Detector objects detect the spatial and angular distributions of light that lands upon them. Data is available in real radiometric and photometric units; including watts, lumens, lux, phot, footcandles, and others. Here for example is an LED illuminating a plane detector:
The most common detector type is the Detector Rectangle, which detects coherent or incoherent illumination on a rectangular surface. The Detector Volume allows the absorbed energy inside a volume object to be measured. Many objects can be used as a detector also.
Detectors may be set to absorb the light that lands upon them or not. In this example, the first detector is placed at the film plane of a condenser optic (and therefore shows a uniform intensity distribution). This detector is set to not perturb the light passing through it. The second (which shows an image of the source object) is set to terminate the ray trace.
Detector data can be read into the merit function for optimization, shown in the Detector Viewer, or copied out of Zemax for analysis in other codes such as Excel or MATLAB®.
Related Knowledge Base articles:
Understanding Sobol Sampling