All aircraft in the Qantas Group fleet must have lights to full bright for take off and landing.
The reasoning is that the aircraft will be made more visable in bad visibility conditions to everyone around - ATC, other a/c etc.
Also if an incident does occur lights in the cabin that may still be operational will provide light to lead pax to their nearest exit.
Of course lights can be dimmed during cruise.
I do know that many asian carriers dim lights for t/o and landing.