Proximity

Optical distance sensors are often described as “using light to measure distance”. That is true, but too broad. Different optical sensors can mean very different output semantics.

A simple reflective proximity sensor may only know that reflected light became stronger or weaker. A ToF sensor estimates distance from light travel time or phase. The reported number is not simply “what the sensor sees”; it depends on reflectance, geometry, ambient light, optics, and algorithms.