A lighting structure for intensely illuminating a narrow linear region. A light source emits light into an end of a hollow, elongate light guide. A longitudinal slit light-emitting aperture extends through an external wall of the light guide. A lens is mounted in the aperture. The lens bears a plurality of prisms which extend substantially perpendicular to the slit, on an inwardly directed face of the lens. The lens may be formed of a film material. A mechanism is provided to maintain the lens flat. A diffuser mounted outwardly of the lens bears a plurality of thin striations extending transversely, relative to the longitudinal slit aperture.