Not to sound dumb, but I have been a primarily mac user for a short time, but what is the light sensor? Are you talking about when you have your screen lit up to your preference, and you turn or tilt your head and it fades a little, kind of like what I think windows laptops can have, it's as far as I know, a thin sheet that you put on your screen and it's like a "privacy veil", so if someone was sitting next to you, they turn their head to see what you are doing, they can't see what's on your screen? I don't know who whole idea of the shield is though.