1. Graduate School of Technology, Industrial and Social Sciences, Tokushima University; Tokushima 770-8506 Japan
2. Laboratory of Advanced Science and Technology for Industry, University of Hyogo, Kamigori; Hyogo 678-1205 Japan
3. Chubu University, Kasugai; Aichi 487-8501 Japan
4. Nichia Corporation, Anan; Tokushima 774-0044 Japan