TUBULAR LIGHT GUIDE FOR LINEAR LIGHTING

Abstract: A row of transparent tubes (32, 34, 36) are each formed from a semi-rigid rectangular plate (10) of transparent policarbonate, which is coated with a total-internal-reflection film (20) on one of its surfaces and is arched with its longer sides brought together and clamped. The clamping means may comprise a grooved shoe (26) for receiving longitudinal, square-bent edges (12, 14) of the plate (10) and a girder (28) bolted to the shoe. A light guide is assembled from several trunks which are connected to one another . Each guide trunk (32, 34, 36) is hung to a horizontal rail (38) by means of hooking brackets (40) which are fastened to straps (41). The trunks are connected end-to-end by means of fittings comprising pairs of rings (42, 44) which are also further described below. At one end of the guide, a light source is attached, i.e. a focused projector (46) which is also hung to rail (38) through a bracket (40).

Description: Tubular light guide for linear lighting DESCRIPTION This invention is concerned with a tubular light guide for diffuse lighting of tunnels, sheds, exhibition halls, and of large-sized buildings generally. Light guides are known which convey light over distances of several tens of meters, where the light emerges from the guide through a longitudinal window for diffusely illummating large-sized spaces such as tunnels. Light guides offer well known advan¬ tages with respect to conventional lighting using individual hanging lamps, mainly consisting in a better lighting uniformity, which also leads to a lower power con¬ sumption for equal performance. Also, when light guides are used for the iUumination of highway tunnels, they avoid glaring and flickering for the drivers of passing vehicles, with improvement of traffic safety. A known hollow light guide uses a metallized tube which conveys the light projected in a quasi-axial direction by a high-power lamp placed at one end of the guide. Light is reflected against the tube wall with a grazing angle, and is thus propagated by successive reflections. A longitudinal slot aperture allows a fraction of the conveyed light to escape to the outside environment to provide illumination. However, the efficiency of this kind of linear guide is very low, since metallic reflec¬ tion is at most 90%, though it decays in time to even lower values. The light guide therefore suffers from a high dissipation, which is heightened by the fact that the light undergoes a large number of reflections in its travel along the guide. Due to the above reason, the linear light guide using metallic reflection has been largely replaced by linear guides based on total reflection. A light guide of this kind comprises an extruded rigid tube of a material such as policarbonate, whose intemal surface is coated with a thin film of total intemal reflection material. This is a film of polimeric material having a smooth surface looking to the inside of the tubular light guide and an opposite surface scored with a myriad, side-by-side isosceles prisms, which impart a total reflection on light hitting in a direction near the axial direction. A film of this kind is disclosed in EP-A-0 225 123, and is manufactured by the 3M Company under the trade name "OLF film" (Optical Lighting Film), and more gen¬ erally known as "TIR film" (Total Intemal Reflection). For a detailed explanation of the physical principles of operation of a TIR film, reference is made to the above document. It is only mentioned here that the light emission in this kind of light guide is usually obtained by placing an "extractor" film, having a matte reflecting surface along a longitudinal strip of the guide's intemal surface, on the side opposite to the desired emission: light hitting the extractor is reflected in a diffuse form, and is propagated, at least in part, along directions which, at their next hit into the tube wall, will make an angle greater than the angle of total reflection, so theat the light will escape from the tube to the outside space. The amount and direction of the emission is controlled by the position and width of the extractor. The efficiency of the total-reflection tubular guide is quite superior to the efficiency of the metallic-reflection light guide, and, moreover, it remains high for long periods without a need for maintenance even in unfavourable environments, such as moist environments, where a metalllic reflector tends to oxidize. However, installing a flex¬ ible film within a tube of a diameter of a few tens of centimeters is cumbersome, and transporting the trunks of tubular guide thus prepared is quite expensive, due to their large bulk. The object of the invention is therefore to provide a tubular light guide using total reflection, based on the TIR film, which is easier to manufacture and cheaper to transport. The above and other objects and advantages, such as will appear from the following disclosure, are achieved by the invention with a tubular light guide for linear Ulumin- ation, comprising a succession of at least partially transparent tubes which are coated with a flexible film of TIR material on their intemal surface, characterized in that each tube is formed from a semi-rigid rectangular plate of a transparent polimeric material, which is coated with said film of total reflection material on one side, and is bent to bring its longer edges together to be clamped by clamping means. The invention will now be described in more