Portable information terminal apparatus having illumination control function

摘要

A portable information terminal apparatus measures the ambient illuminance and exercises illumination control over its display and manual input unit during a predetermined period. The appropriate length of this predetermined period is determined from various parameters including the ambient illuminance and the function(s) to be used by the portable information terminal apparatus. Illuminance measurements are subjected to various corrective computations to obtain proper illuminance decision values. These decision values are used to perform appropriate illumination control,