<p><strong>In-Universe Explanation</strong>
Simply because he can't. <strong>Light doesn't know L's name to write in the Death Note</strong>. <br>You also have to realise L's intelligence and the level of wits they are matching. L made tremendous precautions and implied to Light that he knew how the Note works. He had also made it clear that if he died in the near future, Light is to be the primary suspect for Kira. </p>

<p>Additionaly, the write has given us multiple Rules of Deathnote. Among them the following relate to this scenario. The 23 day rule plays into the fact that 23 days is in the near future and L dying in that period would make the police suspicious of Light.</p>

<blockquote>
  <ol>
  <li>If you write die of disease with a specific disease's name and the person's time of death, there must be a sufficient amount of time for the disease to progress. If the set time is too tight, the victim will die of a heart attack after 6 minutes and 40 seconds after completing the Death Note.</li>
  <li>If you write, die of disease for the cause of death, but only write a specific time of death without the actual name of disease, the human will die from an adequate disease. But the <strong>Death Note can only operate within 23 days (in the human calendar)</strong>. This is called the 23 day rule.</li>
  <li>If you write die of disease like before with a specific disease's name, but without a specific time, if it takes more than 24 days for the human to die the 23 day rule will not take effect and the human will die at an adequate time depending on the disease. <br>
  <a href="http://deathnote.wikia.com/wiki/Rules_of_the_Death_Note" rel="nofollow">How to Use: XXVII/XXVIII</a></li>
  </ol>
</blockquote>

<p>It may also be physically impossible for Deathnote to give a genetic disease. So L may still die from a Heart Attack. Though we have no idea about L's family since he was indeed an orphan.<a href="https://en.wikipedia.org/wiki/Huntington%27s_disease#Genetics" rel="nofollow">Huntington's Disease</a></p>

<p><strong>Out-Universe Explanation</strong> You need to remember this is an Anime, and using such obscure tactics wouldn't make it easily understandable. The point is to understand this is indeed a fantasy thriller anime, that is meant to be an engaging match of wits and not knowledge. Light is just a high school student and not a medical doctor who is trying to find out obscure ways to kill the individual. Point I am trying to make is that the "Rules of Death Note" may be a writing device to cover such plot holes, but they may or may not be enough to cover all.</p>

CC BY-SA 3.0
2016-09-19T15:37:47.313Z
I object that he could not know his name, he had Rem on his side and since Misa knew his name she could haave easily told Rem. Rem might even have seen L's name herself. But the 23 day rule was not known to me which renders my theory useless.
Akshat Batra
CC BY-SA 3.0
2016-09-19T15:40:47.370Z
Also, L already treated Light as the primary suspect even after episode 'Execution' he could have easily fooled the task force with by lending his death note. All that said the 23 day rule really puts up some real limitations.
Akshat Batra
CC BY-SA 3.0
2016-09-19T21:05:57.930Z
@AkshatBatra I’m pretty sure that there is another rule out there that while Shinigami will always know any person’s real name (they do have Shinigami eyes, after all) they are forbidden to *tell* any human. I don’t know where I would find quoteable material, though.
Jan
CC BY-SA 3.0
2016-09-20T02:48:56.723Z
@AkshatBatra Misa didn't know L's name either. She was immediately captured when she came to face with L. Later when she got her memories back, she couldn't remember L's name either. Also as Jan said, Ryuk/Rem wouldn't tell L's name to Light.
Arcane
CC BY-SA 3.0
2016-09-20T17:56:02.227Z
I know she was taken immediately, but she saw L's face and could have told his name to Rem during her torture so she can tell it to Light. That is assuming that Rem was not present when Misa met L. But again, @Jan says something about a rule that does not permit her to. So, once again my theories are crippled by the death note's rules
Akshat Batra
CC BY-SA 3.0
2016-09-20T17:57:24.803Z
Also, if Light was so concerned about not becoming the prime suspect due to what L said to the task force, why does he snear when Misa saw L? He even commented how everything would be fine now that Misa knows his name.
Akshat Batra
CC BY-SA 3.0
2016-09-21T03:58:54.117Z
@AkshatBatra If you rewatch that particular scene, Light assumed he had won, he would simply ask Misa L's name and kill him at his convenience. Misa even commented that "this  ma'n's name is not Ryuzaaki"or something. However when Light calls Misa after excusing from L, L answers MIsa's phone and informs Light that Misa Amane had been captured for suspicions of being the 2nd Kira.
Arcane
CC BY-SA 3.0
2016-09-19T12:27:58.143Z
2016-09-19T12:27:58.143Z
Arcane
<p>I recently started watching Death Note and have reached episode 17's end.</p>

<p>Light hid his notebook in the jungle, could he not have killed L? I know that L said that would  make Light the prime suspect but what if he writes the cause of death to be a slowly degentrative disease like Huntington's (which would make it VERY ironic given how proud L is of his track record)? He can make it kill L early by specifying his date of death like he did with Ray Penber's fiancé. And L would become less and less useful as he loses control over his body.</p>

<p>This method would be especially convincing since no one has yet (as far as I have seen in the series) discovered that he can determine the cause of people's death.</p>

<death-note>
Light's actions before hiding his death note
# Light's actions before hiding his death note
Posted by: username_0 on 2016-09-19
I recently started watching Death Note and have reached episode 17's end.

