Sunlight kills vampires. Right? That’s the assumption of many modern vampire stories. However, this notion seems to have been created for the convenience of movie makers. Nosferatu, an unauthorized German adaptation of Dracula, seems to be the source of this common assumption.
In the book Dracula, the count can walk about during the day but is less strong and fast. There is one other thing about him in the book that is never shown in movies. In addition to not having a reflection, he does not cast a shadow. Try showing that in a movie, at least before the age of CGI. It would be impossible to light. Movie makers needed a dramatic way to kill the vamp at the end and mere exposure to sunlight became the conventional way to do it.
Vampires come from the legends of many countries, and when candles and oil lamps were the only way to have any light at night, the hours of darkness between dusk and dawn could be very scary. Anything could be out there, waiting to catch you and have its way with you. It was better to stay inside and bar your doors. If something seemed to be able to creep inside and attack you no matter how tight your doors were locked, like a disease, then you imagined creatures that could slip through tiny cracks to get you.
If there was a recent death in your village, you might well dig up the corpse and chop off its head to make sure it was dead. It was the only thing people could do, they had no concept of germs and viruses. No one don digs up corpses at night, they wait for daylight hours. Then you find the sinister fiend has returned to the grave after creeping out at night to attack you! Hey, we’re talking superstitious peasants here, logic wasn’t their strong suit.
Now the sunlight kills vampires idea is so standard that writing a story with vampires playing beach volleyball at noon would take some explaining. I understand that the “vampires” in Twilight do carry on in daylight, and that’s when they sparkle. I suppose you really can’t sparkle when there is no light. I don’t know that for sure because I would only read Twilight if I had a gun to my head the whole time.
So writers of horror fiction, urban fantasy, paranormal romance, and any other story that contains a vamp or two, remember that there is nothing that can’t be changed. Vampires are fictional and each writer can pick and choose which classic details to use or ignore them all. Early movie makers created a new convention just because it was easier to show, and you can do what you want with your vampires also.