The voltage distribution in an electrooptic light-valve structure, consisting of an isotropic dielectric layer and a dielectrically anisotropic longitudinal electrooptic crystal sandwiched between conducting electrodes, has been analyzed in detail for the case where a spatial modulation in the charge density is introduced at the interface. The sensitivity of this sandwich structure is then defined as the reciprocal of the charge density necessary to produce the half-wave voltage across the electrooptic material. Several devices reported in the literature are then compared on a uniform plot of sensitivity versus spatial modulation frequency. The theoretical curves indicate graphically that, though the material characteristics alone determine the high-spatial-frequency sensitivity, the layer thicknesses drastically affect the low-spatial-frequency sensitivity. Since the electrooptic material and the isotropic dielectric material are usually chosen because certain characteristics (photoconductivity, optical perfection, low half-wave voltage, etc.) make them uniquely suited for a particular device, the major additional choice available in the design of the electrooptic light valve is this tradeoff of sensitivity for spatial bandwidth.