BACKGROUND OF THE INVENTION

The present invention relates to a light guide system for receiving and transporting light by means of light guides, which system comprises at least one light collecting unit for receiving light, which unit comprises a number of light guides, the light receiving ends of which are arranged in a two dimensional array of rows and columns whilst downstream these ends these light guides stepwise compose to minimal one outgoing transport light guide to transport the light received by the unit to a location remote from the unit. The invention also relates to a light-collecting unit for use in the light guide system and to a road marking system comprising said light collecting units.

In a passive road marking system the light guide system is used for marking road portions ahead a vehicle driver and/or for warning traffic behind said vehicle. In that case said light is ambient light, which generally is understood to mean light that is, in first instance, present in a space for reasons and/or purposes other than irradiating the light guide system. Such ambient light is for example light from a vehicle headlamp, which light is intended to illuminate a road portion in front of the vehicle driver. It may also be light from other radiation sources, which are primary used for other purposes. The light guide system allows a second use of this light at a location remote from the location where it is generated. Ambient light may also be sunlight, light from buildings or streetlight. The light guide system may also be used in combination with a primary light source, i.e. a source that is intended to irradiate the light collecting unit(s), for example in case the light guide system is used to illuminate several location within a home or a building by means of a central light source. The term stepwise composed is understood to mean that primary light guides, which are provided with the light receiving ends, flow together in secondary light guides and the secondary light guides again flow together and so on, such that finally all light received by the receiving ends of the light guides within a unit is concentrated into a few outgoing light guides. Thus the light guide structure in a unit is an inverted tree structure.

A passive road marking system is understood to mean a system that does not comprise own light sources, but uses light that is already present. Such a system may be used, for example for roadways or sections thereof for which full artificial lighting during hours of darkness does not merit, because these roadways do not carry sufficient traffic density. Artificial lighting of roadways requires a lot of energy so that this will be avoided wherever and whenever possible. Also in free or protected natural regions artificial road lighting is not wanted or even not allowed, because this contributes to so called light pollution, which is becoming an increasing global problem, especially in the neighborhood of crowded regions.

Thus there is a need for a road marking, or visibility system that does not consume energy. Such a system has been described in previous, not pre-published European patent application EP 07118074.9. This system, when used as a road marking system comprises a series of light collecting units for receiving light from traffic headlights. Each unit comprises a number of light guides, the light receiving ends of which are arranged in a two dimensional array of rows and columns whilst downstream these ends the light guides stepwise compose to minimal one inner transport light guide, which transports the light received by the unit to an end side of the unit. The light from this side is transported by at least one external transport light guide to a remote location. This location may be that of a succeeding light collecting unit.

As described in previous patent application EP 07118074.9, this system is substantially and in an inventive way different from prior art light guide systems for the envisaged applications. Although the concept of this system is very suitable to be implemented in a passive road marking system, it has turned out that its performance and reliability and manufacture yield can be increased substantially whilst the maintenance costs can be substantially decreased. SUMMARY TO THE INVENTION

It is an object of the present invention to furnish inventive additional means to realize the increased performance and reliability and the yield. The light guide system wherein these means has been implemented is characterized in that main light guides within a light collecting unit are interconnected by transverse light guides.

A main light guide is understood to mean a light guide that belongs to the main light guide structure of a light collecting unit, i.e. the light guide structure described in the above-mentioned previous patent application EP 07118074.9, which main structure transports light from the light receiving windows of the unit to the end side of this unit.

When used as a road marking system the light collecting units may have a considerable length. For example a light collecting unit may comprise nine rows of each five windows and its length may extend to the order of one meter. The length of the light guides depends on the positions of the rows of windows to which they are connected. Thus the length of the light guides may vary from a few centimeters to almost the length of the collecting unit, for example one-meter. Manufacture of a light guide structure having such long light guides by means of an injection molding process, which seems the most attractive process, has turned out to be difficult, mainly because the molding material should be brought to locations relatively far remote from the injection points. By including the said transverse light guides, the light guide structure becomes more open and easier to manufacture.

