The downstand beams in the ceiling of the gallery conceal service walkways which provide access to the light fittings from above.  This allows for the maintenance of the roof lights and the lighting system to be carried out without disturbing the exhibition below.  The intensity of the natural light is controlled by louvres on the exterior of the rooflights.  The artificial lighting operates within zones which are allocated in between the plasterwork detailing in the vaulted section of the ceiling.