A luminaire having a tube-shaped gas discharge lamp (1) contains at least one concavely curved reflector (2) arranged—seen from the region to be illuminated—neighboring the lamp (1), and at least one partially light permeable diffusor (3) arranged—likewise seen from the region to be illuminated—neighboring the lamp (1) but before the reflector (2). The diffusor (3) and the reflector (2) bound next to the lamp (1) at least one light entry surface and run together at their ends away from the lamp (1) such that they enclose at least one light chamber (4), the ratio between the width (a) of a light chamber and the height (b) of a light entry surface being at least 4:1. Further, there may be provided means for the attainment for a uniform light density over the width of the reflector.