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. As described in the article entitled “How to Model Colored and Tristimulus Sources”, a polychromatic source may be defined in ZEMAX 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.  In this article, we’ll provide a brief overview of the Detector Color object and its associated merit function operand NSDE.