A one-way lantern was a magical lantern that projected a light only the bearer could see.
The lantern appeared to project a kind of "one-way" light, visible only to those who grasped the handle and completely unseen by all others. For those who could see it, the lantern radiated bright light to a distance of 30 feet (9 meters), like a light spell. The light hampered the infravision of one who grasped, but not the infravision of others. Owing to the size of the lantern, only three human-sized creatures could try to hold the lantern at once.
The Halruaan mage Daltim Flamefist came across a one-way lantern on an expedition in the 1360s DR. He wrote details of it in his spellbook Daltim's Tome of Fire, which he lost in Tethyr in the 1360s DR. It was possible that more one-way lanterns might be traded in Faerûn or lost in old treasure hoards.
Daltim theorized that the one-way lantern had been fashioned for use by one or more humans in a group of elves or other creatures that possessed infravision. With the lantern in hand, they could see normally without projecting a light that would either spoil the infravision of their companions or revealing their position to others.