Hard Light Bridges and Hard Light Walls are a puzzle element of Portal 2. They are solid slats of light produced by special emitters, and can be redirected through portals (just like lasers and funnels). Bridges are horizontal, and players can use them as a floor or ceiling. Walls are vertical, and can be used to block turret fire or catch flying objects, like cubes. They can also be painted with blue gel.
Use a prop_wall_projector to place one in your map.