A distributed lighting system (10) comprising a waveguide assembly that includes a vehicle interior trim panel (28) having an elongated opening (30) therein and a correspondingly elongated waveguide (12) attached to the trim panel to provide laterally-directed illumination through the opening along the length of the waveguide. The waveguide (12) is attached to the trim panel (28) using a support frame (18) that includes a light-transmissive lower wall (20) which fits within the opening (30) and a pair of opposed side walls (22) that, together with the lower wall, define a channel (24) in which the waveguide is located. The waveguide (12) includes a ligth-scattering region (52) located opposite the opening (30) in the trim panel (28) to direct light laterally out of the waveguide and through the opening. The waveguide assembly (10) also includes a back cover (40) that encloses the waveguide (12) between the cover (40) and support frame (18). Different waveguide cross-sections and light-scattering configurations are disclosed.