A light sensing circuit and an image sensor are provided. The image sensor includes a first pixel unit including a plurality of first photodiodes and a first driving circuit to generate a first pixel signal based on an amount of charges stored in the plurality of first photodiodes, a second pixel unit including a plurality of second photodiodes and a second driving circuit to generate a second pixel signal based on an amount of charges stored in the plurality of second photodiodes, and a switching circuit connected to the first driving circuit through a first diffusion node and connected to the second driving circuit through a second diffusion node. The switching circuit connects or disconnects the first diffusion node and the second diffusion node based on a mode selection signal.