WO1997014914A1

WO1997014914A1 - Uniform direction dependent line light source

Info

Publication number: WO1997014914A1
Application number: PCT/US1996/016730
Authority: WO
Inventors: John F. Dreyer
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1995-10-20
Filing date: 1996-10-18
Publication date: 1997-04-24
Also published as: AU7455396A

Abstract

A direction dependent light source has light exitance portions (42) integral with a totally internally reflecting film to directionally emit light from a light conduit. The light exitance portions, such as asymmetrical notches, emit light at substantially the same direction at which the light strikes the interior side of the light conduit (14) for light traveling in a first direction but has negligible effect with respect to transmission of light for light traveling in the opposite direction. The light exitance portions may be formed integrally with the light conduit in sections of the light conduit that emit less light than other portions of the light conduit to facilitate uniform brightness in a specific direction.

Description

UNIFORM DIRECTION DEPENDENT LINE LIGHT SOURCE

Field ofthe Invention The present invention relates generally to light sources which employ light conduits operating on the principle of total internal reflection. More specifically, the present invention relates to promoting greater uniformity of brightness in such directionally dependent line light sources.

Background ofthe Invention Light sources used in traffic and navigational control are generally point or near-point sources. Common examples include semaphores and hazard lights commonly placed around road construction areas.

More recently line light sources have been introduced in traffic control and hazard conspicuity applications. The apparent brightness of such directionally dependent line light sources are highly dependent on the viewing angle with respect to the light conduit. An exemplary line light source, disclosed in U.S. Pat. No. 5,043,850 (Dreyer, Jr.), employs a light conduit ofthe type disclosed in U.S. Pat. No. 4,805,984 (Cobb, Jr.). Two light sources differing in at least one optical property are optically coupled to opposing ends ofthe light conduit. The hght is emitted from the hght conduit in directions such that the light will appear brightest to a person looking along the conduit. If the optical property which differs is color, the light conduit will appear a first color when viewed from one direction and a second color when viewed from the opposite direction. An additional line light source is disclosed in U.S. Pat. No. 5,258,896 (Dreyer, Jr.). A related type of product is produced when only a single lamp is utilized. When such a structure is constructed, the line source will be visible to a person looking along the light conduit in a direction toward the light source, but will not be readily apparent to a person looking along the light conduit away from the light source. A problem that arises in such directionally dependent line light sources, both unidirectional and bi-directional, arises due to the attenuation of light over the length ofthe light conduit. Light conduits, as described above, do not generate light in addition to the hght provided by the light source at one or both ends ofthe light conduit, but rather only emit that light. When light is emitted from sections ofthe light conduit that are closer to the light source, the emitted light leaves less light available for the light conduit to transport and to emit in sections of the light conduit that are further from the light source. This attenuation of light over the length ofthe light conduit causes nonuniformity of light emission over the length ofthe light conduit, the light conduit appearing brighter in sections closer to the light source and appearing dimmer in sections further from the light source. This contrast in brightness limits the desired distance between light sources when a uniform brightness is necessary, thereby requiring more light sources to generate more light and increasing the cost ofthe system.

Many methods are known in the art for improving the uniformity of light emission in unidirectional light conduits. These methods improve uniformity by increasing the exitance of light in the sections ofthe light conduit furthest from the light source and decrease the exitance in the sections ofthe hght conduit closest to the light source. For example, diffusive reflectors can be placed inside the hght conduit in sections ofthe light conduit furthest from light source to extract light from the light conduit at a rate higher than if no diffusive reflectors were present. Another method of increasing the exitance of light is by introducing imperfections in the totally internally reflecting surfaces ofthe hght conduit, such as by abrading the prismatic structured surface, to allow more light to emit from the light conduit rather than totally internally reflect off the abraded surface. Yet another method of increasing the exitance of light is by coating the hght conduit surface with a material of a different refractive index, thereby increasing the transmission of light. The prior art methods of increasing hght exitance from hght conduits, however, increase the exitance of hght from the hght conduit regardless ofthe direction in which the light is traveling. Thus, these methods cannot be used to increase the exitance of hght at the darker end of a bi-directional hght conduit for hght traveling in a first direction without also increasing the brightness ofthe brighter end ofthe hght conduit for light traveling in the opposite direction. Therefore, there is a need in the art for a method of increasing the exitance of hght in a hght conduit that increases the exitance more for light traveling in a first direction than for light traveling in the opposite direction.

