Scarlet Letter D.J. # 32 - Chapter 16: Part 2.

"As she attempted to do so, the sunshine vanished; or, to judge from the bright expression that was dancing on Pearl’s features, her mother could have fancied that the child 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. There was no other attribute that so much impressed her with a sense of new and untransmitted vigor in Pearl’s nature, as this never-failing vivacity of spirits; she had not the disease of sadness, which almost all children, in these latter days, inherit, with the scrofula, from the troubles of their ancestors. Perhaps this too was a disease, and but the reflex of the wild energy with which Hester had fought against her sorrows, before Pearl’s birth. It was certainly a doubtful charm, imparting a hard, metallic lustre to the child’s character. She wanted—what some people want throughout life—a grief that should deeply touch her, and thus humanize and make her capable of sympathy. But there was time enough yet for little Pearl!" (pg. 160-161 9th paragraph)
It was almost as if Pearl had taken away the sunshine by absorbing it like a flower. the sun to Pearl is like an energy source. This relates back to her being a part of nature. she is a growing flower and the sun gives her life. This means she would die in the shadows or evilness.