Lamp Post
1How to craft it
Anvilwhat makes it different from a torch
Two things. It stays lit underwater, which most placed light sources will not do, so it is the honest answer for an ocean base or a flooded room you do not want to drain. And it takes a wire, so it can run off a switch, a pressure plate or a day and night timer for a lighthouse effect or a sign that only glows after dark.
It also satisfies the light requirement for NPC housing, so a row of them down a street of shop rooms handles the decoration and the housing rule at the same time.