I was looking for a sensor, then I caught this:
In the specs - emitted light section, it says the emitted light is "Red, Clocked", with a switching frequency of 4000 Hz. What I understand from this is the emitted light (and the output) is on and off 4000 times per second.
What kind of an advantage can it have against a continuous light? It definitely would have a simpler circuit (no clock source required).