ambient light sensor (ACPI) (ALS)

Various technical procedures have been developed to save energy by switching individual computer components to an energy-saving mode or switching them off completely. Advanced Configuration and Power Interface( ACPI) is such a concept for power management in personalcomputers.

In addition to various energy-saving modes, it also has a function that adjusts the brightness of displays to the ambient light. The concept works with an Ambient Light Sensor( ALS), which is nothing more than a brightness-sensitive sensor, a photoresistor or a photodiode, which generates the control voltage for brightness control as a brightness sensor.

HP notebook with ambient light sensor (ALS)

In mobile devices, most energy can be saved in the display. That's why the ALS concept adjusts the set brightness and color temperature of the display to the ambient brightness. If the display is exposed to a higher illumination level, the display brightness has to be higher. In darker rooms, however, the brightness can be reduced if one wants to have the same brightness impression.

The ALS concept used in ACPI takes into account not only the brightness but also the color temperature and has a reference curve on which different ambient lighting can be set in reference points: Daylight, office lighting, conference room lighting.