GB619084A - Light refracting and transmitting plates and equipment using the same - Google Patents

Abstract

619,084. Refractors for rectilinear light sources. HOLOPHANE, Ltd. (Holophane Co., Inc.). Nov. 14, 1946, No. 33844. [Classes 75 (ii) and 75 (iv)] A refractor plate for use in lighting apparatus for preventing the emission of light in unwanted directions is of generally uniform thickness and has a plane first surface 23, Fig. 5, and a light transmitting second surface formed with symmetrical prismatic elements having plane sides 36, 36<1>, or with contiguous conical prismatic elements (not shown), the angle P which the sides 36, 361, or the sides of the conical elements, make with the plane 23 being substantially equal to 2/y (90 degrees - C), where C is the critical angle of the medium of which the refractor is made and y is an odd integer greater than one. The plate shown is of glass having a refractive index of 1.5 and a critical angle of 42 degrees, and the angle P, given by the above formula when y=3, is 32 degrees. No rays are transmitted at angles to the vertical higher than that of the ray 28 which is 47 degrees to the vertical. Fig. 12 shows a refractor 90 for use with a rectilinear light source mounted along the aisle of a railway coach and provided on its upper surface with longitudinally extending prisms 92 which spread light away from the vertical and light depressing prisms 93 which lower the light to produce two generally divergent light beams directed towards the seats. Transverse prisms 98 constructed in accordance with the invention are provided on the lower surface of the refractor extending 30 degrees approximately each side of the vertical central plane through the light source, so that the rays at high angles to the vertical are not emitted through the longitudinal central portion of the refractor.