View This Issue - October 2009

MAGAZINE: LED attributes for accurate modeling: An optical designer’s wish list

When using software to design an optical system with LEDs, many LED characteristics must be considered to allow them to be modeled accurately. Manufacturers provide much of this information in their datasheets. Additionally, many manufacturers provide measured data in the form of ray data sets
for their products. As designers, we laud the industry for this increased openness, but there is room to improve the level of detail provided by manufacturers to optical designers. We examine four such LED details that may need to be modeled in an optical design, explain why and under what conditions these details are necessary, and propose ways to supply the requisite data. This is not a comprehensive list of details needed for every LED design, but a subset of significant information barriers that designers have faced over the years.

Attribute 1: Near-field light distribution

One detail that is consistently omitted when modeling LED systems is the accurate representation of the LED’s near-field light distribution (for example, at a distances less than roughly 10 times the size of the source). Of course, some optical designs, such as task lighting, can be accurately modeled without taking the near-field light distribution into account. A task light is often simply an LED shining onto a flat surface. There are no obstructions between the source and its distant target; therefore, the near-field light distribution need not be considered for this scenario. However, if a lens is placed in front of the LED that focuses the die onto the same surface, the near-field light distribution must be considered. The spatial variation of the source emittance due to die masks, wires, phosphors, etc. is all imaged onto the target.


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