We have performed detailed measurements of the far field diffraction pattern of an electrically switchable liquid crystal grating. The grating, with a period of 25 microns, was formed using interdigitated aluminum electrodes with a 15 micron gap between adjacent electrodes. The homeotropically aligned liquid crystal (ZLI-4792) had a thickness of 5 microns. We measured the diffracted intensity profile of HeNe Laser light (633nm) for different applied between adjacent electrodes. The amount of light diffracted into the first order relative to zeroth order is strongly dependent on the applied voltage. The locations of successive maxima and minima also shift with the applied voltage. We studied the diffraction theoretically using geometrical optics coupled with Kirchoff diffraction theory. This theoretical model is in substantial agreement with the empirical results.