WO2020245236A1

WO2020245236A1 - Light-coupling unit with micro-grooves

Info

Publication number: WO2020245236A1
Application number: PCT/EP2020/065405
Authority: WO
Inventors: Hugo Johan Cornelissen; Olexandr Valentynovych VDOVIN; Barry Mos; Johannes Petrus Maria Ansems; Michel Cornelis Josephus Marie Vissenberg
Original assignee: Signify Holding B.V.
Priority date: 2019-06-06
Filing date: 2020-06-04
Publication date: 2020-12-10

Abstract

A light-coupling unit (100) for coupling light into a main light guide body. The light-coupling unit includes a wedge-shaped body comprising a light incident surface (110) adapted for receiving light, which comprises a first (111) edge, and a second edge (112) opposite to the first edge. The body further comprises a first surface (120) having an edge in connection with the first edge of the light incident surface, and a second surface (130) having an edge in connection with the second edge of said light incident surface. The first surface is inclined relative to the light incident surface so that a distance between the first surface and the second surface decreases as the first surface and the second surface extend away from the light incident surface. The first surface includes a plurality of V-shaped micro-grooves (121) extending substantially orthogonal to the first edge of the light incident surface. A top angle of the micro-grooves is greater than 80°.

Description

LIGHT-COUPLING UNIT WITH MICRO-GROOVES

FIELD OF THE INVENTION

The present disclosure generally relates to the field of solid state lighting. More specifically it relates to a light-coupling unit (or light-introduction unit) for injecting (coupling) light into a main light guide body or light guide.

BACKGROUND OF THE INVENTION

The edge-lit light guide architecture is commonly used in various forms of general lightning. In particular, edge-lit light guides are often part of recessed, surface mounted and suspended luminaires.

A light guide is an effective way of mixing and spreading light of directional light sources or point light sources, such as light-emitting diodes (LEDs). Light guide luminaires provide light with a uniform appearance, which is perceived as comforting and aesthetically pleasing. Further, luminaires using light guides may be of relatively small dimensions (low height), which allows for efficient logistics and various elegant suspended luminaire designs.

Common aims for the development of future light guide based luminaires are to further limit costs and the weight of the luminaire. Thus, a goal is to be able to use thinner light guides. Traditionally, light guides have had a thickness of approximately 6 mm. Today, the thickness has been reduced to 3-4 mm, which corresponds to the size of many standards LEDs.

Previously, attempts have been made to reduce the thickness of light guides further by using smaller LEDs. However, smaller LEDs are either more expensive, not as efficient or cannot produce enough flux for use in a general lighting light guide luminaire.

As such, there is a need to provide alternate solutions for providing and using thinner light guides. In particular, there is a need of providing a solution which allows for the use of efficient LEDs in combination with light guides which are thinner than the size of the LEDs, without substantial light loss between LEDs and light guide. SUMMARY OF THE INVENTION

It is therefore an object of the present invention to overcome at least some of the above mentioned drawbacks, and to provide an improved light-coupling unit for coupling light into a main light guide body (or light guide).

This and other objects are achieved by means of a light-coupling unit as defined in the appended independent claim. Other embodiments are defined by the dependent claims.

According to an aspect of the present disclosure, a light-coupling unit is provided. The light-coupling unit includes a wedge-shaped body. The wedge-shaped body comprises a light incident surface which is adapted for receiving light, and a light exit region which is adapted for coupling light into a main light guide body, the light exit region being opposite to the light incident surface. The light incident surface comprises a first edge and a second edge which is opposite to the first edge. The wedge-shaped body further comprises a first surface, which has an edge in connection with the first edge of the light incident surface. The wedge-shaped body further comprises a second surface, which has an edge in connection with the second edge of the light incident surface. Each of the first surface and the second surface connects the light incident surface to the light exit region. The first surface is inclined relative to the light incident surface, so that a distance between the first surface and the second surface decreases as the first surface and the second surface extend away from the light incident surface. The first surface includes a plurality of V-shaped micro-grooves, which extend substantially orthogonal to the first edge of the light incident surface. A top angle of the micro-grooves is greater than 80°.

