Why the lights are dimmed and the blinds need to be raised during takeoff and landing?
This is a security emergency. In case of evacuation - the passengers and crew will already be adapted to the darkness. This in turn will allow them to move faster.
Blinds are to be opened for the same reason, if we consider evacuation during the day. Passengers will benefit from natural light during the evacuation, while the cabin crew will be able to assess the external situation and decide which side will be safer to carry a possible evacuation.