Gloss is an optical phenomenon caused when evaluating the appearance of a surface. The evaluation of gloss describes the capability of a surface to reflect directed light. A gloss meter measures the specular reflection. The intensity of the reflected light is dependent on the material and the angle of the illumination. In order to obtain a clear differentiation over the complete measurement range from high gloss to matte, 3 geometries (ranges) were defined.
Using the 60º gloss angle as a reference angle, the working range for 60º gloss is 10-70 GU (gloss units). This is considered the Semi Gloss range. Below 10 GU or above 70 GU, the 60º gloss measurement does not correlate with a visual assessment of gloss. Therefore for measurements above 70 GU, the 20º glossmeter is used for High Gloss surfaces. For below 10 GU, the 85º glossmeter is used. This is referred to as Low Gloss or Matte.
There are also two additional angles, 45º and 75º. These angles are industry specific for measuring paper and plastic films.