GB191021901A - New Method of and Apparatus for Illuminating Objects. - Google Patents

Abstract

21,901. Mackinney, V. H., and Chalmers, S. D. Sept. 21. Reflectors.-A reflector is so designed that the reflected light uniformly illuminates a plane surface such as a picture. The source of light Z is preferably a line source, and is partly surrounded by the semicircular mirror X Y which reflects light on to the mirror Y W, the profile of which is calculated from the fact that the illumination over the plane surface T has to be uniform. If # represents the angle between a given radius vector to the profile and the vertical through the point Z, and if # represents the angle between this radius and the tangent at its extremity, the differential equation obtained from these considerations is d'# = d (2# + #) /Sin<2> (2 # + #) which gives Cot (2 # + #) = B e + A as the equation of the profile where A and B are constants depending on the size of the surface T and its position relative to the source. If it is required to grade the illumination, an equation such as d# = d(2# + #) / K Sin<2> (2# + #) may be used where K may be a function of (2# + #), and in the case of an approximate point source of light the equation is d # = d (2 # + #) /Sin<3> (2 # + #). If desired, a gap may be left between the point Y and the commencement of the mirror: a diffusing-screen for the more even distribution of the light may also be placed within the reflector. A reflector of the described form may also be employed to light an enclosed space, the reflector being arranged to throw a uniform illumination on the ceiling, from which the light is again reflected throughout the space,