Color Spectrophotometry: reading color through light

What is Color Spectrophotometry and what are its fundamentals

The basic principle is that every color can be described as a spectral distribution of the light reflected or transmitted by an object.

When a light source strikes a surface, part of the light is absorbed by the material and part is reflected or transmitted. The distribution of this light, measured wavelength by wavelength, constitutes the true chromatic identity of the sample.

Unlike chemical spectrophotometry, color spectrophotometry does not measure absorbance and does not determine concentrations.

The goal is not to identify the chemical composition of matter, but to describe color as it is perceived by the human eye.

Differences compared to Chemical Spectrophotometry

Unlike chemical spectrophotometry, in color spectrophotometry the absorbance (absorption of electromagnetic radiation for quantitative purposes) is not measured, and concentrations are not determined.

The goal is not to determine the chemical composition of a material, but to describe the color as perceived by the human eye, since this discipline is exclusively dedicated to the study of visible light and the description of color.

When Color Spectrophotometry is used

Color spectrophotometry is applied whenever it is necessary to measure, compare, or reproduce a color in an objective and reliable way, eliminating the subjectivity of human visual perception.

This technology is essential in several fields:

• Industrial quality control: it allows verification that products maintain consistent coloration across different batches, identifying even minimal color variations that the human eye may not immediately perceive.
• Color formulation and matching: it enables analysis of a target color and the development of the exact formula of pigments, colorants, or inks required to accurately reproduce it on different materials and substrates.
• Verification of color reproducibility: it ensures that color remains consistent over time and under different production conditions, guaranteeing uniformity between samples, prototypes, and final production.

The industries that rely most heavily on this technology include:

• the textile industry,
• automotive,
• cosmetics,
• food,
• paints and printing,

where color accuracy represents an essential quality requirement and often a key brand differentiator.

What Color Spectrophotometry measures and the instruments used

Color spectrophotometry measures the reflectance of opaque surfaces and the transmittance of transparent materials.

Measured parameters

• Reflectance: the percentage of light reflected by opaque surfaces at each wavelength of the visible spectrum. This measurement is fundamental for solid samples such as textiles, paints, plastics, paper, and cosmetic products.
• Transmittance: the percentage of light that passes through transparent or translucent materials, such as glass, plastic films, liquids, gels, and solutions. It allows characterization of both the color and the degree of transparency of the material.
• From these spectral measurements, standardized colorimetric coordinates (L*a*b*, XYZ, RGB) and color difference indices (ΔE) are derived, which are essential for quality control and unambiguous color communication.

Instruments used

Modern spectrophotometers make use of advanced illumination technologies:

• Multispectral LED: ensures stability, long lifespan, and instant switch-on, with reduced energy consumption
• Xenon lamps: provide a continuous and uniform spectrum that faithfully simulates daylight (D65 illuminant)

These instruments are designed to operate exclusively in the visible region (approximately 380–780 nm), corresponding to the sensitivity of the human eye.

There are different measurement geometry configurations (e.g. 45°/0°, d/8° with integrating sphere) to adapt to the specific characteristics of the analyzed materials, such as surface texture, gloss, or metallic effects.

How Color Spectrophotometry works

The instrument illuminates the sample and measures the returned light at each wavelength between 400 and 700 nanometers.

The result is a spectral curve that describes the chromatic behavior of the material.

In the coatings industry, reflectance data are often processed using the Kubelka–Munk model, expressed as the K/S function, to support color formulation systems.

The advantages in Professional Applications

Color spectrophotometry is an indispensable tool for numerous industrial sectors thanks to its ability to provide objective, repeatable, and standardized measurements.

Unlike visual evaluation, which is subject to individual variability and environmental conditions, this technology ensures extreme precision in color quantification, eliminating interpretative discrepancies between operators and production sites.

In the printing and packaging sector, for example, it enables brand consistency to be maintained across different print runs and substrates, while in the textile industry it ensures color uniformity between production batches separated in time and location.

The ability to create and manage digital color libraries greatly facilitates quality control, allowing rapid checks against reference standards and drastically reducing production waste caused by color deviations.

In addition, spectrophotometry significantly accelerates color formulation processes: what once required hours of manual trials can now be optimized in just a few minutes thanks to color matching algorithms that calculate the most efficient recipes.

From an economic perspective, investment in this technology results in substantial savings derived from:

• reduction of material waste,
• minimization of rework,
• optimization of product development time.

All of these factors make spectrophotometry not only a tool for technical precision, but also a strategic asset for business competitiveness.

Further information

Instrument calibration

Calibration is performed using a certified white tile and a black trap, ensuring repeatability and measurement reliability.

Difference between Colorimetry and Color Spectrophotometry

Traditional colorimetry uses filters and provides synthetic values, while color spectrophotometry analyzes the entire visible spectrum, delivering a more complete and accurate description of color.

FAQ

When was spectrophotometry applied to color measurement?

The application of spectrophotometry to color measurement developed during the 20th century, with the introduction of the first instruments capable of analyzing surface reflectance in the visible range.

What is transmittance in Color Spectrophotometry?

Transmittance represents the fraction of visible light that passes through a material and is fundamental for measuring the color of transparent or semi-transparent materials.

What is absorption spectrophotometry?

It is an analytical technique used in chemistry, but it is not applied to color measurement, which is instead based on reflectance or transmittance.

What is visible-range Color Spectrophotometry?

It is a technique that measures the behavior of light between 400 and 700 nm, the only region relevant for color perception.

Which principle is used in Color Spectrophotometry?

The measurement is based on the spectral distribution of light reflected or transmitted by the sample.

What is the K/S function used for?

The K/S function describes the optical behavior of pigments and forms the basis of color formulation systems.

What is Chemical Spectrophotometry?

It is an analytical technique for concentration determination, different from color spectrophotometry.

How is a Color Spectrophotometer calibrated?

Calibration is carried out using a certified white tile and a black trap.

How many reflectance points are required to draw a colorimetric curve?

It depends on the instrument resolution, which can acquire 8, 16, or up to 31 spectral points.