Sunlight in Barovia
By the will of the Dark Powers (Vampyr), the sun never fully shines in the lands of Barovia. Even during the day, the sky is dimmed by fog or storm clouds, or the light is strangely muted. Barovian daylight is bright light, yet it isn’t considered sunlight for the purpose of effects and vulnerabilities, such as a vampire’s, tied to sunlight.
Nevertheless, Strahd and his vampire spawn tend to stay indoors most of the day and venture out at night, and they are subject to sunlight created by magic.
In my game, Strahd is immune to sunlight. He has an additional heart created to subvert the effects of the sun. Shout out to u/Chaouleon and their post: Castle Ravenloft - Underground Laboratory (47x66) for the awesome idea.— Philbo