In the Harry Potter books, Dumbledore’s magical device that removes light is called a Deluminator.
The Deluminator, also known as the Put-Outer, can extinguish nearby lights and later restore them. Dumbledore uses it outside the Dursleys’ home at the beginning of the series, turning street lamps off before leaving Harry on Privet Drive.
In Harry Potter and the Deathly Hallows, the device gains a more complex function. Dumbledore leaves it to Ron Weasley, and it helps Ron find Harry and Hermione after he abandons them. It produces a small light that leads Ron back to his friends.
The Deluminator is not the same as a Remembrall, which reminds its owner that something has been forgotten. It is also unrelated to the Pensieve and Time-Turner, which serve entirely different magical purposes.