The invention is based on the insight that, in contrast to light guides in optical telecommunication or data transport systems, the light guides of a light collecting unit need not to constitute separated light paths and collected light may cross over from one light guide to another light guide. The latter is even preferred in the present light guide system and allows obtaining a more uniform distribution of light over the main light guides of the collecting unit, which is a further advantage. This allows compensating for the effect that the longer the path length in a light guide is, the more the light is weakened. In a glass or quartz fiber attenuation of light is smaller than in a plastics fiber. Instead of for obtaining a more uniform light distribution, the possibility to transfer light from one light guide to another may be used in an another, advantageous and inventive, way. A preferred embodiment of the light collecting unit for use in a guide system wherein this is realized is characterized in that at a location where a main light guide and a transverse light guide meet each other these light guides are positioned relative to each other such that a pre-determined portion of the light transmitted by a first one of the light guides is transferred to the second one of the light guides, whereby this portion is determined by the effective opening of the first light guide occupied by the second light guide. The effective opening of the first light guide, which may be a main light guide or a transverse light guide, is understood to mean the surface area of the first light guide through which light propagating along this guide can enter the second light guide. The dimension of this surface area is determined by the cross-section of the second light guide and the angle between the two light guides. The larger the effective opening is, the larger the portion of light that is split off from the first light guide. This opening is larger as the angle between the waveguides is smaller.

In this way the use of transverse light guides allows realizing an additional degree of freedom in the design of a light-collecting unit, namely choice of the distribution of light intensity over the main light guides. At a transverse position where the first light guide is a main light guide and the second light guide is a transverse light guide, a predetermined amount of light propagating along a main light guide is transferred to the transverse light guide. At a transverse position where the first light guide is a transverse light guide and the second light guide is a main light guide, a predetermined amount of light propagating along the transverse light guide is injected in the main light guide.

Especially in a light guide system for road marking wherein the light collecting units should emit a portion of the light received from preceding units or the windows of the unit itself, this feature can advantageously be used to control, or tune, this portion. A preferred embodiment of a light collecting unit for use in a light guide system, which unit comprises a sub-unit for splitting off a portion of the received light and emitting this portion to a viewer, wherein such use is realized is characterized in that the sub-unit comprises at least one transverse light guide for tuning the split off portion. By accurately setting the angle between this transverse light guide and the main transport light guide the portion of the light to be emitted can be controlled precisely.

A practical embodiment of this light collecting unit is characterized in that the sub-unit 's transverse light guide is provided with a number of split locations for stepwise reducing the light to be emitted.

In this embodiment all light guides may have the same cross section, in case of fibers the same diameter. The split locations may have an identical design and may perform the same splitting function, for example split-off half of the light passing the split location. Moreover, the length of the sub-unit can be limited.

This embodiment is further characterized in that the sub-unit comprises at each split location an auxiliary light guide for receiving from the transverse light guide light for further transport and injecting this in a transport light guide.

In this way, light that otherwise would be wasted is saved for further transport, for example to succeeding light collecting units.

The cross-section of a transverse light and the angle with a main light guide may also be chosen such that the required amount of light is split of in one step.

Since the inventive concept of the invention is a very general concept, it may be used not only in road marking systems such as for road vehicles, trains and airplanes, but also in other systems including systems wherein up to now such light guide transport system have not been used. Examples of such systems are displays for traffic ways or otherwise, and indoor or outdoor lighting systems.

It will be appreciated that the system of the invention is a completely passive system and requires minimal maintenance. The compact light guide structure can be easily embedded in, for example a road surface or a building during construction of the road or building, or afterwards. Although originally designed for use with ambient light, such as from vehicle light, streetlights or sunlight, the light guide system is also very attractive to be used with an external dedicated light, for example for interior lighting with a central light source. The light guide system and the light collecting unit for use in this system may be provided with features described in previous patent application EP 07118074.9. Especially the mechanical design of the light-collecting unit for use in a road marking system may be the same as that described in the previous patent application. The light guides may be optical fibers or optical waveguide. Optical fibers show a circular cross section and light propagates therein along a core that is enveloped by a cladding. A waveguide structure, wherein light propagates in channels having a more or less rectangular cross-section, for this purpose is more sophisticated and requires design efforts. Manufacturing a light-collecting unit including a waveguide structure requires less process steps than manufacturing of a unit including optical fibers. The specific application of the light guide system will determine whether optical fibers or a waveguide structure is preferred.

At several transition locations in the light-collecting unit light from a first fiber should be transferred to a second fiber, which is in line with the first fiber. A maximal transfer is warranted, without putting very stringent requirements on the alignment of the fibers, in an embodiment of the light-collecting unit, which is characterized in that at the transition location the first fiber has a smaller diameter than the second fiber. Then the broader receiving opening of the second fiber can capture the light from the smaller emitting opening of the first fiber, even when the fibers are not well aligned.

This embodiment is preferably characterized in that all fibers have the same diameter at their light receiving ends and that a fiber that ends at a transition location is tapered toward this location.

