My understanding from the Oz CAO's (20.11) is that an aircraft on the ground or below 1000ft with pax on board must have the cabin lighting switched on and the emergency lighting armed, or the emergency lights on.
Because the emergency lighting system is always armed during flight, as long as there is some lighting on, even if dimmed, then this meets the requirements of the CAO's.
I was also taught that dimming the lights illuminates the cabin to the same level as the emergency lighting system would illuminate, so if there was any need to evacuate and the main lights failed, then the eyes would not have to adjust so much to the emergency lights.
Do you have to dim the lights as part of your emergency landing prep at night?