Part 1 covered ambient light sensor basics and key characteristics.
The choice of which ambient light sensor is best for an application is up to the end-user. The digital light sensor approach is becoming the solution-of-choice in terms of performance and flexibilityespecially so in automotive applications where using an I2C digital output signal is desirable because of: Lower noise; the ability to network several sensors on same bus; much better control of sensor characteristics; and better overall sensor performance.
Another key aspect in choosing the right light sensor is spectral response. The problem is that ordinary PIN photodiodes (either passive or active) inherently have a very broad spectral response range that includes ultraviolet (UV) all the way into the infrared (IR, below)not ideal if you want to design an ambient light sensor (remember, we want to sense only visible light, not IR or UV components).
Thus, a light sensor that only "sees" visible light (380 to 770 nm) and attenuates unwanted IR and UV signals, such as the ISL29010 and ISL29013, is desirable (below).
Different light sources have different spectral characteristics (below). Sunlight, for instance, has a very broad spectral response, with approximately 50% of its spectral content falling in the IR range. Filament-based light sources, like incandescent and halogen lights, also exhibit high levels of IR radiation.
The bottom line is you need a light sensor that accurately measures only the visible light that the human eye sees and attenuates all light that has high infrared and UV content.