Patent GB-1390344-A (GB)
Title: Reflecting grid for fluorescent lamps
IPC: F21V11/06
Filed: 1973-01-03
Abstract: 1390344 Lighting fittings P WILLUNSEN 3 Jan 1973 [4 Jan 1972] 342/73 Heading F4R A reflective grid, Figs. 1 and 2, for use with a fluorescent lighting fitting comprises a system of open-ended tubular elements 2 each of which has an external convex reflective surface 3 and an internal concave reflective surface 4, the ends of the tubular elements nearer to the light source 5 being of smaller cross-sectional area than the ends farther from the source and the grid being so constructed that light passes through the spaces 8 between the elements as well as through the elements themselves. The tubular elements may be surfaces of revolution formed by rotating a parabolic arc B 2 D 2 , Fig. 5, about an axis C, the arc being derived from a parabola P having an axis A and focus B 1  by drawing a line through the focus B 1  at an angle V to the axis A to cut the parabola at B 2 , forming the axis C by perpendicularly bisecting the line B 1 B 2 , and drawing a line through the focus B 1  at an angle V to the axis C to cut the parabola at D 2 . The surface has the property that light entering the smaller end at any angle cannot leave the larger end at an angle greater than V to the axis C, so that the tubular elements produce a controlled downwardly-directed luminous flux from the light which passes through the elements. The elements are mounted in a reflective structure composed of mutually perpendicular walls 6, 7, each element being disposed either in a space formed by removing an X-shaped portion from the intersection of two walls, as shown in Fig. 2, or within the alternate square openings formed by adjacent pairs of intersecting walls, as in a chessboard pattern. The light which passes through the spaces 8 between the elements is reflected by the outer surfaces 3 of the elements and by the walls 6, 7, and issues as a diffuse widely-spread luminous flux, this flux being coloured if desired by covering the spaces 8 by a transparent coloured filter or by colouring all the reflective surfaces except the internal surfaces of the elements. The grid is preferably made of plastics material having an aluminium coating which has been treated to make it resistant to corrosion, but may alternatively be made of a reflective material coated with transparent plastics. In an alternative embodiment, (Figs. 3 and 4, not shown) the grid is composed of tubular elements (2<SP>1</SP>) having a square cross-section, the elements being joined together at the corners of their wider ends to form the alternate squares of a chessboard pattern. Each element has four sides, preferably in the form of portions of a parabolic cylindrical surface. In modifications of this embodiment the cross-sections of the elements have the form of other polygons with straight or curved sides. The grid produces a polar curve of light distribution (Fig. 11, not shown) of substantially pear-shaped form. The curvature of the external surface 3 of each tubular element preferably conforms to the curature of the internal surface 4, and each surface is preferably generated by a portion of a curve of the form the parabolic elements described above being obtained when n = 2. Alternatively, the generating curve may be part of an ellipse or hyperbola.