Colorimetry
Colorimetry is the scientific technique used to measure and analyze the color of objects and substances. It involves understanding how light interacts with materials, leading to the perception of color by the human eye. The field has historical roots, with notable contributions from scientists such as Isaac Newton and James Clerk Maxwell, who explored the properties of color and established foundational principles. The development of the colorimeter, initially designed by Louis Jules Duboscq in the 19th century, revolutionized the ability to compare colors quantitatively.
Modern colorimeters utilize light-emitting diodes (LEDs) to assess how samples absorb or reflect light, enabling various applications in fields like chemistry, environmental science, and quality control. This technique can determine concentrations of substances, such as hemoglobin in blood or chemicals in water. Additionally, colorimetry plays a significant role in industries like food and pharmaceuticals, ensuring quality and consistency in products. Beyond practical applications, an understanding of colorimetry is valuable in photography and art, allowing creators to manipulate color to influence viewer perception and emotion. As a standardized system, colorimetry continues to be essential across diverse scientific and artistic disciplines.
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Colorimetry
Colorimetry is the scientific technique of measuring the color of an object or substance. It can also refer to the technique of determining something about an object or substance by its color. Studying an object's or substance's color can be accomplished with a tool known as a colorimeter. Another frequently used technique used is to compare the color of the object or substance to an established standard of colors as depicted in a format such as a chart or slide.
Background
What humans perceive as color is a visual interpretation of how an object interacts with light. Depending on its individual qualities, an object or substance will either emit or absorb light in varying degrees; the human eye and instruments calibrated to record these light emissions see this as colors. The amount of light available to be emitted or absorbed can affect this perception and thereby affect an object's color. This is why paint on a wall looks different when viewed in daylight than when seen by the light of a lamp.
Color intrigued scientists for centuries. Isaac Newton was conducting color experiments in 1666 and was the first to suggest that the color white is the result of an object reflecting all colors equally. Two centuries later, Scottish scientist James Clerk Maxwell conducted a number of experiments with color and demonstrated the differences that determine an object's hue, tint, and shade, all based on the wavelength and intensity of the light to which the object is reacting. As a result of this work, Maxwell is generally considered the father of colorimetry.
French instrument maker Louis Jules Duboscq designed the first known colorimeter that could compare the color of two liquids at the same time in 1854. His device used mirrors and prisms to reflect light through two test tubes, with one holding a control sample of liquid and one a sample to be compared to the control.
In 1931, the International Commission on Illumination, also known as the Commission Internationale de l'Eclairage, or CIE, established the system of colorimetry. This system mapped all visible colors by assigning each a specific x and y coordinate defining each color's hue and saturation and plotting them on a diagram. These two characteristics define chromaticity, or the quality of a color that is not dependent on the brightness of light; in the earlier example of wall paint seen by daylight or lamplight, a blue wall may appear brighter or more subdued in varying types of light, but the color is still recognizable as being a shade of blue. This is because its hue and saturation—its chromaticity—is not defined by the brightness of the room lighting. Despite being nearly a century old, this CIE standard chromaticity remains the best available standard and is used internationally.
Applications
The first colorimeters used mirrors and prisms to send light through samples for comparison. Contemporary models shine an electrically generated light from a light-emitting diode (LED) source through a sample. This sample will absorb and/or reflect a certain amount of this light. The light that passes through the sample, known as the transmittance, is collected by a photodiode that provides data on the transmittance to the unit's operator. By comparing this information to the standard color values for the substance being tested, the operator can determine the concentration of a solution, or how much of a given substance it contains. For example, a colorimeter can be used to test the level of hemoglobin in blood, to check for chemicals such as chlorine and iron in water, and to check soil to determine what nutrients might be needed.
Colorimetry is used in a wide variety of other scientific capacities as well. One familiar example is determining the acidity or alkalinity of a pool—its pH. By treating a sample of the water with a chemical that creates a color change with a known value when exposed to the substances in pool water and then comparing the resulting sample to a color chart that reflects those known values, an individual caring for a pool can tell what chemicals the water needs without knowing anything about chemistry. In much the same way, studying the color of the light emitted by planets, asteroids, moons, stars, and other celestial objects that are millions of miles away can help scientists determine the chemicals, minerals, gases, and other substances of which they are made. Comparing the colors of the faraway objects to the colors of known examples can help identify objects that cannot be touched or directly observed.
The ability to accurately assess colorimetry also plays a role in quality control in the pharmaceutical and food industries. The technique can be used to determine the quality of a batch of medications and to quickly and efficiently identify counterfeit medications, especially in situations where more advanced techniques are not available.
Food manufacturers also use colorimetry to provide quality controls. Appearance and color play key roles in determining food preferences and desirability. Manufacturers know that customers expect their products to have the same consistency and color of appearance each time they are purchased. These companies employ techniques for measuring colorimetry to ensure quality control standards for uniformity—and customer expectations—are met.
Photography is another field that frequently applies principles of colorimetry. A photographer who understands how light affects color can adjust the camera to take a photo that captures the effect he or she wants or even compensates for the presence or absence of extremes of light. Photographers and artists can also use an understanding of the effects of color to create artworks that will evoke a specific feeling or emotion from the viewer.
Bibliography
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"James Clerk Maxwell (1831-1879)." Weinberg College of Arts & Sciences. Northwestern University. Web. 8 Feb. 2016. http://faculty.wcas.northwestern.edu/~infocom/Ideas/maxwell.html
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"The Taste of Success: How Colorimetry Can Exploit the Brain's Perception of Food Quality." HunterLab. HunterLab Inc. 19 Sept. 2014. Web. 8 Feb. 2016. http://www.hunterlab.com/blog/color-food-industry/taste-success-colorimetry-can-exploit-brains-perception-food-quality/