According to Dr Goldberg, who I heard on Huberman's podcast[1], morning sunlight so you can get red light. Dusk/twilight also has red light, but I've heard that it's helpful to combat the effect of bright light before sleep, like that from screens, for some reason I forget. Now I make sure to get a bit of both.

[1] https://www.hubermanlab.com/episode/dr-jeffrey-goldberg-how-...