Such a luminaire is known from U.S. Pat. No. 5,381,321. The known luminaire is designed to withstand hazardous atmospheres and to be explosion proof. The one-piece housing provides a relatively reliable closed housing and also avoids the use of relatively complex sealing steps to seal the housing with an elongated cover, as is well known from for example luminaires used for road illumination. In the known luminaire the housing is used as a protection for a light source, in this case a fluorescent lamp, which is to be accommodated in electrical contacting supports inside the housing. A rigid reflector optic mechanically connects the electrical contacting supports. The reflector optic and the electrical contacting supports, accommodating the fluorescent lamp, are held in a light carriage and together form a complete unit. The fluorescent lamp is only replaceable after removal of the complete unit from the housing. The known luminaire has various disadvantages. For example, replacement of the fluorescent tube is relatively cumbersome as not only the lamp itself, accommodated in the electrical contacting supports, but also the reflector optic has to be taken out and reinserted, involving the risk of a polluted reflector surface, for example by fingerprints, and/or damage to the reflector optic and/or a wrong position of the unit after reinsertion. Another disadvantage is that the reflector optic has to be rigid as it is the mechanical connection between the electrical contact supports and thus must retain its shape and be able to withstand the replacement operations. To render the reflector optic sufficiently mechanically robust, the reflector optic requires relatively much of the relatively expensive reflector material.