WO2011117814A1

WO2011117814A1 - A light emitting device, a color tunable light, an animation presentation device and a luminaire

Info

Publication number: WO2011117814A1
Application number: PCT/IB2011/051196
Authority: WO
Inventors: Coen Adrianus Verschuren; Dominique Maria Bruls
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-03-25
Filing date: 2011-03-22
Publication date: 2011-09-29

Abstract

A light emitting device, a color tunable light device, an animation presentation device and a luminaire are provided. The light emitting device (100) comprising a stack of a first Organic Light Emitting Diode (106), a spacer (104) and a second Organic Light Emitting Diode (102). The first Organic Light Emitting Diode (106) comprising a first set of two contacts (108) for receiving electrical power to operate the first Organic Light Emitting Diode (106). The second Organic Light Emitting Diode (102) being at least partially light- transmitting and comprising a second set of two contacts (112) for receiving electrical power to operate the second Organic Light Emitting Diode (102). The spacer (104) is an electrically non-conductive and light-transmitting layer and is interposed between the first Organic Light Emitting Diode (106) and the second Organic Light Emitting Diode (102), and wherein the first Organic Light Emitting Diode (106) is arranged for emitting, in operation, light towards the spacer (104).

Description

A light emitting device, a color tunable light, an animation presentation device and a luminaire

FIELD OF THE INVENTION

The invention relates to the field of Organic Light Emitting Diodes.

BACKGROUND OF THE INVENTION

Published patent application US2007/0001587A1 discloses a white light tandem Organic Light Emitting Diode (OLED) device with color filters. The tandem OLED device comprises a stack of OLED devices which are separated from each other by an intermediate connector layer. The intermediate connector layers are transparent and conductive. A cathode is provided at one side of the stack of OLED devices. At another side of the stack three anodes are provided which are spatially separated. A color filter is provided on top of each of the anodes, which are a red filter, a green filter and a blue filter. A current starts flowing between the cathode and a specific one of the anodes if a voltage is applied between the cathode and the specific anode. The current flows mainly via the shortest path(s) between the cathode and the specific anode. The separate OLED devices in the stack will light up in the area where the current flows and as such light is generated in the area below the specific anode. The color filter on top of the specific anode transmits only a specific color of the light generated below the anode. By controlling the amount of current, the amount of generated light of the specific color may be controlled. The three separated anodes with their respective color filter may be used to generate a combination of a specific amount of red light, specific amount of green light and a specific amount of blue light.

The tandem OLED cannot be used for generating a uniformly mixed color mix, because the generation of the three colors is separated in space and as such the colors are not mixed by the tandem OLED device. If a uniformly mixed color output is required, additional light mixing means have to be used.

Further, it is difficult to obtain saturated colors by the tandem OLED device of the cited document. If a specific voltage is applied to a specific anode, light is generated in a space between the specific anode and the cathode. However, the generated light is not only emitted into a direction towards the specific anode, it may also be emitted in a direction towards another anode and as such towards another color filter. Thus, a small amount of light will be emitted in another color and thus is it difficult to obtain saturated colors. Further, as drawn in the figures of the cited document, it is possible that a small gap is present between the anodes through which a part of the generated white light may be emitted thereby reducing the quality of the generated color.

OLED devices may be patterned with a device pattern which is visible to the viewer during operation of the OLED. A patterned OLED device has local modifications in the light generation layers, in the current influencing layers, in the light reflection layers or light transmission layers of the OLED device. If the modifications are applied in a specific pattern, the specific pattern becomes visible for the viewer. In the tandem OLED device of the cited document one may pattern one or more OLED devices. However, the pattern will not be visible as a whole in one specific color, because a part of the pattern below the anode with the green color filter will be visible in green, another part will be visible in red, and still another part in blue. Thus, it is not possible to see the pattern completely in a color which is a mix of red, green, and/or blue, for example, orange. Further, it is not possible to present a pattern which comprises several neighboring pixels that have different colors and/or have a color which is a mix of red, green and/or blue.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a light emitting device of which the characteristics of the emitted light are easier to control.

A first aspect of the invention provides a light emitting device as claimed in claim 1. A second aspect of the invention provides a color tunable device as claimed in claim 13. A third aspect of the invention provides an animation presentation device as claimed in claim 14. A fourth aspect of the invention provides a luminaire as claimed in claim 15.

Advantageous embodiments are defined in the dependent claims.

A light emitting device in accordance with the first aspect of the invention comprises a stack of a first Organic Light Emitting Diode, a spacer and a second Organic Light Emitting Diode. The first Organic Light Emitting Diode comprises a first set of contacts for receiving electrical power to operate the first Organic Light Emitting Diode. The first Organic Light Emitting Diode emits, in operation, light towards the spacer. The second Organic Light Emitting Diode is at least partially light-transmitting and comprises a second set of two contacts for receiving electrical power to operate the first Organic Light Emitting Diode. The spacer is an electrically non-conductive and light-transmitting layer and is interposed between the first Organic Light Emitting Diode and the second Organic Light Emitting Diode.

