Patent GB-620121-A (GB)
Title: Improvements in motor vehicle lamps
IPC: F21V7/04
Filed: 1945-03-29
Abstract: 620,121. Vehicle lamps. EVANS, S. C. March 29, 1945, Nos. 7915, 11989 and 20714. [Classes 39(ii), 75(ii) and 75(iv)]. In a motor vehicle lamp comprising at least one bifocal or multifocal reflector whereof at least one quadrant is of parobolic formation characterized in that the major ordinates of the principal sections thereof are unequal, varying from a minimum value KV, Fig. 22, in one plane, e.g. the vertical plane to a maximum value KH in a plane perpendicular thereto, in combination with an electric light source comprising at least one filament or other luminous element disposed substantially at right angles to the reflector axis, the greater part of the whole light source is dispersed substantially at right angles to the reflector axis, and means is provided for varying the vertical and/or horizontal spread of the resultant illumination either at the will of the driver of the vehicle and/or automatically under the control of mechanism in or outside the vehicle whereby the vertical spread of the illumination may be reduced with or without modifying the horizontal spread of the illumination. The means for modifying the spread of the illumination may consist of either electromagnetic deflecting mechanism adapted to change the position of the reflector, or of a plurality of light sources, e.g. 119, 123 and 134, Fig. 4, arranged one behind another along the reflector axis and capable of selective illumination. Any one or more of the filaments 119, 123 and 134 may be decentred with respect to the reflector axis and/or be of parabolic shape. Alternatively the light source may comprise a single parabolic filament the apex of the parabola lying on or off the reflector axis and directed towards the reflector, the latus rectum of the parabola being substantially equal to that of the horizontal principal section of the reflector. Other modifications are described in which the light source comprises either (a) a horizontal straight filament disposed at right angles to an axial straight filament, or (b) a pair of straight filaments disposed in line transversely of the reflector axis, or (c) a transverse straight or parabolic mercury vapour tube, or (d) a main parabolic filament and a secondary straight filament both disposed transversely of the reflector axis, the parabolic filament being nearer the reflector, and either or both filaments being decentred with respect to the reflector axis, or (e) a parabolic filament comprising two or more sections each adapted for independent connection to the electric supply, or (f) a parabolic filament as in (e) in combination with one or more straight filaments, or (g) a transverse horizontal straight filament in combination with two axial filaments, one of which is provided with a cup-shaped screen, or (h) a horizontal transverse straight filament in combination with a V-shaped filament, or (1) one or more filaments mounted in a festoontype lamp. The reflector may be symmetrical in both the horizontal and vertical planes as shown in Fig. 22; or the reflector may be symmetrical horizontally and asymmetrical vertically, or symmetrical vertically and asymmetrical horizontally, or asymmetrical both vertically and horizontally. The edge of the reflector may be provided with a screened or blackened rim portion to prevent light scattering. A unifocal reflector 231, Fig. 36, may be converted to a multifocal reflector by the application at its periphery of a cross member having arms 233, 234, 235, 236, of lengths corresponding- to the lengths of the different ordinates of a desired multifocal reflector. The cross member may have a lens at its centre for condensing the direct light emitted from the source, and such lens may be combined with a prismatic element. In a further construction a condensing lens may be mounted on a cup-shaped carrier on the electric lamp forming the light source, or the lens may be incorporated in the wall of the bulb. Alternatively the electric lamp bulb may be partially coated with reflecting paint or aluminium deposit for screening rays emitted above the horizontal. A lamp of the sealed type is shown in Fig. 54, the sealed enclosure comprising the multi focal reflector 318 closed by a disc 319 formed at its centre into a tube 320 which is closed at its inner end for securing the lead-in wires of the filament 312. An outer glass 325 is provided and the electric supply connections are made at the periphery of the lamp, or in an alternative construction at the centre of the reflector.