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What difference in gloss can a human see?

If two different coatings are measured, what 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 glossmeter is more sensitive to differences in gloss below 10 GU @ 60° and the 20 Degrees has 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 just visible to a trained observer.

 

Why Measure 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 the process for real-time gloss measurement. Please call us at 1-866-462-6832 to discuss the inline application.

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.

Detector

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 angle 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.



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Metals have a much higher reflection and are less angle dependent than nonmetals. 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 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. Glossmeters 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.

 

Gloss Range with 60° Gloss Meter Measure With:
If Semi-Gloss - 10 to 70 GU 60 °
If High Gloss > 70 GU 20 °
If Low Gloss < 10 GU 85 °

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.

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