The first Organic Light Emitting Diode (OLED) emits light when a voltage is applied to the first set of contacts. An OLED emits most of the generated light at two opposite surfaces of the OLED, or emits most of the generated light only at one surface. Thus, at least a part of the light that is generated in the first OLED is emitted towards the spacer. The spacer transmits the light towards the second OLED. The second OLED is at least partially light-transmitting and as such the part of the light of the first OLED is transmitted via the second OLED into the ambient of the light emitting device. The second Organic Light Emitting Diode (OLED) may also generate light when a voltage is applied to the second set of contacts. A part of the light generated by the second OLED device is, together with the part of the first OLED, emitted into the ambient of the light emitting device. By independently controlling the currents through the first OLED and through the second OLED a specific mix of light of the first OLED device and light of the second OLED device may be obtained. Thus, by simply controlling two currents one may control the

characteristics of the emitted light.

Manufactured OLEDs do not always emit light of exactly the same color. However, when used together with other OLEDs it is often required that all OLEDs emit exactly the same color. If, instead of using a single OLED, the light emitting device according to the first aspect of the invention is used, one may control the exact color output of the light emitting device and as such fulfill the sketched condition.

The first OLED and the second OLED are not necessarily of the same size. If, for example, the first OLED is smaller than the second OLED, the light emitting device emits in an area a mix of light from the first OLED and the second OLED, and emits in another area only light that is generated by the second OLED. The spacer may partially or fully cover a surface of the first OLED that is facing towards the spacer. The spacer may also partially or fully cover a surface of the second OLED that is facing towards the spacer. In the context of the invention it is important that the spacer spatially and electrically separates the first OLED from the second OLED and that light from the first OLED is transmitted through the spacer towards the second OLED.

The light-transmitting second OLED and the light-transmitting spacer transmit light which may be done with or without scattering, and thus, light-transmitting comprises the terms translucent and transparent. The second OLED is at least partially light- transmitting, which means that a part of the light of the first OLED which has to be transmitted through the second OLED may be absorbed. This reduces the efficiency of the light emitting device, but today it is still difficult to manufacture OLEDs which transmit more than 80% of the light. In a practical embodiment the first OLED transmits at least 50% of the light which it receives from the spacer towards the ambient of the first OLED. It is to be noted that the spacer is light-transmitting, which does not exclude that the spacer may also absorb some light which has to be transmitted through the first OLED. In a practical embodiment the spacers transmits at least 90% of the light which it receives from the first OLED towards the second OLED.

In an embodiment, the first Organic Light Emitting Diode emits, in operation, light of a first color, and the second Organic Light Emitting Diode emits, in operation, light of the second color, the first color being different from the second color.

By controlling the current through the first Organic Light Emitting Diode (OLED) the amount of emitted light of the first color is controlled. By controlling the current through the second OLED the amount of emitted light of the second color is controlled. Thus, the light emitting device allows controlling the exact color of the emitted light which is a mix of light of the first color and light of the second color. A range of colors comprising the first color and comprising the second color may be obtained by the light emitting device.

In the context of this document, light of a specific color means light having a specific spectrum. The specific spectrum may, for example, comprise a primary color having a specific bandwidth around a predefined wavelength, or may, for example, comprise a plurality of primary colors. The predefined wavelength is a mean wavelength or a radiant power spectral distribution.

In another embodiment, the first Organic Light Emitting Diode and/or the second Organic Light Emitting Diode are a patterned Organic Light Emitting Diode.

One or more of the Organic Light Emitting Diodes (OLEDs) may comprise a pattern, e.g. an image. The pattern influences, or modulates, locally the amount of light that is emitted from an area of the patterned OLED. In this way a pattern or image can be superimposed onto the emitted light pattern of the OLED, thus showing the pattern if the OLED layer is active. The image is visible, depending on the specific type of patterning, while at least one of the OLEDs is emitting light and/or while none of the OLEDs emits light. The visibility of the pattern improves the user experience. The patterns may be patterned with a photolithography technique or with laser image writing technique.

In a practical embodiment, the spacer and/or the second Organic Light Emitting Diode is transparent. Thus, the spacer and/or the second Organic Light Emitting Diode (OLED) do not scatter the light which it transmits. Hence, the pattern of the first OLED and/or the second OLED is clearly visible to the viewer.

In a further embodiment, the first Organic Light Emitting Diode comprises a first pattern, the second Organic Light Emitting Diode comprises a second pattern. The first pattern is different from the second pattern.

If the first Organic Light Emitting Diode (OLED) emits light of a first color and the second OLED emits light of a second color, and if the first pattern is different from the second pattern, the image which is visible to the user is an image that comprises different colors. The different colors in the visible image are combinations of the first color and the second color. One may obtain a specific color for a pixel by patterning the first OLED such that it emits a specific amount of light of the first color, and by patterning the second OLED such that it emits a specific amount of light of the second color. Furthermore, the current through the first OLED and the current through the second OLED determine the emitted light intensity of the first OLED and the second OLED, respectively, and thus the colors in the visible image may also be influenced by influencing the currents through the first OLED and the second OLED.

