Colorimetry is the study of color, which is the response of the human eye to optical radiation in the wavelength range 0.38 to 0.83 microns. The color of any non-sequential source object can be defined in many ways:
If the wavelength spectrum of a source is known, it can be entered directly in the System Wavelength dialog (up to 24 data points) or via an ASCII text file (up to 100 data points). If the source spectrum is not known, then the color coordinates of the source can be entered using several common definitions, and Zemax will synthesize a spectrum of up to 100 wavelengths to produce this color. The fitted color coordinates are provided, along with an RGB equivalent of the fitted color:
Any number of sources, each with its own unique color can be defined. Rays are then traced using either the specified or synthesized spectra of each source, until they are detected by a Detector Color object which can provide either True Color (photometric) or False Color (radiometric) data as required by the user.
In this example, two LEDs are traced, one in the blue and the other in the yellow part of the spectrum (in real LED devices the two phosphors are in the same device, but we separate them here for clarity):
The top pair of LEDs show the yellow and blue radiation producing those colors in the detector. Note that rays can be optionally shown in their photometric color, and that is done here. The bottom pair of LEDs are tilted such that their beams overlap, and they mix to produce a white color:
Note that because the two beams do not overlap perfectly, you can see a blue tinge on one side of the white spot, and a yellow tinge on the other. Optimization operands allow each pixel's color to be analyzed and targeted in the merit function, so that you can optimize for a desired color. Chromaticity can be computed in the CIE tristimulus XYZ, xy, and u'v' color spaces.
Related Knowledge Base articles:
How to Model Colored and Tristimulus Sources
How to Measure and Optimize Color Data