In addition to being able to see the True Color representation of a single wavelength propagated through an optical system, the Detector Color object can of course be used to view the True Color representation of a range of wavelengths as they hit the detector. Thus, this object can be used to see how colors would “mix” as they hit the detector.

A nice example of this is provided in the file “LED 2-color mixing gives white.ZMX”. The archive (.ZAR) file for this example is located on the last page of this article. In this example, two monochromatic sources are mixed together to form a white color. Each source is also shown individually, so that the color for each source can also be seen separately. CAD representations of the source holders are also included in this file, to provide a more realistic image of the system:



The top two sources are not mixed together, so that we may see the yellow and blue colors separately on the Detector Color object. The wavelengths used to define the yellow and blue colors are 0.57 and 0.46 microns, respectively (Tristimulus sources could have also been used to define the color of each source, as described in the article “How to Model Colored and Tristimulus Sources”):



The orientation of each of the bottom two sources is tilted so that the colors will mix together. If 1 million rays are traced from each source, we find:



At the top of the detector, each individual color can be seen separately. On the bottom of the detector, we see that the individual colors have mixed together over some region to form the color white. If we zoom in on the results, the region of overlap may be observed, as well as the regions where light from the two sources does not overlap:



It may be counterintuitive to see only two monochromatic colors mixing together to form white (generally, we think that three colors are needed to form white). However, remember that the Detector Color object shows the True Color representation of the image, which also accounts for the response of the human eye to color. When the human eye (photopic) response is accounted for, we find that there are indeed two monochromatic colors which can mix together to form what the human eye perceives to be white.

Color mixing can also be seen in the radiant intensity distribution:



However, in this case the observed colors correspond to mixing of different sources. The sources at the bottom of the system – which mixed together in Position Space – are tilted at different angles (+/- 25 degrees), so in Angle Space the light from these sources lands on different pixels on the detector. Thus, in this case the two sources at the bottom of the system provide the distinct yellow and blue spots seen in the above image. Conversely, the sources at the top of the system – which did not mix together in Position Space – are both oriented at the same angle (0 degrees), and thus the light from these sources land on the same pixels in Angle Space. In this case, the two sources at the top of the system mix together, providing the white color seen in the center of the image (centered at zero degrees in Angle Space).