"Ah, the Hand of Glory! Insert a candle and it gives light only to the holder! Best friend of thieves and plunderers! Your son has fine taste, sir."
-- Mr. Borgin, when Draco admires the object in Borgin's shop
The Hand of Glory is a magical object which gives light only to the holder. It looks like a shriveled arm.
The Hand of Glory is drawn from English folklore, described as a withered human hand whose fingers, when lit like candles, cast a charmed sleep on members of the household so the thief can rob the house.
From the Web
"Hand of Glory" from Wikipedia