The 2 cases presented illustrate that there are significant differences in simulated results depending on the source modeling method used. These results show that a Photopia model more closely matches the measured performance than the rayset model for both wide and medium beam lenses. The differences are greatest when an index matching gel is used between the LED and lens. The main reasons for this are that in addition to the challenge rayset models have in creating accurate 3D ray emanation points, all of their digital images showing the luminous view of the source are measured in air. When a gel is used between the LED and the lens, light never exits from the LED primary lens into air so the measurements are inappropriate. Since Photopia models include the lens geometry, the material can simply be changed to account for the glass / gel interface instead of glass / air.
The 1st set of data shows that the rayset model fairs better when there is no gel, yet it does not outperform the Photopia model. Wider beam optics are more sensitive than narrower beam optics to exactly how much light is directed onto each part of the lens. As the beam gets narrower, more light is directed to the same angles in the beam and differences in the amount of light sent to each part of the lens between the simulation and physical reality become less important. It should also be noted that other 3D ray emanation point geometry mapping options were tested such as mapping the points to a sphere and the results did not vary significantly from those presented here.
Given a choice between rayset and Photopia source models for the same LED, a Photopia model will likely produce more accurate results, especially as the beam gets wider. If gels are used between the LED and lens, then rayset models should not be used since the measurements on which they are based is not appropriate for this situation.
The simulation data in these case studies was provided by Kurt Wilcox and Chris Strom at Ruud Lighting. ITL in Boulder, Colorado provided the physical measured data for comparison.