A light sensor and a ranging method are provided. The light sensor includes a light source, a sensing sub-pixel, and a control circuit. The sensing sub-pixel includes a diode. The control circuit operates the diode in a Geiger mode or an avalanche linear mode. The control circuit includes a time-to-digital converter, and the time-to-digital converter includes a counting circuit. The counting circuit includes a plurality of counting units. When the time-to-digital converter receives a sensing signal provided by the sensing sub-pixel, the control circuit generates a plurality of count values according to the sensing signal through the counting units of the counting circuit, where the count values are histogram data corresponding to a distance sensing result.