Abstract
The dependence of luminous efficacy on phosphor concentration and thickness for
high-power white light-emitting-diode (WLED) lamps is investigated by employing
three-dimensional ray-tracing simulations. The simulations show that the brightness or
luminous efficacy of WLED lamps highly depends on the combination of phosphor
concentration and phosphor thickness (or phosphor-matrix composite volume). The package
with lower concentration and higher phosphor thickness has higher luminous efficacy
because the light trapping efficiency is lower with the low phosphor concentration. At
the correlated color temperature (CCT) value of around 4000 K, ray-tracing simulation
and experimental results show 20% and 23% improvement in lumen, respectively, with a
1.8-mm-phosphor package over a 0.8-mm-phosphor package. A package with convex lens can
improve the lumen output over flat lens, but this improvement is small, and it requires
higher amount of phosphor, up to 25%, to achieve same CCT value.
© 2008 IEEE
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