Some time ago we were approached with a plastic LED lightpipe assembly designed by someone else that didn't work as anticipated. Unfortunately, a great deal of hardware was already designed around it. The task was to fix the problem by redesigning the lightpipe using the same space allocation and the same LED. No CAD drawings were available - only paper drawings. Despite this, within hours we were able to model the optical behavior of the lightpipe.
Upon review with the customer, we were able to confirm the correlation of our "before" model (upper image) with the actual system behavior. The radiation pattern emitted by the lightpipe was properly predicted, and it was evident that the light was not doing what had been intended. Space constraints required that no major changes be made to the layout of the light pipe.
In a short period of time, the light pipe was modified such that light output was increased by 2.5x, and the angular distribution of light was extended so that the indicator could be readily seen from solid angles many times larger than when the project began.