glossmeter

A glossmeter is an instrument used to measure the gloss or specular reflectivity of a surface. It quantifies how much light is reflected in a specular direction, producing a gloss value that serves in quality control, product specification, and research.

The device works by directing a controlled beam of light at a defined incidence angle onto the surface and measuring the intensity of light reflected at the corresponding specular angle with a photodetector. The gloss value is the ratio of reflected to incident light, calibrated to produce a unitless gloss unit (GU). Standard measurements are taken at specific angles, commonly 20°, 60°, and 85°, chosen to suit the surface roughness and finish.

Glossmeters are available as handheld portable units and benchtop instruments. Many general-purpose measurements use the 60° geometry, while very glossy surfaces are measured at 20°, and very matte surfaces at 85°. Values are expressed in gloss units (GU); some devices display corresponding percent reflectance. High-gloss coatings typically fall around 80–100 GU at 60°, whereas matte surfaces may be well below 20 GU.

Standards governing gloss measurement include ISO 2813 and ASTM D523, which specify the method for determining specular gloss of non-metallic surfaces and related materials. Gloss measurement is widely used in paints and coatings, plastics, paper, cosmetics, automotive finishes, and other industries to ensure product consistency and meet specifications.

Limitations include that glossmeters measure only the specular component of reflectance; diffuse color, texture, and surface roughness can influence results. Accurate measurements require clean, dry, evenly oriented samples and proper calibration against reference standards at the chosen angle.