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Reflectance is light incident on the surface of a material that is reflected at an interface. Light not reflected from the sample is absorbed, scattered or transmitted.
Very smooth or shiny, mirror-like surfaces have high specular reflectance, in which the incident light reflects in the same direction. Rough or matte surfaces have diffuse reflectance, where the incident light gets scattered in all directions. Most surfaces exhibit a combination of specular and diffuse reflectance.
Ocean Insight modular spectrometers and accessories can be configured for a variety of diffuse and specular reflectance measurements, with options for lab use and feasibility or quality control and process monitoring. These are the core components to consider for most applications:
A workhorse spectrometer like the Ocean HDX or Flame is a good choice for most applications, although the super-fast Ocean FX or industrial-grade FD-D8 series are more robust options for online reflectance and color measurements. NIRQuest+ spectrometers cover your NIR (900-2500 nm) needs.
Here are some other considerations in selecting a spectrometer for your setup:
The most important thing about choosing a light source for reflection is to find one with strong output over the wavelength range of interest. For color measurements or when making a measurement to mimic the human eye, the light source needs to cover 380-780 nm. For chemical composition of organic material, near-infrared or infrared light will offer more information. Except in a very few specific cases, a narrow light source will not offer enough useful information, so lasers and most LEDs can be ruled out.
Are you measuring specular or diffuse reflectance? Flat surfaces or irregular shapes? Your choice of sampling accessory depends on various factors.
A reflectance system is not complete without a reference standard. Reflectance measurements are a ratio of the reflected light spectrum to the incident light spectrum. Since there is no way to collect all the light incident on a surface, reflectivity is usually measured relative to a reference standard.
The reflectance standard you select should be similar in reflectivity to the sample you’re measuring, to keep signal levels about the same during measurements and achieve the best signal-to-noise performance. Here are your options:
Here’s a sample reflectance system that uses a probe as the sampling device. The tablet shown here is a stand-in for laptop PCs and other computing devices. Also, this is just one example of dozens of different reflectance and color measurement configurations possible with Ocean Insight spectrometers and accessories.
In this video, we guide users through the basic steps necessary to perform both diffuse reflectance and color measurements using Ocean Insight spectrometers and accessories.