Windshields are susceptible to dirt, dust, acid rain and other elements even it was parked in the shades, thus making your vision unclear/obscure when rubbed by wiper blades especially at night. Try cleaning your windshield first with 3M scratch remover (this product also removes water spots) follow up with TW Clearvue. Clean your wiper blades as well. Wiper blades old or new are most efficient on clean and polished windshields.