GB292867A - Improvements in and relating to illuminating and signalling appliances - Google Patents

Abstract

292,867. Holophane Ltd., (Soc. Anon. Franþaise Holophane). Jan. 12, 1928. Signal and like lamps.-In a signal or like lamp a prismatic glass reflector R has a central spherical portion provided with annular concentric reflecting prisms 8, and an annular parabolic portion provided with radial reflecting prisms 7, the centre of the spherical portion and the focus of the parabolic portion being coincident with the source of light S. This reflector may be used in combination with a prismatic refracting glass G having a central zone provided on its inner face with annular refracting prisms 9, and an annular zone provided on its inner face with concentric prisms 10. The angles between the incident ra.ys and the normals of the prisms 9 increase from the centre outwards so as to produce a parallel beam of light, and the prisms 10 are made shallow so as to diffuse slightly the parallel beam from the annular portion of the reflector R. In another form illustrated in the Specification, the prismatic glass G is spherical in contour. Fig. 4 shows a modification in which the central and annular zones of the prismatic glass are covered respectively with horizontal and vertical prisms g<11a>, g<1a>, so designed as to produce a beam which is concentrated in height and expanded in breadth, so as to illuminate uniformly a surface of extended-width. This prismatic glass may be turned through 90‹ for the illumination of a surface of extended height, and the two sets of prisms may be of other shapes and relative disposition according to the distribution of light required. The great divergence of direct rays passing through the annular portion of such prismatic glasses may be utilized for the production of an indication to an observer close to a signal lamp. The source of light is arranged vertically, or placed in a vertical plane and inclined at most at 45‹ to the optical axis of the lamp, the support 5 being carried by a cap 3 at the top of a ventilating shaft 2 of a metal casing 1. The cap 3 is provided with holes 4 below the top of the shaft 2 so as to be rain-tight.