If the first pattern is only visible when the first OLED is in operation, and if the second pattern is only visible when the second OLED is in operation, and if the first pattern is different from the second pattern, an animation may be obtained by controlling the amount of light emitted by the first OLED and controlling the amount of light emitted by the second OLED. For example, when light emission alternates between the first OLED and the second OLED, the visible image alternates between the first pattern and the second pattern. A cross-fading image may be obtained by gradually increasing the amount of light emitted by, for example, the first OLED while gradually decreasing the amount of light emitted by the second OLED such that the visible image fades from the first pattern to the second pattern. If the light emitting device is meant for presenting a cross-facing image and/or an animation, the color emitted by the first OLED and the second OLED are preferably substantially equal.

In another embodiment, the spacer is a patterned spacer.

The pattern in the spacer may locally and partially block light from the first Organic Light Emitting Diode (OLED). Thus the light emitting device locally emits light which comprises less light from the first OLED, which is visible as an image to the user. Further, if the first OLED emits, in operation, light of a first color and the second OLED emits, in operation, light of a second color, the visible image comprises different colors. Depending on the amount of light that is locally blocked by the spacer, the locally emitted color is a specific mix of light of the first color and light of the second color.

The patterned spacer it not only limited to spacers which locally and partially block light, the patterned spacer may also locally comprise luminescent material which converts light in a first color range to light in a second color range. Such a luminescent material may be phosphors or other dye materials. The use of a luminescent material allows the introduction of an additional pattern and allows the generation of an additional color at those locations where the luminescent material is available in the spacer. Thus, the complete pattern or image that is observed by the user may comprise an additional color.

The spacer may be patterned with a lithographical technique during which a pattern is manufactured in a thin layer of photo sensitive and light blocking material. A layer with a luminescent material may be applied to the spacer and may locally be etched away after lithographically printing a pattern on top of the applied layer. The spacer may also be patterned with a laser beam that is focused in the spacer such that the energy of the laser beams locally changes the (optical) characteristics of the material of the spacer.

In an embodiment, the spacer has a thickness of 15 μιη to 300 μιη which is measured along a shortest line from the first Organic Light Emitting Diode towards the second Organic Light Emitting Diode.

A spacer of such a thickness may be manufactured efficiently and provides a good separation between the first Organic Light Emitting Diode (OLED) and the second OLED. Further, the lower bound of the range is large enough to allow an independently patterning of the first OLED, the second OLED and/or the spacer with a laser patterning technique because it provides enough focal depth discrimination, which means that the minimum thickness of the spacer is chosen such that during patterning of one layer (for example the first OLED), the adjacent layers (for example the second OLED) are unaffected by the patterning process.

A spacer which is thicker than the lower bound of the range is a perfect planarization layer to compensate for a rough surfaces as the result of particles which are undesirably incorporated in one of the OLEDs.

A spacer with the thickness smaller than the upper bound of the range prevents the visibility of parallax effects if in each one of the OLEDs a pattern is patterned.

In a further embodiment the spacer is light-transmitting in a predefined range of wavelengths of light comprising at least a range of visible light. Such a spacer has an additional function, namely, being a color filter. This may be advantageous when the color of the light emitted by the first Organic Light Emitting Diode (OLED) is not exactly the color which has to be mixed with the light of the second OLED.

In another embodiment, the spacer comprises a luminescent material for converting a part of the light received from the first OLED into light of another color.

The use of a luminescent material is an effective solution for controlling characteristics of the light that is received by the second OLED from the spacer and as such it influences the characteristics of the light output of the light emitting device. The light received by the second OLED is a mix of light generated by the first OLED and light of the another color. If, for example, the first OLED generated blue light and a part of this light is converted towards amber, a specific mix of blue and amber is received by the second OLED.

In another embodiment, the spacer is a layer stack comprising a first barrier layer, an organic layer, and a second barrier layer. The organic layer is interposed between the first barrier layer and the second barrier layer.

Such a stack provides excellent barrier properties, which are required to protect both Organic Light Emitting Diodes (OLEDs) against moisture and, for example, oxygen. In general OLEDs are manufactured on top of a barrier layer and are encapsulated between barrier layers. Thus, if the spacer provides at both interfaces to the OLEDs such a barrier layer, the OLEDs may be manufactured by using the same process methods, process equipment and materials as if a single OLED device was manufactured. Furthermore, the organic layer does not have to be completely moisture free, because the OLEDs are protected by the barrier layers, which simplifies the manufacturing process of the organic layer.

In a further embodiment, the first barrier layer and the second barrier layer comprise SiN_x, SiO_x and/or SiO_xN_y.

Si _x, SiO_x and/or SiO_xN_y are well-known and often used materials for barrier layers. Thus, barrier layers comprising the materials may be manufactured efficiently and cost effectively.

