In Chapter 16, sunshine appears as an important symbol.
There are three important features of the sunshine. First, Pearl catches the sunshine and even stands in the sunshine on her way; in contrast, Hester cannot reach it.
The second one is that the phantasmagorical sunshine cannot exist for a long time. Hester herself says that "it will soon be gone".
Third, although Hester is not able to catch the sunshine, Pearl "had absorbed it into herself, and would give it forth again, with a gleam about her path, as they should plunge into some gloomier shade."
To conclude from the first and second features, the sunshine represents innocence. As a woman, who especially committed adultery, the innocence briefly exists in childhood will never appear on her again. But as an elf-like child, Pearl still possesses innocence.
Observing from the third point of view, as an extension of Hester's life and a real Scarlet Letter, Pearl may perform the duty of a protector of Hester later and will save Hester from potential plights.