GB258482A - Improvements in lighting appliances - Google Patents

Abstract

258,482. Stephens, A. J., (Rolph, T. W., and Dorey, W. A.). Feb. 25, 1926. Lantern fronts.-One surface of the front glass of a vehicle, signal, street or like lamp, adapted to illuminate a relatively long rectangular area, is provided with light-directing surfaces adapted to refract light downwards and outwards, these surfaces being separated wherever they occur by corrugated spaces. In the form shown in Fig. 5, a light source 10 is placed slightly above the focus of an ordinary condensing lens 11 having a, smooth inner surface 12 and annular prisms 13 on its outer surface, and the cover gla.ss 15 has its inner surface covered with diagonal lattices 18, 19 separated by smooth spaces 21 and its outer surface covered with laterally-spreading vertical flutes 17. Alternatively, the outer surface of the cover glass may be left smooth and the vertical flutes 17 made between groups of diagonal lattices 18, 19 arranged at different angles and intersecting each other on its inner surface, as shown in Fig. 3. Fig. 6 shows another form, more particularly for use with a parabolic reflector, in which the light is refracted downwards and outwards across the axis of the lamp by means of diagonal lattices 18, 19 of constant width but with inclination to the horizontal and their transverse concave curvature increasing progressively towards the bottom. Alternatively, the diagonal lattices may be of constant transverse curvature, in which case their width and inclination to the horizontal increases progressively towards the top. If the lattices of these two latter forms are made convex and the arrangement turned upside down, the light is refracted downwards and outwards away from the axis of the lamp. If the lamp be placed at the corner of the area to be illuminated, only one set of diagonal lattices is required for example, as shown in Fig. 9 in which diagonal lattices 18 are located in the upper left hand corner of the cover glass of a ditch light to refract light downwards and to the right, the diagonal lattices being intersected by horizontal depressing prisms 22. Fig. 10 shows a still further form using downwardly curved and preferably small prisms 24 the active faces of which may be spherical. The inside contours of these prisms are arcs of a circle but their depth increases from the centre outwards, this curvature being obtained by originally making the prisms of constant depth and cutting out vertical flutes 25 with their full depth corresponding to the centres of the prisms. Alternatively, upwardly curved prisms may be used, or upwardly and downwadly curved prisms may be arranged alternately in wave-like form horizontally or diagonally across the face of the cover glass. When the lamp is placed at one corner of the area to be illuminate ,d half prisms only are used.