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Fifty Shades of Color Measurement in a Laboratory Setting

          Colorimetry, the science of color measurement is regularly used in commerce, industry, and the laboratory to express color in numerical terms, as well as to measure color differences between specimens. Applications include petroleum, paints, inks, plastics, textiles and apparel, food and beverages, pharmaceuticals and cosmetics, displays, and other parts and products that reflect or transmit color.

          The prevalence and relevance of colorimetry has increased in tandem with the rise of global manufacturing and processing. This means that it is necessary to rely on more than the dubious discernment of the human eye since human color perception is extremely variable and subjective, and is affected by factors such as illumination, sample size, surrounding color, and the angle of observation. Therefore, colorimetric instruments provide a set of standardized conditions which assist in assuring consistency and repeatability: Which are two gold standards of empirical experimentation.

          The term colorimetry is often used in a general sense to mean color measurement; however, it should be noted that, it differs from spectrophotometry, a related but separate color measurement methodology. In colorimetry, the quantification of color is based on the three-component theory of color vision, which posits that the human eye possesses receptors for three primary colors: red green and blue, and that all colors visible are combinations of these primaries. In colorimetry, these components are referred to as X-Y-Z coordinates. Colorimeters, based on this theory of color perception, utilized three photocells as receptors to see color in a similar vein to the way the human eye can.

          Conversely, spectrophotometry, uses many more sensors (40 or more in some spectrophotometers) to separate a beam of reflected or transmitted light into the component wavelengths. It measures the spectral reflectance of an object of each wavelength on the visible spectrum continuum. Spectrophotometry provides superb accuracy and is typically used in research and color formulation applications. Colorimeters are generally used in production and quality control applications.

          A colorimeter is comprised of a light source, fixed-geometry viewing optics, three photocells matched to an intentionally established standard observer, and an on-board processor or cable connection to a processor/display unit or computer. In practice, the sensor lens of the colorimeter typically is placed directly over the specimen to be measured, from a piece of dyed cloth or a colored plastic chip, for example. For liquid or colored-film specimens, where transmitted light needs to be measured, the sample is placed in a transmittance compartment of the instrument or, alternately, in a designated specimen holder. Next, an operator activates the light source that is reflected from the specimen and passed through the three photocells, which determine the red, green and blue components and transmit the data to the microcomputer. The microcomputer then calculates the X-Y-Z values and captures the data, which are then printed or displayed.

          Hue is the term used for general classification of color, the region of the visible spectrum (380 to 700 mm) in which the greatest reflectance of light occurs. Hues perceived as blue tend to reflect light at the lower end of the spectrum, greens in the middle region and reds toward the higher end. While lightness and darkness can be measured independently of a hue, for instance, the lightness of a lemon can be compared with the lightness of an apple. Saturation describes the vividness or dullness of a perceived color and, like lightness, can be measured independently of hue.

          A variety of colorimeters are available today for production color sampling, section, and color quality control. Many are portable, battery-operated devices that allow objective color measurement on the production floor or at remote locations. They feature a range of apertures and illumination/viewing geometries for specific applications, various levels of data processing abilities and various accessories.

          Colorimeters in microscopic configurations are used for precise measurements of small objects such as pills and drug reagents. Noncontact colorimeters provide online color measurement of textiles, paper, and coated coils on production lines. Small palm-top instruments have even been designed for very specific applications such as contrast measurements of fried, baked or processed foods.

          Careful monitoring of the consistency of color in production and processing operations, business and industry have significantly reduced the cost of waste and product rejection while improving efficiency and productivity in their operations.

          Color is a primary indicator of quality in petroleum-based products and developing a color range is a crucial part of the refinement process. A color range can often be used for monitoring contamination and quality control. Petroleum-based products make up a large part of manufactured goods, with consumers often depending on color acceptability; therefore, it is imperative to meet quality standards of color perception.

          There exists an array of test methods available for determining the color of refined oils and these are necessary for addressing the use of petroleum within a myriad of applications. From fuel sources to pharmaceuticals, analyzing color plays a crucial part in developing products that are high in quality and safe for use. Spectrophotometric determination and quantification of color is routinely employed for developing color range measurements necessary for monitoring variations in processing and meeting or exceeding standardization requirements.