Patent GB-457542-A (GB)
Title: Improvements in or relating to anti-dazzle equipment for motor vehicles
IPC: F21S8/10
Filed: 1935-05-28
Abstract: 457,542. Antidazzle screens. UNDERWOOD, L. R., 5, Thurlow Park, Torquay, Devon. May 28, 1935, No. 22717. Divided out of 457,443, [Group XI]. [Class 103 (ii)] [See also Groups VIII and XX] In an antidazzle system for motor &c. vehicles of the kind in which the light emitted from one vehicle is polarized in a plane making 45‹ with the horizontal and is viewed by the driver of an approaching vehicle through an analyzer having polarizing properties in the same plane, the analyzer, which is embodied in or associated with the windscreen or embodied in goggles worn by the driver, comprises an optical device for directing incident rays at the polarizing angle upon a polarizer device, and a second optical device for directing the rays transmitted by the polarizing device to the eyes of the driver. The polarizing device preferably comprises a pile of thin, transparent plates or films and the optical devices may comprise respectively double-concave and convex lenses, or, as shown in Fig. 2, plano-concave and convex lenses 10, 11, formed, for example, of glass or of the material known under the Registered Trade Mark " Perspex." To avoid undue edge-thickness of the lenses in the case of a large screen, the outer portions may be grooved to form a series of prisms having alternate plane and curved faces, the plane faces being parallel to the refracted rays and the curved faces having radii 'which gradually increase towards the periphery of the screen. The analyzer P may comprise two prism members A, B, Fig. 4, having interengaging surfaces 12, 13 inclined respectively at 34‹ and 90<0> to the outer plane faces of the members, the surfaces 12 being separated by polarizing means 4 and the surfaces 13 by black material 14. Light rays incident on the outer face of the member A pass without refraction to the surfaces 12 and are thereby refracted so that they strike the polarizing means 4 at the polarizing angle. In a modification in which provision is made only for the horizontal angle of vision, the prism angles increase towards the centre of the analyzer. The inclined surfaces may be curved. In a further modification the analyzer may be curved in plan view. The analyzer shown in Fig. 10, for use in binocular vision, comprises three interengaging prism members 19, 20, 21, the inclined faces of the outer members being laterally displaced by a distance equal to that between the eyes. The plates or films forming the polarizing means may consist of glass or preferably of a substance which can be deposited or produced as a thin transparent film such as celluloid, gelatine, or gelatine hardened with formalin or alum. The films may be formed by coating glass, celluloid, or celluloid-covered glass plates &c. with the substance, allowing it to dry, and then removing it from the plates. The several films of a pile may be stuck together at their edges to provide an air space between them. Alternatively the films may be wound in layers on a drum after removal from the plates and may be cut off to the required size. According to another method the plates may be coated alternately with substances having different refraction indices and which adhere to but do not react on each other ; for example gelatine and celluloid, or transparent plastics such as those known under the Registered Trade Marks " Cellophane " and " Perspex." Other films may consist of cellulose acetate, cellulose nitrate, or other cellulose derivatives which may be dissolved for example in amylacetate, acetone, chloroform, ether or alcohol.