GB814715A - Improvements in and relating to lighting appliances - Google Patents

Abstract

814,715 Lamp refractors. HOLOPHANE Ltd. Sept. 16, 1955 [Sept. 16, 1954], No. 26936/54. Class 75(2) A lantern incorporates a dished refractor to be set vertically and comprising two systems of internal coaxial non-re-entrant concentrating prisms 6 concentically arranged about respective optical axes 07, 07<SP>1</SP> defining a geometric centre O which, when the refractor is viewed from the 'front lie at an angle on each side high above the downward vertical but below the horizontal, the part of the refractor on which each system of prisms is formed being a figure of revolution with its axis coincident with the optical axis of the prism system, the lantern also incorporating a concentrated light source at a point 8 nearer the refractor than is the geometric centre O and below the level of the geometric centre O. Preferably the centre of the light source is about 25 per cent of the distance from the geometric centre to the refractor nearer the refractor than is the geometric centre and is about 6“ per cent of that distance below the geometric centre. The two parts of the refractor having the prism systems may be segments of the same sphere or of different spheres or of toroids or of cones. The refractor may have portions without prisms. The prism angles may increase from the medial vertical plane outwardly and the inner surfaces of the prisms may be made steeper from the centre outwardly. The apices of the prisms may be rounded or flattened particularly the prisms on the lower part of the refractor or clear areas or flutes may be formed between the prisms on the lower part or vertical flutes may be formed on a part or the whole of the outer surface of the refractor or the whole outer surface may be etched or depolished. The refractor has a circular rim and is clamped thereby to the lantern. The rim may have a notch 10 adapted to be engaged by a fixed or adjustable lug on the lantern. Alternatively the refractor is carried in a cover plate hinged to the lantern. The concentrated light source is a filament lamp mounted in an adjustable holder. Specifications 420,922 and 710,127 are referred to.