In an embodiment, the stack of the light emitting device further comprises a third Organic Light Emitting Diode having a third set of two electrical contracts. The stack further comprises a further electrically non-conductive light-transmitting spacer which is interposed between the second Organic Light Emitting Diode and the third Organic Light Emitting Diode. If the light emitting device comprises more Organic Light Emitting Diodes (OLEDs) which may be operated independently of the other OLEDs, the light emitting device provides a better control of the characteristics of the output light. If each one of the OLEDs emits, in operation, another color, the light emitting device is capable of generating more different output colors. Further, if each one of the OLEDs comprises a pattern, the visible image may comprise more colors and/or more advanced animations may be created.

With at least three independently controllable OLEDs one may create a light emitting device which is capable of emitting substantially all colors of the visible spectrum by using three OLEDs of which each one of the three OLEDs generates, in operation, light of another primary color. The primary colors may be Red, Green and Blue, but may also be other combinations of primary colors, including the colors Yellow, Magenta, Cyan and Amber.

In an embodiment, the first Organic Light Emitting Diode is at least partially light-transmitting as well.

In this embodiment, a part of the light generated by the first Organic Light

Emitting Diode (OLED) is transmitted towards the spacer, and another part is directly transmitted into the ambient of the first OLED. Further, because the spacer and the first OLED are light-transmitting, a part of the light generated by the second OLED is also received by the first OLED and transmitted through the first OLED into the ambient of the first OLED. Thus, the light emitting device of the embodiment emits at two sides light which is a combination of light of the first OLED and light of the second OLED. However, the specific composition of each mix may be different.

According to a second aspect of the invention a color tunable light device for emitting light of a tunable color is provided. The color tunable light device comprises a controller and a light emitting device according to the first aspect of the invention. The controller controls a first current through the first Organic Light Emitting Diode and controls a second current through the second Organic Light Emitting Diode to obtain, in operation, emitted light of a specific color.

According to the third aspect of the invention an animation presentation device for presenting an animation to a viewer is provided. The animation presentation device comprises a controller and a light emitting device according to the first aspect of the invention wherein each one of the first Organic Light Emitting Device and the second Organic Light Emitting Device comprises a pattern. The controller controls a first current through the first Organic Light Emitting Device and controls a second current through the second Organic Light Emitting Device to obtain, in operation, an animation which is visible to a viewer.

According to the fourth aspect of the invention a luminaire is provided which comprises a light emitting device according to the first aspect of the invention.

The color tunable device, the animation presentation device and the luminaire according to the second, third and fourth aspect of the invention, respectively, provide the same benefits as the light emitting device according to the first aspect of the invention and has similar embodiments with similar effects as the corresponding embodiments of the system.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

It will be appreciated by those skilled in the art that two or more of the above- mentioned embodiments, implementations, and/or aspects of the invention may be combined in any way deemed useful.

Modifications and variations of the devices, and/or the luminaire, which correspond to the described modifications and variations of the light emitting device, can be carried out by a person skilled in the art on the basis of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. la schematically shows a light emitting device according to the first aspect of the invention,

Fig. lb schematically shows another embodiment of the light emitting device emitting light in two directions,

Fig. lc schematically shows a further embodiment of the light emitting device comprises three Organic Light Emitting Diodes,

Fig. 2 schematically shows another embodiment of the light emitting device comprising patterned Organic Light Emitting Diodes and a patterned spacer,

Fig. 3 schematically shows an encapsulated light emitting device comprising a spacer of three layers,

Fig. 4a schematically shows a color tunable device comprising a light emitting device according to the first aspect invention,

Fig. 4b schematically shows an animation presentation device comprising a light emitting device according to the first aspect of the invention, and Fig. 5 schematically shows a luminaire comprising a light emitting device according to the invention.

It should be noted that items denoted by the same reference numerals in different Figures have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item have been explained, there is no necessity for repeated explanation thereof in the detailed description.

The Figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly DETAILED DESCRIPTION

A first embodiment is shown in Fig. la. Light emitting device 100 comprises a stack 113 of at least three layers. A bottom layer comprises a first Organic Light Emitting Diode (OLED) 106. A top layer comprises a second OLED 102. An electrically non- conductive light-transmitting spacer 104 is interposed between the first OLED 106 and the second OLED 106.

The first OLED 106 has a first set of two contacts 108 for receiving electrical power to operate the first OLED 106 such that the first OLED emits, in operation, light of a first color 114 towards the spacer 104. The spacer 104 is light-transmitting and transmits the light of the first color 114 towards the second OLED 102, which is also light-transmitting, and emits the light of the first color 114 into the ambient of the light emitting device 100. The amount of light of the first color 114 that is generated by the first OLED 106 is controlled, in operation, by a current provided to the first OLED 106 via its contacts 108. Thus, the intensity of light of the first color 114 emitted into the ambient of the light emitting device 100 depends on the current provided via de contacts 108 to the first OLED 106.

