Generating a billion rays by merging near field goniometry data with standard IES-TM25 ray files

Ray files are a blessing and a curse: For most LEDs, they are the best, if not the only way to accurately model the LED source in illumination ray tracing software. However, the information within ray files as provided from LED vendors is limited. From a user’s point of view, it is rare to have more than five million rays, which is often insufficient (e.g. when modeling color across low beam cutoff line). In addition, a model of the color inhomogeneities of white LEDs is either absent in the ray file or given by an awkward superposition of two separate ray sources. From an LED vendor’s point of view, the plethora of proprietary formats is tedious, is a quality control nightmare, and makes ray files occupy huge amounts of online storage, while still not satisfying the user’s needs for larger ray sets. The IES TM25 format, published in 2013 and now gaining simulation software and LED vendor support, offers a way to combine multi spectrum standard ray sets with near field goniometry data into a single file, which can be used to generate a billion high quality random rays on the fly, if needed. We explain how this works and show an application example.