The Night light (Originally Lamp of darkness & Dark lamp) is an item in the Dragon Quest game series series.
The Night light changes the time from day to night and can be used anywhere other than caves or towers. Like the Tick-tock spell, use of it sends the party to the entrance of the area it's activated in.
First game with the Lamp of darkness (called Dark lamp in the Game Boy Color Version). The lamp is found in the shop at Tedanki and can be obtained during the day. In the NES Version it can't be sold, while in the GBC Version, it will sell for 225 gold coins.
The Night light is in a chest within Whealbrook Adit, and can be obtained from there in the 2nd or 3rd Generation of the game.