How to Calculate Luminosity, Dominant Wavelength, and Excitation Purity
Turan Erdogan, Ph.D.
There are many different systems for analyzing and representing the color of an object perceived by a human observer. For the purposes of unambiguously specifying the color an observer sees when looking through an optical filter at a well-defined light source, we have found the CIE Color Specification System to be the most accurate (for a simple and clear description, see ). In this article we briefly describe the method to calculate the three main parameters that fully specify color in this system: luminosity, dominant wavelength, and excitation purity. These terms specifically refer to the definitions in the CIE system given below, but they have analogies in many other systems. A set of more general terms often used to qualitatively describe color are: brightness, hue, and saturation (analogous to luminosity, dominant wavelength, and excitation purity, respectively). These terms (and others) are often used interchangeably. Here we will adhere to the official terms assigned to the CIE system to avoid any ambiguity...
Download the Whitepaper