GB246192A - Improvements in and relating to light ray projectors and reflectors - Google Patents

Abstract

246,192. Halsbury (H. Goulburn), Earl of. July 30, 1924. Testing-apparatus, auxiliary.-In a vehicle headlamp or other light ray projector, the amounts by which the elementary beams issuing from a series of horizontal elements of the lamp front must be deflected in order to make their axes substantially horizontal and to bring them substantially within the main horizontal beam from the lamp are determined by placing in front of the lamp a diaphragm having a narrow horizontal slit and by measuring, for different positions of the slit, the amounts by which the rays of light projected through the slit deviate from the horizontal. In one form, a diaphragm 3, Fig. 5, having a slit 4 is placed in front of a lamp 1 and the distance 8 on a screen 5 and the distance between the diaphragm and the screen are measured so as to determine the angle of deviation # between the projected ray 6 and the horizontal line 7. The refracting angle a which should be given to each of the horizontal prisms d', d<2>, &c., Fig. 1, in order to bring the ray 6 into coincidence with the horizontal line 7 is then calculated from the formula Á=sin(alpha+#)/sin a where Á is the refrective index of the glass &c. from which the prisms are made. The series of prisms d<1>, d<2>, &c. may be replaced by a single composite prism with either a curved front or rear face, the other face being plane, or with both faces curved. In another form, a downwardly directed lamp 9, Fig. 6, has a plane mirror 11 hinged at 12 so that by measuring, for different positions of a slit 14 in a diaphragm 13, the angle of inclination of the mirror 11 necessary to bring the rays of light projected through the slit on to a screen 16 into a horizontal direction, the angles of inclination of the different portions of a curved mirror f, Fig. 3, can be determined. The mirror f instead of being curved may comprise a series of three or more plane surfaces. A certain amount of diffused light for general illumination is provided by rays of light which diverge upwardly from the horizontal axes R of the elementary beams, and, in order to illuminate the roadway a short distance ahead of the lamp, some of the lower prisms d<1>, d<2>, &c. or the lower portion of the mirror f may be arranged to give a somewhat greater downward deflection to a portion of the elementary beams, as shown at R<n> in Figs. 1 and 3.