In this paper, we have demonstrated an efficient speckle-suppressed white light source generation when a blue laser diode illuminates on a micro-vibrated phosphor paper. Both micro-vibrated and color-mixing techniques are used in this system. With only micro-vibrated technique, the speckle contrast can be reduced from about 50% to 7.4% for the scattering blue image for a 16-ms integration time. Together with color-mixing technique, mixing speckle contrast is defined for laser diode pumped phosphor and almost speckle-free result is achieved. For color temperature lower than 5000 K, almost speckle-free mixed white can be obtained even without vibration technique.
In developing a high-quality natural light illumination system (NLIS), the primary considerations include how to increase system efficiency and broaden its applications. This paper describes the conception, design, and analysis of a daylight collector that presents the combined advantages of excellent efficiency and a compact size. The collector structure consists of extendable two-channel collecting units, a planar light guide, and a central coupler to improve light collection efficiency and increase surface area. In this study, two types of daylight collectors are proposed for illumination applications with different light patterns. With these collectors, the NLIS can now provide sufficiently powerful light for indoor illumination.
A multiscale model that enables quantitative understanding and prediction of the size effect on the scattering properties of micro-and nanostructures is crucial for the design of light-emitting diode (LED) surface textures optimized for high light extraction efficiency (LEE). In this paper, a hybrid process for combining full-wave finite-difference time-domain simulation and a ray-tracing technique based on a bidirectional scattering distribution function model is proposed. We apply this method to study the influence of different pattern sizes of a patterned sapphire substrate on GaN-based LED light extraction from the micro-scale to the nano-scale. The results show that near-wavelength-scale patterns with strong diffraction are not expected to enhance the LEE. By contrast, micro-scale patterns with optical diffusion behavior have the highest LEE at a specific aspect ratio, and subwavelength-scale patterns that have antireflection properties show a marked enhancement of the LEE for a wide range of aspect ratios.
This paper presents the optical simulation of the luminous efficacy of radiation (LER) and color spatial uniformity (CSU) of a package-free white LED conducted to boost the LER and simultaneously improve the CSU. According to the simulation results, the main effect on the LER and CSU was the change in the geometrical ratio of phosphor coating. Regardless of the packaging size, when the ratio of the top coating to the sidewall coverage of the phosphor layer thickness was in the range from 0.9 to 1.1, the maximum LER and optimal CSU can be simultaneously obtained. Besides, effectively increasing the volume of the overall packaging dimension to be 30 times the size of the chip can enable a package-free LED to achieve 90% saturated maximum LER without affecting the CSU.
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