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Spectrophotometers empower manufacturers across numerous industries to capture accurate color and spectral data. These measurements support regulatory compliance, conformance with industry standards, and quality assurance that keeps customer satisfaction and loyalty high. Modern solutions offer measurement through either transmission or reflectance optical configurations.

Learning more about these approaches, their ideal substrates and applications, and their differences will guide you to the best solution for your color measurement needs.

Understanding Color Measurement

Light is the foundation of color measurement, with its wavelengths in the visible spectrum ranging from violet at 380 nanometers to red at 780 nanometers. The energy a light source provides varies across the spectrum depending on the light source. When it encounters matter, its wavelengths are either reflected, absorbed, refracted, transmitted, scattered, or diffracted. The object's chemical makeup helps determine what photons it will absorb versus those it emits or transmits. These emitted or transmitted wavelengths then enter the human eye, stimulating its photoreceptors. Emitted or transmitted wavelengths are the colors our eyes ‘see’ depending on where the energy falls within the visible spectrum.

Color perceptions vary between humans, making visual comparisons unreliable and underscoring the need for scientific color measurement solutions. Spectrophotometers simplify the task by analyzing and quantifying color in widely accepted color spaces like CIELAB and CIE XYZ. Transmission and reflectance are the two primary configurations spectrophotometers use to capture and report color and spectral data.

Color Measurement Through Transmission

When spectrophotometers measure color by transmission, they pass light directly through the sample. An optical sensor on the opposite side of the sample collects the energy for analysis and reporting.

The Science Behind Transmission Measurement

Measuring wavelengths through the transmission of color quantifies them into a ratio called transmittance. In scientific terms, transmittance is the percentage of incoming light that passes through a sample. The sample will also absorb a certain amount of the energy, requiring precise calculations using the Beer-Lambert Law, which describes how light is absorbed when it passes through matter.

Transmission measurements typically need at least 30% of the source light to pass through the sample with the light source at a perpendicular angle.

Key Considerations for Choosing Transmissive vs. Reflective Measurement

Transmission measurements work for transparent to translucent materials that allow 30% or more of the light to pass through — even if the surface is textured, like etched glass.

Opaque samples, which don’t let enough light through, are better measured using reflectance.

Applications for Transmission Color Measurement

Common applications for transmission color measurement include quantifying color in:

• Foods and beverages: Products ranging from edible oils to fruit juices and food dyes are compatible with transmittance measurement.
• Plastics: This approach is widely used in the plastics industry for food and beverage containers, transparent sheets and film, eyeglass lenses, and medical equipment like syringes, IV bags, and other clear medical devices.
• Chemicals: Use this method to quantify color in motor oils, lubricants, and petrochemicals.
• Pharmaceuticals: Injectable solutions and liquid medicines to monitor purity and detect any unwanted color changes.

Transmittance is also the most reliable color measurement approach for everyday products like clear liquid detergents and ophthalmic lense

If you work in the biopharmaceutical industry, you’re likely familiar with the concept of light and color measurement and the equipment used in these processes — radiometers, spectrometers, spectroradiometers, and spectrophotometers. While all four solutions are used to detect light and energy, they vary widely in their capabilities, applications, and intended purposes. It’s important to know and understand the differences between these solutions to determine which one will adequately serve your needs.

Radiometer vs. Spectrometer vs. Spectroradiometer vs. Spectrophotometer

These devices have similar names and are used to measure spectral data points and wavelengths within the electromagnetic spectrum. Despite this similarity, they have varying scopes regarding the types and qualities of measurements they produce.

Radiometers can only detect and measure electromagnetic radiation within a particular wavelength range. Spectrometers measure a broader scale of electromagnetic energy and have more capabilities, including breaking down signals based on amplitude.

In comparing spectroradiometers vs. spectrometers, the main difference is that spectroradiometers combine the capabilities of radiometers and spectrometers. These devices also collect details about power, radiance, and other metrics.

