Sea Lantern

"It's dark at the bottom of the ocean. Black, cold, and full of unseen dangers. But a handful of Minecrafters, those brave enough to delve deep below the waves, have reported seeing lights in that darkness. Just before they're attacked by spined monsters with a single, enormous eye. Aargh!"

- Duncan Geere

Sea lanterns are underwater light sources that appear in ocean monuments and underwater ruins.

Obtaining
Sea lantern itself can only be obtained when mined with a tool enchanted with Silk Touch. When broken using anything other than a Silk Touch enchanted tool, it drops 2–3 prismarine crystals. The Fortune enchantment increases the amount of prismarine crystals dropped. This method of obtaining sea lanterns is wasteful though; the 4 prismarine shards and up to 3 of the prismarine crystals used to craft it are non-retrievable.

Natural generation
Sea lanterns generate naturally in ocean monuments as their light source.

Light source
Sea lanterns emit a light level of 15, the brightest possible light level in the game. They produce the same amount of light as glowstone, redstone lamps, jack o'lanterns, and beacons.

Trivia

 * The animation shows a very faint 'rippling' effect.