gloss and low gloss, several different measurement angles are used, with incident angles of 20, 60, and 85 degrees the most common. The 20 degree angle is normally used for high gloss surfaces, the 60 degree angle for medium gloss surfaces, and the 85 degree angle for low gloss surfaces. Other angles of measurement are used for specific applications, such as 75 degrees for plastic film, and 45 degrees for vinyl siding.

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