detail in a preferred embodiment, given by way of example, with reference to the attached drawings, wherein: Fig. 1 is a plan view of a flexible plate-like member belonging to a light guide according to a preferred embodiment of the invention; Fig. 2 is an end view of the plate-like member of Fig. 1, where thicknesses are greatly exaggerated to show its component layers; Fig. 3 is a view in transverse cross-section of the tubular light guide as obtained from the plate-like member of Fig. 1 ; Fig. 4 is a lateral view of the light guide of Fig. 3, on a greatly reduced scale; Fig. 5 is a view in transverse cross-section of the guide of Fig. 1 with a hooking strap, on a slightly reduced scale; Fig. 6 is a view in axial cross-section of the fitting area between two trunks of the tubular light guide of Fig. 4, on an enlarged scale; Fig. 7 is a view in the direction of arrow Nil on Fig. 6; Fig. 8 is a view in axial cross-section of a fitting ring of the tubular light guide of Fig. 4, on an enlarged scale; and Fig. 9 is a view in axial cross-section of a terminal reflector member of the tubular light guide of Fig. 4, on an enlarged scale. With reference to Figs. 1 and 2, the construction of a tubular light guide according to the invention starts from an elongated plate 10 of semi-rigid, transparent polycarbo¬ nate, of about 1.5 mm thickness, and having two lateral, square-bent fins 12, 14 along its longer sides. Plate 10 is typically about 2 to 3 meters long and about 1 meter wide, fins 12, 14 each being preferably 10 millimeters wide. The plate is provided with a masking 16 comprising a flexible, adhesive sheet of white opaque material, such as the material known under the trade name "Tivek". Masking 16 initially covers the entire surface of the plate as manufactured, and is then removed over a central, uniform window as shown with 18, the window having a width which, depending on the desired lighting specification, typically ranges from l λ to l Δ of the width of plate 10. A TIR film 20 is then laid over the entire surface of plate 10, covering both the masked areas and the bared central window 18. The TIR film may be attached with cement along a narrow longitudinal strip. Finally, two extractors 22, 24, further described below, are glued onto TIR film 20. The extractors are two elongated, iso¬ sceles triangles of an opaque reflective film, which extend from their respective bases near one end of plate 10, tapering to its opposite end. Both extractors 22, 24 are arranged symmetrically with respect to the longitudinal axis of plate 10, each near one of lateral fins 12, 14. As shown on Fig. 3, plate 10, prepared as described, is bent transversely to bring fins 12, 14 togemer. The fins are then received into respective longitudinal grooves made in a webbed aluminum shoe 26. Shoe 26 is bolted at intervals to a girder 28, with which it forms a clamping means to fasten the longitudinal finned edges of plate 10, so mat a hollow cylinder is formed, which constitutes a trunk of a tubular light guide according to the invention. Two ribs 30 depend from the longitudinal opposite sides of shoe 26. Ribs 30 are shaped with grooves to elastically grip an arched sheet 32, which is itself coated with a TIR film. The operation of the guide as described above will be evident to the person skilled in the art. Shortly, the light, which is focussed by projector 46 to hit the guide walls with an angle smaller than Brewster's angle, will be reflected in succession by total intemal reflection on TIR film 20, and will zigzag forward along the tube. However, the light hitting extractors 22, 24 is diffusely reflected, and a fraction of such reflected light will hit window 18 with an angle larger than Brewster's angle, and therefore will cross TLR film 20 and emerge to the outside space. The diffused light crossing TIR film 20 outside window 18 is reflected by masking 16 and is retumed to the intemal space of the guide. For a more detailed explanation of the operation of the hght guide, reference is made to EP-A-0225 123 as mentioned above. Fig. 4 shows a light guide as assembled from several trunks as shown on Fig. 3, which are connected to one another. Each guide trunk 32, 34, 36 is hung to a horizon¬ tal rail 38 by means of hooking brackets 40 which are fastened to straps 41, as better described below. The trunks are connected end-to-end by means of fittings com¬ prising pairs of rings 42, 44, which are also further described below. At one end of the guide, a light source is attached, i.e. a focused projector 46 (which is also hung to rail 38 through a bracket 40). Projector 46 is known to a person skilled in the art and does not belong to the invention, so that it is not described further. The oppsite end of the guide is terminated by a reflector 48, further described below, although an identical projector to projector 46 might be mounted in its place. Fig. 5 shows in more detail how the light guide is hooked to horizontal rail 38. Near its opposite ends, each trunk is individually embraced in a stainless-steel strap 41 having terminal flanges for fastening to a hook 40 by means of bolts 50. With reference to Figs. 6, 7 and 8, the connection of two tube trunks such as 32, 34 is made by means of two webbed rings 42, 44 of a technopolymer, each having an intemal bore sized for a snug fit with the associated light guide trunk, and further having a hosing slot for the end of girder 28 and a flaring 52 (see Fig. 8) where a rubber gasket 54 is