Storm Protection Roller Shutters
https://lorenzoufcf499.skyrock.com/3327388746-The-Urban-Dictionary-Of-Roller-Shutters-Templestowe.html
Or the louvered slats of vineyard shutters can be fairly cleverly changed so that even during the day, when you require light to be let into the room, an onlooker's line of sight is disturbed, blocking their view