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Title:
METHOD FOR PRINTING A THREE-DIMENSIONAL LIGHT-GUIDING STRUCTURE
Document Type and Number:
WIPO Patent Application WO/2015/092014
Kind Code:
A1
Abstract:
The present invention relates to a method for printing a three- dimensional light-guiding structure (1), comprising the following steps depositing multiple droplets of a first printing material (10') curing the deposited droplets of the first printing material (10') by light irradiation using a first light source (14) depositing multiple droplets of a second printing material (20') and curing the droplets of the second printing material (20') by light irradiation using a second light source (24), wherein the multiple droplets of the first material (10') and the droplets of the second material (20') are deposed and/or cured such that the first printing material (10) and the second printing material (20) forms a interface (15) that changes the light properties of the light emitted by a light emitting device (2).

Inventors:
VAN DE VRIE, Richard (Veerweg 23, NC Wolphaartsdijk, NL-4471, NL)
BISKOP, Joris (Kalkhok 7, BK Vlissingen, NL-4381, NL)
Application Number:
EP2014/078860
Publication Date:
June 25, 2015
Filing Date:
December 19, 2014
Export Citation:
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Assignee:
LUXEXCEL HOLDING B.V. (Amundsenweg 25, GP Goes, NL-4462, NL)
International Classes:
G02B19/00; B29C67/00; B29D11/00; F21V8/00; G02B1/04; H01L33/54; H01L33/58
Domestic Patent References:
WO2004032250A12004-04-15
Foreign References:
US20090065792A12009-03-12
US20010048968A12001-12-06
Attorney, Agent or Firm:
LOOCK, Jan Pieter et al. (Theodor-Heuss-Ring 23, Köln, 50668, DE)
Download PDF:
Claims:
PATENT CLAIMS

Method for printing a three-dimensional light-guiding structure (1 ), comprising the following steps

— depositing multiple droplets of a first printing material (10')

— depositing multiple droplets of a second printing material (20') and

— curing the deposited droplets of the first printing material (10') and the deposited droplets of the second printing (20') material by light irradiation using a first light source (14)

characterized in that the multiple droplets of the first material (10') and the droplets of the second material (20') are deposed and/or cured such that the first printing material (10) and the second printing material (20) form an interface (15) that changes the light properties of the light emitted by a light emitting device (2).

Method according to claim 1 , wherein the droplets of the first material (10') and the droplets of the second material (20') are deposited into a three- dimensional mold.

Method according to one of the preceding claims wherein the first printing (10) material and/or the second printing material (20) are arranged such that the three-dimensional light-guiding structure (1 ) has a recess (6) for a light emitting device (2).

Method according to one of the preceding claims, wherein

— the droplets of the first material (10') and/or the droplets of the second material (20') are arranged such that the three-dimensional light guiding structure (1 ) is connectable to the light emitting device (2) or a substrate (3) comprising the light emitting device (2) after curing and/or

— the droplets of the first material (10') and/or droplets of the second material (20') forming the three-dimensional light-guiding structure are cohesively connected by curing to the light emitting device (2) or the substrate (3) of the light emitting source (2).

5. Method according to one of the preceding claims wherein the droplets of the first material (10') and/or the droplets of the second material (20) are deposited directly on the substrate (3), wherein the substrate (3) comprises the light emitting device (2).

6. Method according to one of the preceding claims, wherein the refractive index of the first printing material (10) differs from the refractive index of the second printing material (20) after curing.

7. Method according to one of the preceding claims, wherein the interface (15) between the first printing material (10) and the second printing material (20) is arranged such that at least a part of the light from the light emitting device (2) is reflected by total internal reflection.

8. Method according to one of the preceding claims, wherein the interface (15) between the first printing material (10) and the second printing material (20) is arranged such that the interface (15) is curved.

9. Method according to one of the preceding claims, wherein the three- dimensional light-guiding (1 ) structure forms a collimator or side emitter.

10. Method according to one of the preceding claims, wherein the droplets of the second printing material (20') are cured by light irradiation using a second light source (24),

1 1 . Method according to one of the preceding claims, wherein the interface (15) and/or the first printing material (10) at least partially form a filter, a lens, a mirror, a prism, a beam splitter, a light conductors and/or a mean for changing the polarization for the light from the light emitting device (2).

12. Printed article comprising a three-dimensional light-guiding structure (1 ), printed by a method according to one of the preceding claims.