The preference that the fibers have the same diameter can still be fulfilled to a high degree.

Furthermore the maintenance costs of an installed light guide system can be considerably reduced. To that end a road marking system composed of a number of light-collecting units and transport light guides interconnecting the light-collecting units is characterized in that each light collecting unit includes a main body, accommodating the internal light guide structure, and at least one de-mountable coupling module for receiving an end of an external transport light guide and coupling this guide to the internal light guide structure.

Since the alignment of the external and internal transport light guides is already realized in the structure of the coupling module(s), no cumbersome alignment procedure has to be carried out when a defect or not well-performing light collecting unit has to be replaced. BRIEF DESCRIPTION OF THE DRAWING

These and other aspects of the invention will be apparent from and elucidated by way of non- limitative example with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1 shows a top view of an embodiment of a light-collecting unit wherein the invention can be used;

Fig. 2 shows a front view of a row of windows of such a unit; Fig. 3 shows a cross-section of an interior light path to a light guide;

Fig. 4 shows window light guides and row light guides of a light collecting unit;

Fig. 5 shows a small portion of row light guides provided with transverse light guides according to the invention; Fig. 6 shows the interface of a transverse light guide and a main light guide and the effective opening in the latter;

Fig. 7 shows a schematic diagram of a first embodiment of a light-collecting unit that is provided with a sub-unit for splitting off light to be emitted;

Fig. 8 shows a schematic diagram of a second embodiment of such unit; Fig. 9 shows a light-collecting unit having two light-receiving sub-units;

Fig. 10 shows a fiber transition location with a tapered fiber, and

Fig. 11 shows a light collecting unit provided with two coupling modules.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For a better understanding of the present invention, a light collecting unit that has been described extensively in previous European patent application EP 07118074.9 will be briefly discussed. Fig. 1 shows a top view of an embodiment of such a light-collecting unit 1 for use in a road marking system. This unit has a large number of windows, which transmit ambient light towards the interior of the unit. These windows are distributed over large surface area so that a large light receiving area is obtained. In this embodiment the light receiving windows are arranged in nine rows 2. The direction of these rows with respect to the traffic drive direction, or the road axis direction, 4 is determined by the contemplated road position of the unit. The unit of Fig. 1 is intended for placement at the right edge of the road to receive maximum light from the right headlight of vehicles passing the unit. The angle CC between the rows 2 and the drive direction 4 is for example 75°. For a unit that should be placed in the middle of the row the angle α is larger, for example up to some degrees less than 90° and for a unit that should be placed at the left edge of the road, α = -75° for example.

In a road marking system the light guides within a unit 1 do not reach the surface of the unit, but are arranged behind transparent windows, which transmit light incident thereon to the light guides and form a mechanical protection for the light guides and the interior of the unit. Fig. 2 schematically shows an exemplary row 2 of the unit, which comprises six windows 10 being sealed in a housing 12 of, for example a plastic material or rubber. The windows may be made of quartz or another transparent material such as transparent plastics, which may be provided with a hard, protective, coating. If circumstances requires so, the windows may be watertight sealed in the housing. Instead of being perpendicular to the road surface or the unit plate surface, windows 10 may be inclined backward at an angle of, for example 1° to 1,5° with respect to a horizontal light beam from a vehicle headlight, i.e. at an angle of 89° to 88,5° with respect to the plate surface.

Behind each window 10 a number of light guides are arranged for receiving the light transmitted by the window and transporting this light further on. In principle the light receiving ends of these light guides could be arranged to the backside of the window. Since the ambient light enters via a vertical or slightly skew window at the top portion of the unit and should be transported horizontally in the lower part of the unit, preferably a reflecting surface, for example of a prism, is arranged behind the window to reflect the received light downwards. This provides the advantage that the light guide needs not to be bent so that it is prevented that light escapes from the light guide. Fig. 3 shows an embodiment of the light path behind a window 10, which includes such a prism 14 having a light reflecting surface 16. The central ray 30 of a beam of light that transmits the window is incident on the surface 16 at an angle of 45° so that it is reflected in the vertical direction. At the lower side of the unit a further prism 20 having a reflecting surface 22 may be arranged, also at an angle of 45° so that it reflects the ray 30 in the horizontal direction so that the ray can enter a horizontally arranged light guide 24. The prisms 14 and 20 may be discrete elements. It is also possible that the reflecting surfaces 16 and 22 form the inclined upper and lower side, respectively of a single transparent element. Preferably, the reflecting surfaces are integral part of the internal structure of the light collecting unit 1 and are formed during manufacturing of the unit. Satisfying reflection at an inclined prism surface or otherwise inclined surface within the unit can be obtained by covering the surface with a reflecting layer. Alternatively, the surface may be arranged at such angle with the light beam that total internal reflection at the surface will occur.

