Reflectivity Measurement

Reflection and transmission are the basic optical properties of objects and the basic content of the spectral measurement as well. For the different types of samples, in order to obtain the best spectral measurement data, reflection and transmission will contains more information.

When measuring the reflectivity, it is necessary to consider whether it is specular reflection or diffuse reflection or a sample whose reflectivity changes with the angle of the incident light. We observe that most of the color is based on diffuse reflections, and those that are very dazzling or very bright ones are mostly involve both specular reflections and diffuse reflections. When we measure the reflection, it is important to determine which type of reflection it is, and whether we want to receive all or part of the reflected light. In food applications, most of the reflection measurements are based on diffuse reflection.

Typical Reflectivity Measurement System

• Spectrometer: a UV-Vis or Vis-NIR spectrometer is optional based on user requirements.

• Light source: 400nm-2000nm or 200nm-2000nm tungsten light source is optional.

• Reflectance Standard: If it is diffuse, you can use diffuse reflectance standard whiteboard, if it is specular reflection, you can use high mirror reflectivity standard board.

• Probe: The Y-type reflective probe is an ideal choice when we need to quickly measure the sample or apply a very small sampling point on the surface of the sample. It can measure both specular reflection and diffuse reflection, and can choose different types of fiber (UV-Vis or Vis-NIR) based on the configuration of the light source and the spectrometer. The emitted light and the reflected light of the probe are in the same direction, and the received light is part of the reflected light. Therefore, using a reflective probe to measure the reflection spectrum is relative measurement.

• Stage: Light from the fiber to the surface of the sample requires a certain amount of space to form the reflected light, so the probe needs a certain distance from the sample. So the probe will not scratch the surface of the sample. Using a reflectivestage, the distance between the probe and the sample surface can be well fixed, and get good reflection measurement data.

Sampling accessory selection

The light irradiated from the optical fiber to the surface of the sample needs a certain space to form the reflected light, so the probe needs to have a certain distance from the sample. In addition, the probe must not scratch the surface of the sample. Using the reflection probe bracket, the distance between the probe and the sample surface can be well fixed, and good reflection measurement data can be obtained.

For specular reflection, we usually use a reflective fiber through the 0-degree angle incident, 0-degree angle reflection measurement., but also through the 45-degree angle incident, 45-degree angle reflection measurement.

For diffuse reflection, it is generally measured using an integrating sphere, or by a 0 degree angle incident, a 45 degree angle reflection way. It depends on the sample and the measurement criteria.

Figure 1 and Figure 2 are the basic specular reflection stagae. Figure 1 uses the Y-type reflective probe. Figure 2 uses two fibers.

Figure 3 is the inverted specular reflection stage. Since it keeps the distance from the sample to the reflected fiber and the distance from the standard reference sample to the reflected fiber exactly the same, this stage is more suitable for accurately measuring the reflectance.

Figure 4 is the integrated sphere reflection stage, you can use 8 degrees angle incident, 90 degrees angle to accept, you can also use 90 degrees angle of incident, 8 degrees angle to accept. This method is suitable for the measurement of the reflectivity of rough surfaces or suede samples.

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