All low beam lights should have a vertical cut-off built in that prevents the light from shining "upward" and into the faces of the oncoming traffic. This is accomplished by building a shield into the light, and it is the reason that low beams don't shine very far down the road or light up overhead signs.
High beams do not have the vertical cutoff, and they shine a much larger light pattern down the road.
Some cheap LED's don't have a vertical cut off in the low beam, and you should avoid using those.