Spectrometers or spectrophotometers are valuable tools companies use to ensure the quality and consistency of the products they make and sell. They can tell us if the oil is contaminated or if the fruit is ripe. They ensure that your favorite tomato ketchup is the same red, batch to batch. They provide the safety and efficacy of the medications you take. They are a valuable tool to ensure corporate brand integrity and that consistency and performance remain intact across an entire warehouse of products. To understand how spectrophotometers work, we need to comprehend the science of spectrophotometry.

Spectrophotometry is the science of how light interacts with matter. The objects we see daily are different forms of matter – solids, liquids, and gases. You may be surprised to learn that matter does not possess color. An apple appears red because of how light interacts with the chemical composition of the apple. When light strikes matter, some wavelengths are absorbed, and some are emitted. We see and perceive the emitted light as ‘color.’

Spectrophotometers mimic this visual observing condition, providing information about the color of materials that is meaningful and actionable, allowing companies to ensure color accuracy and consistency across their range of products and brand colors.

So, how does all this happen from a spectrophotometer, and how do we use it? The science behind this tool is robust and can be utilized in several different ways. To clarify, we’ve gathered information on how spectrophotometers contribute to the color management of various products and technologies, so let’s dive in.

What Is a Spectrophotometer?


You may remember from chemistry class that light is a form of electromagnetic radiation, like microwaves and gamma rays. When we talk about the spectrum of light, we’re talking about a spectrum of energy, where different energy levels create what we perceive as other colors. The colors of the rainbow follow the progression of visible energy, with red being the lowest and violet being the highest. Materials that absorb all visible light appear black, while those that do the opposite appear white. In between those two are materials that emit certain light energies and absorb others, displaying specific colors.

A spectrophotometer is essentially a calibrated light counter.

“Spectro” refers to the fact that light is dispersed into individual wavelengths in the electromagnetic energy spectrum. Some of that energy is in the ultraviolet and visible spectrum, which spectrophotometers can read, while other spectrometers can measure infrared radiation.

“Photometer” measures light intensity at specific wavelengths and is scaled from 0 to 100. Zero equals total darkness, and 100 is perfect white. Some properties, like fluorescence, make it possible for this scale to go over 100, so most spectrophotometers can reach 150 or 200.

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Spectrophotometers are used to measure the color of materials. Materials can be solid, liquid, opaque, translucent, or transparent. Different methods are used to measure these materials, depending on their form and transparency. Opaque materials are measured using reflectance spectrophotometers, which measure the amount of light reflected from a sample. In contrast, transparent materials use transmission spectrophotometers, which measure the amount of light that passes through the material. Regardless of the method used, all spectrophotometers share the same basic technology and optical design:

  • A controlled light source to illuminate the material.
  • A lens to collimate the light to the monochromator.
  • A monochromator that separates the light into its constituent color wavelengths.
  • A wavelength selector.
  • A detector that quantifies the light emitted from the sample.
  • A display that provides results.
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How Does a Spectrophotometer Work?

The process begins with a controlled light source that illuminates the analyzed sample. In the case of reflection, as this light interacts with the sample, some is absorbed or emitted. The emitted light travels to the detector , which is analyzed, quantified, and presented as industry-standard color scales and indices. Commonly used color scales include Hunter L,a,b, CIELAB, L,C,h, and dE Color Difference. Industry governing bodies typically define specific metrics for specific products, such as Tomato and Coffee indices. The simplified math looks like this:

Where R is the reflection coefficient. All terms are evaluated over the visible spectrum from 400 to 700 nm.

In the case of transmission, when the light interacts with the sample, it is either absorbed, reflected, or transmitted. The transmitted light is algorithmically changed into relevant color scales and indexes. Examples include APHA (American Public Health Association) for watercolor and purity analysis, ASTM D1500 for petrochemical color analysis, edible oil indices used in food, and color analyses of beverages. The simplified math looks like this: . . Where T is the transmission coefficient. All terms are evaluated over the visible spectrum from 400 to 700 nm.

The software displays the color analysis results as spectral data, spectral curves, or color plots.

