I'm sorry, but anyone who doesn't see that Light is an NTJ probably doesn't understand the archetypes behind MBTI. Sometimes one or even two letters are disputable, but not in this case. Ni. Future. Planning. Te. Cold reasoning. The end.
He's the same literary type as Lelouch in Code Geass, even though I suppose Light is an ENTJ and Lelouch is an INTJ, because Lelouch's Fi is clearly more developed.