Ambient light detector, light source lighting controlling device, and reader

摘要

The present invention relates to an ambient light detector that detects a change in light amount of ambient light. The ambient light detector consists of ambient light detecting means for detecting light entering from circumferences and outputting an electrical signal corresponding to the light amount thereof; amplifying means for amplifying the output from the ambient light detecting means; signal producing means for producing a slice level signal based on the output from the amplifying means; comparing means for comparing the output of the amplifying means with the slice level signal; and judging means for judging the level of the output from the amplifying means and then outputting a control signal to control the amplifying factor of the amplifying means, according to the judging result. Ambient light can be stably detected without depending on installation mode or external environment.