Summary ofthe Invention

The present invention improves the uniformity of hght transmission from both unidirectional and bi-directional line hght sources through directional hght leakage. A bi-directional line hght source has light injector assembhes at both ends of a light conduit, the hght conduit formed of a thin, flexible polymeric optical film having smooth surface and a structured surface. The structured surface includes linear array of substantially right angled isosceles prisms arranged side by side. The structured surface and the optical properties ofthe material chosen produce total internal reflection of hght. More specifically, the structured surface transports the majority of incident light through total internal reflection and emits the remaining light at substantially the same angle of incidence as that at which it strikes the hght conduit.

Directional hght leakage, that is increasing the amount of emitted light in substantially the same direction as that at which it strikes the hght conduit, is achieved by placing light exitance portions in sections of a hght conduit where more hght transmission is necessary to increase brightness to achieve uniform brightness along the length ofthe light conduit. Light exitance portions in the form asymmetric notches in the structured surface provide a direct exit window for hght traveling approaching the near vertical face ofthe notch, thereby increasing the amount of hght exiting the light conduit.

Brief Description ofthe Drawings The present invention will be more fully described with reference to the accompanying drawings wherein like reference numerals identify corresponding components, and: Figure 1 is a side cross-sectional view of a first end of a hght conduit having a hght injector assembly; Figure 2 is an end cross-sectional view ofthe hght conduit shown in Figure 1;

Figure 3 is a perspective view of a portion ofthe hght conduit ofthe present invention, showing both the hght transport and emitting portion and the hght exitance portion;

Figure 3 A is a cross-sectional view ofthe light conduit for illustrating the notch depth;

Figure 4 is a side cross-sectional view of a bi-directional line hght source; Figure 5 shows a prior art bi-directional line light source;

Figure 6 is a schematic of a bi-directional line hght source ofthe present invention; and

Figures 6A and 6B are used to show how hght rays behave from two oppositely disposed light sources as they approach walls ofthe light conduit implementing the hght exitance portions.

Detailed Description of a Preferred Embodiment In the following detailed description ofthe preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration of a specific embodiment of which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

Figure 1 is a side cross sectional view of one embodiment ofthe invention, designated as line light source 10 and Figure 2 is an end cross sectional view ofthe embodiment ofthe invention. The embodiment as shown comprises a hght source 16 and a light distribution assembly comprising two generally cylindrical hollow members having a common longitudinal axis, i.e., one within the other such that in cross-section, they are circular and concentric. The outer member is a strong, substantially optically transparent protective cover 12, and while it is preferred, it is not required. The inner member is a substantially optically transparent, notched, totally internally reflecting thin film hght conduit 14, as will later be described. As used herein, the term Optically transparent' is used broadly to describe materials which transmit light without significant absoφtion.

Specifically, as used herein, the term Optically transparent' shall not exclude materials which transmit specific wavelengths of light, and which thereby appear colored to the eye of an observer but are transparent to the wavelengths of interest in a particular apphcation. The diameter of cover 12 may be large enough to create an airspace 13 between cover 12 and hght conduit 14, but this also is not required.

In one embodiment ofthe present invention, cover 12 is a substantially optically transparent cylindrical tube preferably formed from a dielectric acrylic or polymeric material such as polypropylenes, polyurethanes, polystryrenes, and polyvinylchlorides. In a preferred embodiment the tube comprises a polycarbonate matrix. It will be appreciated, however, that cover 12 could be of a different shape or a different material to accommodate different applications. For example, in certain signing apphcations it may be desirable for only a portion ofthe cover 12 to comprise a substantially optically transparent polymeric material.

