Patent GB-339888-A (GB)
Title: Improvements in and relating to illuminating appliances
IPC: F21V5/00
Filed: 1930-02-25
Abstract: 339,888. Holophane, Ltd., (Dorey, W. A.). Feb. 25, 1930. Globes and reflectors.-An illuminating appliance, more particularly suitable for shop window lighting, comprises an inclined reflector adapted to converge the light into an arcuate band which is transmitted by a peripheral arcuate portion of a prismatic cover plate disposed below the source of light and completely closing the opening in the reflector. The appliance may be so designed that the projected beam is narrow transversely and concentrated along the axis of the reflector, but restricted at high angles on one or both sides of this axis. In the form shown in the Figure, an electric lamp filament 2 is disposed on the rearwardly inclined axis 12-12 of a reflector 3 which is completely closed by a prismatic cover plate 5 whose centre is to the rear of the vertical axis of the bulb 1. The reflector may be supported by means of a lip 8 on a metal extension 7 or it may be secured in a recess in the shop window ceiling by means of a metal flange 9. The upper portion 10 of the reflector is made spherical with its centre coincident with the filament 2, and it may be made of metal or provided externally with totally reflecting prisms. The lower portion 11 of the reflector is provided on its outer surface with tiers of radial reflecting prisms 13 and on its inner surface with refracting ribs 14, 15 disposed respectively to the rear and front of a division line A-A and arranged at right angles to the axis 12-12. The external prisms 13 and the internal ribs 14 direct light downwardly in a slightly convergent and nearly vertical beam B<1>, C<1> on to an outwardly bowed arcuate portion 22 of the cover plate 5. The portion 22 is provided internally with transverse parallel prisms 23 adapted to refract direct rays M from the filament 2 rearwardly into the window in an almost horizontal direction and to bend the reflected light B<1>, C<1> slightly inwards. The ends of the portion 22 are provided with a smooth internal surface and externally with concentric prisms adapted to prevent lateral spreading of the light and to refract it downwardly. The external prisms 13 and the internal ribs 15 direct light downwardly and rearwardly in a convergent beam D', E<1> on to an inwardly bowed arcuate portion 19 of the cover plate 5. The portion 19 is provided internally with transverse prisms 20 arranged parallel to the axis 12-12 and designed to further converge the light and to direct it inwardly. The outer surface of the portion 19 is provided with longitudinal parallel prisms 21 adapted to make the convergent light parallel and to condense it inwardly to prevent lateral spread. The central portion 16 of the cover plate 5 is provided internally with parallel prisms 18 and externally with concentric prisms 17 so as to produce an inwardly directed and laterally narrow beam of light. The portions 16 and 19 are joined by a smooth connecting surface 27 which is preferably plane and arranged to intercept a minimum of direct rays from the filament 2. Two modified forms are described and illustrated in the Specification, one for use with open-backed or island windows, the arcuate portion towards the back of the cover plate being bowed inwardly so as to avoid rearwardly directed light at high angles, and the other for use with inclined ceilings, the axis of the electric lamp bulb coinciding with the inclined axis of the reflector.