GB245139A - Improvements in or relating to light reflectors - Google Patents

Abstract

245,139. Lancelot, R. Dec. 27, 1924, [Convention date]. Overhead lamps; mounting electric lamps in lanterns.-The reflector of an overhead electric lamp comprises two superposed portions ab, bc of shapes obtained as described below, the effect obtained being that the direct light flux plus the reflected flux is so distributed that the surface to be lit has a central area of uniform illumination surrounded by an annular area in which the illumination decreases substantially uniformly in intensity towards the circumference . Lighting units thus constructed, if suitably spaced, thus provide substantially uniform illumination over any desired area. The upper portion bc has a collar h by which it is secured to a telescopic chimney de carried by a ventilating cap f. The inner tube d is provided with two bosses into which are inserted set screws projecting through two slots e<1> in the outer tube e. The two slots e<1> each have a series of diametrically opposite notches such as e", e<111> one of which is engaged by one of the set screws according to the intensity of the sources of light used in the reflector. The special curves of the two reflecting surfaces are built up of parabolic curves having a common focus but with different axes and obtained by a method described with reference to a usual type of lamp in relation to the polar curve of light intensity corresponding to the particular distribution of light required. The particular example dealt with is based on the use of enamel sheet metal having an absorption co-efficient of 30 per cent, but other material such as nickel sheet metal, glass, silica, &c. may be used. According to the Specification as open to inspection under Sect. 91 (3) (a) a single reflector having no upper portion bc may be employed for uniformly illuminating a relatively small area. This subject-matter does not appear in the Specification as accepted.