GB818401A - Improvements in or relating to lighting fittings - Google Patents

Abstract

818,401. Lighting fittings. GENERAL ELECTRIC CO. Ltd. Aug. 22, 1956 [Aug. 25, 1955], No. 24495/55. Class 75(2) A lighting fitting for street lighting, especially for tree-lined roads, comprises one or more electric lamps within a single housing and optical means arranged to concentrate the light from the lamps mainly into four different directions each inclined at an angle between 65 degrees and 85 degrees to the vertical and each lying in one of four quadrants formed by two mutually perpendicular planes through the vertical axis and each having its orthogonal projection on a horizontal plane at an angle of less than 40 degrees to one of these planes. In the form shown in Fig. 1, the vertical deviation is produced by a dome 6 having annular prisms 7 and mounted around the lamp 5 and the horizontal deviations are produced by vertical prisms 10 in four similar sets in different quadrants on the interior of a bowl 1 surrounding the lamp. Alternatively the dome may be omitted and the annular prisms be arranged on the outer surface of the bowl. A typical distribution of vertical prisms for use with a light source having a diffusing envelope is shown in Fig. 7, in which the directions OP1, OP2 of the maximum light distribution are inclined at about 25 degrees to the plane or containing the vertical axis. The angles between the directions of maximum light distribution and the plane or need not be equal. In a modification, the optical means may comprise within a single housing two back-toback parabolic reflectors each surrounding an electric lamp and provided with reflectors arranged across their mouths to spread the light into two principal planes.