Color measurement is used to specify, quantify, communicate, formulate, and verify color quality for color critical work. Because everyone perceives color differently, color measurement is more precise than visual evaluation.
How to Measure Color Wavelength
To measure color, a color measurement device called a spectrophotometer shines light onto a sample and captures the amount of light that is transmitted or reflected in the 380 nm to 780 nm wavelength range, which is the wavelength range visible to the human eye. The spectrophotometer makes calculations based on spectral wavelength measurements across the wavelength range to quantify spectral data.
What is a Color Measurement Device?
There are two types of color measurement devices: colorimeters and spectrophotometers.
A colorimeter “sees” color like the human eye using three different types of color receptors that are used to mix red, green and blue to create the wide range of colors we can see. A colorimeter can determine a color’s location in color space by quantifying the tristimulus values of red, green, and blue (colorimetry).
A spectrophotometer offers more accurate color measurement by capturing color across the entire visible spectrum and filtering the light into very narrow bands of color. These bands pass up through the instrument’s optics and into a receiver where they are analyzed and recorded as the color’s unique reflectance curve (spectrophotometry).
Although a densitometer can read process colors—cyan, magenta, yellow and black, the CMYK of four-color printing—it measures density rather than color and is not considered a color measurement device.
What Kinds of Color Can be Measured?
Color measurement devices can capture and quantify color on just about anything, including liquids, plastics, paper, metal, and textured fabrics. The most popular color measurement geometry is the 0°:45° (pronounced zero forty-five) or 45°:0°, which excludes gloss from the measurement to most closely replicate how humans see color. A 0°:45° device can measure color on most flat, matte, smooth surfaces.
Another common geometry is the sphere, which can measure surface texture and include gloss as part of the measurement. It is ideal for formulating ink, pigment, and dye recipes.
Industries using special effects like pearlescent and metallic (such as cosmetics or the finish on cars that appear to change colors depending on your viewing angle) should use a multi-angle color measurement device to capture the way the color looks at different angles.
Who Measures Color?
Color measurement devices are used in many industries, including electronics, consumer goods, textiles and apparel, food, photography, paint, plastics, and even pharmaceuticals. Brand owners and designers use color measurement devices to specify and communicate color, and manufacturers use them to measure a target color and compare it with the color they produce to ensure it is correct. Manufacturers also use the spectral data from a color measurement device to evaluate the color of incoming raw materials, formulate colorants like dyes and inks, and ensure the color of parts manufactured at different locations match at assembly.
What is the History of Color Measurement?
Early 1700s: The Colors of Light
Isaac Newton used glass prisms to demonstrate that a beam of white light could be separated into the visible spectrum. His experiments with refracting and bending a light’s path to break it into individual components gave us a meaningful way to describe the range of colors we can see with ROY G. BIV – red, orange, yellow, green, blue, indigo and violet. This work also led us to understand and define standard illuminants like daylight (D50 and D65) and others.
1920's: Color Spaces
This graph shows the amount of red, green or blue light energy needed to match any color across the visible spectrum.
W. David Wright and John Guild did experiments to evaluate how much red, green, or blue light energy was necessary to see any color across the visible spectrum. Their work taught us that there is a link between color wavelengths in the visible spectrum and the colors the human eye can perceive. The Commission International de l’Eclairage (CIE) published Guild and Wright’s research as the 1931 RGB Color Space, which led to the CIE 1931 XYZ Color Space. Published around the same time as the CIE 1931 Color Space, the CIE chromaticity diagram was a 2-dimensional attempt to document colors on a graphic scale.
1940s: Color Measurement Tolerancing
David MacAdam was the first to look into how much color change it took for a standard observer to notice. From master (target) samples, he changed the hue, chroma (or saturation) and lightness until his observers noted a difference. He then plotted the results on the CIE chromaticity diagram and created the first tolerancing diagram. He discovered the distribution of matching points formed a three-dimensional ellipse, and the ellipsoids were different sizes depending on the position of the color in color space. This proved a color’s hue and saturation – known as chromaticity – are independent from brightness and form the basis of the CIE chromaticity diagram. 
These perceptibility limits around each color target show the amount of difference that is allowed before the human eye will notice.
Richard Hunter created a new tristimulus color model in the 1940’s. This color space, which he called Hunter Lab, uses three axes to represent near uniform spacing of perceived color difference. With this color model, Hunter developed a way to plot exact color coordinates in color space and characterize total color difference using Delta E.
Thirty-one years later, the CIE published an updated model – CIE L*a*b* – with only a few small changes to Hunter’s original math. Today it is the recommended method for reporting colorimetric values, and the math that is used by many of our color measurement instruments.
Tolerancing in CIE L*a*b*
