Display units with periscopic arrangement

Claim 1

A display unit for a head-up display system comprising a projector having an optical element defining its exit pupil, at least one periscopic arrangement and a combiner, the projector projecting light representing a display onto the combiner for reflection thereby to provide an observer with an image of the display superimposed on his view of the distant scene viewed by transmission through the combiner, each periscopic arrangement comprising a first reflective element and a second element parallel to said first reflective element possessing both light transmissive and light reflective properties, each periscopic arrangement being positioned adjacent to the optical element such that projected light from lateral portions of the exit pupil which would not otherwise be received by the observer without lateral head movement is transmitted to the appropriate portion of the combiner by successive reflections of said light at the said second element and the said first element.