Patent GB-408504-A (GB)
Title: Improvements relating to headlamps for vehicles
IPC: F21V5/00
Filed: 1933-08-28
Abstract: 408,504. Vehicle lamps. GUIDE LAMP CORPORATION, Anderson, Indiana, U.S.A. Aug. 28, 1933, No. 23876. Convention date, Aug. 29, 1932. [Classes 75 (ii) and 75 (iv).] Lantern fronts ; reflectors.-In a vehicle lamp a cover glass and/or a substantially parabolic reflector are so constructed as to project the light primarily to one side of the lamp axis but with the brightest portion of the beam substantially in line with this axis. Preferably a lower portion of the beam extends substantially across the full width of the road, and a pair of such lamps are mounted on a vehicle with their axes parallel so that the two beams overlap to produce maximum illumination at the centre of the road. Each lamp may be fitted with an electric lamp bulb having one filament at the focus and another above the focus of the reflector so that the beam projected to one side of the road is elevated or depressed when the lower or upper filament respectively is energized. In the form shown in Fig. 13 the cover glass of the near-side lamp is provided on its rear surface with upper and lower zones of vertical flutes 4, intermediate zones of vertical flutes 6, and central zones of shallow vertical flutes 5 and deeper vertical flutes 7, the flutes 4 being symmetrical full flutes adapted to spread light across the full width of the road, and the flutes 5, 6, 7 being asymmetrical and slightly greater than half flutes so as to project the greater portion of the light to the off-side and a smaller portion to the near-side. It may also be provided with a few shallow symmetrical vertical flutes 8 to spread the light a few degrees on either side of the centre of the road. The front surface of the cover glass is provided with zones of horizontal prisms which are slightly curved in vertical section, those in the top and bottom zones 17, 17<1>, 18, 18<1>, Fig. 12, being the strongest and adapted to distribute the light towards the bottom of the beam, those in the central zone 19 being of medium strength and used to form the centre of the beam, whilst those in the side zones 20 are the weakest and are used to form the top of the beam. If desired the flutes and prisms may be formed together on the front or rear surface of the cover glass. The cover glass for the off-side lamp is similarly constructed to project light in the opposite directions except that the asymmetrical vertical flutes project all the light to the near-side and none to the off-side. A few symmetrical flutes may be interspersed among the asymmetrical flutes, and vice versa, in order to blend the rays into a smooth beam, each pair of filaments may be replaced by a single movable filament, and the prisms 20 may be dispensed with by using lamps which are tilted slightly downwards. In the form shown in Fig. 32 the upper and lower portions 32, 34 of the reflector are tilted downwards and they are axially displaced with their foci at F<1>, F<2> respectively, the filaments 14, 16 being disposed between the foci. In this case the horizontal prisms are dispensed with in both lamps and the vertical flutes are similar to those described with reference to Fig. 13 except that the symmetrical flutes are preferably confined to the lower zones of the cover glasses. For use with a plane cover glass such a reflector is formed with upper and lower zones of full flutes 51, Fig. 41, and an intermediate zone of asymmetrical part flutes 53. Figs. 24-31 (not shown) illustrate diagrammatically the beams obtained by energizing one or more of the four filaments of a pair of lamps of any of the above constructions.