Principles and Usage of Gloss Meters

The gloss meter measures the reflective gloss of the surface. The gloss is measured by shining light on the surface at a fixed angle and then check how much light bounces back at the same angle.

What is a Gloss Meter?

A gloss meter is a device which measures the mirror’s reflective gloss on the surface. The shine is measured by projecting rays of constant strength and angle on the surface. The measuring amount of light reflected at an equal but opposite angle. There are various shapes of gloss measurement, depending on the type of surface. For non-metals like coating and plastic, some light passes through the surface and gets absorbed by the color. As the angle of light increases, more light is reflected. Metal has a higher reflectivity, which makes it less sharp.

Gloss Meter Principle

Glossiness is a physical quantity that evaluates the ability of a material's surface to reflect light under a set of geometric conditions. Gloss is often called 'mirror surface gloss,' so a gloss meter is sometimes referred to as a 'mirror surface gloss meter." The concept of "smoothness" and "roughness" in the gloss and machining industries is completely different, and the second one has tiny spots on the surface of the material. The reference standard is black glass with refractive index np=1.567. Assuming that the plane reflects natural rays in an ideal polishing state, the gloss value at this point is defined as 100.0 gloss units.

How Does a Gloss Meter Work?

Gloss meter structure

A common gloss meter is a consistent light source that projects parallel rays to the test surface to be measured. It is also used to fix a mechanical assembly which consist on a filter detector to receive light reflected from the test surface. Figure 1 says that it is necessary to define the lighting so that CIE emission efficiency V (l) is corrected with CIE illuminance SC.

In terms of measurement geometry, many measuring instruments are commercially available that meet the above standards. These instruments are usually calibrated with special black gloss reference tools. These tools have refractive index of 1.567 (based on sodium D-Ray) and are set to a gloss value of 100 for every measurement angle.

Choosing the correct angle for gloss measurement

Three measuring angles (20 °, 60 °, 85 °) are specified, and most applications of industrial coatings can be covered. The angle is selected on the basis of expected gloss range, as shown in the following table.

For example, if the measurement performed at 60 ° exceeds 70GU, the measurement angle must be changed to 20 ° to optimize the measurement accuracy. Two types of measuring instruments are available on the market: a single 60 ° angle measuring instrument and a combination of 20 °, 60 ° and 85 ° measuring instruments. Two more angles are used for other materials. For ceramic, film, textile and anodized materials, 45 ° angle is specified, and 75 ° angle is specified for paper measurement.

Understand gloss units

Gloss Units (GU) are used to measure surface gloss. This scale is based on polished black gloss standards that reflect light like a mirror and is set at 100 GU at a specific angle.  This standard is used to set the lower end point to 0 and to establish the calibration of the upper limit point of 100 on the surface of the complete round. This scaling is suitable for most non-metal coatings and materials (paints and plastics).

Other materials with high reflectivity (mirrors, plated/raw metal parts) can achieve high values reaching 2000 GU. In transparent materials, this value may be higher due to multiple reflections in the material.

Glossmeter Standards

Comparison of standards for gloss measurement

Gloss Meter Applications

The gloss meter is used in many industries from paper mills to automotive.

Examples include:

· Paints & coatings

· Powder coatings

· Additives

· Inks

· Plastics

· Wood coatings, polishes and flooring

· Yacht manufacture

· Automotive manufacture and re-finis

· Aerospace

· Polished stone and metals

· Consumer electronics

· Anodized metals

Types of Gloss Meters

The gloss meter contains one or more measurement geometry (usually 20 °, 45 °60 °75 °, 85 °, or a combination of these measuring angles (geometry)) which depends on the application or gloss type.

The Threenh Glossometer has three models.

           

YG45 Gloss Meter

YG45 Gloss Meter is ideal for measuring most gloss applications and is suitable for semi-gloss.

           

YG47 GLOSS Meter

YG45 45 °/ 75 ° is suitable for high to semi-gloss measurement and haze index calculation.

           

HG268 Tri-angle Gloss Meter

HG268 Tri-angle Gloss Meter 20 °/60 °/85 ° is suitable for measuring high gloss, semi-gloss and matte gloss and calculating haze index.