The light-coupling unit is adapted to receive (couple in) light via the light incident surface. The light may for example come from a light source, such as a light- emitting diode (LED). The received light may propagate through the light-coupling unit with a main direction of light being normal to the light incident surface. At the light-exit region, the light-coupling unit is arranged to couple out the light, for example into a main light guide body.

Along a light-coupling unit, light-loss may appear if light reaches the surface of the light-coupling unit with an incident angle which is smaller than the critical angle. In an arrangement with a light source and a light guide, light-loss may also appear at a light- incident surface if light emitted by the light source is not coupled into the light-coupling unit, and at a junction between a light-coupling unit and a main light guide body if light from the light-coupling unit is not coupled into the light guide body. The light-coupling unit as defined by the independent claims may reduce such light-loss, and thus increase efficiency.

The wedge-shape of the body of the light-coupling unit may concentrate the light received at the light-incident surface, so that it may be coupled out into e.g. a main light guide body having smaller thickness than the height of the light source, without the need for pre-collimation of the light. This shape allows for the light incident surface of the light- coupling unit to be adapted to efficiently receive light from the light source. At the same time, a region of the light-coupling unit which is adapted for coupling out light into a main light guide body (a light-exit region) may be adapted to efficiently couple light into the main light guide body.

Throughout this disclosure, the height of the light-coupling unit refers to the distance between the first surface and the second surface. The length of the light-coupling unit refers to the dimension along the main direction of propagation of light through the light- coupling unit. The width refers to the dimension which is orthogonal to the height and the length, i.e. along the length of the first and second edges of the light-incident surface.

The first surface may be referred to as the“top” surface of the wedge-shape, and the second surface may be called the“bottom” surface. These terms are used to facilitate the reading of the disclosure together with the appended figures. However, the first surface and the second surface may be any surfaces which fulfil the requirements of the claims, and may be arranged in any direction which is allowed by the requirements of the claims. In other words, the first surface may be any surface which has the first edge in common with the light incident surface. And the second surface may be any surface which shares the second edge with the light incident surface.

The V-shaped micro-prismatic grooves are provided on the top surface in order to minimize light loss from the light-coupling unit and to induce angular redistribution of the received light. The characteristics and the arrangement of the grooves may lead to an increase in the angle of incidence of the received light relative to the inside of the top surface. Specifically, the grooves may increase the angle of incidence so that a larger portion of the light is reflected back into the light-coupling unit.

Further, the grooves may reflect (redirect) light in more directions. Such angular redistribution of the light may contribute to a uniform appearance of the light, and a more comfortable, aesthetically pleasing illumination. Restricting the top angle to being larger than 80° may allow for a slim light- coupling unit, which in turn may lower production and material cost while still increasing angular redistribution and lowering light loss.

According to some embodiments, the wedge-shaped body may further comprise a first lateral side and a second lateral side. The first lateral side may connect the first surface to the second surface. The second lateral side may be opposite to the first lateral side, and it may also connect the first surface to the second surface. Both of the lateral sides may be smooth.

This configuration may be translationally invariant, for example if the first lateral edge and the second lateral edge are parallel, and thus, the configuration may be modular. As such, there may be no need for a major re-design in order to adapt the light- coupling unit to a wider light guide body or to a different number of light sources. In applications using light-emitting diodes (LEDs), the present embodiment may be suitable both for square and rectangular LEDs.

According to some embodiments, the second surface may be inclined relative to the light incident surface. The second surface, thus, may extend from the light incident surface in a direction towards the first surface. As such, a distance between the first surface and the second surface may decrease as the first surface and the second surface extend away from the light incident surface.

Inclining both the top (first) and the bottom (second) surface may allow for more tapering of the light-coupling unit. More tapering of the light-coupling unit may facilitate the coupling of the light-coupling unit to even slimmer main light guide bodies.

According to some embodiments, the second surface may include a plurality of V-shaped micro-grooves which extend substantially orthogonal to the second edge of the light incident surface. A top angle of the micro-grooves may be greater than 80°.

Including grooves on the bottom surface of the light-coupling unit may further reduce the light loss from the light-coupling unit, and may consequently improve efficiency. Additionally, the grooves may allow for further angular redistribution and, thus, a more pleasant and even illumination may be obtained.

