| 摘要 |
PROBLEM TO BE SOLVED: To provide a portable information terminal device having excellent visibility, operatability and electric power saving property, in which lights of a display unit and an operation unit are turned on or off by rapidly and properly responding to a fluctuation in surrounding illuminance. SOLUTION: In this portable information terminal device, surrounding illuminance is measured for a predetermined period to control illumination for a display unit and an operation unit. As this determined period, an appropriate length is determined based on various parameters such as the surrounding illuminance, functions used in the portable information terminal device, etc. Furthermore, various calculations are performed for correction of a measured value of illuminance to obtain a proper determined value of illuminance. Illumination is appropriately controlled by using this determined value. |
