Size-dependent performance of white light LEDs for intelligent vehicle lighting and communication.

In this paper, size-dependent illumination performances of white light micro light-emitting diodes (LEDs) and a visible light communication (VLC) system were demonstrated. The white light LEDs from 10 m to 200 m were prepared by exciting three phosphors with blue LEDs and the current density versus voltage, luminous efficiency, and electroluminescence (EL) spectra were measured. At 300 A/cm, the luminous efficiency of the 60 m white LED was 1.6 times greater than that of the 200 m white LED, and we found that the smaller chips are more advantageous in luminous efficacy at higher current densities. The trend of the CIE chromaticity diagram versus the current density for the 200 m, 60 m, and 10 m white light LED were analyzed, revealing that the smaller white light LED had the advantage of reducing the shift of the coordinate in CIE 1931. Further, we investigated the communication characteristic of white LEDs and found that the -3 dB modulation bandwidth of the 60 m white light LED was 151.57 MHz at 2000 A/cm and a data rate up to 1.741 Gbps could be attained when it was used in a VLC system at a free space transmission distance of 0.25 m by combining orthogonal frequency division multiplexing (OFDM) modulation without optical filters or equalization circuits. Our work is significant in accelerating the applications of white light LEDs for intelligent vehicle lighting and communication.