A luminaire (1) or a system of a first luminaire (1) and a second luminaire (11) for lighting an object (V). Each luminaire has a housing (2; 12) provided with a plurality of tubular lamps (3, 3, 3"; 13). The housing (2; 12) has a diffuser (7; 17) positioned in a light emitting window (4; 14) and a side wall (5, 5; 15), which is orthogonal with respect to the light emitting window (4; 14). In the system, the first and the second luminaire (1; 11) abut one another via the side wall (5, 5; 15) and/or via the light emitting window (4; 14), wherein an edge (6) of the light emitting window (4) of the first luminaire (1) abuts upon an edge (16) of the light emitting window (14) of the second luminaire (11). The diffusor (7; 17) and the side wall (5, 5; 15) are made from an optically transparent material. Preferably, the light emitting window (4; 14) is provided with a curtain (21; 31). Preferably, the curtain (21; 31) exhibits a variation in layer thickness, the layer thickness being thicker at a location on the curtain (21; 31) close to the tubular lamps (3, 3, 3"; 13) than farther removed from the tubular lamps (3, 3, 3"; 13). The object (V) is homogeneously and uniformly illuminated by the system.