Spectrophotometers measure light reflected or transmitted by objects, while radiometers measure light emitted by a light source. Unlike the other tools, spectrophotometers focus on how transmitted and reflected light generates color rather than on the qualities of the light itself.

What Is a Radiometer?

A radiometer measures the electromagnetic energy present in a specific wavelength range. This solution is typically used to detect and quantify energy outside the visible light spectrum and measure infrared and ultraviolet light. The radiometer begins by measuring the incoming current or voltage in watts, then corrects the signal to create a calibrated, quantitative light level measurement. With this information, the meter provides one reading over the specific wavelength range it is designed to measure.

Pros and Cons of Radiometers

Radiometers are inexpensive and portable, making them a cost-effective and practical choice. This solution can identify troublesome UV energy and detect and measure heat energy on surfaces. It also has one sensor that allows it to quickly measure all intended wavelengths.

However, radiometers cannot identify emitted wavelengths or their individual amplitude. Sometimes, variations exist in the filter used to match the light source, which creates difficulty when comparing results from radiometers of different manufacturers. Also, radiometers only measure a particular range of wavelengths, unlike other tools. 

Applications

Radiometers' ability to detect the presence of UV energy makes them valuable tools for any application where it is undesirable, such as museum lighting. In this atmosphere, UV energy could degrade artifacts or artwork.

The device also measures infrared light, enabling surface temperature measurements in settings such as along an assembly line or on a road's surface. Other applications include monitoring weather, like precipitation and wind speeds.

Tomatoes are essential in meeting global nutritional needs, improving health, and generating economic impact for communities worldwide. Billions depend on this crop — the second most grown vegetable on Earth — for better physical well-being and financial gain. As a result, color is a critical factor in quality control for tomato manufacturing.

The Role of Color in Tomato Quality Control

Tomato color influences customer preference, quality perceptions, grading classifications, and market value.

Meeting Consumer Preferences

Assessing color is one of the primary ways consumers make buying decisions. They see a tomato with a rich, red hue as a promise that it was harvested at the peak of freshness and flavor. Unripe ones and heirloom green varietals hint at a delightfully tart taste, perfect for a favorite Southern dish. Similar color associations exist for tomato-based products, such as tomato paste and sauce.

Beyond taste, tomatoes are prized for their nutraceutical content — they're high in several vitamins and minerals, antioxidants, and fiber that offer physical benefits. The more their color meets or exceeds customer expectations, the higher the consumer perceptions of the product's safety and quality. Increased confidence in those traits directly translates into a rise in purchase likelihood.

Conforming With Standards

Modern tomato processing facilities are covered entities under Title 21 of the Code of Federal Regulations, which subjects them to oversight by the Food and Drug Administration and the United States Department of Agriculture (USDA). As a result, they must follow Current Good Manufacturing Practices, which include measuring color as part of quality assurance. The USDA sets color tolerances for tomatoes to help determine their grade, meaning quantifying color is essential for proper classification.

Those operating under voluntary frameworks may also need to evaluate color for conformance with the guidelines. For example, the Safe Quality Food standards specify color analysis as a vital quality assurance measure under several codes.

Leveraging Financial Potential

Businesses that thrive often do so by maximizing their profitability, and color quality is a key driver in that quest. Generating high consumer quality perceptions through color can help goods fetch premium prices, as buyers with increased product confidence are frequently willing to pay more for extra peace of mind.

For companies seeking to expand, color quality becomes even more essential. Tomatoes and tomato-based products must meet specific standards to access new markets that can help spur organizational growth.

For example, the EU has multiple standards that apply to imported tomatoes and tomato-based products. These help establish the minimum grades acceptable for sale within the bloc, and color is a primary determinant in that classification. Individual EU countries may also impose their own standards for the crop and its processed goods. Accurately quantifying color to prove conformance with the standards makes it easier to access these high-value markets.

In preparation for holiday cooking, I decided now was a good time to organize my spices, and I have to admit that my spice cabinet was a bit of a disaster. I quickly realized that the task was long overdue as I began to compare my duplicates (and yes, even triplicates) to decipher which to keep and which to throw out.

