| 摘要 |
PROBLEM TO BE SOLVED: To always automatically adjust brightness of a panel surface of a liquid crystal display and brightness of the ambient light to the relative optimal relationship so that visibility according to a service environment can be obtained. SOLUTION: A difference between brightness of the ambient light and luminance of an image screen is supplied to a comparator 12, and a triangular wave having a constant cycle period is modulated on a pulse width, and a fluorescent tube 2 being a back light of a liquid crystal display is controlled on luminance by a pulse width-modulated light dimming signal. Since a difference between brightness of the ambient light and luminance of an image screen is kept constant, visibility of the liquid crystal display can be optimized in various environments. |