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Spectrophotometer Geometry

Spectrophotometer geometry defines the arrangement of the light source, the sample plane, and the detector. Choosing the correct geometry depends on your intended application:

Diffuse (sphere) geometry

Uses a white coated sphere to diffusely illuminate the sample with 8° (d/8°) Specular viewing. A diffuse sphere instrument can measure with the specular included or excluded.

  • Specular Included measurements negate surface differences and provide values corresponding to color changes.
  • Specular Excluded measurements negate specular reflectance on smooth surfaces, measuring only diffuse reflectance.

This geometry is ideal for applications like color formulation of coatings, inks, and dies applied to various mediums like textiles, automotive coatings, and print media, where it is essential to remove the effects of surface appearance (texture and gloss) on the measured color and look exclusively at color changes.


Directional Geometry

Directional 45°/0° geometry has illumination at a 45° angle and measurement at 0°. The inverse 0°/45° geometry has illumination at 0° and measurement at 45°. For most applications, these two geometries are considered synonymous.

Both exclude the specular reflection in the measurement (specular excluded). This provides measurements that correspond to visual changes in sample appearance due to either changes in pigment color or surface texture and more closely match how the human eye ‘sees’ color. These geometries are best used for end-of-line color quality control.

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Multi-Angle Spectrophotometer

This spectrophotometer views a sample's color at multiple angles. It measures special effect pigments that change color depending on the viewing and illumination angles, commonly used in automotive coatings and cosmetic products like nail polish.

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What Is a Spectrophotometer Used For?

Spectrophotometers have more uses than you may think. Research, product development, quality control, and diagnoses can all benefit from a spectrophotometer’s data. Here are a few specific examples of how these powerful tools are used:

  • Beverages: Color can indicate quality in many beverages, from soft drinks and juices to spirits and beer, and consistent color is critical to inspire confidence in customers.
  • Pharmaceuticals: The color of a pill is an integral part of identification. It may not affect its functioning, but it tells people what they use. Other pharmaceutical products, like liquid ingredients, have strict standards, some of which involve color and transparency. Spectrophotometry helps ensure brand colors and identify counterfeit medications.
  • Building products: If a contractor builds a house with mismatched pieces of vinyl siding, the client isn’t likely to be happy with the results. When appearance is involved, color is critical. Many materials also reflect property changes in their color. Anodized metal, for instance, uses a layer of natural oxide to increase its resistance and adhesive properties. Color analysis can confirm that each piece produced reflects these improvements.
  • Chemicals: Chemicals must be clean, consistent in color, and free of contaminants to ensure proper functionality and that your customer trusts them. Color is vital in classifying many chemical products and identifying their composition.
  • Food: Food production uses spectrophotometry in many ways. From evaluating the ripeness of fruits to identifying the appropriate baking contrast of bread and buns, color analysis lends itself to plenty of food-based applications.

These are just a few examples, but spectrophotometers can be found in various industries and applications, including uses outside production, like vital biological research. Other applications include marketing for brands that must find the most appealing colors for their audiences or improve consistency across materials.

Common Categories of Spectrophotometers

Aside from color measurements, spectrophotometers are available in different shapes and sizes to suit your operation's needs. Some common spectrophotometer categories include:

Benchtop Spectrophotometers

Benchtop spectrophotometers are ideal for laboratory-based operations. No-contact directional geometry offers a unique measurement method that avoids contact with your samples, reducing sample preparation and cleanup time. Benchtop options provide the highest levels of precision and control.

Portable Spectrophotometers

Portable spectrophotometers can measure samples anywhere, from storage areas to the production floor. They are robust enough to carry with you and comfortable to use whenever you need them. With state-of-the-art software, portable models can process, monitor, analyze, and report results.

In-Line Spectrophotometers

An in-line or in-process spectrophotometer is installed within your process to deliver constant color measurement data throughout a production run. As your product goes through production, in-line models provide real-time continuous color data and notify operators of color drift that can be corrected before a failure occurs.

Request a Spectrophotometer Quote From HunterLab

HunterLab spectrophotometers can boost product appearance and consistency, improving customer perceptions and building trust in your brand. They can also streamline your production processes, helping you consistently deliver quality products.

HunterLab has delivered quality color measurement and testing solutions for over 70 years. We carry a range of spectrophotometers for samples of all sizes and varieties. Contact the professionals at HunterLab today to learn how our spectrophotometers can support your work!