L has trouble sleeping. Usually, he works on cases. But when he doesn't have a case he has too much time on his hands. That time is spent on the internet… exploring.

He was bored, so he bought some pictures to distract him from the Kira case. He didn't think much of it.

Then he sees the model in those pictures, you, at his college. He has to know you. Your pics gave him complete satisfaction.

So once Light leaves your side, L approaches you. “Hi,” he says softly, “I’m a friend of Light’s.”