A lit oil lantern is a light source used for exploring dark caves. It is created by lighting a oil lantern (oil) and can be extinguished to return it to the unlit state. It is made with level 26 crafting by using an oil lamp (empty) with an iron oil lantern frame to create a oil lantern (empty)(requires 26 smithing), then filling the empty lantern with lamp oil (requires Swamp Tar) at the Chemist's west of Rimmington. 26 Firemaking is required to light it. It will eventually go out, and will require more lamp oil before it can be relit. Although it does make dark places lighter, they are still darker than the outside world. If you wish, you can carry another light source along with your lantern or use the bat familiar to brighten dark areas even further.
An oil lantern can be made by combining with an oil lantern frame (forged from iron) with an oil lamp (blown molten glass) for 50 Crafting experience. Combining the lantern frame with the lamp does not require a furnace or anvil.