Desert Spirit Lamp

Desert Spirits only appear once the underground desert has been taken over by the Corruption or the Crimson, so on a fresh Hardmode world you need the spread to reach the sand before you can start looking. They are uncommon on their own and the lamp is a rare roll on top of that, which adds up to a long stay in a biome that is unpleasant to camp in.

It looks like a light source and is not one. Placed on a table it stays dark, and a room built around it still needs a torch or a candle before the game will count the housing. Treat it as a prop. It also only sits on flat furniture surfaces, so a shelf or a bare wall will not take it.