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Gloss Meters

Gloss Introduction

What is Gloss?

Gloss is an optical property that indicates how well a surface reflects light in a specular (mirror-like) direction. It is one of the important parameters that are used to describe the visual appearance of an object. The factors that affect gloss are the refractive index of the material, the angle of incident light, and the surface topography.

The apparent gloss depends on the amount of specular reflection – light reflected from the surface in an equal amount and the symmetrical angle to the one of incoming light – in comparison with diffuse reflection – the amount of light scattered into other directions.

Gloss is an aspect of the visual perception of objects.

Gloss is the attribute of surfaces that causes them to have shiny or lustrous, metallic or matte appearances.

Gloss is a visual impression that is caused when a surface is evaluated. The more direct light is reflected, the more obvious will be the impression of gloss.

Gloss effects are based on the interaction of light with the physical properties of the sample surface. The other influencing component is the physiological evaluation scale. The human eye is still the best tool to evaluate gloss differences. However, the visual surface control is insufficient, because evaluation conditions are not clearly defined, and people see and judge differently.

In addition to that, the subjective perception of appearance is dependent on personal experience: what is glossy for a paper manufacturer might be dull for an automotive maker. Gloss is measured by focusing on the reflected image and not by focusing on the surface. Eyesight and mood have a decisive role in visual judgment. Also, important is what our eye is focused on. We evaluate a surface by focusing our eye on a reflected image of a light source. In order to guarantee reliable and practical quality assurance, it is necessary to define appearance with objective, measurable criteria. Accurate characterization of appearance does not only help to control quality but improves quality and optimizes manufacturing processes.

High Gloss

Smooth and highly polished surfaces reflect images distinctly. The incident light is directly reflected on the surface, i.e. only in the main direction of reflection. The angle of incidence is equal to the angle of reflection.

Matte to Semi-Gloss

On rough surfaces, the light is diffusely scattered in all directions. The image forming qualities are diminished: A reflected object does no longer appear brilliant but blurred.

The more uniform the light is scattered, the less intense is the reflection in the main direction, and the duller the surface will appear.

The difference in Gloss as perceived by humans

If two different coatings are measured, what the number of gloss units would be detectable by the human eye, how many units would be perceived as significantly different?

When measuring at 60 Degrees these detectable differences depend on the gloss level of the sample, for instance, 3.0 GU difference measured on a very matte surface (perhaps 5GU), would be seen by the human eye but on a higher gloss coating (perhaps 60 GU) the difference would be very difficult to notice.

The only way that you can determine tolerances for your products would be experimental, perhaps preparing printed samples at different gloss levels that you can show to end-users of your coatings or internal "experts".

The other option is to change to a 20/60/85 degrees instrument, the 85-degree gloss meter is more sensitive to differences in gloss below 10 GU @ 60° and the 20 Degrees has a higher resolution on high gloss coatings (above 70 GU @ 60°). The advantage of using the three angles is that there is more equality to the gloss differences, in our experience a gloss difference of 5 GU, when measured with the correct geometry, is visible to a trained observer.

Measuring Gloss

Gloss is an aspect of the visual perception of objects that is as important as color when considering the psychological impact of products on a consumer. In other words, "Gloss Sells" Gloss has been defined as the attribute of a surface that causes it to have a shiny or lustrous, metallic appearance.

The gloss of a surface can be greatly influenced by a number of factors, for example, the smoothness achieved during polishing, the amount and type of coating applied, or the quality of the substrate. Manufacturers design their products to have maximum appeal. Such examples are; highly reflective car body panels, glossy magazine covers, or satin black designer furniture. Now, what happens when products all of a sudden look different? Customers see this as a defect or poor quality. Using a glossmeter and having good quality control practices eliminates this variable as a problem.

It is important therefore that gloss levels be consistent on every product or across different batches of products. Gloss can also be a measure of the quality of a surface, for instance, a drop in the gloss of a coated surface may indicate problems with its cure, leading to other failures such as poor adhesion or lack of protection for the coated surface.

It is for these reasons that many manufacturing industries monitor the gloss of their products, from cars, printing, and furniture to food, pharmaceuticals, and consumer electronics. We also have Gloss Sensors used in processes for real-time gloss measurement.