13. Printed article according to claim 12, wherein a three-dimensional light- guiding structure (1 ') comprises multiple printing materials having different refraction indices, wherein the multiple printing materials are arranged such, that light having a first beam profile enters the three-dimensional light-guiding structure (1 ') and light having a second beam profile leaves the three- dimensional light-guiding structure, wherein

— a second spot size of the second beam profile is greater than a first spot size of the first beam profile and/or

— a second intensity profile along the second beam profile is more homogeneous than a first intensity profile along the first beam profile and/or

— the light having the first beam profile propagates in a different direction than the light having the second beam profile.

14. Printed article according to claim 12 or 13, wherein the printed article is a collimator or side emitter for a light emitting device (2).

15. Light emitting device comprising a printed article according to the claims 12 to 14.

Description:
DESCRIPTION

TITLE

METHOD FOR PRINTING A THREE-DIMENSIONAL LIGHT-GUIDING STRUCTURE

BACKGROUND

The present invention relates to a method for printing a three-dimensional structure by depositing a plurality of droplets of printing material onto a substrate. A suchlike method is already known from the international patent application WO 2010/091888 A1 and can successfully be used for printing light-directing structures, for instance.

Such a success motivates developing the light-directing structure further, especially in terms of light-direction structures provided for specific light emitting devices, such as LED-lights. However, adapting the light-directing structure to specific light emitting devices is not straightforward and usually leads to problems such as hot spots in the light directing structure wherein the hot spots adulterate the performance of the light- directing structure, for example. Additionally it is desirable to adapt the light-directing structure individually in order to optimize the collaborated performance of the three- dimensional light-guiding structure and the light emitting device compared to the performance of the light emitting device on its own.

SUMMARY

It is therefore an object of the invention to provide a method for printing a three- dimensional light-guiding structure that is optimized for use with a light emitting device. It is also object of the present invention to provide a method for generating a three-dimensional light-guiding structure, wherein the three-dimensional light-guiding structure is able to transform light from a light emitting device to light that suits a specific potential application.

The object is solved by a method for printing a three-dimensional light-guiding structure, comprising the following steps: depositing multiple droplets of a first printing material, depositing multiple droplets of a second printing material and curing the deposited droplets of the first printing material and the deposited droplets of the second printing material by light irradiation using a first light source, wherein the multiple droplets of the first material and the droplets of the second material are deposed and/or cured such that the first printing material and the second printing material form an interface that changes the light properties of the light emitted by a light emitting device.

It is herewith advantageously possible to print a three-dimensional light guiding structure using an inkjet printer that can be adapted to the properties of the light emitting device individually. In particular it is provided to use an inkjet printer for depositing the droplets of printing material. Preferably the light emitting device is a LED-diode or a laser such as an excimer laser. In particular it is provided that the light guiding structure, in particular its interface, transforms light properties such as intensity, propagation direction, light collection and/or polarization, for example.

Preferably it is provided that the interface is arranged within the three-dimensional light-guiding structure. Especially a light guiding device may be realized according to the present invention, wherein the three-dimensional light-guiding device transforms the light properties of the light emitting device to light properties necessary for a special application. For example the light-guiding structure forms a collector or a side emitter. The first printing material and the second printing material comprise preferably a printing ink, e.g. a transparent or translucent printing ink. Preferably the printing ink comprises an UV curable liquid monomer which becomes a polymer by curing. It is further conceivable that the first printing material and the second printing material have different colors. Furthermore it is provided to use a printing head for depositing the droplets of the first printing material and/or second printing material. Furthermore the first printing material has a first viscosity and the second printing material has a second viscosity. Consequently the droplets of the first printing material and the droplets of the second printing material may spread or diffuse, preferably on different timescales, and as a result of spreading or diffusing the first printing material and the second printing material form the interface. In such a scenario it is provided that the light illumination for curing starts whenever the first printing material and the second printing material are arranged such that the first printing material and the second printing material form the interface or at least a part of the interface. It is also considerable that the curing process has been already started before the first printing material and the second printing material form the interface or at least a part of the interface. Alternatively it is considerable that depositing the droplets defines the interface and the first printing material and/or the second printing material are cured immediately. In particular it is provided that the multiple droplets of the first printing material and the multiple droplets of the second printing material are deposited simultaneously and therefore the three-dimensional light-guiding structure having an interface is generated preferably fast.

According to a preferred embodiment of the present invention it is provided that the droplets of the first material and the droplets of the second material are deposited into a three-dimensional mold. Using a mold has the positive effect that even complicated outer surfaces of the three-dimensional light-guiding structure may be realized easily and fast. In addition it is herewith possible to restrict the amount of first printing material and second printing material to that amount that may needed for constructing the desired three-dimensional light-guiding structure otherwise.

