Usually we say that a person is wan, or that their face is wan. But we can also say that their smile or their laugh is wan: weak, barely a smile or a laugh at all, maybe suggesting that they're sick or worried.
We could even describe light as wan: too weak, too pale, not strong. The wan light from this lamp isn't bright enough to make us feel cheerful or allow us to read a book.
You might look at the word "wan" and want to pronounce it to rhyme with "ban," "can," and "fan." But "wan" rhymes with "con," "Don," "fawn," "gone," "lawn," "pawn," "Ron," and "yawn." It's weird. You could try to remember this rhyme: When your strength is gone, your face is wan.