The second OLED 102 has a second set of two contacts 112 for electrically connecting the second OLED 102 to electrical power to operate the second OLED 102. The current that is provided to the second OLED 102 determines, in operation, the intensity of the light of a second color 110 generated by the second OLED 102. The generated light of the second color 110 is, together with the light of the first color 114, emitted into the ambient of the light emitting device 100. The second OLED 102 is at least partially light-transmitting, which means that it transmits a part of the light of the first color 114, which it receives from the spacer 104, into the ambient of the light emitting device 100. However, some light of the first color 114 may be absorbed by the second OLED 102, because it is almost impossible to manufacture a 100% light-transmitting OLED. Current state of the art OLEDs transmit 75% of the light which impinges on the OLED.

Thus, a mix of light of the first color 114 and light of the second color 110 is emitted into the ambient. The specific composition of the mix of the first color 114 and of the second color 110 is determined by the current provided to the first set of contacts 108 and the current provided to the second set of contacts 112. Hence, by accurately controlling the currents through the first OLED 106 and through the second OLED 102 the characteristics of the emitted light is accurately controlled.

The spacer 104 has a specific thickness d which is measured along the shortest line from the first OLED 106 to the second OLED 102. The spacer is at least 15 μιη thick and at most 300 μιη. The spacer 104 is electrically non-conductive and provides a good electrical isolation between the first OLED 106 and the second OLED 102 such that the current through the first OLED 106 is not influenced by the current through the second OLED 102 and vice versa. Further, the spacer is light-transmitting, which means that the spacer transmits almost all the light that it receives from the first OLED 106 towards the second OLED 102. Hence, the spacer 104 is almost absorption free.

It is to be noted that the spacer 104 and/or the second OLED 102 may be transparent, which means that the light is transmitted without scattering, and that the spacer 104 and/or the second OLED 102 may be translucent, which means that the light is transmitted with scattering. Further, the spacer 104 and/or the second OLED 102 may be partially transparent and thus partially translucent, meaning that only a part of the light which is transmitted through the spacer 104 and/or the second OLED is only scattered to some extend.

In Fig. lb shows light emitting device 117. The first OLED 115 is of the light emitting device 117 is at least partially light-transmitting as well. The first OLED 115 as well as the second OLED 102 emit light towards the spacer 104 and emit light in a direction away from the spacer 104. Because the spacer, the first OLED 115, as well as the second OLED 102 are light-transmitting, the light emitting device 117 emits light in both directions 116, 120 away from the spacer 104. Further, the spacer 104 does not have exactly the same size as the surfaces of the first OLED 115 and of the second OLED 102 which face towards the spacer 104. However, the spacer 104 is for a large part in contact with the surfaces that face towards the spacer 104 such that the spacer 104 receives a substantial part of the light generated by the first OLED 115 and/or the second OLED 102. Further, the first set of contacts of the first OLED 115 and the second set of contacts of the second OLED are drawn schematically with two thick lines 118.

In another embodiment of the light emitting device 117, the spacer 104 comprises a luminescent material for converting light of a first color into light of a second color. The light of the first color may originate from the first OLED 115 or the second OLED 102. The effect is at least that light of the second color is emitted by the spacer 104 towards the first OLED 115 and the second OLED 102. Luminescent materials often emit the converted light in all directions and as such the mix of light emitted by the light emitting device 117 comprises light of the second color in addition to the specific colors of light generated by the second first OLED 115 and the second OLED 102.

In Fig. lc is shown a light emitting device 121 of which the stack 130 of layers comprises three OLEDs 102, 106, 124 and between each neighboring pair of OLEDs 102, 106, 124 is interposed an electrically non-conductive and light-transmitting spacer 104, 122. Each one of the OLEDs 102, 106, 124 has a set of contacts which is drawn schematically with the thick lines 132. A first OLED 106 generates light of a first color and this light is emitted via the first spacer 104 towards the second OLED 102 and subsequently into the ambient of the light emitting device 121. It is to be noted that the first OLED 106 is, as well as the second OLED 102, a light-transmitting OLED. The second OLED 102 generates light of second color and this light is emitted into the ambient of the light emitting device 121. The third OLED 124 generates light of a third color which is emitted towards the second spacer 122, which transmits the light of the third color towards the first OLED 106, and

subsequently the light of the third color is transmitted through the first OLED 106, the first spacer 104 and the first OLED 102 into the ambient of the light emitting device. Thus, when each one of the OLEDs 102, 106, 124 receive a specific current via their contacts 132, a mix of light 128 is emitted away from the light emitting device 121.

The light emitting device 121 is capable of generating light of a wide range of colors by combining light of three different primary colors, for example, blue, red and yellow light. The specific color that is emitted depends on the currents provided to each one of the OLEDs 102, 106, 124. By accurately controlling each one of the currents, the contribution of the respective OLED to the color mix may be controlled accurately.