As I was sorting, I noticed a direct correlation between spice color and my perception of freshness and decided to investigate what color control really means to the quality of spices. The truth is that color control is a primary factor in quality analysis, which is used during the production of spices around the world. Process monitoring of color control is highly dependent on the use of spectrophotometers to ensure the quality and safety of spice products.

The Yellowness Index from ASTM International provides a measurable standard for assessing the yellowness in white or light-colored materials, such as plastics. This standard determines the degree of yellowness present, allowing companies to perform quality control processes to maintain product consistency. The test uses a spectrophotometer to quantify the color measurement.

The APHA color system is the most common measurement scale for measuring yellowness in liquids. It serves industries ranging from chemical production to pharmaceutical development.

Materials That Require Yellowness Observations

Various plastics require yellowness observations due to the changes these materials undergo in processing. These plastics include:

• Polyvinyl chloride (PVC)
• Polycarbonate (PC)
• Purified terephthalic acid (PTA)
• Polyethylene terephthalate (PET)

Yellowness appears in PET due to oxidation. With the increasing use of recycled PET (rPET), manufacturers must measure color to counter yellowness and determine the correct ratio of optical brighteners required to mitigate it.

What Is the Yellowness Index?

The Yellowness Index (YI) measures yellowness due to product changes. The ASTM E313 Yellowness Index is the most common method for determining yellowness in materials like plastics. The standard gives defined indices for measuring the shift from ideal white. It is calculated according to the following formula:

YI = (100CxX - CzZ)/Y

The X, Y, and Z variables are CIE Tristimulus values, which express color and how it is perceived. Cx and Cz depend on the illuminant and observer. During calculations, users choose the values for these coefficients from a table to correspond with spectrophotometer settings. The ASTM E313 combines the calculations into a single value, defining the yellowness amount in a sample. The lower the number, the less yellow the material is.

The YI value is commonly reported as the difference in yellowness between a product sample and the original or reference, designated as delta YI (∆YI).

Color measurement is a precise science requiring an objective, practical, and effective approach. Accurate data and consistency improve customer satisfaction and product quality across industries ranging from food to plastics. When you know the most common mistakes made in taking accurate measurements, you can proactively prevent or avoid them and capture data you can have confidence in.

1. Relying on Subjective Descriptions and Visual Assessment

People perceive color differently, so subjective descriptions like “navy blue” can't accurately quantify it. In contrast, measuring according to the CIELAB color scale might give you a value of L*= 15, a*= -6, b*= -25, so you'll have an exact number to compare. 

Visual assessment leads to color measurement problems due to a lack of optical memory and physiological dysfunctions that influence perception. Even trained eyes with superior detection ability can become fatigued, compromising accuracy. 

2. Not Using a Software Program

A software solution simplifies measurement collection and comparison, making it a powerful tool for enhancing spectral data analysis.

3. Not Considering Environmental Factors

Metamerism describes the phenomenon where two colors match under one light but not another, which creates issues with color consistency. A spectrophotometer, which contains a standard light source, combats this phenomenon. Other environmental factors that can influence color include temperature and humidity, which alter the way a material interacts with the wavelengths. Controlling these within your facility can help promote more accurate measurements.

Color plays a vital role across diverse industries, from the foods we love to eat to the vinyl siding we put on our homes and the chemicals we rely on for equipment power and performance. Objectively and scientifically measuring color is a cornerstone of quality that offers manufacturers several benefits.

Color Measurement Promotes Higher Customer Satisfaction

Measuring color quality helps promote higher satisfaction by ensuring the products meet customer expectations. One of the first ways consumers judge a brand and its quality is through color. Your goods' appearance can evoke emotions and indicate superior freshness, flavor, nutrition, purity, or safety — all of which are influential in buying decisions. Manufacturers whose goods remain consistent in appearance generate higher customer satisfaction, leading to increased brand loyalty and repeat purchases.