| 摘要 |
This portable lighting apparatus which comprises a case having a parabolic reflector, a bulb whose filament is situated substantially at the focus of the parabolic reflector and a square or rectangular shaped diffusing lens fixed at the periphery of the reflector, perpendicularly to the optical axis thereof, is characterized in that the lens carries a series of rectilinear and adjacent scores on each of its internal and external faces, in that the scores of the same series are formed by concave cylindrical surfaces having transversely the same radius and are perpendicular to those of the other series and in that the radii of the scores of the internal face of the lens are slightly smaller than those of the scores of the external face of said lens, the depth and the radii of the two series of scores being chosen so that the pyramidal light beam therefrom gives constant illumination in any plane perpendicular to the optical axis.
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