As the grooves may reduce the light loss of the light-coupling unit for a given inclination of the second surface, a wedge-shaped body of a light-coupling unit with grooves on the first and second surfaces (top and bottom) may be more tapered without substantial light loss. Consequently, even slimmer light guides may be used with such light-coupling units. According to some embodiments, a height of the light incident surface may be adapted, or correspond, to a height of a light source from which the light-coupling unit is adapted to receive light.

Adapting the height of the light incident surface to the height of the light source may provide a more efficient (in-) coupling (reception) of light from the light source into the light-coupling unit.

According to some embodiments, a length of the light-coupling unit may be larger than, or substantially equal to, a height of the light incident surface.

A longer length of the light-coupling unit may allow for more tapering, with a smaller inclination of the first surface, and optionally the second surface. A smaller inclination may further reduce light-loss from the light-coupling unit.

According to some embodiments, the top angle of the micro-grooves may be in the range 100-140°. Specifically, the top angle may be equal to 110°.

According to some embodiments, the width of a micro-groove may be in the range 0.04-0.8 mm.

According to some embodiments, a top angle of the V-shaped micro-grooves is the same in a light-entrance region, which is a region of the light-coupling unit close to the light incident surface, as in a light-exit region, which is a region of the light-coupling unit at which light is coupled into the main light guide body.

For example, the V-shaped grooves may have the same top angle along the entire length of the grooves.

Having the same angles at the light-entrance region and the light-exit region may increase the efficiency of the light-coupling.

Alternatively, a decrease in the height of the grooves, and consequently an increase in the top angle, may provide certain manufacturing benefits.

According to some embodiments, the wedge-shaped body includes a material having a refractive index in the range 1.40-1.8.

Choosing a material with a higher refractive index may allow for further tapering of the light-coupling unit without substantial light-loss. A higher refraction index may lead to a smaller critical angle, and thus a larger portion of the light may be reflected back into the light-coupling unit. Such materials may for example include

polymethylmethacrylate (PMMA), polystyrene (PS), polycarbonate (PC), cyclic olefin copolymer (COC) and glass. According to some embodiments, there is provided a light guide module comprising a light-coupling unit, as described above in relation to any of the previous embodiments, and a main light guide body. The light-coupling unit is adapted to direct light, which is received at the light incident surface, through the wedge-shaped body. The main light guide body is arranged to receive light from the light coupling unit.

Light from a light source is received into the light-coupling unit as previously described. At the light-exit region of the light-coupling unit, light is coupled out of the light- coupling unit and into the main light guide body.

According to some embodiments, the light-coupling unit and the main light guide body may constitute a single body.

The light-coupling unit and the main light guide body may be produced as one piece.

According to some embodiments, the light-coupling unit and the main light guide body may constitute two distinct bodies.

The light-coupling unit and the main light guide body may be separate units in connection such that light may be coupled from the light-coupling unit into the main light guide body. For example, the light-coupling unit may be connected to the light guide body with an optically transparent adhesive. Such an adhesive may have a refractive index which is close to, or equal to, the refractive index of the light-coupling unit and/or the refractive index of the main light guide body. A specific light-coupling unit may be used with different types of main light guide bodies, and vice versa. Light sources of different size may thus be used with the same main light guide body, as light-coupling units with different dimensions may be employed.

According to some embodiments, a dimension of the light-coupling unit, along a direction perpendicular to the main direction of propagation of light through the light- coupling unit, may be equal to a dimension of said main light guide body along the same direction. In other words, the light-coupling unit may have the same width as an edge of the main light guide body. In these embodiments the light coupling unit may be arranged along an entire edge of the main light guide body. This may provide the possibility of varying the number of light sources for a single light guide module, and improve efficiency of the light- coupling.

According to some embodiments, a dimension of the light coupling unit, along a direction perpendicular to the main direction of propagation of light through the light- coupling unit, is smaller than a dimension of the main light guide body along the same direction. In other words, the light-coupling unit is not as wide as an entire edge of the main light guide body.

In such embodiments, more than one light coupling unit may be arranged along an edge of the main light guide body. For example, the number of light-coupling units may be adapted to the intended number of light sources.

