A light sensing unit for a light sensing circuit of an image sensor includes a first light sensing element, a first floating node and at least one coupling element. The first light sensing element is used for sensing light to obtain a light sensing result and generating a plurality of carriers accordingly. The first floating node is used for receiving and storing the plurality of carriers generated by the first light sensing element. The at least one coupling element is used for coupling the first floating node to at least one second floating node, and transmitting a part of the plurality of carriers stored in the first floating node to the at least one second floating node to be stored in the at least one second floating node.