WO2009040724A2

WO2009040724A2 - Window system combining window and illumination functionalities

Info

Publication number: WO2009040724A2
Application number: PCT/IB2008/053848
Authority: WO
Inventors: Hans P. Loebl; Herbert F. Boerner; Claudia M. Goldmann
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2007-09-26
Filing date: 2008-09-23
Publication date: 2009-04-02
Also published as: TW200920987A; WO2009040724A3

Abstract

The present invention discloses a window system (10) comprising a transparent window element (1), a transparent organic light-emitting element (2) comprising at least one organic light emitting layer (21) arranged between electrodes (22) to emit artificial light (51, 52) and an optical element (3) comprising at least one functional layer (31) arranged between switching electrodes (32), which is electrically switchable between a transparent mode in order to enable a transmission of window light (4) through the window system and a reflective or absorbing mode in order to reflect or absorb at least an essential part of the artificial light (51, 52) emitted towards the optical element (3) as well as a building system comprising a multitude of window systems and a method of operating a window system.

Description

WINDOW SYSTEM COMBINING WINDOW AND ILLUMINATION FUNCTIONALITIES

FIELD OF THE INVENTION

This invention relates to window systems for effective day and night illumination combining window and illumination functionalities, and to building systems comprising a multitude of window systems and to a method of operating such a window system.

BACKGROUND OF THE INVENTION OLEDs are promising, thin, large-area light sources, where the combination of a diffuse (or indirect) light emission and the large light emission area is very suitable for room illumination purposes. US 6639357 discloses an OLED layer stack with transparent electrodes allowing the application of transparent OLEDs on windows, combining the window functionality of the transparent OLED-window system during daytime and the light-emitting capability of the OLED during nighttime. However, a transparent OLED emits light to both sides of the window. Therefore only half of the light can be used to illuminate the inside of a room or a building. The light emitted to the outside can be considered as a kind of light pollution of the environment and is lost for room illumination purposes. Administrative regulations of an increasing number of countries try to reduce such kind of light pollution. A number of cities in the United States already have developed standards for outdoor lighting to protect the rights of their citizens against light trespass. The OLED light emitted to the outside can be re-directed to the inside by using a sort of Venetian blind with mirror-like appearance, as disclosed in EP0461137. However, such a combination of OLED with a Venetian blind or other corresponding blind systems requires suitable mechanics to reflect the light back to the inside, as well as a positioning of the blinds to obtain the desired illumination, and is likely to fail. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a window system combining the window functionality with an effective and reliable artificial illumination suitable to at least essentially avoiding light pollution of the environment. This object is achieved by a window system comprising a stack of elements arranged in any order: a transparent window element, a transparent organic light-emitting element comprising at least one organic light emitting layer arranged between electrodes to emit artificial light and - a optical element, where the optical element is an reflective element or an absorbing element, comprising at least one functional layer arranged between switching electrodes, which is electrically switchable between a transparent mode in order to enable the transmission of window light through the window system and a o reflective mode if the optical element is the reflective element in order to reflect at least an essential part of the artificial light emitted towards the optical element, or o an absorbing mode if the optical element is the absorbing element in order to absorb at least an essential part of the artificial light emitted towards the optical element.

Here, a window element may be a complete window or a part of a window pane. The window element may comprise one or more window panes, such as for example double windows. The Term "window" denotes transparent panes for any kind of window functionality (window function), e.g. windows in facades of buildings or windows in doors, walls, roofs etc to transmit daylight and/or light emitted by any other light source. The term "window light" denotes any kind of light not emitted from the organic light emitting element, e.g daylight from the outside or light emitted by another light source apart from the window system. The term "artificial light" denotes the light emitted by the organic light-emitting element within the window system. The material of the transparent substrate can be any transparent material suitable for the application in windows, e.g. glass, plastic etc. The term "transparent organic light- emitting element (OLED)" denotes the complete layer stack necessary to operate an OLED, the materials within the OLED stack being transparent, e.g. transparent indium- tin-oxide (ITO) electrodes.

The optical element may be a reflective element or an absorbing element. Here, the term "reflective" denotes the reversal of the light direction, the incident angle being equal to the angle of reflection, in contrast to diffuse scattering. The emitted artificial light can be mono-colored or multicolored light, depending on the applied organic light emitting material and the OLED layer stack, e.g. white light emitted by red-green-blue stacked OLEDs. The term "absorbing" denotes the absorption of at least a part of the artificial light. The optical element as an absorbing element may reduce the brightness of the artificial light transmitted through the absorbing element for the whole spectrum of the artificial light or for a part of the spectrum of the artificial light. In the latter case, an e.g. with light emitting OLED may be visible as a weak red emitting light source from the environment. The mentioned color of light is only one example a can be any color depending on the light absorbing properties of the absorbing element.

