Gloss Meters

Gloss Meters

Color and Gloss (SCE and SCI Methods)
Even for objects composed of the same materials, variances may be seen in the colors due to differences in the gloss of the surfaces. For example, why is a duller blue color seen when sandpaper is applied to a shiny or high gloss blue sample?

Light which reflects directly back (but opposite angle) from the light source, as if by a mirror, is called specularly reflected light. The rest of the light that is scattered in many directions is called diffuse reflectance. The sum of the two is called total reflectance. Shiny objects have higher specular reflectance/lower diffuse reflectance and the opposite is true for dull objects. The total amount of reflected light is always the same if the materials and color are the same. Therefore, if a glossy blue plastic part is sanded, the specular reflectance is reduced and the diffuse reflectance increases.

Two key terms when talking about gloss are:

• SCE, Specular Component Excluded
• SCI, Specular Component Included.

The names are counter intuitive. SCE values include the gloss and texture while SCI exclude them. SCI values represent the true color that lies beneath.

Why a Gloss Meter instead of a Spectrophotometer?
A Gloss Meter, or Glossmeter, will measure the specular reflection of the object at multiple angles. Results will correlate to known standards unlike a spectrophotometer which can only give relative values between samples. 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 have a much higher reflection and are less angle dependent than non-metals.

Spectrophotometers measure SCI and SCE but only at one angle. The results they present are only relative between samples. This may be fine for a lab comparing their own samples. But as soon as comparison to another lab is needed, then a dedicated Gloss Meter is needed.

Information of Gloss

• Gloss Measurement. 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.
• 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
• Matt 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.