A Type of Light Valve for Television Reproduction

The desirability of a light valve for the reproduction of television pictures is discussed, and the use of a suspension of opaque platelike particles for this purpose is shown to offer the particular advantages that the electron beam would be only a control mechanism and the picture brightness would be limited only by the light source and lens system. The theory of operation of such a suspension is described and it is demonstrated that inertial effects may be neglected and that the rate of orientation of the particles is independent of particle size and is a function of the viscosity and dielectric constant of the suspending medium and of the square of the applied voltage. The contrast ratio obtained may be made very high, although the optical efficiency will decline as the contrast ratio rises. It is found that suspension resistivity must be considered in practical application of the light valve, for if the field is applied through an insulating wall the valve will respond only to changes in potential of the outside of this wall, since leakage will prevent a constant wall potential from maintaining a field across the suspension. From the results of tests, the conclusions are drawn that the fundamental optical behavior of the suspensions considered is in accordance with the predictions of a theory based on simple assumptions, and that the suspensions fulfill the basic requirements of a television light valve.