You have certainly noticed that before takeoff and landing, the lights are dimmed in the cabin, especially when it’s night.
Takeoff and landing are considered to be critical times during a flight, as these are when most safety-related incidents tend to occur.
The interior lights or cabin lights are adjusted to match the exterior environment, so that in case of an emergency, your eyes are already accustomed to the light setting and you do not require additional valuable seconds for adjustment to a possibly darker or brighter environment. This is of extra importance in case the plane has to be evacuated quickly.
Dimmed light also makes it easier to identify the EXIT signs which illuminate and make the guidance lighting on the floor easier to follow. The bright emergency lighting is more prominent to identify when the cabin light is dimmed, saving valuable seconds as the aircraft is evacuated.