Geometry errors may be an indication of a serious flaw in your setup, leading to erroneous ray tracing results.  Thus, it is very important to be able to determine where the error is occurring. 

However, it is also important to note that some perfectly good systems occasionally have a few rays fail.  This is primarily due to the fact that these rays are incident upon boundaries between facets or surfaces…and accurate intercept points are not possible to compute.  These rays are generally “trapped” internally by ZEMAX, and are absorbed or terminated.  For the most part, the amount of “lost energy” associated with these rays is small relative to the total power of all sources defined in the design.  Therefore, these rays can be safely ignored, as they do not have much significance in the final system results.

So how can you determine the proportion of energy which is lost due to errored rays? 

Once a ray trace is complete, ZEMAX will report the lost energy due to thresholds as well as the lost energy due to errors.



This value is reported in absolute units (Watts, for example).  If the value of the lost energy is significant, further investigation is required.  If the lost energy is extremely small, then chances are just a few rays cannot be traced, and these can be ignored.  If the lost energy is small enough to be negligible or if it is zero, then you may proceed with your design in confidence that the ray trace results are correct!