The Light in Ariel’s Grotto Comes From the Surface.
That’s all. That’s so cool and perfect. It has to be hidden, but it’s not a dark and gross place, because to Ariel, everything in it is beautiful. Because it comes from her beloved Surface.
Of course, all light under the sea logically comes from the surface, that isn’t special. But in the rest of the ocean, the light from the surface is just generally dispersed so you don’t notice it. In her grotto, it’s not general—it’s focused on. The circular, tower-like shape of her grotto means all the attention is drawn up, to the surface, not just to the gallery of stuff she’s collected.
The Surface is the light that Ariel can see everything in her grotto by. Just like how she sees everything differently than the others under the sea, because she’s been up to the surface before. Her perspective is different. She literally sees everything in a different light.
The set design for this part of the movie is so cool.
(I know it’s obvious but I feel like if we appreciated the obvious more often we would realize why these movies are so good)