Lighting device with closed form for a motor vehicle

The device has an optical waveguide (1), and a light source (4) i.e. LED, that is coupled at an end (2) of the waveguide for feeding light into the waveguide. Two sections (7, 8) of the waveguide intersect at an intersection (6) such that the two sections lie one above the other in a plan view. An adjustment unit (11) is arranged at the intersection and is provided with a light intensity that is measurable in direction opposite to the plan view. The adjustment unit covers an underlying section of the waveguide at the intersection.