Abstract: A lighting device (1401; 1402; 1403; 1404) comprises a semi-transparent plate-shaped light source (1409; 1400). The transparent plate-shaped light source may be a passive plate-shaped light source (1400) comprising a transparent light guide plate body (1410) with two substantially parallel main surfaces (1411; 1412), and wherein at least one of the main surfaces (1411; 1412) is provided with permanent obtrusions (1415). The obtrusions (1415) may be implemented as material portions projecting from the surface and/or as indentations recessed in the surface. The obtrusions (1415) may be arranged by sandblasting, preferably in a pattern of dots, wherein the dots may have sizes in the range between 20 and 200 ?m, preferably approximately 100 ?m, and wherein the dot density may be in the range between 5 and 500 dots/cm2.