| 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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This article was published in the Sept/Oct 2009 issue of LEDs Magazine.
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