White light emitting diodes with enhanced CCT uniformity and luminous flux using ZrO2 nanoparticles.

To enhance the uniformity of correlated color temperature (CCT) and luminous flux, we integrated ZrO2 nanoparticles into white light-emitting diodes. This novel packaging scheme led to a more than 12% increase in luminous flux as compared to that in conventional dispensing structures. This was attributed to the scattering effect of ZrO2 nanoparticles, which enhanced the utilization of blue light. Moreover, the CCT deviation was reduced from 522 to 7 K in a range of -70 to +70°, and essentially eliminated the yellow ring phenomenon. The haze measurement indicated strong scattering across the visible spectrum in the presence of ZrO2 in the silicone layer, and this finding also substantiates our claim. In addition, the chromaticity coordinate shift was steady in the ZrO2 dispensing package structure as the drive current increased, which is crucial for indoor lighting. Combined with its low cost, easy fabrication, and superior optical characteristics, ZrO2 nanoparticles can be an effective performance enhancer for the future generation of white light-emitting devices.

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

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.

High thermal stability of correlated color temperature using current compensation in hybrid warm white high-voltage LEDs.

This study experimentally and numerically examines the correlated color temperature (CCT) stability issue for hybrid warm white high-voltage light-emitting diodes (HV-LEDs) by using a current compensation method. This method could efficiently maintain the CCT stability factor at approximately 1.0 and yield greater color uniformity with Δu'v' values ranging from 0.017 to 0.003 in CIE 1976 chromaticity coordinates. The simulation results show that the red chip intensity drop is the primary cause of CCT instability in the hybrid warm white system when the temperature increases. Therefore, Furthermore, results indicate that the relative lumen drop improves from 21% to 15% by using a current compensation method.

Improvement in uniformity of emission by ZrO2 nano-particles for white LEDs.

The high luminous efficiency and superior uniformity of angular-dependent correlated color temperature (CCT) white light-emitting diodes have been investigated by ZrO2 nano-particles in a remote phosphor structure. By adding ZrO2 nano-particles with silicone onto the surface of the phosphor layer, the capability of light scattering could be enhanced. In particular, the intensity of blue light at large angles was increased and the CCT deviations could be reduced. Besides, the luminous flux was improved due to the ZrO2 nano-particles with silicone providing a suitable refractive index between air and phosphor layers. This novel structure reduces angular-dependent CCT deviations from 1000 to 420 K in the range of -70° to 70°. Moreover, the enhancement of lumen flux was increased by 2.25% at a driving current 120 mA, compared to a conventional remote phosphor structure without ZrO2 nano-particles. Consequently, the ZrO2 nano-particles in a remote phosphor structure could not only improve the uniformity of lighting but also increase the light output.