Are you ready for your Christmas Eve gig? It's a rare Christmas Eve service that doesn't dim the lights. Be sure your stand light is packed. If you don't own one, buy or borrow one so you're ready to perform in the dark.
If you've never played harp in the dark, practice at home a few times. You can do this even without a stand light. Turn all the lights in the room off, save a lamp that shines on your music stand. A dark room changes how your strings look and for most of us, the first time is a surprize. Expect the dark to be different. Plan ahead. Take a light for your music and prepare your eyes to find the strings without bright light.