Patent GB-756245-A (GB)
Title: Improvements relating to electric lighting lanterns more particularly for street lighting
IPC: F21S8/08
Filed: 1954-05-25
Abstract: 756,245. Street lanterns. GENERAL ELECTRIC CO. May 25, 1954 [May 25, 1953], No. 15433/54. Classes 75(2) and 75(4). A lantern of the type comprising an elongated translucent member 15 extending at least around the sides of one or more elongated light sources 22, 23 has a frame supporting the translucent member and comprising spaced side members 40 extending along the opposite sides of the translucent member and secured thereto at an intermediate position in its length, and the translucent member is provided adjacent its ends with side flanges making sliding engagement with the side members 40 of the frame to permit differential expansion of the translucent member and frame. The translucent member is an elongated prismatic plastic bowl formed of two complementary parts 52, 53, each defining an end of the bowl, clamped together by straps 54 secured to mid portions of the side members 40 of the frame. The side flanges on the bowl are grooved to accommodate the side members 40 of the frame and the ends of the bowl are clamped to cross members 41 forming end members of the frame and adapted to slide on the side members 40. The frame is hinged at one end and releasably fastened at the other end to an elongated hood 1 made of a material having the same coefficient of expansion as the frame and secured to a bracket 2 extending from a pole or the side wall of a building. The frame hinge comprises a member 43, Fig. 9, attached to the hood and having turned over end portions 44 for receiving the inwardly bent ends of the side members 40 of the frame. End openings in the turned over portions 44 for the passage of the ends of the side members 40 are closed by rotatable latches 46 having slotted portions 45 located within the closed portions of the turned over portions 44. The releasable fastener at the other end of the bowl comprises a member 48 pivoted to the supporting bracket 2 and having a cammed striking face spring- urged into engagement with a member 47 connected to the inwardly bent ends of the side members 40 of the frame and adapted to be held in a slot in the member 48. The hood 1 supports within the bowl two elongated reflectors 12, 13 mounted back to back. The upper edges of the reflectors are stepped to provide seats for the bowl, a rain and dust proof joint being provided by strips of neoprene sponge attached to the seats. The lower edges of the reflectors are bent inwardly and fastened together. Each reflector directs the light emitted by two side by side horizontal fluorescent lamps 22, 23 below 85 degrees from the nadir and comprises upper and lower parabolic portions 24, 25 having a common axis 28 inclined at 78 degrees from the nadir and central flat portions 26, 27. The focus M of the upper parabolic portion 24 is positioned close to the inner edge of the inner lamp 22 and the focus N of the lower parabolic portion 25 is positioned close to the outer edge of the outer lamp 23 and the focal length of the upper portion 24 is shorter than that of the lower portion 25. The arrangement is such that the angle at any point 30 of the upper portion 24 between the focal radius 30, M and the tangent 30, 29 to the inner lamp 22 at its inner edge and the angle at any point 32 of the lower portion 25 between the focal radius 32, N and the tangent 32, 31 to the outer lamp 23 at its outer edge are not greater than the angle, in this case 7 degrees, between the common axis and the upper limit of light emission. An elongated louvre 35 comprising a block of transparent material having a series of parallel longitudinal cuts extending about three quarters of the way through it to define parallel strips is mounted in the bowl to extend in front of each pair of lamps and with the strips inclined to the horizontal. The cut surfaces are left rough by the cutting operation to produce a light diffusing effect. Specifications 756,317 and 756,318 are referred to.