To increase the amount of light that is received by the light guides associated with a window, the external window surface may be shaped such that it functions as a lens. This is indicated in Fig. 3 by the interrupted curved line 18. It is also possible that the light receiving side of each fiber is provided with a lens so that the part of the light transmitting the window that enters the light guide is increased. This is indicated by interrupted curved line 26 in Fig. 3. It is also possible that a unit shows both lens features in combination.

The number of light guides belonging to one window 10 may be chosen by a designer and adapted to circumstances. For example the number may vary between three and nine. If five light guides are provided for each window, behind the row 2 of Fig. 2 thirty light guides will be present and the embodiment of unit 1 shown in Fig. 1, which has nine rows will comprise two hundred and seventy light guides.

In addition to these light guides, which end facing the windows constitute light receiving openings, this embodiment also comprises at least one, for example two, light- emitting openings 8, as shown in Fig. 1. These openings are end faces of a corresponding number of, emitting, light guides included in the unit, which receive light from one or more preceding unit(s). Preferably the light-emitting openings form part of a window 10, as indicated by reference numeral 8' in Fig. 1. Light to be transmitted may be supplied to the opening 8' via a separate light guide or via a light guide that is already present for receiving ambient light.

The road marking system further comprises transport means to transport light from a light collecting unit to another one. For each unit 1 this transport means is constituted by a small number, for example two, outgoing light guides 6 as shown in Figure 1.

By way of example, the embodiment of Fig. 1 may have a length 1, in the drive direction, from 40 up to 100 cm and a width w of 15 up to 20 cm. The mutual distance of the units may be up to 15 m, for example.

To obtain a road marking system, a number of the units 1 will be arranged one after the other in the drive direction 4. The distance between succeeding units 1, thus the length of the light transport means, or transport light guides 6 usually will be prescribed by the road authority and may have a value between zero and for example 10 meters. With a distance of zero meters, i.e. the light collecting units 1 are arranged against each other, and a continuous lighting strip is obtained then. If it suffices to have road marks at a given mutual distance, the units 1 are arranged at said given distance, which distance may be determined by specific circumstances, for example a bent road portion. The distance between a first unit and the most remote unit that will still receive some light from the first unit may be hundreds of meters.

As described in EP 07118074.9 the new road marking system is made feasible for practical use by minimizing the height of the light collecting units as well as the volume of the light transport means between the units, so that the system can be embedded in a road way easily and without affecting the mechanical strength of the road way. This is realized by a special design of the light guide structure within a unit. The light guides downstream the windows stepwise compose to secondary light guides, which further compose and so on, such that the structure within a unit ends in a few, preferably one outgoing light guide, which constitutes the light transport means. The light transport means thus has only a small cross-section so that it can be easily embedded in a roadway and without affecting the mechanical strength of the roadway. The special guide light structure within a unit also allows limiting the height of the unit to a practical dimension.

In general, the light received by n rows each having m windows of a light collecting unit of the light guide system is transported to at least one position, for example a traffic display or mark where this light is needed. In case of a road marking system including more than one unit, a small portion of the light from a first unit is emitted at the position of at least one another unit by means of the emitting light guide(s) 8 shown in Figure 1. Light collected by the said another unit is added to the remaining light from the first unit and transported to still another unit, and so on.

A relative long light-collecting unit such as used in a road marking system includes light guides, which are relatively long, as shown in Figure 4. This Figure shows very schematically an embodiment of the light-collecting unit 1 having nine rows 2a-2i each having six windows. The light received by these rows of windows is collected and transported by light guides 31-39, respectively, which may be called row light guides. It will be clear that the row light guides have substantially different lengths. The light guides of a light-collecting unit may be constituted by optical fibers, which are laid formed in a body having a specific structure of channels corresponding to the required light guide structure. Alternatively the light guides are optical waveguides, which are constituted by the channels of said body. To that end the channels have an index of refraction that is lower than that of their environment. For manufacturing the channel structure and reflecting surfaces, such as surfaces 16 and 22 in Fig. 3, an injection molding process is used. This is a well- proven and cheap process and also the most suitable for the required structure. Manufacture of separate reflecting prisms, which would have been necessary if the process was not used, is expensive. Moreover the optical properties of the structure that is manufactured by means of the injection molding process match very well those the fiber light guides, which are preferably made by an extrusion process. In case the light guides are fibers, first a fiber core material is injected in the channel structure and after this material has solidified, i.e. the fibers cores have been formed, a fiber cladding material is injected along the cores so that the fiber claddings can be formed. However, especially molding a light guide structure having a large length dimension may cause difficulties, because the molding material may not reach locations relatively far remote from the injection points.

