Patent GB-536887-A (GB)
Title: Method of and means for directing and diffusing light
IPC: G09F13/26
Filed: 1939-11-29
Abstract: 536,887. Light conductors. COTTON, F. H. Nov. 29, 1939, No. 31098. [Class 75 (ii)] [Also in Group XVIII] An illuminating device conveying light by virtue of repeated internal reflection and diffusing it in pre-determined directions comprises one or more transparent rods of high refractive index presented at one or both ends to a light source. Each rod is locally surface treated so that the trapped light can emerge there and is subsequently reflected to re-enter at angles which allow it to leave substantially the whole width of the opposing rod-to-air interface as a wedge or wedges of limited contained angle. The light conducting rod may be of coloured or colourless glass, fused quartz, polymerized methyl methacrylate, polyvinyl acetate, polystyrene, or urea-formaldehyde resin composition. Instead of a homogeneous rod, a tube filled or nearly filled with a liquid or jelly of high refractive index may be employed. To permit light to pass through part of the surface of the rod, a transparent medium such as linseed oil or cellulose lacquer is applied, and to obtain reflection of the light back into the rod, a light reflecting pigment may be suspended in the oil or lacquer. Alternatively, the material of the rod may be etched or ground so as to present to the impinging light rays different angles of incidence some of which will allow penetration by the light, or the reflection may be obtained by attaching white paper to the rod by an adhesive of suitable refractive index, or the etched surface may be silvered. For use with a hand torch, the device may comprise a rod A-B, which may be bent at a gentle radius at the end B which is inserted in a cap C fitting over the end of an existing torch. A line of white paint P is applied to the upper surface of the rod. The line P may increase in width towards the end A to compensate for the loss in intensity as the light travels from B to A. The paint may cover the end A or an internally polished metal cap may be applied to that end. The back of the reflecting white paint may be covered by gold or silver leaf, metal foil or an opaque paint or lacquer. The torch may have alternative lamps; one for normal use, and the other for reflecting and diffusing the light. The device may be used for weak but uniform illumination of signs or hoardings. The rods may be bent into the form of letters or designs, and a number of such rods may be supplied with light from a single source. The round ball of a pedestrian crossing sign may be replaced by an annular rod, orange paint P being arranged over approximately a quarter of the diameter of the rod. If the orange paint is unbacked, it transmits sufficient light to a pedestrian approaching from behind and the right hand portion of Fig. 6 indicates the illuminated appearance to oncoming traffic. For advertising or road signs, a bank of rods may be used, and the light reflecting paint may be applied to the back of the rods by a stencil to form dots, strips. By arranging the position of the reflecting paint on each of the rods, the direction from which the sign is visible can be controlled, and by providing two areas of paint, Fig. 10, two distinct illuminated displays are provided, visible to observers in different directions, so that the subject-matter of the sign appears to change as a person approaches or walks past the sign.