A well-known, if extremely rough, convention in the world of color measurement says that in CIEL*a*b* or CIEL*C*h space, a dE* value of less than one indicates that two colors are visually indistinguishable to the human eye. The reality is far more complex than this. The limits of visual perception actually differ depending upon which portion of color space is being discussed.
Color instruments and software packages all contain references to CIE standard illuminants and observers. What do these terms mean and how are they used in practical color evaluations? The CIE (from the French Commission Internationale de L’Eclairage), or International Commission on Illumination, is the worldwide authority on how we see and measure color. BYK-Gardner uses many of these standards in its instruments and available software packages. This paper will give some easy to understand explanations of these standards and how they should be used.