Effect of phosphor sedimentation on photochromic properties of a warm white light-emitting diode *Project supported by the National Natural Science Foundation of China (No. 11474036), the Natural Science Foundation of Shanghai (No. 12ZR1430900), the Shanghai Institute of Technology Talents Scheme (No. YJ2014-04), the Shanghai Municipal Alliance Program (Nos. Lm201514, Lm201505, Lm201455), the Science and Technology Commission of Shanghai Municipality (CN) (No. 14500503300), Shanghai Cooperative Project (No. ShanghaiCXY-2013-61), and Jiashan County Technology Program (No. 20141316). (December 2018)