Light conduit 14 comprises a first portion for hght transport and emission and a second portion substantially for directionally dependent hght exitance. The first portion of light conduit 14 comprises a longitudinal hollow structure preferably made from a substantially optically transparent dielectric material, as taught in U.S. Pat. No. 4,805,984 (Cobb, Jr.,). The hollow structure is formed of a thin, flexible polymeric film having a smooth surface (the inner side as shown in Fig. 2) and a structured outer surface. The structure ofthe first portion of the film suitable for hght transport and emission is similar to 3M Optical Lighting Film commercially available from the Minnesota Mining and Manufacturing Company of St. Paul, Minnesota and described in U.S. Pat. No. 4,906,070 (Cobb, Jr.). A preferred structured surface includes a linear array of substantially right angled isosceles prisms arranged side by side. The perpendicular sides of each prism make an angle of approximately 45° with the tangent to the adjacent smooth surface opposite the structured surface. While right angled isosceles prisms are preferred, those skilled in the art will readily recognize that other isosceles prisms may be used, such as those disclosed in commonly assigned U.S. Patent Apphcation

Serial No. , entitled "Totally Internally Reflecting Light Conduit", filed

October 17, 1995 to Dreyer. While the prisms totally internally reflect (TIR) the majority of incident light, thereby transporting light along the light conduit, hght that approaches the prism at less than the critical angle as well as some hght striking imperfections in the hght conduit will be emitted from hght conduit 14. In one construction, the prisms extend longitudinally along the length ofthe outer surface of hght conduit 14. However, it will be appreciated that the prisms may extend along the longitudinal axis of hght conduit 14 in a helical fashion, as disclosed in commonly assigned U.S. Patent No. 5,363,470 to Wortman, which further facihtates hght emission from the hght conduit.

Figure 3 is a perspective view of a portion of hght conduit 14, showing both a emission and transport portion 40, as described above, and a hght exitance portion 42. Light exitance portion 42 provides directional light leakage, by increasing the amount of emitted light in substantially the same direction as that at which it strikes the interior wall ofthe hght conduit. Because of refraction at the interfaces between air and the hght conduit material, the hght will not exit at the same angle as the angle at which it approached the inner wall ofthe hght conduit when it exits through hght exitance portion 42, but will exit in substantially the same direction. As used herein, the term "in substantially the same direction" describes directional hght leakage whereby most ofthe light emitted by the hne light source is visible only to a viewer looking along the length ofthe hne hght source and toward the light source ofthe line light source. By placing hght exitance portions in sections of a light conduit where more hght transmission is necessary, increased brightness in those sections achieves uniform brightness along the length ofthe hght conduit. Light exitance portions 42 in the form asymmetric notches in the structured surface have a first near vertical face and a second near horizontal face, with respect to the longitudinal axis ofthe hght conduit. The notches provide a direct exit window for light traveling through the light conduit that strike the near vertical face ofthe notch, thereby increasing the amount of hght exiting the light conduit.

In one embodiment, the near vertical face ofthe notch is preferably substantially perpendicular to the longitudinal axis of hght conduit 14. In another embodiment, however, the near vertical face ofthe notch has an angle in the range of zero to thirty degrees from the normal, and more preferably between two and fourteen degrees, such that incident hght will approach the near vertical face ofthe notch closer to normal and thereby be easily emitted from hght conduit 14. It will be appreciated that hght exitance portions 42 need not be placed uniformly along light conduit 14, but rather, only on sections ofthe hght conduit where increased hght extraction is desired. In sections of light conduit 14 where light exitance portions 42 are desired, the orientation ofthe prisms of light emission and transport portions 40 must be slightly modified to accommodate hght exitance portions 42. For example, peaks 44 ofthe prisms may be slightly angled over the length ofthe prismatic structure between hght exitance portions 42, thereby forming the near horizontal portion ofthe asymmetric notch that is almost parallel to the longitudinal axis ofthe light conduit. For example, for perpendicular notches spaced by 2 meters with a notch depth of .003 inches (.0076 cm), the near horizontal portion of the asymmetric notch is angled .00218 degrees to accommodate the notch depth. Grooves 46 ofthe prisms may also be situated at an angle similar to peaks 44, such that the entire prismatic structure of hght conduit 14 remains intact.

