Measuring the time of flight of light poses many challenges. Since all photons are the same, ambient light and light from the emitter are all counted the same. The VL6180X uses a pulsed laser signal to distinguish between the two. Photons reflected off an object do not arrive at the exact same time. They have a Poisson distribution due to different paths photons travel, the shape of the object, and the width of the laser pulse. The VL6180X checks the signal-to-noise ratio to determine the reflected pulse from the ambient light.