I wondered for a long time why the light inside an aircraft is always turned off when taking off or landing.
In case of emergency (which is more likely during take offs and landings) people should be prepared just in case. So during daytime, opening window shades and putting cabin lights to full makes the eyes used to sunlight so if something goes wrong and passengers need to be evacuated there will not be sudden change in light contrast which might lead to temporary blurred vision.
Same thing at night flights, window shades are open and cabin lights are dimmed.
Cabin lights interfere with vision out of the plane for flight crews. They cast a night time reflection and glare that affects them, but also affects uptake of actual navigation lights by others, such as collision and landing lights. With the cabin lights on, the collision and landing lights are difficult to pick out, especially from the air by other planes.
As a secondary consideration, power on takeoff is better spent by the engines and other systems than by lights in the cabin.