Patent GB-1339255-A (GB)
Title: Veiling glare control with luminaires using extended linear sources
IPC: F21S8/04
Filed: 1971-04-01
Abstract: 1339255 Lighting fittings HOLOPHANE CO Inc 1 April 1971 8407/71 Heading F4R In order to reduce glare produced by specular reflection from a horizontal surface such as a sheet of paper on a desk, the means of illumination for the matter on the surface comprises a plurality of identical luminaires arranged on the ceiling above the surface and each having a light distribution pattern in relation to the direction from which the surface is viewed by an observer such that specular reflection of light from those luminaires which illuminate the surface is not visible to the observer. The luminaires may be of narrow oblong form or circular in horizontal section; in any event each has an effective longitudinal axis and a light distribution pattern transverse to this axis as shown in Fig. 7, with the light concentrated between approximate angles of 30 degrees and 60 degrees to the vertical. In the longitudinal direction the light from each luminaire is concentrated almost entirely below 60 degrees from the vertical; an observer who thus arranges his viewing direction to be parallel to the longitudinal axes of the luminaires (which are distributed above the viewing area, e.g. an office, with their longitudinal axes all parallel) is not affected by glare directly from the luminaires themselves. Thus for a person seated at a desk in an office lit as above, the light which illuminates a sheet of paper before him arrives at such an angle of incidence that he cannot see the specularly reflected light and he sees the paper and the matter on it solely by diffusely-reflected light; owing to the light-radiation patterns of the luminaires, the luminaires more directly above him do not effectively illuminate the paper he is studying. Fig. 5 shows a transverse section through an elongated luminaire housing a fluorescent lamp 43 and comprising a metallic housing 40 for ballast equipment 42, a reflector 41 with a diffuse white finish and a glass or plastics refractor 44. The refractor has parallel prismatic formations on both its inner and its outer surfaces; those covering the greater part of the inner surface extend longitudinally and those covering the greater part of the outer surface extend transversely. However these formations do not extend over a central strip at the bottom of the refractor and the outer surface of this strip is provided instead with longitudinally extending prismatic formations. Figs. 10 and 11 show respectively vertical and horizontal sections through a second form of luminaire housing a metal vapour lamp comprising a housing 72 for the ballast equipment, a specular reflector 71 and a refractor 70. The inner surface of the side wall of the refractor comprises vertically extending prismatic formations and the outer surface comprises horizontally extending formations encircling the refractor. The formations on the inner and outer surfaces extend over the bottom portion of the refractor except for a central longitudinally extending strip, which comprises longitudinally extending prismatic formations 77 on its inner surface and formations 78 transverse thereto on its outer surface. This luminaire produces an illumination distribution pattern with respect to a longitudinal axis 32-32<SP>1</SP> as shown in Fig. 12. Fig. 14 shows a modified form of illumination pattern produced by a luminaire similar to that of Figs. 10 and 11 but with a modified form of base portion, Fig. 13 (not shown). This has circular symmetry; the radially extending formations over the inner surface being replaced by circularly extending formations over a central portion and the circularly extending formations over the outer surface being replaced by radially extending formations over the same portion. In this case the direction in which a person faces in an office installed with such luminaires is not of importance.