What is the difference between light reflectance and gloss?

January 26, 2024

Light reflectivity and gloss are two different concepts, there are many different differences between them, but there is a certain connection, in general, the higher the light reflectivity of the object the higher the gloss. When light is emitted from a medium to the interface of another medium, a part of the light returns to the original medium, so that the propagation direction of light has changed, this phenomenon is called light reflection, the ratio of reflected light and incident light, is the reflectivity. Gloss refers to the ability of the surface of the object to reflect the light from a certain Angle, and the main factors affecting gloss are the roughness of the surface of the object and the molecular structure of the object itself.

We know that the reflectivity of different objects is also different, the reflectivity mainly depends on the nature of the object itself and the situation of the surface, as well as the wavelength and incidence Angle of the incident inductance wave, the range of reflectivity is less than or equal to 1, the use of reflectivity can judge the nature of the object. The reflectance formula is that when the beam is close to normal incidence (the Angle of incidence θ is about 0), the reflectance formula is R=(n1-n2)^2/ (n1 +n2)^2. Where n1 and n2 are the true refractive indices (that is, refractive indices relative to vacuum) of the two media respectively. Refractive index refers to the phenomenon that the Angle of light changes when it enters different media, and is characterized by sinθ1/sinθ2. θ1 and θ2 are the angles of incidence and refraction, respectively, that is, the Angle between the light and the normal.

In general, the reflectivity of light on the critical plane is only related to the physical properties of the medium, the wavelength of the light, and the Angle of incidence. In the case of continuous change of refractive index of the medium, the reflectivity is also related to the thickness of the medium because of the interference effect of reflected light at different interfaces. Thus, we can design a coating with a specific thickness and a specific refractive index to obtain a coating with a large reflectivity or transmittance to a specific wavelength of light. The reflectivity is related to the refractive index of the two media, the incident Angle, the wavelength of the light, etc. The greater the incidence Angle, the stronger the reflected light. In the case of a certain medium and wavelength, when the incidence Angle is greater than a certain (critical) Angle, the reflected light is equal to the incident light, which is called total reflection. Fiber optic transmission takes advantage of this phenomenon.

The gloss unit (GU) scale is linear, and each Angle of incidence has a different measuring range. 0-2000GU (20°), 0-1000GU (60°), 0-160GU (85°). % Reflectance compares the light energy sent and received with a gloss meter and expresses the full measured range of Angle incidence of the value in percentage, and the value is displayed as a percentage with respect to the selected Angle of incidence.

Therefore, the light reflectance and gloss are not only different in the concept of light reflectance and gloss, but also in the calculation method is different, light reflectance is a percentage value, and gloss has GU units. The optical reflectance of the human eye can not be subjective and objective effective judgment, and the gloss can be judged by the human eye.