According to the invention between the main light guides, for example the row light guides, additional and relatively short, light guides are arranged as is shown in Fig. 5. This Figure shows a small portion of the light guide structure, namely only four light guides 31-34 and only a small portion of the length of these light guides. The small additional light guides, who may be called transverse light guides, are indicated by reference numerals 42 and 44. By including the transverse light guides, the light guide structure becomes more open and thus easier to manufacture. The invention makes inventive use of the fact that the light guides of the light- collecting unit need not to be optically isolated from each other, in contrast to light guides in optical telecommunication or data transport systems. It is even preferred that collected light is allowed to transfer from one row light guide, 31-39 in the present embodiment, to another one, because a more uniform distribution of light over the light guides can be obtained then. A required light distribution can be obtained by arranging the transverse light guides 42 or 44 at a sharp angle, β or γ, to the row light guides 31-34 such that light propagating through a row light guide in the direction 46, which may be the drive direction 4 in Fig. 1, meets an opening of a transverse light guide and can enter the latter. In this way the transverse light guides perform a second and very important function, which is unique in optical light guide technology.

By continuous mixing of the available light by means of the transverse light guides the distribution of the light is substantially less affected by dirt in, and/or damage of, the main light guides. Moreover, the original color of the light will be better maintained.

If the only purpose of the transverse light guides is to easy the injection molding process for manufacturing the light guide structure, the transverse light guides may be arranged perpendicular to the main light guides 31-34. In that case only few light from the main light guides will enter the transverse light guides. Strictly spoken these guides will then not be used as light guides, but they still have the same structure as the main light guides.

In case row light guide 31 is the longest light guide, belonging to the first row 2a of windows and row light guides 32- 34 and further row light guides have a decreasing length, transverse light guides arranged at the angle γ will be used so that a longer light guide, which shows more loss of light, will receive additional light from a shorter light guide. In case row light guide is the shortest light guide, for example if the direction of the ambient light is the reverse of the direction 46, transverse light guide arranged at the angle β will be used.

By way of example, the mutual distance, along the direction of a main light guide, of the transverse light guides 42 or 44 may be of the order of 1 cm and the mutual distance of the main light guides may be of the order of 1 mm. The main light guides may have a diameter of the order of 3 mm. A third new and inventive application of the transverse light guides is their use for splitting and combining light propagating along row light guides and transport light guides. If the light guide system is used in a road marking system its light collecting units should emit a small portion of the light received from preceding light collecting units. In the same time light collected by the first light guided should be combined with the larger portion of the light from the preceding units and transported to the succeeding units. In the system described in previous patent application EP 07118074.9 this splitting and combining is realized by means of reflecting elements arranged at locations where light splitting and-combining should take place. Positioning and alignment of the reflecting elements is quite critical. When the transverse light guides are arranged such that they can perform the splitting and combining function the reflecting elements are no longer needed and the manufacture process of a light collecting unit is made substantially easier.

The splitting ratio, i.e. the amount of light that is split off from a main light guide to a transverse light guide divided by the total amount of light that propagates along the main light guide at the position of the transverse light guide, may can be chosen at will Furthermore this ratio can be realized easily. At the location where a transverse light guide meets a main light guide the latter shows an opening. Fig. 6 shows a top view of such an opening 46 at enlarged scale The relevant dimension of this opening is determined by the inner dimension d of the transverse light guide 42 and the angle β between this light guide and the main light guide, for example a row light guide 31. In case the light guide is an optical fiber the dimension d is the diameter of the core of the fiber and in case the light guide is an optical waveguide the dimension d is the inner dimension of the waveguide in the plane of drawing. Preferably, the diameter, respectively the cross-section of the transverse light guide is equal to that of the main light guide, but they may also differ. The opening 46 in the wall of light guide 31 has a width w that is given by: w = d. /sinβ. The light rays propagate along light guides by means of total internal reflection at the walls of the light guides, as indicated by rays 48 and 50 in Fig. 6. It will be clear that the larger the width w, i.e. the smaller angle β, is the more light rays can enter the transverse light guide. In this way another degree of freedom of design is obtained: the amount of light split off from a main light guide to a transverse light guide can be set simply by a proper choice of angle β between the two light guides. This allows transfer of light from one main waveguide to another in a controlled way.

