ST has been working on Time-of-Flight technology for approximately six years-plus now. There are two features this technology brings to the VL6180X device: counting photons and measuring the photon time of flight. The VL6180X measures the exact time the photon leaves the emitter, and the time it hits the sensor. The accurate distance measurement can be calculated by dividing the time of flight by the speed of light. Since photons travel at a constant speed, the calculated distance is independent of the amount of photons returned. Object reflectance affects the amount of returned photons.