According to another preferred embodiment of the present invention the first printing material and/or the second printing material are arranged such that the three- dimensional light-guiding structure has a recess for a light emitting device. As a consequence the light emitting device may be interconnected with the three- dimensional light guiding structure in a space saving way advantageously.

According to another preferred embodiment of the present invention it is provided that the droplets of the first material and/or the droplets of the second material are arranged such that the three-dimensional light guiding structure is connectable to the light emitting device or a substrate comprising the light emitting device after curing. In particular it is provided that the droplets of the first material and/or the droplets of the second material forming the three dimensional structure are cohesively connected by curing to the light emitting device or the substrate of the light emitting source. It is considerable that the three-dimensional light-guiding structure is designed such that three-dimensional light-guiding structure has means for connecting such as a thread, a clip, a catch or a protuberance. It is considerable that the means for connection are designed such that the three-dimensional light-guiding structure is connected reversibly to the light emitting device and/or to the substrate comprising the light emitting device. This has the positive effect that a plurality of three-dimensional light- guiding structures, preferably different three-dimensional light-guiding structures, can be combined with one light emitting device. Furthermore it is considerable to cohesively connect the three-dimensional light-guiding structure after the three- dimensional light-guiding structure has been generated. According to another preferred embodiment of the present invention it is provided that the droplets of the first material and/or the droplets of the second material are directly deposited on a substrate, wherein the substrate comprises the light emitting device. It is herewith advantageously possible to cohesively connect the three-dimensional light-guiding structure to the light emitting device during the manufacturing process of the three-dimensional light-guiding structure. As a result it is possible to save time compared to a manufacturing process that additionally includes the coupling of the light emitting devices and the three-dimensional light-guiding structure. Another advantage is that the light emitting device is directly arranged next to the three- dimensional light-guiding structure and consequently the amount of light not reaching the three-dimensional light-guiding structure is reduced in a positive fashion. According to another preferred embodiment of the present invention it is provided that the refractive index of the first material differs from the refractive index of the second material after curing. In particular the refraction index comprises a wavelength dependent part describing the absorption of light. In that context the first and/or the second material may form a filter for light that passes the interface. Additionally, the refractive indices of the first printing material and the second printing material define the reflection properties of the interface. Therefore it is advantageously possible to adopt the reflection properties of the interface to that needed for the specific three- dimensional light-guiding structure. In particular, the three-dimensional light-guiding structure is provided for changing the direction of light propagation.

According to another preferred embodiment it is provided that the interface is realized such that the interface comprises a reflective material. For example the interface comprises aluminum. It is herewith advantageously possible to realize a reflective surface as interface. Consequently it is possible to integrate a mirror into the three- dimensional light guiding structure by the printing method. In particular it is provided that the reflective interface redirects light that is emitted by the light emitting device.

According to another embodiment it is provided that a layer is added to the three- dimensional structure light guiding structure, wherein the layer is arranged along the interface. It is thinkable that the layer differs from the first printing material and/or the second printing material. Furthermore it is convincible that the layer is included without depositing and/or curing. In particular it is provided that a thin layer is deposited and droplets of the first printing material and/or the second printing material are deposited next to the layer, wherein the droplets of the first printing material and the second printing material are separated by the layer. It is also thinkable that the first printing material is deposited and cured firstly and subsequently the layer is deposited along the surface of the cured first printing material. Furthermore it is provided that after arranging the layer the second printing material is deposited onto the layer and is cured. In particular it is provided to adhesively connect respectively the first printing material and the second printing material to the layer that forms the interface. Moreover it is thinkable that the second printing material is deposited onto the layer such that the layer is fixed by the deposited and cured first and/or second printing material.

According to another preferred embodiment of the present invention it is provided that the interface between the first printing material and the second printing material is arranged such that at least a part of the light from the light emitting device is reflected by total internal reflection. This has the positive effect that at least a part of the light of the light emitting device is redirected and therefore the undirected light of a LED- diode becomes more directional. As a consequence the combination of the LED- diode and the three-dimensional light-guiding structure according to the present embodiment is able to emit light being more directional and having a higher intensity compared to the light leaving the LED-diode.

