In many applications the intensity of visible light has to be measured. The crucial point is that the word “visible” introduces a physiological element into the problem. The output signal of the sensor has to correspond to the subjective impression of the human eye, i. e. if the subjective impression of the human eye is “bright”, the sensor signal should also be high.

And for the impression “dark” the sensor should show a low signal. Ambient Light Sensors (ALS) were designed as optical detection devices which have a similar sensitivity characteristics compared to the Human eye. Those components are mainly used for backlight control of LC-displays or in lighting applications.