Ambient Light Sensing (ALS) is the ability to measure the brightness of light incident on a surface. It is often useful to utilize this brightness information to control certain aspects of a system, such as the brightness of a display, or the size of an aperture. End products that can benefit from ALS implementation include laptops, monitors, cell phones, televisions, digital signage, cameras and any device with a visual user interface.

Ambient light sensors (ALS) are used to detect light or brightness in a manner similar to the human eye. They are most commonly found in industrial lighting, consumer electronics, and automotive systems, where they allow settings to be adjusted automatically in response to changing ambient light conditions. By turning on, turning off, or adjusting features, ambient light sensors can conserve battery power or provide extra safety while eliminating the need for manual adjustments.

Advantages of Ambient Light Sensor (ALS)

  • Display Backlighting Power Management & Control – Display backlighting typically constitutes a large share of a systems power resources. It is common for a laptop PC display to consume between 30% and 40% of the total power budget. Substantial power savings can be realized when the brightness of a display is effectively controlled by ambient light.
  • Improved Visual Experience to the User – Regulating system lighting based on ambient conditions in essence allows for the system to anticipate and act upon the needs of the user. This could be achieved by increasing display brightness in a bright setting or enabling system lights in a dark setting.

When Ambient light is measured, it is the illuminance that is quantified. This gives the system the ability to make decisions based on what a user would see. The goal of the ambient light sensor is to mimic the response of the human eye, in order to measure illuminance. The response of an ambient light sensor should be linear.

The human eye can see light with wavelengths from 380 nm to 780 nm. Illuminance is the measure of the intensity of light incident on a surface and can be correlated to the brightness perceived by the human eye. In the visible range, it is measured in units called “lux.” Light sources with the same lux measurement appear to be equally bright.