Exploring the Inner Workings of Gloss Meters: How They Measure Surface Glossness

Glossiness refers to the specular reflection of light on the surface of an object, which is the ratio of the intensity of the reflected light on the surface to the mildness of the incident light, usually expressed as a percentage. Glossiness can be understood as the subtle “roughness” of an object’s surface. The smoother the surface, the more “reflective” it is, the brighter it appears to the human eye, and the higher the glossiness. Nowadays, many industries require glossmeters for measurement and application.

Glossmeter, English name, is an instrument used to measure the surface gloss of ceramic, paint, ink, plastic, marble, aluminum, hardware and other materials. According to the different ability of the material surface to reflect light, the gloss of the material surface can be divided into three types: high gloss, medium gloss, and low gloss.

Principle 1 of glossmeter:
1. Glossiness is a physical quantity that evaluates the ability of a material’s surface to reflect light under a set of geometric specified conditions, with directional reflective properties. Gloss is completely different from the concept of “smoothness” or “roughness” in the mechanical processing industry, which is a continuation of small surface irregularities of materials.

2. The measuring head of the glossmeter consists of a transmitter and a receiver, which is composed of an incandescent light source and a set of lenses, and generates a certain required incident beam. The receiver consists of a lens and a photosensitive element, which is used to receive a conical beam of light reflected back from the surface of the sample.

Glossiness is a relative measurement of specular gloss. The reference standard is black glass with a refractive index of np=1.567. Assuming that its plane is in an ideal polished state, it reflects natural light beams in a mirror direction, and the glossiness value at this point is defined as 100.0 gloss units.

The glossiness board is divided into three types based on the glossiness value: high, medium, and low. The high gloss plate is made of black optical glass or other materials. Medium gloss plate and low gloss plate are made of glazed ceramic or black optical glass frosting. The glossmeter uses the principle of light reflection to measure the glossiness of the sample. That is, irradiate the sample under the conditions of a specified incidence angle and a specified beam of light, and obtain the reflected light in the direction of the mirror reflection angle.

Many optical properties of materials can be qualitatively explained using wave theory. According to wave theory, the ratio of the energy W of incident light passing through unit area per unit time to the energy flow W of reflected light can be derived.

W1 sin2（i-r） tg2(i-r)

——=[——————— + ——————]

W02 sin2（I+r） tg2(i-r)

In the formula, i is the angle between the incident light and the normal (incident angle),
R is the refractive angle.

Gloss is the property of directional selective reflection on the surface of an object, which presents different bright spots or forms images of objects overlapping on the surface. Glossiness is the ability of an object’s surface to reflect light when illuminated, usually expressed by multiplying the reflectance of the sample in the mirror (positive reflection) direction relative to the standard surface by 100, i.e. G=100R/R.

R in the formula – the reflectivity of the sample surface,/R—— The reflectivity of the standard plate. With polished black glass as the reference standard plate, the refractive index of sodium D-rays is 1.568, and the specular gloss calibration for each geometrical optics condition is 105 gloss units.

How is gloss measured?
The measurement of glossiness is achieved by shining a certain amount of light on the surface of an object, and then quantifying the amount of reflected light. The testing method for the angle and reflection of light is determined by the surface and appearance of the object.

So when measuring gloss, it is necessary to choose an appropriate angle. The NHG268 glossmeter complies with ISO2813 and GB/T9754 (Chinese national standards), and the three angles can fully cover the measurement of all surface glossiness.

The unit of gloss is (GU), which can be traced back to the reference standards of BAM (Germany), NRC (Canada), and NPL (UK).

Medium gloss (universal angle): 60 °
60 ° is the measurement angle applicable to all surfaces. It is also used as a reference angle for measuring surfaces with low gloss of 85 ° and high gloss of 20 °.

Low gloss: 85 °
To improve the resolution of low gloss surfaces. Gloss can be measured at 85 °, and when the surface glossiness value of an object measured at 60 ° is below 10GU, it is recommended to use an 85 ° angle for measurement.

When measuring different glossy textures or slightly uneven surfaces at 85 °, it is necessary to take the average of multiple measurements.

High gloss: 20 °
Measuring an angle of 20 ° can improve the resolution of high gloss surfaces. When the surface luminosity value of an object measured at 60 ° is higher than 70GU, it is recommended to use a 20 ° angle for measurement.

The 20 ° angle (optical path) is very sensitive to the phenomenon of surface fog and shadow on an object. Because fog shadow is a unique phenomenon on high gloss surfaces.

The measurement results of a glossmeter are usually represented by the glossiness value, which is measured in units of GU (Gloss Units), a scale based on a highly polished reference black glass standard. The higher the glossiness value, the better the glossiness of the object surface, usually between 0 and 100.

Setting the subscript endpoint to 0 on an excellent matte surface is suitable for most non-metallic coatings and materials (paint and plastic) as they are within this range. For other high reflective materials (reflectors, electroplated/originally metal parts), it can reach 2000 gloss units. For transparent materials, these values may also increase due to the presence of multiple reflections.

Gloss meters AGM-580 are mainly used in the surface gloss measurement for paint, plastic, metal, ceramics, building materials. It conforms to the DIN67530, ISO2813, ASTM D523, JIS Z8741, BS 3900 Part D5, JJG696 standards and so on.

Gloss Meter with Single Angle AGM-500PRO:

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