GB953813A - Improvements relating to lighting fittings and to refractors for use in such fittings - Google Patents

Abstract

953,813. Light refractors. GENERAL ELECTRIC CO. Ltd. Feb. 22, 1963 [March 15, 1962], No. 9992/62. Heading F4R. A trough-shaped or bowl-shaped refractor for use mouth upwards in a lighting fitting has at least the major part of a side wall formed on one surface with a band of prisms parallel to the plane of the mouth, all the prisms having the same tip angle and being inclined to the side wall at progressively changing inclinations so that the upper faces of the prisms are inclined to the wall at angles which at the top of the band are greater and at the bottom of the band are less than those of the lower faces. For a bowl refractor, the side walls are defined as those parts of the bowl inclined at less than 45 degrees to the vertical. The tip angle is preferably 90 degrees. The refractor is made by extrusion and may have the bottom formed with a light diffusing finish, e.g. a pattern of hexagonal recesses as described in Specification 851,217. Fig. 4 shows part of an extruded sheet of plastics material before bending into trough shape. The end 13 is plane and is bent over to form a lip for engaging a support on the lighting fitting. Within this is a band 14 of fine ribs followed by a band 15 of prisms which will form the sides of the trough. A further band 16 of fine prisms which will be located at the lower corner of the trough is followed by a portion 17 having a pattern of recesses which forms the bore. The strip is bent into trough formation and may be used to cover a length of ducting or cut into shorter lengths to which end-plates are cemented to form individual troughs. The sides, ends and bottoms of the troughs may alternatively be separately made and cemented together.