A back-light driving circuit controlling red, green, and blue back lights providing light to a liquid crystal panel in a field sequential liquid crystal display. The monitoring system uses electronics to adjust the light relative to the dust accumulation, thus maintaining an accurate counting cell signal, so that the system can continue to function. The optical communication device also includes optical communication means made of a flexible material and having both end faces substantially perpendicular to its optical path of transmitting, and a pair of optical elements having their respective optical functional portions that are mounted on the rigid sections of the flex-rigid substrate.