GB1092276A - Lighting units - Google Patents

Abstract

1,092,276. Fresnel lenses. IMPERIAL CHEMICAL INDUSTRIES Ltd. June 3, 1965 [June 24, 1964; Sept. 23, 1964] Nos. 26140/64 and 38797/64. Heading G2J. [Also in Division F4] In a street lighting unit of the type comprising a trough shaped transparent body having a top cover and one or more tubular light sources mounted inside the body parallel to the long flat side walls thereof, a refractor plate having a plurality of light directing prismatic formations on one surface thereof is attached to each of the long flat side walls, each plate being inclined to the vertical away from the light source by an angle of from 8‹ - 20‹ and being so constructed that the maximum light intensity of the downwardly refracted light occurs at angles of from 60‹ to 85‹ to the vertical. The light sources are mounted so that the vertical distance between the lowest prismatic surface and the lowest point on the light emitting surface does not exceed 30% of the distance between the highest and lowest points on the light emitting surface, and each prism is so shaped that the angle between its rising face and the normal to the plane surface of the plate is substantially equal to, or up to 25‹ less than, the inclination to the normal of the least refracted ray within the prism from the lowest point on the light emitting surface. The transparent body and the refractor plates may be made from polymethyl methacrylate or the transparent polymers and copolymers of vinyl chloride. The Specification gives detailed numerical data for constructing plates with 42, 27 and 70 prisms respectively.