Shields in Star Wars are generally not visible unless bounded on one or both sides by atmosphere. They may or may not allow physical objects to pass through, depending on the type of shield, but always block turbolaser blasts. Hull armoring may be present; if it is present, it may offer protection equivalent to anywhere from 0.25-3 meters of solid steel, via analyses of impacts on Imperial Star Destroyers which have succeeded or failed to do significant damage. However, large unarmored windows are present. It is thus desirable to have shields up at all times.