An ambient light sensor that is operable in high gain mode and low gain mode is provided. The high gain mode may help provide satisfactory sensitivity at low light levels but may generate saturated output levels in bright ambient lighting conditions. Low gain mode may therefore be switched into use when bright ambient lighting conditions are detected. The ambient light sensor may be placed in high gain mode by default. An auto-gain switch controller may detect whether the ambient light reading is saturated during as given period of time. In response to determining that the ambient light reading is saturated for a programmable number of consecutive time periods, the auto-gain switch controller may reset and switch the ambient light sensor to the low gain mode. The gain state may optionally be embedded into the ambient light sensor output.