Why Measure Gloss

It is important therefore that gloss levels be consistent on every product or across different batches of products. Gloss can also be a measure of the quality of a surface, for instance, a drop in the gloss of a coated surface may indicate problems with its cure- leading to other failures such as poor adhesion or lack of protection for the coated surface.

It is for these reasons that many manufacturing industries monitor the gloss of their products, from cars, printing, and furniture to food, pharmaceuticals, and consumer electronics.

How is Gloss Measured?

Gloss is measured by shining a known amount of light at a surface and quantifying the reflectance. The angle of the light and the method by which the reflectance is measured are determined by the surface.

Gloss is measured using a Gloss Meter also known as a Glossmeter) which directs a light at a specific angle to the test surface and simultaneously measures the amount of reflection. The type of surface to be measured determines the gloss meter measuring angles to be used and thus the gloss meter model.

The intensity is dependent on the material and the angle of illumination. In case of nonmetals (coatings, plastics) 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

Metals have a much higher reflection and are less angle-dependent than non-metals. The measurement results of a glossmeter are related to the amount of reflected light from a black glass standard with a defined refractive index, and not to the amount of incident light. The measurement value for this defined standard is equal to 100 gloss units. Materials with a higher refractive index can have a measurement value above 100 gloss units (GU), e.g. films.

In the case of transparent materials, the measurement value can be increased due to multiple reflections in the bulk of the material. Due to the high reflection capabilities of metals values of up to 2000 GU can be reached. For these applications, it is common to document the measurement results in % reflection of the illuminated light. Gloss meters and their handling procedures had to be internationally specified to allow comparison of measurement values. The angle of illumination is of high influence. In order to obtain a clear differentiation over the complete measurement range from high gloss to matte, 3 different geometries, i.e. 3 different ranges, were defined using a 60° glossmeter.

In this case study, 13 samples were visually ranked from matte to high gloss and measured with the 3 specified geometries. In the steep slopes of the curves, the differences between the samples can be clearly measured, while in the flat part the measurement geometry no longer correlates with the visual. Gloss measurement for any application, whether you are dealing with specific applications or need a universal solution for high to matte gloss samples, www.gloss-meters.com offers a complete line of glossmeters.

How do I choose a Gloss Meter?

You first require a flat surface of approximately 2" by 0.5" (50 x 10mm) to position a glossmeter properly on a surface. If the surface area you have is smaller, then please call us to discuss a tabletop gloss meter for 2 x 2mm areas. One must now judge your product by how glossy it is. Most products fall into a semi-gloss range. Some are matte and designed to have the very low gloss and others such as metals or car finishes are very high. There are three types that cover the complete range of gloss, namely the 20 degrees, the 60 degrees, and the 85-degree gloss meters. Certain industries, however, prefer a different angle. These industries are; paper, ceramic, film, and vinyl. If you fall into one of these industries, please read Gloss Meter Selection by Industry. Some customers produce a range of products from very glossy to matte, then you would require a Universal gloss meter that measures all three angles, or maybe you only make products from semi-gloss to very high gloss, then you need the DUAL 20-60 degree gloss meter.

Low Gloss - 85°

For the improved resolution of low gloss, a grazing angle of 85° is used to measure the surface. This angle is recommended for surfaces that measure less than 10 GU when measured at 60°. This angle also has a larger measurement spot which will average out differences in the gloss of textured or slightly uneven surfaces.

Medium or Semi-Gloss - 60° - The Universal Measurement Angle

One must remember that all gloss levels can be measured using the standard measurement angle of 60°. This 60-degree angle is used as the reference angle for all products. So why choose some other angle? Because of extreme gloss, one obtains better measurements with the complementary angles of 85° or 20° often used for low and high gloss levels respectively.

High Gloss - 20°

The acute measurement angle of 20° gives an improved resolution for high gloss surfaces. Surfaces that measure 70 GU and above at the standard angle of 60° are often measured with this geometry. The 20° angle is more sensitive to haze effects that affect the appearance of a surface. The different gloss of these two samples is more clearly shown in the 20° readings.