Creatures vulnerable to sunlight suffer burns, blindness, or even death when exposed to daylight. Sunlight weakens their powers, leaving them unable to fight or defend themselves effectively. They must avoid exposure by hiding in dark places or avoiding the outdoors during the day.
In mythology, the sun is often linked to purity and life, making it fatal to creatures of darkness. Vampires and other nocturnal beings are prime examples of those who suffer greatly from sunlight exposure.