The invention relates to an assembly for disinfecting/sterilizing surfaces and lumens of a device with a light source which emits disinfecting/sterilizing light. The assembly comprises a device (9) for transporting fluid having a lumen and a connector part (10), at least one light source (100) configured to emit light having disinfecting/sterilizing effect, and a separate unit (8)； where the light source (100) comprises: a housing (1) comprising a light emitting unit (11) emitting light having disinfecting/sterilizing effect and a connector part (5). The separate unit (8) comprises: an optical window (4) being transparent for light emitted from the light emitting unit (11), a first coupling part and a second coupling part, where the first coupling part during use is attached to the connector part (5) of the light source (100), and the second coupling part during use is attached to the connector part (10) of the device, such that the device (9) are in complete extension of the light source (100) with no overlap, and the first coupling part is located at one side of the optical window (4) and the second coupling part is located on the other side of the optical window (4), when disinfection/sterilization of the device takes place.