The preferred light conduit 14 is made from a material which must be substantially optically transparent, and preferably is flexible, homogeneous, and isotropic. Suitable materials include commercially available acrylics and polycarbonates having nominal indices of refraction of 1.49 and 1.58, respectively. Other possible materials, selected to provide the required functionality, include polypropylenes, polyurethanes, polystryrenes, and polyvinylchlorides. Generally, polycarbonates are preferred for their relatively high indices of refraction and physical properties. In another embodiment, first hght transport and emission portion 40 may be made from a first material and second hght exitance portion 42 may be made from a second material. Many processes exist to mass produce the light conduit 14 having the light exitance portions therein. Manufacturing processes to produce the present invention are similar to those used to manufacture the structured surface film having the linear array of prismatic structures used in the present invention and are well known to those skilled in the art. For example, a master mold may be formed by machining parallel V-grooves into a smooth horizontal surface of a metal block, the V-grooves corresponding to the prismatic structures ofthe film. Two metal blocks having the prismatic structures cut thereon may be offset in the vertical direction, and horizontal direction if an angle is desired, a predetermined amount to incorporate the light exitance portions ofthe hght conduit, such as the asymmetrical notches, into the master mold. Alternatively, the master may be completely machined on a single metal block. After the master is assembled or cut, it then serves as a master mold for the manufacture of negative molds. Duplicates ofthe master mold can be made from the negative molds by electroforming or other well- known techniques for mold duphcation. A transparent polymeric film or sheet may then be pressed against the duplicate mold or die to form or emboss in the film or sheet the pattern ofthe master mold. Alternatively, a liquid fihn forming material could be cast onto the mold. In yet another method of constructing the present invention, sheets ofthe structured surface film may be telescoped to form light exitance portions. The particular manufacturing process is not essential to the present invention and is a matter of choice based upon economics and availability. A suitable thickness of film used for light conduit 14 is about 0.38 millimeters, measured from the smooth inner surface to the lowest point ofthe grooves. For such a film, about 27 peaks per centimeter of perimeter is preferred. This film can be curved into a cylinder as small as about 7.6 centimeters in diameter without substantially affecting the optical properties ofthe film. Light conduit 14 may be a single section or multiple sections joined together, as required by the particular apphcation. In a preferred embodiment, light conduit 14 is approximately 10 centimeters (4 inches) in diameter and 30 m (100 feet) long. In such an embodiment, sections of hght conduit 14 having hght exitance portions therein preferably have hght exitance portions spaced between 0.25 meters and 3 meters apart, depending on the level of brightness desired. As the hght exitance portions are placed in closer proximity, more light is emitted from light conduit 14, thereby increasing the brightness level in the direction of light travel.

The preferred notch depth, N, as shown in Figure 3 A, for the preferred embodiment ranges between .0005 and .050 inches (0.127 - 12.7 mm). The necessary notch depth to extract a predetermined amount of hght depends on the amount of light that is needed to be extracted in a section ofthe hght conduit and the spacing ofthe hght exitance portions. For example, a deeper notch allows more hght to escape than a shallower notch, but shallower notches can be used to extract the same amount of light if more hght exitance portions are placed in closer proximity.

