u/Mahaute

Yotsuba Light is Light under specific circumstances, when he has actually a goal, when he has to be on his best behavior since he is under heavy monitoring and not free, when he has to fight to get his life back on track and reclaim his freedom. He is the real Light, but Light being bored and apathetic at the beginning of the story is also the true Light, as Light being Kira is again the true Light, but the true Light who had committed murders and committed to a new god-identity. His core personality does not change, only his motivations, because circumstances/constraints around him change.