It is to be noted that, as seen in Fig. lc, the OLEDs 102, 106, 124 and the spacers 104, 122 do not necessarily have the same size. Further, the light emitting device 121 has at a surface of the third OLED 124, being a surface opposite the second spacer 122, a light blocking layer 126, which may be implemented as a light reflecting layer 126. The light blocking layer 126 prevents that the light emitting device 121 emits light at the side of the third OLED 124. Further, if the light blocking layer 126 is a light reflecting layer, the light from the first OLED 106, the second OLED 104, and the third OLED that impinges on the blocking layer 126 is reflected back into the direction of the second spacer 122 and, thus, may be transmitted via the second spacer 122, the first OLED 106, the first spacer 104 and the second OLED 102 into the ambient of the light emitting device 121.

In another embodiment, the light emitting device 100 has a sensor close to the surface of the light emitting device 100 where a mix of light is emitted into the ambient. The sensor measures the amount of light of the first color 114 and the amount of light of the second color 110 that is emitted into the ambient. A controller is provided which controls the current through the first OLED 106 and the current through the second OLED 102 to obtain an emission of a predefined mix of the first color 114 and the second color 110. The controller further received the measurement results of the sensor and uses the measurement results to adjust the current through the first OLED 106 and the current through the second OLED 102 to obtain the emission of the predefined mix of the first color 114 and the second color 110. It is to be noted that the light emitting device 117 of Fig. lb may have two sensors at both sides where light is emitted to measure the spectrum of the light emission at both sides of the light emitting device 117. The light emitting device 121 of Fig. lc may have a controller which controls the currents through the first, the second and the third OLED 106, 102, 122 in order to obtain a predefined mix of light of three colors.

Fig. 2 shows another embodiment of the light emitting device 200 according to the first aspect of the invention. The light emitting device 200 comprises a stack of, seen from the left to the right side of Fig. 2, a light reflection layer 204, a patterned first OLED 202, an electrically non-conductive transparent patterned spacer 210 and a patterned second OLED 212. The first OLED 202 has a first set of contacts 208 to receiving electrical power to operate the first OLED 202. The second OLED 212 has a second set of contacts 218 to receive electrical power to operate the second OLED 212.

The patterned first OLED 202 is patterned by locally modifying the light reflection layer 204. The modifications 206 of the light reflection layer 204 scatter and/or reflect light which impinges on the reflection layer 204 differently from the environments of the modifications 206. The different scattering and/or reflection of light may be seen by the viewer when he looks from the right side of Fig. 2 towards the light emitting device 200. Depending on the amount of light generated by the first OLED 202, which is controlled by providing a specific current to the first set of contacts 208, the pattern is well visible to the viewer or invisible. It is to be noted that the modifications 206 to the light reflection layer 204 may be more or less visible to the viewer when the first OLED 202 does not generate light, while at the same moment the intensity of the ambient light is relatively high and ambient light impinges on the light reflection layer 204. Thus, the visibility of the pattern in the first OLED 202 may be controller by controlling the current provided to the first set of contacts 208.

The patterned spacer 210 comprises local areas 216 which are only partially transparent or non-transparent. At least the areas 216 are less transparent than the environment of the areas 216. Thus, light generated by the first OLED 202 is locally absorbed and not transmitted towards the second OLED 212. Thus, if the first OLED 202 generates light when the first OLED 202 receives a current at its contacts 208, the viewer sees a pattern which is the result of the blocking of light by the less transparent areas 216 of the spacer 210. Depending on the amount of current through the first OLED 202, the pattern of the patterned spacer 210 is visible or invisible. It is to be noted that the pattern in the patterned spacer 210 may more or less be visible if light from the ambient, or light generated by the second OLED 212 is reflected by the light reflection layer 204 while the first OLED 202 does not generate light. In another embodiment, the patterned spacer 210 comprises, in the local areas 216, a luminescent material for converting a part of the light of a first color to light of another color. Thus, the local areas 216 influence, or modulate, locally the color of light that is emitted from the areas of the patterned spacer 210.

The patterned second OLED 212 is patterned by means of local modifications 214 in at least one of the layers of the second OLED 212 such that the current flow through the second OLED 212 is locally influenced. When the current flow is locally reduced, the second OLED 212 locally generates less light. The local modification 214 may also locally influence the light generation efficiency of a light generating layer. Thus, the viewer may see a pattern in the second OLED 212 according to a pattern of local modifications 214. If the second OLED 212 receives a current on its second set of contacts 218, the second OLED 212 generates light in the unmodified areas of the second OLED 212 and, thus, is the pattern visible. If the second OLED 212 does not receive a current, the pattern is invisible.

Thus, by controlling a current through the first OLED 202 the visibility of pattern of the first OLED 202 and/or of the patterned spacer 210 may be controlled, and by controlling a current through the second OLED 212 the visibility of the pattern of the second OLED 212 may be controlled. This allows the generation of, for example, animations which are, for example, a cross-over from the pattern in the first OLED 202 towards the pattern in the second OLED 212.

