Buy OSRS Lantern lens
The Lantern lens is a round disc of glass in Old School RuneScape. It is a members-only item, and it is tradeable. Its main use is to finish a bullseye lantern. Add the lens to a bullseye lantern (unf) to make a bullseye lantern (empty). This step needs level 49 Crafting.
The bullseye lantern is one of the best light sources in the game. It has the highest brightness value of three. It is great for dark places like the Lumbridge Swamp Caves, since it does not ignite swamp gas there. It also stays lit when falling into water in most areas.
The lens has other uses too. Use a cut sapphire on a finished lantern to swap the lens out and make a sapphire lantern. The lens can also be combined with a bullseye lantern to make an emerald lantern or a sapphire lantern. Mix it with pink dye to create a rose-tinted lens.
Making a lens yourself takes 1 molten glass and level 49 Crafting, and it gives 55 Crafting experience. Buying the lens saves you that work, so you can light up dark caves and dungeons right away.