A flick of a switch can change the opacity of a window, turning it cloudy, clear or somewhere for privacy and camouflage purposes, according to Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences. David Clarke and colleagues describe details in the journal Optics Letters. The tunable window comprises a sheet of glass or plastic, sandwiched between transparent, soft elastomers sprayed with a coating of silver nanowires, too small to scatter light on their own. Applying a voltage cause the nanowires to attract, deforming the elastomer layer randomly make the sheet opaque. Switch off the power and the sandwich reverts to its clear state.