US Patent 10031356 Fail safe mechanism for switchable window

An optical device, having an active matrix, containing polymer dispersed liquid crystals, guest-host liquid crystals, suspended particles and/or polymer stabilized cholesteric liquid crystals, the active high transmissive mode has at least 40% of incoming light transmitted through the optical device and in low transmissive mode less than 40% of incoming light transmitted through the optical device, the active matrix is switchable between high transmissive mode and low transmissive mode. The optical device containing a fail-safe mechanism, which is capable to switch the active matrix from a low transmissive mode in a high transmissive mode without the power of an applied grid.