According to another embodiment of the present invention it is provided that the interface between the first printing material and the second printing material is arranged such that the interface is curved. As a result light from the light emitting device is scattered or refracted due to the interface such that the light of the light emitting device is not focused within the three-dimensional light-guiding structure. In that manner a hot spot and therefore damages within the three-dimensional light- guiding structure may be avoided advantageously.

According to another embodiment of the present invention it is provided that the three-dimensional light-guiding structure forms a collimator or a side emitter, also known as batwing. In such an embodiment the first printing material and the second printing material form one or more interfaces in order to collimate or focus light leaving the three-dimensional light-guiding structure, for example. It is also considerable that the one or more interfaces are arranged such that the light leaving three-dimensional light-guiding structure is collimated. In particular the propagation direction of the light leaving the three-dimensional light-guiding structure may be tilted compared to the propagation direction of the light leaving the light emitting device. It is an advantage of the presented embodiment that the three-dimensional light-guiding structure adjusts the light leaving the light emitting device in order to optimize the light properties for specific application. According to another embodiment of the present invention it is provided that the droplets of the second printing material (20') are cured by light irradiation using a second light source (24). .In particular it is provided that the first and the second light source are individualized for the first printing and the second printing material respectively. For example the wavelength and/or the intensity of the first light source differ from the wavelength and/or the intensity of the second light source, because the first printing material may need light for curing that is different from the light that is needed for curing the second printing material.

According to another embodiment of the present invention it is provided that the interface and/or the first printing material at least partially form a filter, a lens, a mirror, a prism, a beam splitter, a light conductor and/or a mean for changing the polarization for the light from the light emitting device. In particular it is provided that the interface forms a part of a wavelength dependent mirror, preferably a dielectric mirror.

Furthermore it is provided that the interface is a wavelength dependent filter allowing reflection or transmission of light having a specific wavelength. By this the three- dimensional light-guiding structure may extract light from the light emitting device that is undesirable. It is also considerable that the interface acts as a (wavelength dependent) beam splitter, i.e. a specific amount of light passes the interface whereas another amount of light is reflected. It may be also possible that the interface corresponds to a λΙ 2-plate or a λΙ 4-plate that manipulate the polarization of light. In particular the first printing material forms a lens (a concave lens, a convex lens or a Fresnel lens) embedded in the second printing material. It is also considerable that several interfaces form one or more light conductor, such as one or more optical fibers, being embedded within the three-dimensional light-guiding structure. In that manner the positive effects of several devices that change the light properties may be advantageously integrated in the three-dimensional light-guiding structure easily.

Another subject of the present invention is a printed article comprising a three- dimensional light-guiding structure that is printed by a method described above.

It is herewith advantageously possible to generate a three-dimensional light-guiding structure that may be individually adapted to a specific sort of light emitting device in order to optimize the light properties and/or adapt the light properties for the specific application of the light emitting device. According to another embodiment of the present invention wherein a light-guiding structure comprises multiple printing materials having different refraction indices, wherein the multiple printing materials are arranged such, that light having a first beam profile enters the light-guiding structure and light having a second beam profile leaves the light-guiding structure, wherein a second spot size of the second beam profile is greater than a first spot size of the first beam profile and/or, a second intensity profile along the second beam profile is more homogeneous than a first intensity profile along the first beam profile and/or the light having the first beam profile propagates in a different direction than light having the second beam profile.

It is herewith advantageously possible to generate a three-dimensional light-guiding device that changes one or more light properties such as spot size, intensity profile and/or propagation direction. In particular the three-dimensional light-guiding structure may be used for backlight devices using the edge lid principle for illuminating screens.

According to another embodiment it is provided that the printed article is a collimator or a side emitter for a light emitting device.

Another subject of the present invention is a light emitting device comprising a printed article according to the present invention.

It is herewith advantageously possible to generate a light emitting device that comprises a three-dimensional light-guiding structure that provides light having optimized light properties, in particular with respect to its application respectively.

These and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a method for printing a three-dimensional light guiding structure according to a first exemplary embodiment of the present invention. Figure 2 illustrates a first exemplary three-dimensional light-guiding structure printed with the first exemplary method according to the present invention.

Figure 3 illustrates a second exemplary three-dimensional light-guiding structure according to the present invention.

Figure 4a and 4b illustrate a light emitting device and a three-dimensional light- guiding structure comprising an array of reflective elements according to a third exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The present invention will be descripted with respect to particular embodiments and with the reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some elements may be exaggerated and not drawn on scale for illustrative purposes.

Where an indefinite or definite article is used when referring to a singular noun, e. G. "a", "an", "the", this includes a plurals of the noun unless something else is specifically stated.

