The invention relates to a light application apparatus (1) for applying light to an object (3). A light source (4) generates processing light (2) and sensing light (5), which are coupled into the object (3). A light detector (8) detects the sensing light (5) after having left the object (3), and a control unit (9) controls the light source (4) such that processing light (2) in a processing time interval and sensing light (5) in a sensing time interval are alternately generated. Since processing light and sensing light are generated alternately, the generation of the processing light and of the sensing light is decoupled, i.e. the processing light can be optimized for processing purposes and the sensing light can be optimized for sensing purposes. This allows improving the quality of sensing the object and, thus, the quality of controlling the application of light depending on properties of the object.