ray of light
1. Literally, a beam of light. A ray of light warmed my face through the window. How can you read in here? There's hardly a single ray of light!
2. Someone or something that brings one joy and/or hope, especially in a challenging situation. My daughter has been a real ray of light these days—I'm so glad to have her here as I fight this illness. After we moved, we got a puppy, which has been such a ray of light for the kids as they adjust to life in a new place.