A number of optical systems (e.g. digital displays and projection systems) require knowledge of the photometric (human eye) response of the system to a broadband source. In ZEMAX, a polychromatic source may be defined either by using multiple system wavelengths or by defining the Tristimulus (or associated) values for the source. The resultant color distribution of the output image may be visualized using the Detector Color object, as described in the article entitled “How to Measure and Optimize Color Data”. A brief overview of the various source models available in non-sequential mode is provided in this article.