Exploring the Inner Workings of Spectrophotometer: How To Measure Color Difference

The spectrophotometer is a color measuring instrument with superior performance, wide use, and easy operation. This instrument is suitable for color detection and color difference control of complex industrial products, such as measuring the reflection and transmission colors of objects, as well as measuring the whiteness, chromaticity, and the most basic color difference between two objects.

Currently, the main industries in industrial production that use spectrophotometers include textiles, printing and dyeing, coatings, metal coatings, glass coatings, paint films, building materials, printing, and other industries that have strict and difficult color requirements to control. Using spectrophotometers to quantify, compare, and analyze the color information of products can be easily understood. At the same time, connecting to a PC can clearly restore color information, providing the best guarantee for color transmission and replication.

The spectrophotometer is designed to provide a 45 °/0 ° geometric observation angle suitable for human eye observation, displaying the reflectance and transmittance of visible light in the 300nm-700nm quality inspection range, and is connected to a computer through an interface to expand its functionality.

The more advanced spectrophotometer in color measurement, also known as the spectrophotometer, contains an optical element that can separate light dispersion. Spectral colorimeters generally use prisms, gratings, interference filters, adjustable or discontinuous series of monochromatic light sources to achieve spectral separation. Then, based on the principle of dispersion, single color information is analyzed to achieve color digitization.

（ λ） Multiply the three excitation values of the CIE spectrum separately, and integrate these products separately over the entire visible spectrum range.  According to the standard colorimetry system specified by the International Commission on Illumination CIE, the calculation method of the color triple excitation value is the color stimulus function

This formula is the main basis for color detection in spectrophotometer, which can perfectly convert the measured color brightness, brightness, and chromaticity information into different color information, ultimately achieving the measurement of whiteness, chromaticity, and color difference.

（ λ） It can be represented as equal to three different objects being tested. Å Among them
（ λ）= S（ λ）—— Relative spectral power distribution of (self luminescent body) Å
（ λ）=β （ λ） S（ λ）—— The product of the reflectance factor of a reflecting object and the relative spectral power distribution of a standard illuminant. 
（ λ） S（ λ）—— The product of the transmittance factor of a transparent object and the relative spectral power distribution of a standard illuminating body Å（ λ）= 

At the beginning of the development of a spectrophotometer, R&D personnel generally consider configurations suitable for different industries, products, and measurement environments, including the selection of light sources (A, C, D65, D50, etc.), various color difference formulas for selection, and the ability to set tolerance ranges based on product qualification requirements, which can quickly detect product color differences and is suitable for color control in large-scale industrial production.

The working principle of a spectrophotometer:
The principle of grating spectroscopy is used for color measurement. A grating is an optical element that is engraved with a set of parallel periodic lines or grooves (often inclined) on a plane.

When a beam of compound light is incident on the grating plane, its periodic structure will undergo diffraction, and the transmitted or reflected diffraction light will also interfere. The energy of the light will be redistributed, and different wavelengths of light will travel in different directions, forming a specific wavelength superposition extremum at a certain position, thereby achieving light splitting.

Spectroscopic colorimeters can produce spectral curves, which are equivalent to a color’s ID card and are unique. Therefore, the color data read by the spectrophotometer is absolutely accurate.

At the beginning of the development of a spectrophotometer, R&D personnel generally consider configurations suitable for different industries, products, and measurement environments, including the selection of light sources (A, C, D65, D50, etc.), various color difference formulas for selection, and the ability to set tolerance ranges based on product qualification requirements, which can quickly detect product color differences and is suitable for color control in large-scale industrial production.

Characteristics of spectrophotometer:
We know that light is observed by the human eye in the form of electromagnetic waves, and different wavelengths of light present different colors to us on the spectrum. Red light has the longest wavelength and purple light has the shortest wavelength.

The others are arranged in order of red, orange, yellow, green, indigo, and purple. The spectrophotometer analyzes these lights using the rules of the spectrum.

Generally, a spectrophotometer has a composite sensor to measure the spectral reflectance of an object’s wavelength. A microprocessor is used to calculate the spectral reflectance data using the color difference calculation method equipped inside the spectrophotometer to calculate the third excitation value. With three excitation values, we can calculate the color information we need based on the different color space calculation formulas provided by CIE.

For a spectrophotometer, it not only has all the functions and features of a general color difference meter, but also has higher sensitivity. Because the spectral sensor measures light at various wavelength intervals, the color difference meter is generally between 0.01 and 0.02 Δ E * ab, which can be said to have very small error.

The measurement speed is much faster than a regular color difference instrument, which can measure both colors in about 0.3 seconds. This application in batch industrial production color detection can greatly improve the speed of color detection and production efficiency.

The spectrophotometer can display chromaticity information based on the internally set chromaticity space and calculation formula, and output it in digital form. In addition, spectrophotometer can also analyze potential spectral data information based on chromaticity data.

The spectrophotometer is designed for data comparison and simulation of visual chromaticity, and is also an important auxiliary tool for computer color matching, which can help major manufacturers complete the analysis, processing, and monitoring of spectral and chromaticity information perfectly.

The use of spectrophotometer involves a crucial data equation – the color tolerance equation, which is actually the tolerance range we usually refer to. In industrial batch production, there is a tolerance to control the product and qualification status, which is fast and reasonable.

The spectrophotometer wants to measure the color difference of the product and control it, which is the same as a regular color difference meter. Firstly, it needs to measure the information of the standard sample product, and then compare the color information of the measured sample to obtain color difference data.

In fact, color measurement and management are generally the same, except that the spectrophotometer has higher accuracy and more comprehensive functions.

Benchtop Spectrophotometer (Reflectance and Transmittance) DSCD-920 adopts 7 inches touch screen, full wavelength range, Android operate system. Illumination : reflectance D/8° and transmittance D/0°(UV included / UV excluded), high accuracy for color measurement, large storage memory, PC software, because of above advantages, it is used in laboratory for color analysis and communication.

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