Safety on flight

In each case, it is for safety reasons. Most accidents to planes happen at takeoff or landing. In daylight the blinds are raised, and at night the lights are dimmed so that if the passengers need to get out fast their eyes do not need to adapt to the outside light conditions, whether dark or bright. That way they will move quicker.

In addition to what Contrex posted, lights are dimmed to be able to see the the lighted emergency exits signs & the floor emergency exit lighting.

Thanks both contrex and TTH. Happy New Year!