received. Ring 42 has an annular groove on the side facing ring 44, which groove matches an annular rib 56 (Fig. 8) on the side of ring 44. When two guide trunks provided with their respective fitting rings, are brought together end-to-end, the rings match together by coupling of the rib within the groove, and the edges of both tubes abut against each other. The rings are then locked to each other with three clips 58 having toggle levers 60, which are received in recesses 62 made in the outside peripheries of rings 42, 44. Clips 58 lock rings 42, 44 against each other, thus compressing gaskets 54, which in their turn squeeze the associated guide trunks and ensure a leakless assembly between them. Fig. 9 shows a preferred terminal reflector 48. The reflector is similar to a fitting ring 42 and, similarly, is assembled against a ring 44 having gaskets 54 and clips 58. Teπninal 48, however, is different from the fitting ring substantially in that it is shut by a cross-wall 64, having a projection issuing from its center, to which a convex, metal-coated reflector 68 is bolted. The above described tubular light guide structure is definitely cheaper than known light guides based on TIR films, with respect both to the cost of the starting materials and, even more, to the costs of processing, transport and assembly. The plates can be pre-assembled in the factory with masking, TIR film and extractors, and be then transported in a stacked condition to the site of installation, where they can undergo their final assembly by means of easy steps and of simple tools. As a person skilled in the art will readily understand, laying the several optically active films is much easier than in light guides based on extruded tubes; the decrease in bulk with respect to guides made from extruded tubes is also considerable, and it entails a corresponding decrease of the transport costs. The preferred embodiment of the invention as described above is e evidently liable to changes and modifications, within the inventive idea as defined in the attached claims.

Claims: CLAIMS 1. A tubular light guide for linear lighting, comprising a row of at least partly trans¬ parent tubes, which are coated with a flexible TIR film on their intemal surface, char¬ acterized in that each tube is formed from a semi-rigid rectangular plate of transparent polymeric material, which is coated with said total reflection film on one of its surfaces and is arched with its longer sides brought together and clamped by clamping means. 2. The tubular light guide of claim 1, characterized in that the polymeric material of said plate is polycarbonate. 3. The mbular light guide of claim 2, characterized in that said plate is 1.5 mm thick. 4. The tubular light guide of one of claims 1 to 3, characterized in that a film of white matte material, covering only a part of the plate to define a light-emission window, is inserted between the TIR film and the plate. 5. The tubular light guide of one of claims 1 to 4, characterized in that a strip of white matte material is laid on the TIR film in a position substantially opposite to said emissione window, to act as a light extractor. 6. The tubular light guide of one of claims 1 to 5, characterized in that the edges of the plate along its longer sides are bent square to form fins, and in that said fins are received in grooves in said clamping means. 7. The tubular light guide of claim 6, characterized in that said clamping means comprise a shaped shoe having parallel, longitudinal grooves for receiving said fins and receiving said fins and a girder which can be fastened to said shoe over said grooves to said fins and a girder which can be fastened to said shoe over said grooves to grip the fins. 8. The tubular light guide of claim 7, characterized in that said girder can be fastened onto said shoe by means of bolts. 9. The tubular light guide of any of claims 7 or 8, characterized in that an arched, TIR-film-coated sheet is attached to the side of said shoe which is opposite to the girder. 10. The tubular light guide of any of claim 1 to 9, characterized in that each of said tubes is connected to the adjacent tube by means of a pair of fitting rings, each being inserted over the end of a respective one of said tubes, and each being provided with a respective rubber gasket, the rings being locked together by means of toggle clips arranged at intervals along their peripheries. 11. The tubular hght guide of claim 10, characterized in that said rings in each pair are provided with mutually mating members. 12. The tubular light guide of claim 11, characterized in that said mating members comprise a frontal annular rib on one of the rings and a complementary frontal annular groove on the other ring of the pair. 13. The tubular light guide of any of claims 10 to 12, characterized in that said clips are provided with a toggle lever. 14. The tubular hght guide of any of claims 10 to 13, characterized in that said clips are received in recesses in the rings. 15. The tubular light guide of any of claims 10 to 14, characterized in that it further comprises a reflector terminal at one end of the guide, having a shutting wall which is internally provided with a metal-coated reflector, the terminal being adapted to mate with one of said fitting rings.

Inventors: CASALONE ROBERTO, CASALONE, ROBERTO
Applicants: TUBOSIDER ITALIANA S P A, TUBOSIDER ITALIANA S.P.A.
Application year: 1997
Main classification: F21V8
IPC codes: F21S2, F21V8, G02B6