The optical element as a reflective or absorbing element can be arranged on top of the transparent window element or on top of the transparent organic light- emitting element. The optical element can be any optical element comprising at least one functional layer, which functional layer can be switched between both modes (firstly, transparent and reflective in case of the optical element as reflective element and secondly, transparent and absorbing in case of the optical element as an absorbing element) via an applied voltage to the switching electrodes. For instance, the functional layer of the reflective element may be an electrochromic layer such as hydrogen containing WO₃, NiO, Polyanilin (PANI) or magnesium-rich Ni-Mg layers, where the optical properties are changed between transparent and reflective by an applied electrical field and/or charge injection leading to a reversible reaction between a metallic or oxidic mode (e.g WO₃) and a hydride mode (e.g H_xWO₃) or the function layer may be an electrophoretic foil comprising cavities which contain electrophoretically mobile particles, e.g aluminum particles or TiO₂ coated particles, suspended in a liquid, e.g a non-polar organic liquid such as paraffin oil or other oils. People skilled in the art may also consider other electrically switchable functional layers (electrochromic layers, electrophoretic layers or other suitable layers) according to the present invention such as Gd-Mg alloys. The switching electrodes can be made of any transparent conducting materials, for instance ITO. The reflectivity of electrochromic layers and of electrophoretic layers in the reflective mode are typically 60 - 80% and 60 - 90% of the incident visible light, respectively. The transmission in the reflective mode is below 20%, in some cases close to 0%. In the transparent mode, the reflectivity is strongly reduced, for example to values of about 20% while a transmission of up to 80% is obtainable. For Gd-Mg-alloys, the transparent mode of 70% transparency can be switched to a reflectivity of 70%. For instance, the functional layer of the absorbing element may be any suitable electrochromic layer (organic polymers or inorganic compounds) changing its transparency from 60% up to more than 70% in the transparent mode to 25%, for more preferred electrochromic layers to less than 5% transmission in the absorbing mode. An example of such an absorbing element is a layer sequence of ITO-electrode / WO₃ / H⁺- polymer / PANI (= Poly- Aniline) / ITO-electrode. The required operation voltage of such electrochromic layers is in the order of 0.5 - 5V.

In an embodiment, the transparent window element is arranged between the optical element and the organic light-emitting element. This enables an individual, subsequent placement of optical and organic light-emitting elements (OLED element) onto the window element. Especially windows already equipped with OLED elements can be modified into the window system according to the present invention by adding the optical element on the other side of the window element.

In an alternative embodiment, the optical element is arranged between the transparent window element and the organic light-emitting element, or the organic light-emitting element is arranged between the optical element and the transparent window element. Here, the optical and organic light emitting elements may be glued together or prepared directly on top of each other.

In another embodiment the window system comprises at least two window panes (e.g. double pane window) arranged with a gap between the two window panes and wherein the optical element is arranged in the gap on one window pane and the organic light-emitting element is arranged in the gap on the other window pane facing towards the optical element. The gap may be filled by the organic light-emitting element and the optical element. In other embodiments there may be a remaining gap between optical element and organic light-emitting element. The gap may be filled with additional optical coupling layer(s), e.g. silicon layer, to obtain a good optical transition between organic light emitting element and optical element. Both window panes may serve as an encapsulation of the organic light-emitting element, which is known to be sensitive to moisture and oxygen. The window panes may be glued together in a gas- tight way via a seal (e.g. glass seal) fixing both panes essentially parallel to each other with a certain gap between both panes after providing a certain vacuum between the panes. Any other methods to decrease to amount of moisture and oxygen below a required level in order to obtain a sufficient life-time performance of the organic light- emitting element could also be applied by the skilled people. In another embodiment, the optical element and the organic light emitting element are connected in such a way as to obtain either no artificial light in the transparent mode of the optical element or artificial light in the reflective or absorbing mode of the optical element. Here, the window function is not disturbed by artificial light from the OLED, and during nighttime the artificial light is essentially not emitted to the environment. Therefore, any light pollution of the environment on the other side of the window element is essentially prevented. In case of the optical element as a reflective element, the artificial light is additionally essentially reflected back in one direction to improve the room illumination by the OLED element. Both can be achieved in an embodiment where one switching electrode of the optical element serves both as an anode or a cathode of the organic light-emitting element. The double function of an electrode layer reduces the number of layers in a stacked layer system comprising an optical element and an organic light-emitting element.

