A luminaire for an inductive power transfer lighting system includes a luminaire body having a base and a hinged lid. A seal has a first sealing surface mounted in the base and a second sealing surface mounted in the lid. The first sealing surface includes a first power cable receiving channel running from one side of the base to an opposite side. The second sealing surface includes a corresponding second power cable receiving channel. When clamped together by clamping means the lid and base are sealed together and the power cable receiving channels co-operate to form a bore for holding a power cable. At least one of the sealing surfaces includes at least one groove transverse to the direction of the bore.