Browsing by Author "Chu, Mu-Tao"

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Failure and degradation mechanisms of high-power white light emitting diodes
(2010-07-01)
Yang, Shih-Chun
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Lin, Pang
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Wang, Chien-Ping
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Huang, Sheng Bang
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Chen, Chiu-Ling
The investigation explores the factors that influence the long-term performance of high-power 1 W white light emitting diodes (LEDs). LEDs underwent an aging test in which they were exposed to various temperatures and electrical currents, to identify both their degradation mechanisms and the limitations of the LED chip and package materials. The degradation rates of luminous flux increased with electrical and thermal stresses. High electric stress induced surface and bulk defects in the LED chip during short-term aging, which rapidly increased the leakage current. Yellowing and cracking of the encapsulating lens were also important in package degradation at 0.7 A/85 degrees C and 0.7 A/55 degrees C. This degradation reduced the light extraction efficiency to an extent that is strongly related to junction temperature and the period of aging. junction temperatures were measured at various stresses to determine the thermal contribution and the degradation mechanisms. The results provided a complete understanding of the degradation mechanisms of both chip and package, which is useful in designing highly reliable and long-lifetime LEDs. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.
Visible Light Positioning and Lighting Based on Identity Positioning and RF Carrier Allocation Technique Using a Solar Cell Receiver
(2016-08-01)
Hsu, Chin-Wei
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Wu, Jhao-Ting
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Wang, Hao-Yu
;
Chow, Chi-Wai
;
Lee, Chun-Hsing
We propose and experimentally demonstrate an indoor positioning system which combines identity positioning and the radio frequency carrier allocation technique in order to reduce the signal interference from nearby light-emitting diodes (LEDs) and improve the accuracy of positioning. In addition, the solar cell is used as an optical receiver for the visible light positioning system. Due to the benefits of solar cells such as low-cost, high light sensitivity, and ease in integration with wearable devices, the proposed system could be an energy-efficient and environmentally friendly choice for indoor positioning in the future.