We performed photo-current experiments on various liquid crystal (LC) cells, and compared with the results of conventional evaluations of reliability of LC display (LCD) such as voltage holding ratio (VHR), ion density, and flicker. The accumulated charges in LC cells were estimated by the time integration of photo-currents. Good correlations among observed photo-current, estimated charges, and flicker drift were obtained, which revealed that the accumulated charges in LC cells are one of the major factors to cause the flicker drift.