Obscuring system for an aircraft gyroscopic instrument

An obscuring system for an aircraft gyroscopic instrument arranged to avoid distracting the attention of crew members during critical flying conditions and comprising means for energizing said system, a liquid crystal light valve constructed so as to be transparent when not powered and opaque when effectively energized, an electric transformer arranged so as to energize said liquid crystal light valve whenever said power supply is effective to operably energize said transformer, a protective sensor switch responsive to a predetermined fault condition to energize said transformer and to render said light valve opaque, a control switch having a plurality of circuits one of which directly connects said power supply to said transformer in a shunt circuit parallel to said sensor switch, another of said circuits which is in series with said sensor switch causes said light valve to become energized when said sensor switch closes in response to the detection of a fault condition, yet another of said circuits when closed causes said light valve to remain transparent.