Furthermore, the terms first, second, third and the like in the description and in the claims are used to distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described of illustrated herein.

Figure 1 shows a method of printing a three-dimensional light-guiding structure 1 according to a first exemplary embodiment of the present invention. According to the invention it is provided that the three-dimensional guiding structure 1 is build up by droplets of a first printing material 10' and droplets of a second printing material 20'. In this first embodiment it is provided that a first nozzle 1 1 drops the droplets of the first printing material 10' along a first flight direction 13 on a body 19 and that a second nozzle 21 drops the droplets of the second printing material 20' along a second flight direction 23 on the same body 19, wherein the droplets of the first printing material 10' and the droplets of the second printing 20' material are at least partially arranged next to each other. Preferably it is provided that the first and the second flight direction 13 and 23 are determined by gravity. In particular the first nozzle 1 1 and/or the second nozzle 21 are part of a print head of an

inkjet printer. The droplets of the first material 10' and the droplets of the second material 20' form a layer 18 that covers the body 19. According to the presented embodiment it is provided that light from a first light source 14 cures the droplets of the first printing material 10' and light from a second light source 24 cures the droplets of the second material 20'. Preferably the first and the second light source 14 and 24 emit cw- and/or pulsed UV-light. Using two different light sources 14 and 24 allows adjusting the requirements for curing to the first and second printing material 10' and 20', respectively. For example, it is conceivable that the first printing material 10' needs light for curing that differs from that one for the second printing material 20' with respect to wavelength or intensity, for instance. In another scenario it is desirable to cure the first printing material 10' and the second printing material 20' differently, in particular to cure the first and the second printing material 10' and 20' on different timescales. That may be motivated by the following printing strategy: Firstly the droplets of the first material 10'are cured, secondly the droplets of the second material 20' fill vacancies left over and finally the droplets of the second material 20' are cured. In that case it should be avoided that light of the first light source 14 triggers the curing of the second printing material 20' by scatter light for example. Using at least two different light source14 and 24 having different wavelengths may circumvent such a problem provided the first and the second material 10' and 20' are chosen suitably. It is provided that the process of depositing the droplets 10' and 20' on the body 19 and subsequently curing the droplets 10' and 20' is repeated iteratively till the three dimensional light-guiding structure 1 is build up. Actually the body 19, which comprises the first and the second printing material 10 and 20 and which is arranged below the layer in figure 1 , is also generated by such a processing. In particular, the presented body 19 comprises a recess 6. Preferably such a recess 6 is generated by leaving areas in the layer 18 uncovered on purpose during the depositing of droplets on the body 19. It is provided that the recess 6 leaves space for a light emitting device 2, such as a LED-diode. According to the present invention it is provided that the droplets of the first material 10' and the droplets of the second material 20' are arranged such that an interface 15 is generated, wherein the interface 15 changes the light properties of the light of the light emitting device 2. In more detail it is provided that the interface 15 between the first printing material 10 and the second printing material 20 is made for manipulating and/or guiding the light emitted by the light emitting device 2. That means that the light of the light emitting device 2 change the light properties such as intensity, polarization and/or propagation direction due to the interface 15. In figure 1 the light emitting device 2 and the body 19 are arranged on a substrate 3. It is conceivable that the light source was arranged on the surface of the substrate 3' at first and subsequently the bodyl 9 has been built up around the light emitting device 2. Preferably the droplets of the first and/or the second printing material 10' and 20' are cohesively interconnected as a result of curing. In another embodiment the substrate is detached after the construction of the three-dimensional light-guiding structurel has been finished. It is also provided that the extension of the layer 18 in a direction parallel to the main plane of the substrate 3 becomes greater layer by layer. As result the body 19 has a curved outer surface.

Figure 2 shows a first three-dimensional light-guiding structure 1 printed according to the first exemplary embodiment of the present invention, i. h. it is shown the light- guiding structure 1 after the build-up according to the method shown in figure 1 has been finished. The three-dimensional light-guiding structure 1 is arranged on the substrate 3 such that the light emitting device 2 is located in the recess 6 of the light- guiding structure 1 . It is provided in this embodiment, that the interface 15 is curved in the direction perpendicular to the main plane of the substrate 3. Such an arrangement of the first printing material 10 and the second printing material 20 has the positive effect that the probability for generating a hot spot can be reduced due to the interface 15. In particular, it is provided that the light from the light emitting device 2 is not focused to one spot of the three-dimensional light-guiding structure 1 . Hot spots usually are generated by light from the light emitting device 2 and influence the performance of the three-dimensional light-guiding structure 1 , negatively. Another advantage of the presented first three-dimensional light-guiding structure 1 is that the three-dimensional light-guiding structure 1 has a smooth front end 9. The smooth front 9 end has the advantage that the three-dimensional light-guiding structure 1 has no edges or protuberances that may damage other surrounding elements that may come in contact with the front end 9 of the light guiding structure 1 .