It is noted that other embodiments using all possible combinations of features recited in the above described embodiments may be envisaged. Thus, the present disclosure also relates to all possible combinations of features mentioned herein. Any embodiment described herein may be combinable with other embodiments also described herein, and the present disclosure relates to all combinations of features.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

Figure 1 is a schematic view of a light-coupling unit with micro-grooves on the first surface, in accordance with some embodiments;

Figure 2 is a schematic view of a light-coupling unit with micro-grooves on the first surface and the second surface, in accordance with some embodiments;

Figure 3 is a schematic side-view of a light guide module, in accordance with some embodiments;

Figure 4 is a schematic side-view of a light guide module in which the light- coupling unit and the main light guide body constitute two different bodies, in accordance with some embodiments;

Figure 5 is a schematic side-view of a light guide module in which the light- coupling unit and the main light guide body constitute one body, in accordance with some embodiments;

Figure 6 is a schematic view of a light guide module in which a width of the light-coupling unit is the same as a width of the main light guide body, in accordance with some embodiments; and

Figure 7 is a schematic view of a light guide module in which a width of the light-coupling unit is not the same as a width of the main light guide body, in accordance with some embodiments. As illustrated in the figures, the sizes of the elements and regions may be exaggerated for illustrative purposes and, this, are provided to illustrate the general structures of the embodiments. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

With reference to Figure 1, a light-coupling unit in accordance with some embodiments will be described.

The light-coupling unit 100 comprises a wedge-shaped body, having a light incidence surface 110, a first surface 120, a second surface 130, a first lateral side 140 and a second lateral side 145. The wedge-shaped body may be made from a material with a refractive index in the range 1.40-1.8.

The light-incident surface 110 has a first edge 111 and a second edge 112. The first surface 120 (the top surface) has an edge in connection with the first edge 111 of the light incident surface. The second surface 130 (the bottom surface) has an edge in connection with the second edge 112 of the light incident surface. In the present example, the second surface 130 extends at a right angle from the light incident surface 110, while the first surface 120 is inclined relative the light incident surface 110, so that a distance between the first surface 120 and the second surface 130 (i.e. the height of the light-coupling unit 100) decreases as the first surface 120 and the second surface 130 extend from the light incident surface 110. In other words, the first surface 120 extends in a direction of the second surface 130. The first lateral side 140 connects the first surface 120, the second surface 130 and the light incident surface 110 on one side. The second lateral side 145 is located opposite to the first lateral side 140. The second lateral side 145 connects the first surface 120, the second surface 130 and the light incident surface 110 at the other side.

The first surface 120 includes a plurality of parallel micro-grooves 121, which are shown in more detail in a magnified circle. The micro-grooves 121 extend in a direction substantially orthogonal to the first edge 111. As is shown in a cross-sectional view of some micro-grooves in the figure, the micro-grooves have a width G1 and a top angle Q. The width G1 may be in the range 0.04-0.8 mm. Specifically, the width G1 may be in the range 0.05-0.4 mm. More specifically, the width G1 may be in the range 0.06-0.2 mm. The top angle Q is larger than 80°. Specifically, the top angle Q may be in the range 100-140°. More specifically, the top angle Q may be in the range 110-130°. All the other surfaces and sides are without grooves. However, in other embodiments, more than one surface/side may have grooves. The micro-grooves may have sharp tips or rounded tips.

Light from a light source may enter (be coupled into) the light-coupling unit 100 through the light incident surface 110. The light may propagate within the light-coupling unit body, and be reflected back into the light-coupling unit when the light reaches the inside of a side or surface. The grooves 121 on the first surface 120 may decrease any portion of light which may otherwise have been coupled out through the first surface, partially due to the inclination of the first side 120. The grooves 121 may also induce angular mixing of the light, spreading the light in more directions as the light reflects off of surfaces with different inclination.

With reference to Figure 2, a light-coupling unit in accordance with some embodiments will be described.

