Polarized Glass Roof

Polarized glass only allows a fraction of light through based off the direction of wave length of the light.  If you double up on panes and then slowly rotate one of the panes the amount of light coming through will be directly related to the angle of rotation of the second pane.  The long and short is make a window with polarized glass where one of the panes and rotate (perhaps round windows).  Then if you needed privacy or wanted to block the harsh summer sun you could rotate the panes.  I see the best viable option for it in sky lights where it's difficult to get blinds that work horizontally.