Patent GB-660531-A (GB)
Title: Improvements in or relating to street lighting luminairs
IPC: F21V5/00
Filed: 1949-09-07
Abstract: 660,531. Luminaire for street lighting. HOLOPHANE, Ltd. (Holophane Co., Inc.). Sept. 7, 1949, No. 23186/49. Classes 75(ii) and 75(iv) A luminaire for street lighting comprises a reflector directing light from a compact source downwardly across the vertical axis of the luminaire and a bowl refractor which elevates the direct and reflected rays so as to illuminate remote areas of the street, the refractor comprising upper tiers of horizontal prisms extending around the whole or part of the refractor and constructed to elevate uniformly the highangled reflected light and lower tiers of horizontal prisms extending around the whole or part of the refractor and constructed to refract upwardly, by amounts varying from a maximum at 'the uppermost prism to a minimum at the lowest prism, the relatively steep direct and reflected light. The lower annular part of a dome-shaped reflector 10 is, in axial section, a parabola with a downwardly inclined axis 13, and focus 15 at the centre of the reflector mouth where a compact light source is disposed; the upper part 10a of the reflector is spherical with centre at the focus 15. A refractor bowl of spherical contour with centre 26 above the light source closes the mouth of the reflector. The upper part of the refractor down to the line 28 is formed with horizontal circular coaxial prisms 29 which refract all the parallel rays from the parabolic portion of the reflector upwardly by the same amount viz. 11 degrees. The lower part of the refractor below the line 28 is formed with horizontal prisms 30 which refract upwardly both the direct rays and the rays reflected by the spherical upper portion 10a of the reflector, the amount of refraction decreasing downwardly from a maximum by the prism at the line 28 to zero at the apex of the bowl. The prisms may be formed on the inside or on the outside which alternatively may be smooth or provided with a diffusion pattern. The refractor shown in Fig. 4 is intended to be mounted above the centre-line of a street and has two diametrically opposed sectors of about 20 degrees angular width formed with two sets of horizontal prisms 29a, 30a as described with reference to Fig. 1. These sectors are flanked by areas 35 carrying oblique prisms for elevating and for laterally deviating the light, and the remaining sectors 36 are formed with laterally refracting prisms disposed in central vertical planes. The various prism sectors terminate short of the centre of the refractor where a series of parallel prisms deviating the light away from the nadir may be formed. In a refractor suitable for mounting above the crossing of two streets, Fig. 5 (not shown), four sectors of 20 degrees angular width are formed with two sets of prisms as described with reference to Fig. 1 and the intervening sectors have oblique prisms similar to the areas 35 of Fig. 4. The circular area at the apex of the refractor may be made diffusing. The refractor shown in Fig. 6 is for side of the street mounting, the notch 63 facing the houses, and emits strong beams in the directions E, W inclined at 10 degrees to the kerb. The areas 70 are provided with horizontal prisms corresponding to the prisms 29 of Fig. 1 and the areas 71 have prisms corresponding to the uppermost of the prisms 30, of Fig. 1. The prisms 72 cause less deviation of the light than the prisms 71 and correspond to the lowest of the prisms 30 of Fig. 1; they extend generally at right angles to the kerb with slight convergence towards the street side. The prisms 73, 74, 75 are oblique to give both lateral and vertical deviation and converge upwardly towards each other. The prisms 73 elevate to the same extent as the prisms 70 and deviate the light away from the house side with power increasing toward the house side. The prisms 74 give less elevation and less maximum lateral deviation than the prisms 73. The prisms 75 have still less vertical refracting power but have the same lateral refracting power as the prisms 74. The sector facing the house side is provided with radial prisms 78 laterally refracting the direct light towards the beams E, W. On the street side the oblique prisms 76 are similar to the prisms 73 and the oblique prisms 77 are similar to the prisms 74 but the prisms 76, 77 deviate the light towards the house side. The prisms 79 are radial to deviate light towards the beams E, W. In a further embodiment Fig. 9 (not shown), the reflector is similar to the reflector shown in Fig. 1 but is of deeper form and is wholly parabolic in section with the mouth of the reflector well below the focus. Specification 524,334 is referred to.