The light-coupling unit 200 may be equivalent to the light-coupling unit 100, described with reference to Figure 1 except that the second surface 230 is inclined relative to the light incident surface 110, so that the distance between the first surface 120 and the second surface 230 decreases as the first surface 120 and the second surface 230 extend from the light incident surface 110. Furthermore, the second surface 230 includes a plurality of micro-grooves 231, which may have the same properties (features/characteristics) and effects as the micro-grooves 121 described with reference to Figure 1. In particular, the micro grooves 231 may extend orthogonally to the second edge of the light incident surface 110.

With reference to Figure 3, a light-coupling unit and a light guide module, in accordance with some embodiments, will be described.

The light guide module 350 comprises a light-coupling unit 300, which may be equivalent to the light-coupling unit 200 described in relation to Figure 2, and a main light guide body 360. Illustrated is also a light source 370, which is drawn with dashed lines to show that the light source may not, as such, be part of the light guide module.

The light-coupling unit 300 has a light incident surface 310 which is adapted to receive light from the light source 370. The light incident surface 310has a height HI, which is adapted to the height of the light source 370. The light source 370 may for example be a LED, such as a mid-power LED. Mid-power LEDs often come in standard sizes, such as 3x3 mm, 3x5 mm, or 5x7 mm.

However, other types of LEDs and other light sources are possible to use. In case of an asymmetric, rectangular, light source, the height HI of the light-coupling unit 300 may be adapted to the smaller of the two dimensions of the light source.

The light-coupling unit 300 tapers from the height HI in a light-entrance region 301, close to the light-incident surface, towards a height H2 in a light-exit region 302 at which the light guide body 360 is arranged. The light-exit region 302 is adapted to couple light out of the light-coupling unit 300, and into the main light guide body 360. The height H2 is the same as the height of the main light guide body 360, such that the coupling of light from the light-exit region 302 of the light-coupling unit 300 to the main light guide body 360, may be substantially loss-less (or at least with significantly reduced light-loss). However, the height H2 may be smaller than the height of the main light guide body 360.

The length LI of the light coupling unit 300 is larger than, or substantially equal to, the height HI of the light-incident surface 310. Specifically, the length LI may be larger than, or substantially equal to, twice the height HI of the light-incident surface 310. The height HI, the height H2 and the length LI determine the tapering (slope/inclination) of the wedge-shaped body of the light-coupling unit 300. A longer length in relation to the first height HI of the light-coupling unit may allow for a shorter second height H2 (i.e. a slimmer main light guide body 360) while maintaining the tapering of the wedge at a level at which the light-coupling may be efficient.

With reference to Figure 4, a light guide module, in accordance with some embodiments, will be described.

The light guide module 450 may be equivalent to the light guide module 300, as described with reference to Figure 3. The light guide module 450 comprises a light- coupling unit 400 and main light guide body 460. Figure 4 illustrates that the light coupling unit 400 and the main light guide body 460 may be two separate bodies. The light coupling unit 400 and the main light guide body 460 may be in connection such that light may efficiently be coupled from the light-coupling unit 400 to the main light guide body 460.

With reference to Figure 5, a light guide module, in accordance with some embodiments, will be described.

The light guide module 550 may be equivalent to the light guide module 300, described with reference to Figure 3, except that the light guide module 550 comprises a light coupling unit/portion 500, and a main light guide body/portion 560 forming part of the same body. The light coupling unit/portion 500 and the main light guide body/portion 560 may thus be manufactured in one piece.

With reference to Figure 6, a light guide module, in accordance with some embodiments, will be described.

The light guide module 650 may be equivalent to any of the light guide modules 300-500, described with reference to Figures 3-5. The light guide module 650 comprises a light-coupling unit 600, having a width W61, and a main light guide body 660 having a width W62. The width W61 is smaller than the width W62. For example, the width W61 may be adapted to the width of a light source. In applications where the width of the light coupling unit is smaller than the width of the main light guide body, more than one light coupling unit may be in connection with the same main light guide body.

With reference to Figure 7, a light guide module, in accordance with some embodiments, will be described.

The light guide module 750 may be equivalent to any of the light guide modules 300-500, described with reference to Figures 3-5. The light guide module 750 comprises a light-coupling unit 700, having a width W71, and a main light guide body 760 having a width W72. The width W71 is the same as the width W72, such that the light- coupling unit 700 is arranged along an entire edge of the main light guide body 760.

