Spectrometry at Its Best: Meet Regula's Solutions

A spectrometer is a special device that helps to measure and analyze the spectrum of a substance—the distribution of its properties across specific wavelengths. The trick is that, by studying the spectrum, specialists can gain insights into different aspects of a substance, e.g., its composition, structure, and physical or chemical properties.

In the Regula product line, you will find an integrated optical spectrometer in some models of video spectral comparators, and a portable spectrometer that combines the features of a microscope in the Regula 5006. These devices, together with software features, determine color values for further comparative analysis.

Let’s say we need to distinguish whether the ink on two banknotes is the same or not. We can’t trust our eyes here as we know that colors are subjective and depend on the person seeing the color. So we need to replace subjective evaluation with an objective numerical system.

In addition, Regula spectrometers feature a light source with a wider wavelength range than what is typically used in colorimetry. While traditional colorimetric methods use wavelengths up to 730 nm, we’ve extended ours to 1000 nm. This enhancement enables a more detailed comparative analysis of reflection spectra. As we like to say, a broader range provides a deeper spectrum of insights.

Let’s illustrate how it works. Suppose there is one genuine banknote and two counterfeits. The task for law enforcement authorities will be to investigate whether these counterfeits have a single source of origin—i.e., whether they were produced at the same clandestine printing house or different ones.

A spectrometer can help to obtain data to clarify the characteristics of the inks used. Further comparative analysis can show whether or not these dyes belong to the same group of dyes.

The first sample is a genuine one, so its graph is used as a reference graph for comparing the other two graphs. Based on the color similarity (all three samples are red), the graphs have a similar shape. In the 400 to 570 nm range, there is a weak reflected signal with some differences in the shape of the graphs. In the 570 to 850 nm range, different levels of the reflected signal are observed, and accordingly, the shapes of the graphs have different peak locations. Thus, we can conclude that the ink characteristics in these samples are different, which may indicate that dyes with different compositions were used.

The same principle can be applied when dealing with ballpoint inks.

The following illustration shows a case where we need to determine whether the digit “4” is genuine, or if it was a “1” until someone added the necessary part to make it look like “4”.

Like in the first case, we select areas where we want to measure the reflection spectrum. The software builds two graphs. According to the graphs, we can say that this digit “4” contains two different pen inks, as their graphs completely differ from each other in their shape and peaks. Consequently, the ink characteristics are not the same, so we’re dealing with two inks that have different compositions.

In colorimetry, as in any science, certain research methods are preferred. A traditionally used technique is the contact method, which requires the object to fit tightly against the device to ensure accurate results. Obviously, this tight contact has many cons, since it is not always desirable to touch the object, as it might be, for example, an ancient text, and every in-depth examination may harm it.

At Regula, we offer a non-contact method of examination that has several advantages, including ease of use and the ability to visualize the area under study. With this approach, a camera displays the area, allowing precise selection of a specific point.

For instance, if we need to capture color data from a tiny fiber, we can be confident that we have captured the exact point. Additionally, the Regula spectrometer module provides an adjustable field of view, tailored to the specifics of each sample. Whether the object is relatively large and uniformly colored or has gaps and varying colors, this flexibility provides reliable results.

Even if the non-contact method may introduce a slightly higher measurement error, we compensate for it with several calibration steps. These calibrations minimize errors introduced by the lens system and the distance to the object.

Plus, to increase the accuracy of measurements, with each Regula device that has an integrated spectrometer we supply a White Diffuse Reflectance Standard with a NIST (National Institute of Standards and Technology) Traceable Calibration Certificate. This is an object that reflects 99% of light in the visible range, and it is used to obtain the reference signal of our light source before every session of spectrum studies.

Besides the capability to measure reflection, examples of which were illustrated above, Regula spectrometers can measure luminescence and color.

You excite the object of examination using an ultraviolet light source, but you observe the results of this excitation in the visible range.

Why focus on the visible range? The visible light you observe is not the ultraviolet light itself but the light emitted by the material as a response to UV illumination through fluorescence or phosphorescence.

For more information, watch the video:

Just like in the measurement of reflection, you can see the practical benefits of the examination of luminescence when determining the authenticity of banknotes or any other secure documents—namely, you can investigate the differences in the luminescence spectra and determine the UV luminescence colors relative to each other. Our clients also use this module to study the behavior of UV inks on banknotes under various conditions, such as washing, heating, etc.

As we mentioned earlier, the perception of color is a very subjective thing. That’s why colometrists describe and analyze colors objectively by using standardized color systems, such as CIE 1931, RGB, XYZ, Lab, and others. These systems define colors numerically, using coordinates in a color space to ensure precision and consistency.

Our engineers have adapted the mathematical apparatus of the spectrometer, which allows you to instantly obtain color coordinates, and recalculate and visualize them in different color spaces, for example, a chromatic locus.

Let's see how it works in practice:

These systems also make it possible to predict how a color will look under specific standardized light sources, such as D50, which simulates daylight. This capability is critical in fields like manufacturing and quality control of banknotes and secure documents, where consistent color matching is essential.

In this article, we covered several aspects concerning colorimetry in general, and the spectral technology used in Regula solutions in particular.

Let us know if you have any questions concerning this topic. We will be more than pleased to answer them.