Many supernatural beings of evil are repelled, or even physically harmed by the holy rays of the sun. This is not the case for Zombies who are technically neutral, and not evil since they’re only acting on instinct. However this isn’t the reason they can come out during the day. The sun only has paranormally negative effects on those beings who have a certain level of demonic based DNA. This includes vampires, and werewolves. Zombies don’t have demonic DNA as they are merely living dead corpses under the power of the zombie virus.
The supernatural virus itself doesn’t have any demonic links but rather originates in magic, and alchemy commingling with dead flesh. This is also why religious artifacts like crosses, crucifixes, Bibles, Holy Water, etc. don’t work when it comes to repelling or killing zombies. Besides a few herbs that work as repellents you must eradicate zombies the hard way with brute force. Despite the zombies ability to exist in sunlight they are most often encountered at night since the glare of the solar rays impairs the vision of their less than perfect eyes. Eyes that are slowly entering a complete necrotic state as their body rots over the course of years. During the day a zombie will be drawn to the shade of foliage, caves, or human made structures. During a zombie apocalypse it makes sense to avoid wooded areas, and unsecure buildings, that provide them comforting shade.