In a road marking system this possibility can be used to determine the percentage of the total amount of light present in a light-collecting unit that is emitted by this unit towards a vehicle driver. This will be explained at the hand of Fig. 7, which Figure shows very schematically an embodiment of such unit and an example of light splitting performed in this unit.

The light collecting unit 1 of Fig. 7 includes a light-receiving sub-unit 51 that comprises nine rows of each five windows. The left top portion of the Figure shows one of the windows 10 with its associated, for example three, primary light-guides 52, 54 and 56. These light-guides flow into one window light guide 58. In the main portion of the Figure the window light guides 58 are represented by the short horizontal lines. The window light guides of each row flow into a row light guide 2a - 2i, respectively. In this embodiment all row light guides flow into one internal transport light guide 60. Alternatively, the unit my comprise more than one internal transport light guide, which each receive light from different groups of row light guides. As indicated by arrow 62 at the left side of the Figure, this unit receives radiation from one or more preceding units. This means that if vehicle light is present the unit will be fed with light even if the unit itself is not irradiated by vehicle light. The right portion of Fig. 7 shows a sub-unit 64 wherein light to be emitted by one window of unit 1 is split off from the light propagating along the inner transport light guide 60. The unit comprises a first splitting location SLi where the light guide 60 meets a first transverse light guide, which is schematically represented by line 66. The w and β values at this location (and the succeeding split locations) are chosen such that transverse light guide 66 receives 50% of the radiation propagating along transport light guide 60. At a second splitting location SL ₂ half of this 50% is split off to a first auxiliary light guide 68 so that 25% of the original light propagates further in transverse light guide 66. At a third splitting location SL3 half of this 25% is split off to a second auxiliary light guide 70 so that 12,5% of the original light propagates further in transverse light guide 66. At a fourth splitting location SL ₄ half of this

12,5% is split off to a third auxiliary light guide 72 so that 6,25% of the original light propagates further in transverse light guide 66. Finally, at a fifth splitting location SL ₅ half of this 6,25% is split off to a fourth auxiliary light guide 74 so that 3,125% of the original light propagates further in light guide 66. This portion is the light to be emitted L _t b _e and is guided via light guide 76 to a window of, for example the last row 2i, of the light-collecting unit 1. It has turned out that this small amount of light is sufficient to be clearly visible to a vehicle driver, even at a distance of 200 m. This means that the very largest portion of the light that is available in the unit can be sent to a succeeding unit.

For that purpose the light collecting unit comprises a number of light combining (CL) locations which are formed by crossings of auxiliary light guides 60, 68-74 with a transverse light guide 78. At location CLi the 6,25% portion from auxiliary light guide 72 is added to the 3,125% portion from auxiliary light guide 74 so that 9,375% of the original light is re-obtained. At location CL ₂ the 12,5% portion is added so that 21,875% of the original light is re-obtained. To this the 25% portion from auxiliary light guide is added at location CL ₃ so that 46.875% of the original light is re-obtained. This is combined with the 50% portion at location CL ₄ so that at this location the inner transport light guide 60 re-obtains 96,875% of the original light. Thus nearly 97% of the light received from preceding units and received by the windows of this unit is available for transport to succeeding units, as indicated by arrow 80. Because of this large percentage, the light received by the units can be transported over large distances. The design of sub-unit 64 with the 50% splitting at each splitting location allows using fiber light guides having the same diameter and the same orientation (angle β), which is advantageously from a manufacturing point of view.

It will be clear that splitting off the said 3% of the light in the transport light guide 60 can also be realized in one step and by means of only a transverse light guide. Parameters w and β should then have values substantially different from those in sub-unit 64 of Fig. 7.

If circumstances require so the light splitting means may be designed such that more than said 3% of light is coupled out from light guide 60 and emitted. Instead of nine rows of each five windows, a light collecting unit may include another configuration of windows, for example eight rows of each six windows. The choice of the number of windows and their arrangement will be determined by the required amount of light to be captured. Fig. 8 shows an embodiment of a light collecting unit, which light-receiving sub-unit 61 has still another configuration. It comprises six rows of each six windows. This embodiment can be used in applications wherein a smaller amount of captured light suffices. Splitting off of the light to be emitted L _t b _e is performed in the same way and by the same means as in the embodiment of Fig. 7. Only the last splitting now takes place at the location where auxiliary light guide 74 meets light guide 78.

