Have you ever been driving your car and as you turn at different angles the Sun is in different spots and you have to keep squinting or move the Sun Visor? Why not have the Sun Glasses, which are clear, but upon a voice command are instantly shaded? How can someone build such a thing you are probably saying? And you probably want a pair when they do.
Of course for all we know the military already has such a thing for special helmets used in operating very high tech equipment and you are now thinking that you may have even remembered such a thing in some Sci Fi Space War thriller movie. Since the sunglasses would be fairly close to your mouth you could use these on Motorcycles without worrying about engine noise disruptions and that would mean better safety too.
But the applications are endless and such technologies could protect your eyes at the beach and perhaps cut down on the huge number of traffic accidents each year in the United States. Truck drivers, pilots and even skateboarders would use them and love them, so when are you going to design them?