Many optoelectronic devices are concerned with the absorption/emission of sub-visible ionizing radiation (gamma, X-rays, etc.), but optical distance sensors typically exploit light in the visible and near-visible electromagnetic spectrum. Among the different principles of optical distance sensing, the most common use either a laser or a light-emitting diode (LED) to generate a modulated light beam who's detected reflection by an object is used for distance measurements. These modulated beams are used to calculate distance as a function of the Time-of-Flight (ToF) principle.
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/blog/show/optical-distance-sensors-principles-applications