Improvement of emission uniformity by using micro-cone patterned PDMS film

Abstract

Micro-patterned PDMS film was fabricated and combined with LED chip on board (COB) package to improve the emission uniformity of LED chip. The micro scale patterned sapphire substrate (PSS) was used as a mold to fabricate micro-cone patterned PDMS (MC-PDMS) film. A strong scattering effect from this MC-PDMS film can be verified by the high haze ratio and the Bi-directional Transmission effect. The angle dependent color temperature measurement system was used to measure the ΔCCT of COB with and without MC-PDMS. The measurement results indicate that the ΔCCT was reduced from 1025K to 428K. This improvement can effectively eliminate the yellow ring effect of LED chip. This technology can be thus considered as a cost-effective way for the next generation of light source packages.

Microlens arrays with adjustable aspect ratio fabricated by electrowetting and their application to correlated color temperature tunable light-emitting diodes

“…As a new type of intelligent LED light source, a CCT-tunable LED changes the CCT by independently adjusting the light intensity of cold and warm color light [21,22]. Because of the lack of a proper light mixing scheme, CCT-tunable LED lamps suffer from a poor color uniformity and from the appearance of a blue circle and a yellow halo, which are detrimental to the illumination quality [23]. In our previous research, we effectively improved the ACU of CCT-tunable LEDs by MLA, reducing the CCT deviation from 1090 K to 218 K within the CCT range of 3000-4000 K [20].…”

Novel Method for Estimating Phosphor Conversion Efficiency of Light-Emitting Diodes

“…This has become the most common approach for white light generation [9]. To achieve different color gamut, color rendering index (CRI), light quality, and efficiency specifications for various applications, many novel phosphors that increase the efficiency or color performance of LEDs have been developed [10][11][12][13]. Among the several phosphors for LED applications, yttrium aluminum garnet (YAG)-, silicate-, and nitride-based phosphors are used most widely in WLEDs because of their well developed fabrication processes and outstanding features.…”

A Cylindrical Tuber Encapsulant Geometry for Enhancing Optical Performance of Chip-on-Board Packaging Light-Emitting Diodes

“…On the flat interface, the TIR phenomenon happens at a critical angle c as small as 38 $ 45 caused by the refractive index difference of the materials (encapsulant % 1:4 $ 1:6, air ¼ 1), as a consequence, amount of light propagates back and forth inside the device and fails to emit outwardly [6]- [8]. Meanwhile, due to the flat interface, the COB packaging modules also fail to have good angular color uniformity performance (ACU) [8], [9]. The low LE and poor ACU hinder the further applications of COB packaging modules.…”

“…Some methods were reported to diminish the TIR effect, such as patterned LED chip [10], [11], patterned leadframe substrate (PLS) [6] and roughened encapsulation layer [7], [9]. Although these can improve the LE and ACU of COB packaging modules, they are highly relied on the precise and expensive equipment or complex molds which add the cost as well.…”