Abstract
We report an investigation of the optical performance of a conformal-shaped
phosphor coating fabricated using pulsed spray techniques on horizontal LED chips. Both
the nitride and YAG:Ce phosphor mixed configuration and the multilayer configuration
were studied. Also, 3535-packaged LED devices with the two typical phosphor
configurations were prepared and analyzed. The results revealed that the LED devices
with multilayer phosphor configurations emitted an average of 5.6% more radiant flux
than those with mixed phosphor configurations. However, such LED devices presented an
interesting reversed tendency in the luminosity measurements, which were 0.3 lm and 6 lm
lower at 10 mA and 350 mA, respectively. Finally, the color rendering index (CRI) and
correlated color temperature (CCT) homogeneity of the LED devices were further analyzed.
A twofold reduction in CCT variation was observed compared with the conventional
phosphor coating methods. It was found that the mixed phosphor LED devices demonstrated
outstanding angular CCT distributions for viewing angles ranging from -80° to
0°, and a CCT variation of only 45 K was detected, while the multilayer phosphor
coating had higher color rendering capabilities, reaching a CRI<sub>general</sub> value
as high as 85.6. A promising guideline found through this work is that the pulse-sprayed
conformal phosphor configuration would particularly be able to improve the light quality
of LED devices by a significant amount: the mixed phosphor configuration achieves
excellent CCT homogeneity, and the multilayer phosphor configuration reveals a novel
concept for fabricating a low-CCT and high-CRI LED device with less nitride phosphor.
The findings of our research should provide valuable insight to LED
industries.
© 2012 IEEE
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