In one embodiment ofthe invention, a hght injector assembly 16 is disposed adjacent at least one end of hght conduit 14 and cover 12 for directing light into light conduit 14. Light injector assembly 16 includes a case 18, which may be made of any suitably rigid, weatherable material, but is preferably of a metal, such as aluminum. Inside case 18 is a partially-collimated light source. As shown in Fig. 1, the hght source includes a lamp 20 and a parabolic reflector 22. It will be appreciated, however, that other collimated hght sources may be used. Figure 4 shows an embodiment ofthe present invention as a bi-directional line hght source. A light assembly similar to that shown in Figure 1 is placed on the opposite end of the light conduit to provide hght in the opposite direction. The second light injector assembly 16' also has a lamp 20' and a parabolic reflector 22' inside a case 18'.

Line light source 10 may optionally include an absorber 24 for absorbing highly uncolhmated hght, as shown in Figure 1 and as disclosed in U.S. Pat. No. 5,258,896, which is incoφorated herein by reference. Absorber 24 may be of any material and color that will absorb the hght emitted by lamp 20. If, as often is the case, lamp 20 emits white hght, absorber 24 is preferably flat black in color. Metallic absorbers painted flat black may be used. If, however, lamp 20 emits colored hght, absorber 24 may be of any color that will absorb light ofthe color emitted by lamp 20. The combination ofthe shape ofthe structured surface for the transport and emission portions ofthe light conduit, and the optical properties of the material chosen for those portions, produce total internal reflection of hght, if the light is properly directed into the hght conduit 14.

Use and Operation In operation, hght emanating from lamp 20 either directly enters the hght conduit 14, or is reflected into it by reflector 22. If the line hght source 10 includes an absorber 24, as discussed above, highly uncolhmated light will be absorbed by absorber 24. The remaining hght from the hght injector assembly 16 is directed into the hght conduit 14. Because the hght conduit 14 operates on the principle of total internal reflection, the majority of hght entering the hght conduit 14 propagates down the length ofthe hght conduit 14 without being absorbed or otherwise extinguished. Because the light conduit 14 is closed at each end, the only way hght in the light conduit may escape is through leakage.

In hght transport and emission portions of light conduit 14, light leakage occurs due to imperfections in the hght conduit 14 such as anisotropy in materials, or flaws in construction. Light exiting a light conduit by leakage leaves the conduit in substantially the same direction as that at which it strikes the conduit. This is in contrast to the extraction of hght from light conduits taught in the prior art, which rely on diffusers or extractors to significantly change the direction of light rays within the light conduit by scattering, so that the rays strike the light conduit inner surface at angles approaching normal incidence. Such techniques produce relatively small intensities when observed at angles near the axis ofthe light conduit, the opposite ofthe effect produced by the present invention.

Figure 5 shows a prior art bi-directional hne hght source 50 having a first light source 52 at a first end ofthe light conduit 56 and a second hght source 54 at a second end ofthe hght conduit 56. As described earlier, hght detector 62 detects a higher level of light, or brighter light, from hght rays leaking from sections of hght conduit 56 that are closer to hght source 52 providing hght in the detector's direction, such as light ray 66, than from light rays leaking from sections of light conduit 56 that are further from light source 52, such as light ray 68. Similarly, hght detector 64 will detect a higher level of light from hght rays leaking from sections closer to light source 54, which provides light in the opposite direction of light source 52, than from hght rays leaking from sections of hght conduit 56 that are further from hght source 54, such as hght ray 72. This lack of uniform directional brightness over the length ofthe light conduit occurs because as hght is emitted from light conduit 56 nearer a hght source, less hght is available for emission from the light conduit in sections ofthe hght conduit further from the hght source. Further, because the light conduit emits hght in a directional manner, a hght source closer, to an end that would appear darker from the opposite direction, for example, hght source 52 with respect to detector 64, will not provide any substantial levels of directional hght that would brighten the hght conduit in that direction.

