“Happiness can be found even in the darkest of times … if one only remembers to turn on the light.”
Meant to include that in my original post about the movie–I rather liked it, not least for being not nearly as trite as it could have been, if written even a little differently.
lnhammer points out that this thread is picked up from the moment the film opens, when we see Harry learning to light a magical light to read by beneath the covers.
Perhaps someone who knows the book better than me can say whether this line was also in the book, or created for the movie.