Fig. 9 shows an embodiment of the light-collecting unit 1, which is optimized with respect to the light capturing capability. This embodiment includes the same split-off sub-unit 64 as the embodiment of Figs. 7 and 8 and a light-receiving sub-unit 51 ', which is similar to that of the embodiment of Fig. 7 with the exception that the associated internal transport light guide 60' is arranged centrally in the window structure. Transport guide 60' thus meets the row light guides at the middle of these guides and receives light from both halves of each row light guide. The embodiment of Fig. 9 further comprises a second light-receiving sub-unit 81 and an also centrally arranged internal transport light guide 84. One end of this light guide is connected to the split-off sub-unit 64 whilst at the other end it is connected to transport light guide 60'. Transport light guide's 60' and 84 may also be constituted by one light guide passing through both sub-units 51 ' and 81, as shown in Fig. 9.

The split-off light L _t b _e from the sub-unit 64 may be supplied to the window unit 81. This light may be emitted by, for example two, windows of one row or by windows of different rows, for example the first and last row, as shown in Fig. 9. In the latter case an additional emitting point is created for a viewer, for example a vehicle driver.

The windows of light receiving sub-unit 51 ' may receive light from the left direction, whilst light-receiving sub-unit 81 may receive light from the right direction. It is also possible that sub-units 51 ' and 81 both receive light from the same direction. In this way the amount of light received from one direction may be doubled.

The Ltbe light from the sub-unit 64 may also be supplied to the window unit 51 ' or to both window units 81 and 51 '. In the latter case L _t b _e light may be emitted in two opposite direction. This possibility may be used to warn a vehicle driver for oncoming traffic. In general the embodiment with two windows may be designed such that light is received from one or two directions and light is emitted in one or two direction. This embodiment offers a large freedom of design. Road circumstances and requirements of the road authority will determine the actual chosen design.

In case the light guides in the new light-collecting unit are optical fibers it is preferred that they all have the same diameter, in particular the same core diameter. At several transition locations light from a first fiber should be transferred to a second fiber, which is in line with the first fiber. To warrant that the transfer is maximal the fibers should be aligned very accurately, which complicates manufacturing. The accurate alignment can be avoided if the at the transition location the first fiber has a smaller diameter than the second fiber. Then the broader receiving opening of the second fiber can capture the light from the smaller emitting opening of the first fiber, even when the fibers are not well aligned

Since a smaller diameter of the first fiber is required only at the transition location this fiber is preferably tapered towards this location. The taper of the first fiber should extend over such a length; i.e. the taper angle should be such small that the taper does not affect the light propagation in the fiber. This means that the remaining length of the first fiber may have the same diameter as the other fibers. Since this aspect relates to easy manufacturing of the light-collecting unit it forms part of the present invention.

Fig. 10 shows a transition 90 where a first, emitting, fiber 92 meets a second, receiving, fiber 94. This Figure shows only a small portion of the length of the fibers. Fiber 94 has diameter d ₂ and fiber 92 starts with also a diameter d ₂ , but is tapered at the side of the transition to end with a diameter (I ₁ . The taper angle δ, and thus the length of the tapered portion, of fiber 92 is chosen such that the taper has no influence on the light propagation The new light-collecting unit may be composed of a base plate, which comprises the light guide structure and the optical connector and a cover plate, which comprises the windows 10 and reflectors 16, 22 (Fig. 3). Both plates may be manufactured by a molding or casting process, which are well known by a person skilled in the art, and fixed to each other after they have been finished. The base plate may be provided with a groove structure corresponding to the required light guide structure and then fiber core material is injected into this structure. After this material has solidified a cladding material in injected so that optical fibers having a core and a cladding are formed in the groove structure. Alternatively the grooves can be shaped such that they form optical wave-guides so that no optical fibers are needed. In case the unit is provided with optical fibers it is composed of three different components: the base plate, the cover plate and a third component comprising the fibers united with reflecting surfaces and lenses (Fig. 3). The solutions described in previous patent application EP 07118074.9 for specific problems, which occur when the light collecting unit is used in a road marking system may also be used in the present unit. Thereby it is warranted that sufficient light is collected whilst the unit has sufficient mechanical strength and its performance is not affected by water and dirt falling on the road. The number of external transport light guides for connecting a unit with another one, thus for transporting light over larger distances, can be chosen at will and in practice will be adapted to specific circumstances and the requirements of the road authority. For each row of windows a separate transport light guide may be present. It is also possible that one transport light guide serves for transportation of the light received by two or more rows of windows. Preferably the number of external transport light guides is as small as possible.

