means many non mechanical means 11 can be employed to render clear glass plastics and liquids opaque or transparent by direct electrical means for example in liquid crystal displays as used in computer displays watches calculators etc the application of the electric field to certain liquids renders them opaque a sandwich construction of glass with such liquid and electrode arrays enclosed could be utilized to render the windshield 12 opaque techniques also exist for applying electric fields to certain specially formulated glass and plastics which will render them opaque in the case of plastics this would require a layer of such plastic on the inside of a regular safety glass windshield 12 since plastics are easily scratched by dust and debris when driving at high speeds techniques also exist for polarizing glass by means of electric fields it is well known that two pieces of polarized glass with the planes of polarization parallel are transparent but with the planes of polarization at ninety degrees are opaque this principal is used in polarized sunglasses to eliminate glare since reflected light is polarized a windshield 12 consisting of two layers in a composite sandwich construction in which one layer is permanently polarized in one plane and the other is polarized electrically in a plane at ninety degrees to the former can be made alternatively transparent or opaque upon the application of an electric field in a different embodiment both layers may be of electrically polarized material in which the planes of polarization.