Figure 6 shows a bi-directional hne hght source ofthe present invention having first light source 82 at a first end of hght conduit 86 and second hght source 84 at a second end of hght conduit 86. As described in relation to Figure 5, more hght is available from hght source 82 at the first end of hght conduit 86 such that detector 92 detects a relatively high level of directional hght, such as hght ray 88, exiting light conduit 86. Because less hght is available from light source 82 at the second end of hght conduit 86, due to hght emission from light conduit 86 along the length of conduit 86, light exitance portions 100 are placed on sections of light conduit 86 near the second end of light conduit 86, or near light source 84. Light exitance portions 100 may be evenly spaced or may be placed in increasing frequency as less light is available, thereby increasing the hght transmissions from the light conduit and improving the uniformity in the direction of detector 92. Alternatively, hght exitance portions 100 may be evenly spaced but, in an embodiment with asymmetric notches, the notch depth may increase for notches further from the originating hght source, thereby increasing the light emission from the hght conduit in those sections. As will be described in further detail below, the hght exitance portions in the hght conduit provide directional hght exitance from the hght conduit in the same direction at which hght rays strike the interior side ofthe light conduit. In a bi-directional line hght source, the light exitance portions corresponding to a first light source directionally emit light rays originating from the corresponding first hght source but have negligible effect on light rays originating from the second hght source at the other end ofthe hght conduit. Thus, observers moving parallel to the hght conduit and toward the first light source will observe a substantially uniformly bright line hght source. By also integrating light exitance portions corresponding to the second hght source on the end ofthe light conduit closer to the first light source, the bi-directional line light source appears uniform along the length ofthe light conduit for observers approaching the line hght source from either direction. Figure 6B is an enlarged portion of a wall ofhght conduit 86, showing how hght rays behave as they approach a hght exitance portion. As shown in Figure 6B, hght exitance portion 100 is directionally dependent, meaning that it only allows transmission ofhght that approaches hght exitance portion 100 from a predetermined direction. With respect to Figure 6, light exitance portion 100 as shown in Figure 6B would preferable be disposed on the hght conduit closer to hght source 84 to emit hght from hght source 82. In Figure 6B, hght exitance portion 100 is a asymmetrical notch having a near vertical face 111 that may be normal to the longitudinal axis ofthe hght conduit or angled between zero and thirty degrees from the normal, and a near horizontal face 110 that is almost parallel to the longitudinal axis.

Light ray 106, originating from light source 84 at the second end of hght conduit 86, strikes near horizontal face 110 ofthe notch acting as light exitance portion 100 and is totally internally reflected, except for the small portion ofhght that is emitted and detected by detector 94. Because near horizontal face 110 is slightly angled to accommodate near vertical face 111, hght ray 106 may have an insignificant change in exit angle from near horizontal face 110 compared to its entrance angle. Light ray 104, originating from light source 82 at the first end of hght conduit 86, however, approaches near vertical face 111 ofthe notch acting as hght exitance portion 100 and is emitted from hght conduit 86 through near vertical face 111. More specifically, light ray 104 is emitted from light conduit when it strikes near vertical face 111 ofthe notch. Because hght ray 104 is substantially completely emitted from hght conduit 86, detector 92 will receive a substantially higher amount of ght from the section of light conduit 86 near light source 84 than if hght exitance portion 100 were not present, thereby improving the umformity of hght received by detector 92 between the first end and the second end of light conduit 86.

