Abstract: An elongated light-diffusive body having a trapezoidal cross-section encapsulates an axially elongated self-luminous light source. The body has a wide base, a narrow base, and slanted sides between the bases. Opening to its narrow base, the body has a longitudinal slot in which the light source fits. A substantially total reflector extends around the slanted sides and the narrow base, including the exposed portion of the light source, to reflect all the light toward the wide base. Distribution of the light emitted from the tube is changed as it leaves the wide base by a partially transmissive coating on the portion of the wide base through which light rays from the tube pass normal to the wide base.