In another embodiment, the patterned first OLED 202 generates light of a first color, for example, blue, and the patterned second OLED 212 generates light of a second color, for example, red. If both patterned OLEDs 202, 212 generate light, the pattern which is visible to the viewer comprises multiple colors. At locations where no blue light is emitted by the patterned first OLED 202 or light from the first OLED is blocked by the patterned space

210, the viewer only sees the red color. At the locations where no red light is emitted by the patterned second OLED 212, the viewer only sees the blue color. At areas where the first OLED 202 and the second OLED 212 emit light, the viewer sees a color that is a mix of red and blue. At areas where both OLEDs 202, 212 do not emit light, the viewer may experience the areas as being black.

The patterning of the patterned OLEDs 202, 212 or patterned spacer 210 may be performed by locally changing the characteristics of one or more layers of the patterned OLEDs 202, 212 or the patterned spacer 210. This may be done e.g. by generating scratches in a substrate or a light reflective layer of the OLEDs 202, 212. Other embodiments of patterning are, for example, locally modifying or even destroying a layer with organic light emitting material with a laser beam or by the local ablation of the material of a layer of the

OLEDs 202, 212 or spacer 210.

It is to be noted that the patterned spacer 210 and the patterned second OLED

212 are substantially transparent such that a clear image of the pattern may be seen by the viewer.

Fig. 3 shows an embodiment of an encapsulated OLED device 300. The encapsulation 304 completely encloses a light emitting device 305 according to the first aspect of the invention and packages the light emitting device 305 in an air-tight manner. Inside the encapsulation 304 a getter 310 is provided which absorbs gasses and moisture which lead to degradation and/or even malfunction of the light emitting device 305. The contact wires 318 of the light emitting device 305 are lead through the encapsulation such that the light emitting device 305 may receive electrical power for its operation. Further, the encapsulation may partially block the light generated by the light emitting device 305, or may be fully transparent. The encapsulation comprises at least a substantially transparent light exit window 302 through which most of the light generated by the light emitting device 305 is transmitted into the ambient of the encapsulated OLED device 300. The light emitting device 305 comprises a first OLED 106, a non conductive transparent spacer 306 and a transparent second OLED 102. The spacer 306 is interposed between the first OLED 106 and the second OLED 102. The first OLED 106 and the second OLED 102 each have a set of two electrical contacts which are connected to the wires 318. The wires 318 are lead through the encapsulation 304 for receiving electrical power to operate the first OLED 106 and/or the second OLED 102. Further, a reflection layer 308 is provided at a surface of the first OLED 106 which is substantially opposite a surface of the first OLED 106 that is in contact with the spacer 306. The reflection layer 308 reflects light which impinges on the reflection layer 308 and the reflected light is transmitted via the first OLED 106, the spacer 306, the second OLED 102 and the light exit window 302 to the ambient of the encapsulated OLED device 300.

The spacer 305 is non conductive and transparent and comprises three layers. At the interface to the first OLED 106 is provided a first barrier layer 316. At the interface to the second OLED 102 is provided a second barrier layer 312. An organic layer 314 is interposed between the first barrier layer 316 and the second barrier layer 312. The barrier layers 312, 316 comprise SiN_x, SiO_x and/or SiO_xN_y. The barrier layer protects the first OLED 106 and the second OLED 102 against moisture and, for example, oxygen. Thus, the organic layer 314 does not have to be moisture free. Further, the barrier layers 312, 316 provide a proper layer on which an OLED may be manufactured. The organic layer comprises a suitable organic material.

The complete spacer stack 306 has a thickness which is indicated with d. The thickness is measured in a shortest line form the first OLED 106 towards the second OLED 102. The thickness is in the range from 15 μιη to 300 μιη. Such a thickness provides a good planarization of unwanted extrusions of the surfaces of the first OLED 106 or the second OLED 102 that are facing towards the spacer 306. During manufacturing the first OLED 102 may be manufactured first and as the result of unwanted particles enclosure in the first OLED 106, the top surface may be relatively rough. The spacer 306 provides a relatively good planarization such that the second OLED 102 may be manufacture on a substantially flat surface of the spacer 306. Further, the spacer 306 of such a thickness provides enough focal depth discrimination when one of the OLEDs 102, 106 is patterned with a laser beam, which means that the other one of the OLEDs 102, 106 is not affected by the patterning. The spacer 306 is preferably not thicker than 300 μιη, because otherwise parallax effects will be visible if the light emitting device 305 which comprise two patterned OLEDs. Once again it is to be noted that the stack 306 of layers forming the spacer and/or the second OLED 102 have to transmit light and, in another embodiment, may be translucent.

Fig. 4a shows an embodiment of a color tunable light device 400 according to the second aspect of the invention. The color tunable device comprises a cone 402 in which a light emitting device according to the first aspect of the invention is provided. At the bottom of the color tunable light device 400 is provided a controller 406 which controls a first current through the first OLED of the light emitting device, and which controls a second current through the second OLED of the light emitting device. The color tunable device 400 further comprises a remote control 404. The remote control 404 has a so-termed color wheel which may be used by a user to select a preferred color. The remote control 404 sends a signal to the controller 406 according to the provided preferred color, and the controller 406 controls the currents through the OLEDs such that the light emitting device emits a combination of light from the first OLED and light from the second OLED that is consistent with the preferred color.