Similarly, as shown in Figure 6 , hght exitance portion 102 is also directionally dependent, allowing transmission ofhght that approaches light exitance portion 102 from a direction opposite that of ght exitance portion 100. With respect to Figure 6, hght exitance portion 102 as shown in Figure 6B would preferable be disposed on the light conduit closer to hght source 82 to emit hght from hght source 84. Light ray 114, originating from hght source 82 at the first end ofhght conduit 86, strikes near horizontal face 108 ofhght conduit 86 and is totally internally reflected, except for the small portion ofhght that is emitted and detected by detector 94. Light ray 112, originating from hght source 84 at the second end of light conduit 86, however, approaches light exitance portion 102 and is emitted from light conduit 86 through near vertical face 102 ofthe notch. Because hght ray 112 is substantially completely emitted from light conduit 86, detector 94 will receive a substantially higher amount ofhght from the section of light conduit 86 near hght source 82 than if light exitance portion 102 were not present, thereby improving the uniformity of light received by detector 94 between the second end and the first end of light conduit 86. Thus, light exitance portions 100 and 102 improve the uniformity ofthe bi-directional hght conduit by increasing the amount of light emitted from the light conduit in one direction without substantially affecting the transportation ofhght in the opposite direction. It is readily appreciated that the hght exitance portions may be place on only one end of a unidirectional light conduit to improve the uniformity in only one direction.

Although a preferred embodiment has been iUustrated and described for the present invention, it will be appreciated by those of ordinary skill in the art that any method or apparatus which is calculated to achieve this same puφose may be substituted for the specific configurations and steps shown. This application is intended to cover any adaptations or variations ofthe present invention. Therefore, it is manifestly intended that this invention be limited only by the appended claims and the equivalents thereof.

Claims

1. A direction dependent line hght source, comprising: a hollow hght conduit having an interior side and a first end and a second end with a longitudinal axis running therebetween, said light conduit being longer in length than in cross sectional width, comprising a thin film of a totally internally reflecting material; a first illumination source directed into said first end of said light conduit; and first directionally dependent light exitance means for emitting hght from said hght conduit at substantially the same direction at which it strikes said interior side of said hght conduit for light traveling in a first direction, said directionally dependent light exitance means emitting a greater quantity ofhght from said hght conduit than would otherwise be emitted from said hght conduit.

2. The direction dependent line hght source according to claim

1, wherein said first directionally dependent light exitance means comprises a asymmetric notch located in said thin film, said asymmetric notch comprising: a first face substantially normal to said longitudinal axis of said hght conduit; and a second face almost parallel to said longitudinal axis of said light conduit.

3. The direction dependent line hght source according to claim

2, wherein said asymmetric notch is oriented such that said first face is closer to said second end of said light conduit and said second face is closer to said first end of said hght conduit.

4. The direction dependent line light source according to any of the preceding claims, wherein said thin film comprises a substantially transparent film having a structured surface on one side and a smooth surface opposite said structured surface, said structured surface having a linear array of substantially right angled isosceles prisms arranged side-by-side.

5. The direction dependent line hght source according to any of claims 2, 3, and 4, wherein said plurahty of asymmetrical notches are disposed in equal intervals along selected sections of said hght conduit.

6. The direction dependent line hght source according to any of claims 2, 3, and 4, wherein said plurahty of asymmetrical notches are disposed in decreasing intervals along selected sections of said light conduit.

7. The direction dependent line hght source according to any of claims 2, 3, and 4, wherein the length of said first face of said plurality of asymmetrical notches increases along selected sections of said hght conduit.

8. The direction dependent line light source according to any preceding claim, further comprising a second illumination source directed into said second end of said light conduit.

9. The direction dependent line hght source according to claim 8, further comprising second directionally dependent light exitance means integral with said thin film for emitting hght from said hght conduit at substantially the same direction at which it strikes said interior side of said hght conduit for hght traveling in a second direction, said second directionally dependent hght exitance means emitting a greater quantity ofhght from said hght conduit than would otherwise be emitted from said hght conduit, said second directionally dependent light exitance means emitting light traveling in substantially the opposite direction ofhght that is emitted by said first directionally dependent hght exitance means.

10. The direction dependent hne hght source according to claim 9, wherein said second directionally dependent hght exitance means comprises a asymmetric notch located in said thin film, said asymmetric notch comprising: a first face substantially normal to said longitudinal axis of said hght conduit; and a second face almost parallel to said longitudinal axis of said hght conduit.