Apparatus comprises a first light source (11)； and a second light source (12) connected in series with the first light source (11) between first and second supply terminals. A controllable switch (18) is coupled in parallel across the first light source (11). A controller (14) is configured to selectively control the controllable switch (18) to conduct, thereby selectively switching the first light source (11) on and off whilst the second light source (12) remains switched on.
