This would be an interesting addition, as a lightsaber does create light, and so having night vision would make sense. I just wonder if it's not a bit overpowered, especially if the night vision is infinite, as usually you a spell like lumos that gives night vision for a limited amount of time. If I understand this correctly, the lightsaber would give unlimited night vision, which seems slighly overpowered, in my opinion. To balance this, there could be a time limit on it, forcing you to close and reopen your lightsaber, so the lightsaber would pretty much function as a replacement for lumos, which could be interesting.