This unit also allows building in reflectors to reflect directly light from vehicle headlights to the driver of the vehicle. Furthermore color filters may be included in the unit so that the emitted light has the required color, for example red if a driver has to be warned that a vehicle is ahead on the same road lane.

A further aspect of the invention relates to maintenance costs of an installed light guide system. A road marking system includes a large number of light collecting units, which are interconnected by means of external transport light guides. If one of the units is damaged or otherwise does not perform as required, this unit has to be removed from the system and a new unit has to be installed. Without further measures the interior transport light guide(s) have to be aligned with the light supplying external transport light guide at one side and with the carry-off external transport light guide(s) at the other side of the unit. This is a difficult and time-consuming process. Such alignment can be avoided if the light collecting unit is composed of a main body, which includes the windows and light guide structure, and one or two coupling modules.

Fig. 11 shows a perspective view of an embodiment of such composed light- collecting unit 100. This unit comprises a main unit 102 and a first coupling module 104 at the left side and a second coupling module 106 at the right side. The coupling modules are fixed to the main body in a de-mountable way, for example by means of clicking or screws or by means of fixing strips 106 shown in Fig 11. The upper part of Fig. 11 shows the composed unit in a mounted state and the lower part shows the unit in a dismounted state. A coupling module includes fixing means for receiving and fixing the external transport light guide(s) and coupling means for optically coupling the external transport light guide(s) at one side of this means to the internal transport light guide(s) at the other side. The fixing means and coupling means are well known in the art and need not to be described in detail. Since alignment of the external and internal light guides is already realized in the structure of the coupling means, no cumbersome alignment procedure is needed when a light-collecting unit has to be replaced. In case of failure of a light-collecting unit it suffices to replace the main body and the coupling modules can be used again, because in a light guide system all main bodies and all coupling modules are identical. In the embodiment of Fig. 11 the main body and the coupling modules are designed such that these modules can be clicked laterally to the main body at the right and left side respectively. It is, for example also possible that the base plate of the main body 102 is longer than the upper side and that the coupling modules 106 and 108 are clicked onto the base plate thereby closing the light-collecting unit. Then the lower side of the modules may be open and their fixing and coupling means may be fixed to their upper sides. Mechanical connection of the main body and coupling modules can also be realized in another way.

In the preferred embodiment of Fig. 11 the light-collecting unit 100 is provided with two coupling modules. It is also possible that only one side of the main body is provided with a coupling unit and that at the other side the external transport light guide is fixed to the internal light guide. When the unit has to be replaced then both the main body and the external transport light guide at said other side has to be replaced.

The intermediate part of Fig. 11 shows the interior of the unit 100. This is still another embodiment of the window and light guide structure that may be used in the light collecting unit of the invention. This structure includes a first light-receiving sub-unit 110 comprising ten rows of five windows and the associated light guides arranged and a second light-receiving sub-unit 112 comprising eight rows of five windows and associated light guides. Sub units 110 and 112 are arranged at a first side and a second side of the centerline of the light-collecting unit 100 and their windows face the same direction.

Light collecting units according to the concept of the invention may be arranged not only in a road surface, but also in or on a safety rail of a highway or in or on poles at the border of a road, whereby the design of the units may be adapted to the specific carrier or holder. The units may be used to illuminate all kind of traffic signs or warning devices.

The new light guide system may also be used as a warning system at cross roads. The light from one or more collecting units arranged in one road is then transported to warning signs installed at the other roads to warn traffic on the other roads that traffic is approaching the crossing from another direction.

Since a road marking system is a main application of the new light guide system, this system has been elucidated at the hand of the road marking system. Since the new light guide system shows a very high light collecting capability and very compact light transportation means, it can be used in large variety of known or new applications. For example for collecting light from street-lights and bring this light to a remote location, outside the reach of the streetlight(s), where it is used to lit a display or transport it to a house or another building where the light is used for a safety light.

The new light guide system may also be used for interior lighting of houses or buildings whereby use is made of outside ambient light, for example sunlight. The light collecting unit(s) may be placed on the roof of the house or building. Since the light transportation means of the system requires little space drastic changes in the construction of the building are not needed. This allows implementation of the new light guide system in protected monumental buildings, which should be kept in their original state.

When applied for interior lighting the light guide system, which includes the one or a few light collecting unit(s) may be irradiated by a dedicated radiation source instead of by ambient light. Then several external transport light guides are couple to the last unit to transport the collected light to the rooms of a house or a building.