Which nervous system dilates the pupils and allows more light to enter the eyes?

The correct answer is sympathetic nervous system.

The sympathetic nervous system is a component of the autonomic nervous system, together with the parasympathetic system. Their functions are opposite but coordinate to maintain homeostasis. The sympathetic system has a role to control the body's response during perceived threat (fight and flight reactions). According to this, it dilates the pupils, contracts the muscles, increases heart rate ...