1. A lighting unit, havinglighting unit housing comprising a profiled element having a U-shaped cross section with a center portion and opposed side walls, the profiled element extending axially along a longitudinal axis defining a planar surface having a plurality circular opening extending there through sized to receive a plurality of lighting unit tubular sleeves,a plurality of retaining elements, arranged in longitudinally spaced apart relation along the axis of the profiled element, for retaining the plurality of lighting unit tubular sleeves aligned with the plurality apertures, each of the plurality of retaining elements have an upwardly oriented extension protruding from the profiled element along the vertical direction, and each of the plurality of lighting unit tubular sleeves include a clamp arranged around the lighting unit tubular sleeve and the extension of a corresponding retaining element, anda plurality of lighting unit components mounted within the plurality lighting unit tubular sleeves such that they can move relative to the lighting unit tubular sleeves in a vertical direction along a vertical axis (A),
wherein the circular openings formed in the profiled element, through which the lighting unit tubular sleeves extend enable the tubular sleeves to be moved up and down along the axis (A);
convexly shaped latching elements formed on opposite sides of each of the plurality of the retaining elements engage under the two shoulder limbs formed on the opposed side walls of the profiled element,
wherein the profiled element and the retaining element are configured in such a way that the retaining element is held on the profiled element side walls solely via a latching connection of the latching elements.