Abstract
In this paper, we propose a novel differential equation method for
designing a total internal reflection (TIR) LED lens with double freeform
surfaces. A complete set of simultaneous differential equations for the
method is derived from the condition for minimizing the Fresnel loss,
illumination models, Snell's Law of ray propagation, and a new
constraint on the incident angle of a ray on the light-exiting surface of
the lens. The last constraint is essential to complete the set of
simultaneous differential equations. By adopting the TIR structure and
applying the condition for minimizing the Fresnel loss, it is expected
that the proposed TIR LED lens can have a high luminous flux efficiency,
even though its beam-spread angle is narrow. To validate the proposed
method, three TIR LED lenses with beam-spread angles of less than
22.6° have been designed, and their performances evaluated by ray
tracing. Their luminous flux efficiencies could be obviously increased by
at least 35% and 5%, compared to conventional LED lenses with a single
freeform surface and with double freeform surfaces,
respectively.
© 2016 Optical Society of Korea
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