Color is an important aspect of coatings, and the color of a coating needs to match the desired specification. There are several ways to measure color, but one of the most common methods is the CIELAB color scale. The CIELAB color scale is a three-dimensional color model that was developed by the International Commission on Illumination (CIE) in 1976. It is based on the tristimulus values of a color, which are the amounts of red, green, and blue light needed to produce that color. The CIELAB color scale measures color based on three values: L*, a*, and b*.
L* represents lightness, or how bright or dark a color is. The value ranges from 0 (black) to 100 (white). A* represents the red-green axis, with negative values representing green and positive values representing red. B* represents the blue-yellow axis, with negative values representing blue and positive values representing yellow. The values of a* and b* range from -128 to +128. To measure the color of a coating using the CIELAB color scale, a spectrophotometer is used. A spectrophotometer is a device that measures the reflectance or transmittance of light at different wavelengths. When measuring the color of a coating, the spectrophotometer is set up to measure the color at a specific angle and with a specific light source. A spectrophotometer measures the reflectance or transmittance of light at different wavelengths and converts the data into tristimulus values. These values are then converted into L*, a*, and b* values using a mathematical formula. The resulting L*, a*, and b* values are then used to plot the color of the coating in three-dimensional space on the CIELAB color scale.
Interpreting CIELAB Color Measurements
When interpreting CIELAB color measurements, it's important to keep in mind that small differences in L*, a*, and b* values can be difficult to discern with the naked eye.
Of course, even small differences in color can be significant, depending on the application. The CIELAB color scale is designed to simplify calculation of color differences between two coatings. The color difference, or Delta E (ΔE), is calculated by taking the square root of the sum of the squares of the differences between the L*, a*, and b* values of two coatings. This means that if you picture two colors, each with their L*a*b* values averaged and plotted on a three dimensional graph, the ΔE would be the difference between the two points. A ΔE value of 1.5 or less is generally considered to be imperceptible to the human eye, while a ΔE value of 3 or less is considered acceptable in most industries. In short, the CIELAB color scale is a standardized method for measuring color that is widely used across coatings. It allows for accurate and precise measurements of coating color, which is critical for ensuring consistency and meeting specific color standards. Where small differences in color can be subjective and difficult to discern with the naked eye, the CIELAB color scale allows objective measurement of color differences, useful for identifying color variations and ensuring consistency. It's an important part of coatings, and a tool Ultra Metal Finishing uses to ensure our parts meet our customers' specifications every day.