Fig. 4b shows an embodiment of an animation presentation device 410 according to the third aspect of the invention. The animation presentation device 410 comprises a light emitting device according to the first aspect of the invention. One of the OLEDs of the light emitting device 410 comprises a first pattern, and the other one of the OLEDs or the spacer comprises a second pattern. The first pattern is, in the example of Fig. 4b, an image of a smiling face, and the second pattern is an image of a sad face. The animation presentation device 410 further comprises a controller which controls a first current through the first OLED and which controls a current through the second OLED. By providing a current in alternation to the first OLED and to the second OLED the viewer is able to see an animation 414 of a face which alternates between a happy and a sad expression. In another embodiment, the first current gradually increases when the second current gradually decreases or vice versa, such that the animation 414 comprises a cross- fading from a face with a happy expression towards a face with a sad expression, or vice versa.

Fig. 5 shows an embodiment of a luminaire 500 according to the fourth aspect of the invention. The luminaire comprises a light emitting device 504 according to the first aspect of the invention. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A light emitting device (100, 117, 121, 200, 300, 412, 504) comprising a stack (113) of

a first Organic Light Emitting Diode (106, 115, 202) comprising a first set of two contacts (108, 208) for receiving electrical power to operate the first Organic Light Emitting Diode (106, 115, 202),

a spacer (104, 210, 306) being an electrically non- conductive and light- transmitting layer,

a second Organic Light Emitting Diode (102, 212) being at least partially light-transmitting and comprising a second set of two contacts (112, 218) for receiving electrical power to operate the second Organic Light Emitting Diode (102, 212),

wherein the spacer (104, 210, 306) is interposed between the first Organic Light Emitting Diode (106, 115, 202) and the second Organic Light Emitting Diode (102, 212), and wherein the first Organic Light Emitting Diode (106, 115, 202) is arranged for emitting, in operation, light towards the spacer (104, 210, 306).

2. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the first Organic Light Emitting Diode (106, 115, 202) is configured for emitting, in operation, light of a first color (114), wherein the second Organic Light Emitting Diode (102, 212) is configured for emitting, in operation, light of a second color (110), and wherein the first color (114) is different from the second color (110).

3. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the first Organic Light Emitting Diode (106, 115, 202) and/ or the second Organic Light Emitting Diode (102, 212) is a patterned Organic Light Emitting Diode (202, 212).

4. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 3, wherein the first Organic Light Emitting Diode (106, 115, 202) comprises a first pattern, the second Organic Light Emitting Diode (102, 212) comprises a second pattern, and wherein the first pattern is different from the second pattern.

5. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the spacer (104, 210, 306) is a patterned spacer (210).

6. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the spacer (104, 210, 306) has a thickness of 15 μιη to 300 μιη measured along a shortest line from the first Organic Light Emitting Diode (106, 115, 202) towards the second Organic Light Emitting Diode (102, 212).

7. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the spacer (104, 210, 306) is light-transmitting in a predefined range of wavelengths of light comprising at least a range of visible light.

8. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the spacer (104, 210, 306) comprises a luminescent material for converting a part of the light received from the first OLED into light of another color.

9. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the spacer (104, 210) is a stack (306) of layers comprising a first barrier layer (316), an organic layer (314) and a second barrier layer (312), wherein the organic layer (314) is interposed between the first barrier layer (316) and the second barrier layer (312).

10. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 9, wherein the first barrier layer (316) and the second barrier layer (312) comprise Si _x, SiOx and/or SiOxNy.

11. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the stack (130) further comprises a third Organic Light Emitting Diode (124) having a third set of two electrical contacts, and comprises a further electrically non- conductive light-transmitting spacer (122) interposed between the second Organic Light Emitting Diode (102, 212) and the third Organic Light Emitting Diode (122).

12. A light emitting device (100, 117, 121, 200, 300, 412, 504) according to claim 1, wherein the first Organic Light Emitting Diode (106, 115, 202) is at least partially light-transmitting.

13. A color tunable light device (400) for emitting light of a tunable color, comprising a light emitting device (402) according to claim 1 and comprising a controller (406), wherein the controller (406) is configured for controlling a first current through the first Organic Light Emitting Diode and controlling a second current through the second Organic Light Emitting Device to obtain, in operation, emitted light of a specific color.

14. An animation presentation device (410) for presenting an animation (414) to a viewer, comprising a light emitting device (412) according to claim 1 and comprising a controller (416), wherein the controller (416) is configured for controlling a first current through the first Organic Light Emitting Device and controlling a second current through the second Organic Light Emitting Device to obtain, in operation, an animation (414) that is visible to a viewer.

A luminaire (500) comprising a light emitting device (504) according to