Throughout this disclosure, the terms“V-shaped micro-prismatic grooves”, “micro-grooves” and“grooves” are used interchangeably.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

It will be appreciated, for example, that although the figures show one light- coupling unit per light guide module, two or more light-coupling units may be connected to one main light guide body.

Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word“comprising” does not exclude other elements, and the indefinite articles“a” and“an” do not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

CLAIMS:

1. A light-coupling unit (100) including a wedge-shaped body, wherein the wedge-shaped body comprises:

a light incident surface (110) adapted for receiving light, and

a light exit region adapted for coupling light into a main light guide body, wherein the light exit region is opposite to the light incident surface (110), wherein said light incident surface (110) comprises a first edge (111), and a second edge (112) opposite to said first edge (111),

wherein the wedge-shaped body further comprises:

a first surface (120) having an edge in connection with said first edge (111) of said light incident surface (110), and

a second surface (130) having an edge in connection with said second edge (112) of said light incident surface (110),

wherein each of the first surface (120) and the second surface (130) connects the light incident surface (110) to the light exit region,

wherein said first surface is inclined relative to said light incident surface so that a distance between said first surface and said second surface decreases as said first surface and said second surface extend away from said light incident surface,

wherein the first surface includes a plurality of V-shaped micro-grooves (121) extending substantially orthogonal to said first edge of said light incident surface, and

wherein a top angle (Q) of said micro-grooves is greater than 80°.

2. The light-coupling unit of claim 1, wherein the wedge-shaped body further comprises:

a first lateral side (140) connecting said first surface with said second surface; and

a second lateral side (145), opposite to said first side, connecting said first surface with said second surface;

wherein said first lateral side and said second lateral side are smooth.

3. The light-coupling unit of any of the previous claims, wherein said second surface is inclined, relative to said light incident surface, to extend in a direction of the first surface, so that said distance between said first surface and said second surface decreases as said first surface and said second surface extend away from said light incident surface.

4. The light-coupling unit of any of the previous claims, wherein said second surface includes a plurality of V-shaped micro-grooves (231) extending substantially orthogonal to said second edge of said light incident surface, wherein a top angle of said micro-grooves is greater than 80°.

5. The light-coupling unit of any of the previous claims, wherein a height (HI) of said light incident surface is adapted, or corresponds, to a height of a light source (370) from which said light-coupling unit is adapted to receive light.

6. The light-coupling unit of any of the previous claims, wherein a length (LI) of said light-coupling unit is larger than, or substantially equal to, a height of said light incident surface.

7. The light-coupling unit of any of the previous claims, wherein said top angle of said micro-grooves is in the range 100°-140°.

8. The light-coupling unit of any of the previous claims, wherein a width (Gl) of a micro-groove is in the range 0.04-0.8 mm.

9. The light-coupling unit of any of the previous claims, wherein a top angle of said V-shaped grooves is substantially the same in a light-entrance region (301) close to said light-incident surface as in a light-exit region (302) at which light is coupled into said main light guide body.

10. The light-coupling unit of any of the previous claims, wherein said wedge- shaped body includes a material having a refractive index in the range 1.40-1.8.

11 A light guide module (350) comprising:

a light-coupling unit in accordance with any of claims 1-10; and a main light guide body (360);

wherein said light-coupling unit is adapted to direct light, received at said light incident surface from a light source, through said wedge-shaped body; and

wherein said main light guide body is arranged to receive light from said light coupling unit.

12. The light guide module of claim 11, wherein said light-coupling unit and said main light guide body constitute a single body.

13. The light guide module of claim 11, wherein said light-coupling unit and said main light guide body constitute two distinct bodies.

14. The light guide module of any of claims 11-13, wherein a dimension (W71) of said light-coupling unit, along a direction perpendicular to the main direction of propagation of light through said light-coupling unit, is equal to a dimension of said main light guide body along said direction.

15. The light guide module of any of claims 11-13, wherein a dimension of said light-coupling unit, along a direction perpendicular to the main direction of propagation of light through said light-coupling unit, is smaller than a dimension of said main light guide body along said direction.