Light Yagami is the protagonist of the popular anime and manga series Death Note. In the series, Light discovers a mysterious notebook that has the power to kill anyone whose name is written in it. He begins to use this power to rid the world of criminals and establish himself as a god-like figure. Throughout the series, Light is pursued by a highly intelligent detective known only as “L,” who is trying to uncover his true identity. The question of how Light knows L’s name is a central plot point in the series and is revealed in a dramatic scene later in the story.
Initially, Light has no idea who L is and has only a vague description of him. L is a highly secretive figure who operates entirely in the shadows, and Light has never met him in person. However, as the series progresses, Light becomes increasingly obsessed with uncovering L’s true identity and defeating him. He uses a variety of tactics to try and uncover L’s name and face, including manipulating the media and planting surveillance devices in L’s headquarters.
It is not until episode 17 of the anime series (or chapter 22 of the manga) that Light finally discovers L’s true name. In this episode, Light has arranged a meeting with L, disguised as a member of the Task Force that is working with L to catch Kira (Light’s alter ego). During the meeting, Light manages to touch L’s hand and write his name on a small slip of paper hidden in his watch.
Once Light has L’s name, he is able to use the Death Note to kill him. However, L has also been planning for this eventuality and has set up a number of backup plans to ensure that his legacy will continue even if he dies. Ultimately, L’s true successor is revealed to be a young detective named Near, who uses his own intelligence and cunning to bring Light to justice.
So, in short, Light knows L’s name because he manages to touch L’s hand and write it down without L realizing what is happening. This is a key moment in the series, as it marks the beginning of Light’s ultimate downfall and the start of L’s legacy continuing through Near. The revelation of L’s name is also a significant moment for the audience, who have been waiting eagerly to discover the true identity of this enigmatic character.