An apparatus for lighting or indicating purposes in a motor vehicle includes a light guide associated with at least one light source for transporting light rays emitted by the light source from an input face to an output face via and intermediate section of the light guide. 0, wherein said composition contains at least 30 weight percent of spinel crystals, at least 10 weight percent of glass, and less than 10 weight percent of ferrometalsilicate. The array has unit lenses arranged at an incident plane of the transparent substrate in a periodic structure in an up-and-down direction.