User blog comment:Zathronas/Analysis by an Author: "This Will Be The Day"/@comment-15108745-20140110211826/@comment-24218038-20140111153352

Pyrrha said that we are the light to the grimms darkness. She also said the  have light and darkness inside. And when we acknowledge it, we can activate our semblance. So the light fading could be humans too.

Same with the day and night comment it could be the human as a species.