Abstract: A liquid crystal display arrangement is provided with two liquid crystal cells containing twisted-nematic material, and positoned one cell behind the other. Both cells are between a pair of crossed polarizers, and the arrangement can be used to selectively reverse the contrast of a display or it can be used as a matrix display in which cross-talk between adjacent elements is minimized.

Abstract: An oscillator uses a delay line in a feedback loop to determine its frequency of operation. As the loop is capable of sustaining oscillations at more than one frequency the desired frequency is generated by an auxiliary delay line and is gated into loop at the correct instant by gating circuitry C.

Abstract: An LED display is provided with a reflective surface over those parts of the display which do not themselves emit light. This enables a polarizer to be used to enhance the display contrast under conditions of bright ambient light.

Abstract: A method of manufacturing an array of light emitting diodes in which a first insulating sheet carrying a first set of mutually isolated conductors is bonded to a sheet of thermally conductive material, a second, perforated, sheet carrying a second set of mutually isolated conductors is bonded to the first insulating sheet with the perforations overlying the conductors of the first sheet and the two sets of conductors crossing one another, light emitting diodes are placed in the perforations to contact each with one electrode a conductor of the first set and the other electrode of each diode is electrically connected to a conductor of the second set.

Abstract: The invention relates to the manufacture of arrays of light emitting diodes (L.E.D.'s) from a wafer consisting of an n-type epitaxial layer on an n.sup.+ substrate. The method includes the steps of forming p-type islands by diffusing a p-type dopant into the epitaxial layer of an n on n.sup.+ wafer, establishing contact with all of the p-type islands by means of a first set of conductors, mounting the wafer on a transparent support with the first set of conductors adjacent the support, depositing a second set of conductors on the n.sup.+ substrate and etching both the substrate and the epitaxial layer from between the conductors of the second set, the two sets of conductors being orthogonal and each p-n junction formed by a p-type island and the epitaxial layer being in contact with one and only one conductor from each set.