A control unit for use in a lighting system. The control unit comprises: a localization module which detects when a portable lighting device is within a predetermined vicinity of a fixed light source; and a controller which selects between different roles for the portable light source, the roles comprising (i) an independent role where the light output of the fixed and portable light sources are controlled independently of one another, and one or both of (ii) a slave role where the light output of the portable light source is adjusted in dependence on that of the fixed light source, and/or (iii) a master role where the light output of the fixed light source is adjusted in dependence on that of the portable light source. The controller is configured to switch to one of the slave role oi the master role in response to the detection of the predetermined vicinity.