Variable CCT constant illuminance white LED light communication system with dimming feature

Abstract

This paper proposes a novel approach of visible light communication (VLC) system through variable correlated color temperature (CCT) and constant illuminance white LED lighting system with dimming feature in indoor. To validate the concept, a 2 MHz optical communication channel bandwidth is implemented and the effect on lighting quality is experimentally verified in this article. The CCT changing and constant illuminance lighting system is developed using the warm white (CCT 2800 K), red and blue LEDs. Color mixing of lights is based on the Grassmann’s color mixing Law by controlling the duty cycle of the light sources. This prototype produces the CCT ranging from 2300 K to 11000 K with dimming control. The measured CCT is very accurate with respect to the set point CCT and it is within the tolerance range as specified in the ANSI standard C78.377 (ANSI 2008) where the CCT may follow daylight CCT pattern or any set range throughout the day and in evening it may glow at any constant CCT as the user wishes. A very high CRI value (Ra 89) is successfully achieved with the constant illuminance of 240 lx in the working plane at 7.5ft distance from the luminaire and during the data transmission that light level is dimmed to 151 lx, so that user realizes that the data transmission has been started. This type of system is especially designed for closed room office lighting, conference room lighting, classroom lighting where the CCT changing lighting system is required along with a communication channel.