Ching-Ching YANG, Hsin-Yi TSAI, and Kuo-Cheng HUANG^*

Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu, 30076, Taiwan

(Received August 10, 2012; Accepted December 3, 2012)

White LEDs (WLEDs) have various yellow-ring (YR) effects when projected onto differing backgrounds. These effects are determined by the material that the WLED is projected onto. In our previous study, the YR phenomenon was expressed as the yellow-ring index (YRI), which comprises yellow light intensity (Y) and light intensity (I), and the maximum value of the YRI curve is a crucial optical parameter for determining the degree of the YR phenomenon. This study presents a modified evaluation model using YR degree and four YR diagrams (the YRIs are less than 5, 5 to 10, 10 to 15, and greater than 15) as the criterion for WLED quality control.

Key words: yellow-ring, white LED

^*E-mail address: huangkc@itrc.narl.org.tw