Light hid his notebook in the jungle, could he not have killed L? I know that L said that would make Light the prime suspect but what if he writes the cause of death to be a slowly degentrative disease like Huntington's (which would make it VERY ironic given how proud L is of his track record)? He can make it kill L early by specifying his date of death like he did with Ray Penber's fiancé. And L would become less and less useful as he loses control over his body.

This method would be especially convincing since no one has yet (as far as I have seen in the series) discovered that he can determine the cause of people's death.
**Tags:** death-note
---
## 1 answers
### Answer by username_1 on 2016-09-19. Score: 4 | Accepted answer
**In-Universe Explanation**
Simply because he can't. **Light doesn't know L's name to write in the Death Note**.   
You also have to realise L's intelligence and the level of wits they are matching. L made tremendous precautions and implied to Light that he knew how the Note works. He had also made it clear that if he died in the near future, Light is to be the primary suspect for Kira.

Additionaly, the write has given us multiple Rules of Deathnote. Among them the following relate to this scenario. The 23 day rule plays into the fact that 23 days is in the near future and L dying in that period would make the police suspicious of Light.

> 1. If you write die of disease with a specific disease's name and the person's time of death, there must be a sufficient amount of time for the disease to progress. If the set time is too tight, the victim will die of a heart attack after 6 minutes and 40 seconds after completing the Death Note.
> 2. If you write, die of disease for the cause of death, but only write a specific time of death without the actual name of disease, the human will die from an adequate disease. But the **Death Note can only operate within 23 days (in the human calendar)**. This is called the 23 day rule.
> 3. If you write die of disease like before with a specific disease's name, but without a specific time, if it takes more than 24 days for the human to die the 23 day rule will not take effect and the human will die at an adequate time depending on the disease.   
>    [How to Use: XXVII/XXVIII](http://deathnote.wikia.com/wiki/Rules_of_the_Death_Note)

It may also be physically impossible for Deathnote to give a genetic disease. So L may still die from a Heart Attack. Though we have no idea about L's family since he was indeed an orphan.[Huntington's Disease](https://en.wikipedia.org/wiki/Huntington%27s_disease#Genetics)

**Out-Universe Explanation** You need to remember this is an Anime, and using such obscure tactics wouldn't make it easily understandable. The point is to understand this is indeed a fantasy thriller anime, that is meant to be an engaging match of wits and not knowledge. Light is just a high school student and not a medical doctor who is trying to find out obscure ways to kill the individual. Point I am trying to make is that the "Rules of Death Note" may be a writing device to cover such plot holes, but they may or may not be enough to cover all.
> **Comments:**
> **username_0** (2016-09-19): I object that he could not know his name, he had Rem on his side and since Misa knew his name she could haave easily told Rem. Rem might even have seen L's name herself. But the 23 day rule was not known to me which renders my theory useless.  
> **username_0** (2016-09-19): Also, L already treated Light as the primary suspect even after episode 'Execution' he could have easily fooled the task force with by lending his death note. All that said the 23 day rule really puts up some real limitations.  
> **username_2** (2016-09-19): @AkshatBatra I’m pretty sure that there is another rule out there that while Shinigami will always know any person’s real name (they do have Shinigami eyes, after all) they are forbidden to *tell* any human. I don’t know where I would find quoteable material, though.  
> **username_1** (2016-09-20): @AkshatBatra Misa didn't know L's name either. She was immediately captured when she came to face with L. Later when she got her memories back, she couldn't remember L's name either. Also as Jan said, Ryuk/Rem wouldn't tell L's name to Light.  
> **username_0** (2016-09-20): I know she was taken immediately, but she saw L's face and could have told his name to Rem during her torture so she can tell it to Light. That is assuming that Rem was not present when Misa met L. But again, @Jan says something about a rule that does not permit her to. So, once again my theories are crippled by the death note's rules  
> **username_0** (2016-09-20): Also, if Light was so concerned about not becoming the prime suspect due to what L said to the task force, why does he snear when Misa saw L? He even commented how everything would be fine now that Misa knows his name.  
> **username_1** (2016-09-21): @AkshatBatra If you rewatch that particular scene, Light assumed he had won, he would simply ask Misa L's name and kill him at his convenience. Misa even commented that "this  ma'n's name is not Ryuzaaki"or something. However when Light calls Misa after excusing from L, L answers MIsa's phone and informs Light that Misa Amane had been captured for suspicions of being the 2nd Kira.  
---
