Ambient light sensors are mechanisms which seek to maximize both energy conservation and visual quality in an electronic device. Common sites for these mechanisms are computers and palm-held consumer products.
An ambient light senor is mounted in an electronic device, so that it can detect the light quality and intensity outside. The sensor is made to mimic the function of your eye. It perceives that light in the exterior environment and then uses that information to adjust a display, such as a computer screen. At all points, the user perceives the same "intensity" of color and visibility in the display.
As the light on the outside changes, the display can alter its own use of light and its use of power. If the full power of lighting the display is not needed, then the device can figure this out through the data provided by the sensor. By adjusting its contrast and power-use accordingly, wear on the screen can be avoided, and energy stored in the battery can be preserved.
There are a great many devices that can use an ambient light sensor. Some of the most common are television sets and computers. They can be located in increasingly small applications, including hand-held devices like Apple Corporation's iPad.