Patent GB-457443-A (GB)
Title: Improvements in or relating to polarised light anti-dazzle lighting equipment for motor vehicles, and for general use
IPC: F21S8/10
Filed: 1935-05-28
Abstract: 457,443. Optical polarizing-apparatus. UNDERWOOD, L. R., 5, Thurlow Park, Torquay. May 28, 1935, No. 35906/34. [Class 97 (i)] [See also Group XI] In a road vehicle headlamp, street lamp, or other lamp projecting a concentrated beam of light polarized in a plane at 45‹ with the vertical and horizontal, polarizing means, such as a transparent laminated member 4 shown in Fig. 3, are disposed transversely across the light beam, and a transparent member 6 is disposed between the light source and polarizing means to deflect and direct the light upon the polarizing means at the required angle to effect polarization. The transparent members 4, 6 are comprised in a self-contained fitting for the front of the lamp, and the arrangement is such that substantially the whole of the beam is projected after polarization in the plane at 45‹ to the horizontal and vertical. In the lamp shown in Fig. 3, a pile of flat glass plates or films, forming a polarizer 4, is placed between two plates 5, 6 which are transparent and prismatically ribbed at 45‹ to the horizontal. The beam incident on the polarizer 4 is partly transmitted polarized in one plane at 45‹ to the horizontal, and partly reflected, polarized in a plane at right-angles to the first plane. The reflected component is refracted by the plate 6 so as to emerge as a beam parallel to the beam from the reflector 3 but in the reverse direction. The reflected beam component is reflected forward again parallel to the axis of the reflector, and, during reflection by the reflector 3, the plane of polarization of part of this beam component is rotated through 90‹. To rotate the plane of polarization of a further portion of this component, sectors 7 of mica, selenite or other material are provided on the lamp side of the polarizing system, disposed about axes XX, YY which are respectively parallel and perpendicular to the prismatic ribs. This component then passes forwardly through the polarizer 4 with the transmitted beam component, and the two components are redirected in a direction parallel to the lamp axis by the plate 5, which is prismatically ribbed similarly to the plate 6. In the case shown in Fig. 3, the refractive index of the material of the plates 5, 6 is 1À700. When the refractive index is 1À5, the members on each side of the polarizer 4 may be composed of two prismatically ribbed plates which may, as in Fig. 7, interengage so that total reflection takes place as shown, or may be arranged as shown in Fig. 8. Alternatively, each member may comprise a single prismatically ribbed plate with the apices of the prisms adjacent to the polarizer. The polarizer may be composed of about twenty thin plates of glass, or of a pile of thin films of gelatine, gelatine hardened with formalin or alum, celluloid, or other material. Such films may be formed by coating glass, celluloid, glass coated with celluloid or other flat material with the substance, e.g. gelatine, and allowing it to dry. The film, or a number of films, may be wound on a drum, the edges being gummed, so that a series of films is formed which may afterwards be flattened to form a pile. A glass or celluloid plate may be coated alternately with transparent substances of different refractive indices, e.g. gelatine and celluloid, or transparent plastics, e.g. those known under the Registered Trade Marks " Cellophane " and " Perspex," or cellulose acetate, cellulose nitrate, or other cellulose derivatives, which may be dissolved in amyl acetate, acetone, chloroform, ether, alcohol &c. Specification 457,542 is referred to.