If it is an old film it could be The Love War starring Lloyd Bridges and,I think,Angie Dickinson.Two sets of aliens bring their war here and their sunglasses are the only way of seeing the alien bodies beneath their human disguise.When killed they glow and disintegrate.
Definitey John Carpenter's 'They Live', starring 'Rowdy' Roddy Piper. The glasses also let you read bill boards adverts properly by showing their hidden poilticol messages.