A coupling with a built-in light source for use with a handpiece body is disclosed. The coupling has a body-side connecting part to be connected to a handpiece body, a hose-side connecting part to be connected to a hose for delivering fluids, the hose-side connecting part connecting to the proximal end of the body-side connecting part, fluid channels extending through the body-side and hose-side connecting parts for communicating fluid lines in the handpiece body with the hose, and a light source disposed in the body-side or hose-side connecting part. The light source is an LED lighting device including light-emitting means having an LED chip, and a circuit board electrically connected to the light-emitting means for controlling the voltage supplied to the LED chip. The circuit board is placed in the body-side or hose-side connecting part.
