Abstract: A light guide (1) comprises a housing (3) defining a light-guiding optical cavity having first and second opposed major faces (5, 6), and a light source (11) arranged to direct light into the cavity from one end, to be guided between the major faces. The first major face (5) comprises a window through which light can be emitted from the optical cavity to be used, for example, for illuminating a graphic display. To improve the light distribution across that first major face (5), the second major face (6) comprises a sheet material (23) having a specularly-reflecting surface (24) that faces into the optical cavity and has diffusely-reflecting light-extraction elements (27) applied thereto in a predetermined configuration for causing light to be emitted from the optical cavity through the said window.