What Is Peak Specular Reflectance (RSpec)?

Gloss, express as gloss unit (GU), is commonly used to describe a product appearance or the quality of a surface. However, the visual appearance of two surfaces can be different even when their gloss readings are the same. This is due to limitation of gloss meter in detecting subtle surface texture which our eyes can notice.

Moving beyond gloss, parameters like Peak Specular Reflectance (RSpec) can provide a better representation of gloss and surface quality. RSpec is the peak gloss value measured at the specular angle. It is highly sensitive to surface texture and is used to determine a surface smoothness.

When RSpec value is close or equal to gloss value measured at 20° geometry, it indicates a smooth surface. As the difference between gloss and RSpec values become greater, texture on surface becomes obvious.

In the example below, we can see that sample B has a higher gloss reading than sample A. When further analyzed using RSpec, sample B has a poorer surface quality than sample A.

The example also demonstrates the need for additional appearance parameters as gloss alone fall short of giving us a true indication of appearance quality.

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