Gloss Meter

The glossmeter, gloss meter is an instrument used to measure the specular reflection (gloss) of a surface. Gloss is determined by projecting a beam of light with fixed intensity and angle onto a surface and measuring the amount of reflected light at an equal but opposite angle. A range of different geometries is available for gloss measurement, each depending on the type of surface to be measured. For non-metals, such as coatings and plastics, the amount of reflected light increases as the illumination angle increases, as part of the light penetrates the surface material and is absorbed by it or scattered by it depending on its color. Metals have much higher reflectance and therefore are less angle-dependent. Many international technical standards are available that define the method of use and specifications for different types of gloss meters used on various types of materials, such as paints, ceramics, paper, metals, and plastics. Many industries use gloss meters in their quality control to measure product gloss to ensure consistency in their production processes.

The parts of a glossmeter

A typical glossmeter consists of a standardized light source that emits a parallel beam of light onto the surface to be measured and a filtered detector positioned to receive the rays reflected from the surface.

The ASTM method states that the illumination must be defined so that the source-detector combination is spectrally corrected to give the CIE luminous efficiency, V(l), with CIE illuminant SC.

Selecting the correct angle

The measurement angle refers to the angle between the incident and the reflected light. Three measurement angles (20°, 60° and 85°) are specified to cover the majority of industrial coating applications. The angle is selected based on the expected gloss range, as shown in the table below.

For example, if the measurement taken at 60° is greater than 70 GU, the measurement angle should be changed to 20° to optimize measurement accuracy. Two types of instruments are available on the market: single-angle 60° instruments and a type that combines 20°, 60° and 85°. For other materials, two additional angles are used. An angle of 45° is specified for measuring ceramics, films, textiles, and anodized aluminum, while the 75° angle is used for paper.

Understanding Gloss units

The measurement scale, Gloss Units (GU), of a glossmeter is a scale based on a highly polished black glass reference standard with a defined refractive index, with specular reflection of 100GU at the specified angle. This standard is used to establish a 100 upper-point calibration with the lower endpoint at 0 on a perfectly matte surface. This scale is suitable for most non-metallic coatings and materials (paints and plastics) as they generally fall within this range. For other materials, highly reflective (mirrors, plated / unprocessed metal parts), higher values can be achieved, reaching 2000 gloss units. For transparent materials, these values can also increase due to multiple reflections within the material.

Glossmeter Standards

Gloss meter applications

The glossmeter is used in many industries, from paper mills to the automotive industry, and is used by both the manufacturer and the user. Examples include: Paints & coatings Powder coatings Additives Inks Plastic items Wood coatings, polishes and floors Yacht building Car manufacturing and refurbishment Aerospace Polished stone and metals Consumer electronics Anodized metals

Wood coatings, polishes and floors

The gloss of a wooden floor is usually measured at 60°. Wooden floor manufacturers have used gloss meters for many years to measure the gloss level in quality control (QC) to ensure that they always achieve a consistent, measurable visual finish.