GB530492A - Improvements in optical systems comprising reflectors and linear light sources - Google Patents

Abstract

530,492. Bridge &c. lighting fittings. GENERAL ELECTRIC CO., Ltd., BEGGS, S. S., and THOMAS, E. R. June 26, 1939, No. 18555. [Classes 75 (ii) and 75 (iv)] In a lighting fitting having a linear source of light and reflectors which direct substantially all the light to one side of a plane BC through the source in a manner such that the light distribution in all other planes through the source is substantially the same and such that a maximum of intensity is formed in these planes at an angle to the source, one at least of the reflectors, BAC, CE or BD as the case may be, takes the shape formed by the semi-revolution of a parabolic arc having its axis in the direction of maximum intensity about an axis BC through its focus, F, in the case of BAC, F 2 in the case of CE or BD, and one end of the linear source lies at or near the said focus and the opposite end inside or outside the axial cone (or plane) traced out by the axis, F,Y or F,X, of the parabolic arc accordingly as the reflector lies on the same or opposite side of the plane BC as that to which the light is directed. Rays reflected from the paraboloidal reflector are thus distributed beneath or mainly beneath the cone of rays of maximum intensity. In an extreme case the angle of the or each parabolic axis to the axis of revolution may be a right angle. Preferably each reflector is a parabolic half surface of revolution about the axis BC with the light source, such as a HPMV lamp, extending between the focus F, of reflector BAC and the common focus F. of reflectors CE and BD and with the axes F 2 Y, F,X parallel. Alternatively, Fig. 3, one of the reflectors, GH, may be spherical with its centre F 3 between the foci F 1 , F 2 of the reflectors AB, BD, and a part conical reflector JK may be arranged to direct upward rays downward. HG and AB may be spaced or continuous. A slightly diffusing glass with ribs parallel to the axis BC or a refractor which concentrates the light into particular vertical planes through BC may also be used with the reflectors. The fitting is particularly adapted for lighting streets and bridges, and for floodlighting.