GB584666A - Improvements in or relating to light projectors - Google Patents

Abstract

584,666. Vehicle lamps; lenses. SOC. POUR LA FABRICATION DES PROJECTEURS ELECTRIQUES MARCHAL. Aug. 12, 1939, No. 23315. Convention date, May 11. [Classes 75 (ii) and 75 (iv)] In a light projector for automobiles comprising a reflector and stepped refractor, the luminous beam passing through the central zone of the refractor has such an angle of divergence as to illuminate the whole of the required field and the beams passing through the peripheral zones illuminate only central zones within the field where a higher illumination is required. Fig. 10 shows a vehicle headlamp comprising an ellipsoidal reflector 6 haying a light source 7 arranged at its focus F and fitted with a refractor formed in several steps f1, f2, f3, f4, f5, all having their focus at the other focus F' of the reflector but of differing focal lengths, the beams passing through the various steps illuminating areas G1 H1 I1 J1, .... G5 H5 I5 J5 respectively on a distant screen. In another construction the reflector is of hyperbolic section. In a further construction the reflector consists of several surface elements of which some may be elliptical in section and others parabolic or hyperbolic. Fig. 15 shows a reflector composed of three ellipsoidal portions 61, 62, 63 having one focus at F and the others at F<1>1, F<1>2, F<1>3 respectively used in conjunction with a refractor composed of steps f1, f<1>1 having their focus at F<1>1, steps f2, f<1>2 having their focus at F<1>2, a step f3 having its focus at F<1>3, and steps f4, f5 of caustic form having foci between the foci F<1>1, F<1>2, F<1>3. The reflectors may be formed by the rotation of a parabolic are about a line parallel or slightly inclined to its axis. The arcs of the steps of the refractor may be so arranged that the illuminated areas instead of being concentric are offset relatively to one another. In order that the light flux collected by the reflector shall be a maximum the dimensions of the reflector should approximately be such that (d1/d2)<3> = (R1/R2)<2> R1, R2 being the radii of the ends of the reflector and d1, d, being the distance of the edges of the reflector from the light source.