A small, transparent container holding a transparent medium of large dielectric constant (such as nitrobenzene) and a pair of metallic plates to which is applied a large voltage producing a strong electric field across the medium. The cell is usually placed between a pair of prisms transmitting only plane polarized light. The assemblage is used in one of two ways. (a) The prisms are so oriented that their planes of polarization are parallel. Light transmitted by the one is then normally transmitted by the other. With no difference of voltage between the plates, the electric field is zero and light can pass through the system. When voltage is applied to the plates, the resulting electric field rotates the plane of polarization of light passing through the Kerr cell and no light passes through. (b) The prisms are so oriented that their planes of polarization are not parallel. No light normally passes through, and applying voltage to the plates then rotates the plane of polarization of the light passing the first prism until it does pass through the second prism. The Kerr cell is used as a shutter, e.g., to generate pulses of light or to time the intervals between pulses. Some distance measuring instruments use Kerr cells for timing pulses or determining phase difference.