Cathode-ray tube with excitation-time-dependent color for moving-target-indication

A cathode-ray tube that has been developed for radar applications differentiates between fixed and moving targets by a change in color. The tube employs a two-layer screen separated by a barrier that is transparent to light but opaque to an electron beam. The layer facing the electron gun is comprised of a mixture of an ultraviolet-emitting phosphor (P16) and a red-orange phosphor (an improved P 19 type). The layer facing the observer is a long-decay green phosphor (P2). The buildup and decay times of the P2 phosphor are lengthened under UV excitation as compared with electron-beam excitation. Under operating conditions when the displayed information is stationary, the mixed phosphor layer of P16 and P19 is excited, emitting UV and red-orange light. The UV in turn excites the P2 to a level so that red and green combine to appear white. For moving targets, excitation time is insufficient for the green to reach its steady-state maximum, therefore the moving target appears red-orange. Differentiation between fixed and moving targets is shown by variation in the color shift because of different excitation times involved.