The Lab is a room in Gloomy Manor in the game Luigi's Mansion: Dark Moon. It is located southwest of the Common Hall and directly below the Secret Pocket. The Lab is also the place where Luigi first obtains the Dark-Light Device.
During A-4: Visual Tricks, Luigi must head here to get the Dark-Light Device. However, as Luigi heads toward the Lab, the door to it suddenly disappears and E. Gadd tells Luigi that he has to find another way around. Luigi eventually enters the Lab through a fireplace from the Parlor and locates the Dark-Light Device. However, the Greenies aren't going to have him get it so easily and proceed to fight him while wearing shades. Luigi vacuums up the Greenies and earns the Dark-Light Device.