Figure 3 shows a second exemplary three-dimensional light-guiding 1 structure printed according to the present invention. Again the three-dimensional light-guiding structure 1 is arranged on the substrate 3, wherein the light emitting device 2 is located within the recess 6 of the three-dimensional light-guiding structure 1. In the present embodiment it is provided, that the interface 15 is curved such that at least a part of the light 8 emitted from the light emitting device 2 is totally reflected on the interface 15. Further it is provided that the amount of light experiencing total reflection is defined by the refractive indices of the first printing material 10 and the second material 20. Especially the relation between the refractive index of the first printing material 10 and the refractive index of the second printing material 20 determinates the angle for total reflection. Such an interface 15 allows directing the light emitted by the light emitting device 2 in a direction depended on the arrangement of the interface 15. In particular the three-dimensional light-guiding structure 1 forms a batwing or side emitter in collaboration with the light emitting source 2, as it is shown in figure 3. Figure 4a and 4b show a three-dimensional light-guiding structure 2 and a light- guiding device V comprising each an array of reflective elements according to a third exemplary embodiment of the present invention. The light emitting device 2 and the three-dimensional light-guiding structure 1 are arranged such that the light from the light emitting 2 device enters the three-dimensional light-guiding structure 1 through a surface mainly perpendicular to the main plain of the three-dimensional light-guiding structure V. That arrangement is known from backlight devices using the edge lid principle for the illuminating of screens. It is provided that the three-dimensional light- guiding structure V redirects the light such that light leaves the three-dimensional light-guiding structure V along a direction perpendicular to the main plane. For that purpose the array of reflective elements is located inside the three-dimensional light- guiding structure V by using the method of printing the three-dimensional light-guiding structure V according to the present invention. Especially the second printing material 20 is embedded in the first printing material 10 and the generated interfaces 15 cause reflection or scattering that redirect the propagation direction of the light from the three-dimensional light-guiding structure V. In figure 4a the elements of the array are arranged such that the generated interfaces 15 are arranged parallel to the main plane of the three-dimensional light-guiding structure V, mainly. Preferably it is provided that a plurality of printing materials are used for printing the three- dimensional light-guiding structure V, wherein the refractive index of each printed array element is chosen such that light leaving the three-dimensional light-guiding structure 1 is homogenously and uniformly distributed. For example it is provided that the printing material is chosen such the absorbance of the array elements next to the light emitting device 2 is smaller than the one of array elements located further away from the light emitting device 2. In that case the amount of light reaching the array elements located further away from the light emitting device 2 is still enough for generating a uniform distribution of light leaving the three-dimensional light-guiding structure. Furthermore it is provided to increase the spot size of the beam profile and change the propagation direction of the light. In an alternative embodiment it is provided to tilt the elements of the array with respect to each other as it is shown in figure 4b. Such a geometry of array elements is easily generated by the method for printing the three-dimensional light-guiding structure V according to the present invention. Tilting each element of the array has the positive effect, that array elements further away from the light emitting device 2 can reflect a greater amount of light with respect to a non-tilted array element because a greater amount of light reaches the tilted element of the array. This is necessary because the other array elements block at least a part of the light that otherwise would reach the tilted array element. In particular the method for printing the three-dimensional light-guiding structure 1 ' facilities arranging the first printing material 10 and the second printing material 20 such that the angle of each tilted array element can adapted flexibly for guaranteeing a uniform distribution of light leaving the three-dimensional light-guiding structure V.

REFERENCE SIGNS

1 , r three-dimensional light-guiding structure

2 light emitting device

3 substrate

3' surface of the substrate

6 recess

8 light

9 front end of the light emitting device

10 first printing material

10' droplet of the first printing material

11 first nozzle

13 first flight direction

14 light irradiation using the first light source

15 interface for light guiding

18 layer comprising the first

19 body

20 second printing material

20' droplet of second printing material

21 second nozzle

23 second flight direction

24 light irradiation using a second light source

31 array of at least partial reflecting mirrors

32 array of tilted at least partial reflecting mirro