To locate the cause of the errors, turn Ignore Errors OFF and update the system by pressing Ctrl+Shift+U.

Take note of the information in the dialog, close all error message windows by pressing “No.”  Turn Ignore Errors back ON.  This particular ray failure originated from Source Object 13, which is the Source Volume representing the source of the upper LED.  In addition, the error occurred at object number 11.  Object 11 represents the LED body the upper LED.

Zoom up on the region where Source Volume 13 is located, to see if anything looks suspicious.  It is very obvious that the Source Volume is straddling the boundary of a volume object, which is an unsatisfactory condition.  All rays emanating from a specific source must emanate from inside the same volume; no two rays from a single source can initially start inside of different volume objects.

The Source Volume object should be touching the contact wires (Objects 16 and 19).  Change the Z Position of the Source Volume 13 to 1.6 so that it no longer straddles the boundaries of the die and instead sits in contact with the contact wires.

In addition to this, it is important to note that the geometry errors will not be solved at this point.  The upper LED emitter source object is inside the LED body, and needs to be indicated as such.  The upper LED body is described by Object 11.  Change the “Inside Of” flag in the NSC Editor to 11 for the Source Volume 13.

Re-run the Monte Carlo Ray Trace.  The chances of experiencing a geometry error have been greatly reduced.  And, as you can see, the lost energy has been reduced by many orders of magnitude.  Take note that the lost energy is so small, that it can be neglected altogether, and the results at the Detector Viewer can be evaluated with great certainty.

It is important to note that geometry errors may indicate a serious flaw in the system being traced. However, some perfectly good systems occasionally have a few rays fail. This is primarily due to the fact that these rays are incident exactly upon boundaries between facets or surface 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 the sources defined in the design. Therefore, these rays can be safely ignored, as they do not have much significance in the final system results.