In another embodiment, the area size of the optical element exceeds the area size of the organic light-emitting element. In this case, the illumination source can be varied from a more diffuse large-area light source to a more concentrated light source, e.g. for directed light beams or spot light beams. In this embodiment, additional layers with integrated optics to form a certain artificial light beam may be added to the window system. In another embodiment, the area size of the organic light-emitting element exceeds the area size of the optical element in order to illuminate also the other side of the window system. This may be advantageous in the case of indoor window systems serving as a combined room illumination and corridor illumination device. The major part of the light is emitted by the organic light-emitting to one side of the window system to illuminate a room on this side (high brightness) and simultaneously the minor part of the light is transmitted through the window system to the other side of the window system for instance to illuminate a corridor (low brightness). In case of a reflective element as the optical element, the light reflected back to the side, where the room should be illuminated will enhance the brightness of the room illumination, because no light is absorbed. People skilled in the art may also consider other applications using such a window system.

In another embodiment, the window system further comprises a light scattering element arranged on top of the side of the organic light-emitting element facing away from the optical element in order to enhance the light out-coupling from the organic light-emitting element to the environment. In an advantageous embodiment the light scattering element is switchable between a transparent mode and a light scattering mode in order to fully maintain the window function (transparency) of the window system. In another embodiment, the window system further comprises a control unit to switch at least the transparent organic light-emitting element and the optical element in response to a received signal. The signal may be a signal originating from a clock, a brightness (day/night sensor) sensor, a remote control, a computer, a cell phone, an internet connection or any other suitable devices.

This invention further relates to a building system comprising a multitude of window systems according to claim 1, characterized in that the building system further comprises a building control unit to switch the transparent organic light- emitting element and the optical element of different window systems simultaneously or separately. For example, building facades comprising a multitude of window systems or a number of doors in a corridor equipped with window systems can be operated simultaneously in the same mode (reflective/transparent or absorbing/transparent and/or light emitting / non-light emitting). The same is possible for some of the window systems of the building facades and/or indoor applications such as doors in a corridor. People skilled in the art may also consider additional applications, where more than one window systems may be operated simultaneously.

This invention further relates to a method of operating a window system according to claim 1, characterized in that the following steps: switching on the organic light emitting element in order to emit artificial light and switching the optical element to the reflective or absorbing mode are performed simultaneously.

In another embodiment of the method of operating a window system, the method further comprises the steps: - switching off the organic light emitting element and switching the optical element to the transparent mode, which steps are performed simultaneously.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter BRIEF DESCRIPTION OF THE DRAWINGS

Fig-1: window system comprising an optical element, window element and organic light-emitting element shown in a side view: (a) only window light (b) and (c) artificial light emitted by the organic light emitting-element.

Fig.2: window system comprising a window element, optical element and organic light-emitting element shown in a side view: (a) only window light (b) and (c) artificial light emitted by the organic light emitting-element.

Fig.3: window system comprising an optical element, organic light- emitting element and window element shown in a side view: (a) only window light (b) and (c) artificial light emitted by the organic light emitting-element.

Fig.4: window system with electrodes and functional layers, shown in a side view.

Fig.5: another embodiment of the window system with electrodes and functional layers, shown in a side view.

Fig.6: window system shown in a top view with more than one organic light-emitting element and different area sizes of optical and OLED elements.

Fig.7: window system shown in a top view with an area size of the optical element exceeding the area size of the organic light- emitting element.

Fig.8: window element with additional scattering element: (a) only window light (b) artificial light emitted by the organic light emitting-element. Fig.9: building system operating multiple window systems.

Fig.10: window system shown in a side view comprising an optical element, an organic light-emitting element and a sealed window element with two window panes

DETAILED DESCRIPTION OF EMBODIMENTS

The organic light emitting element (OLED) comprises a number of stacked layers. The OLED layer stack comprises at least a light-emitting organic layer arranged between two electrodes (anode and cathode). Usually, one electrode is transparent and the other electrode is reflective. In the case of the present invention, both electrodes have to be transparent. As an example, a known transparent electrically conductive material is Indium- Tin-Oxide (ITO). The OLED may comprise additional organic layers between the electrodes such as electron and/or hole conducting layers, electron and/or hole injection layers or several different light-emitting layers emitting light of a different color instead of one light-emitting layer. The term "color" denotes emitted light within a certain wavelength range, resulting in a certain color of the emitted light. To people skilled in the art, a large number of suitable organic materials are known which enable an OLED layer stack emitting light of a desired color and/or brightness to be obtained.

The optical element can be any reflective or absorbing element comprising at least one functional layer, which functional layer can be switched between both modes (transparent / reflective or transparent / absorbing) via a voltage applied to the switching electrodes such as electro-chromic elements, gas-chromic elements or photo-chromic elements. For example, the electro-chromic element consists of a WOx layer and redox electrolytes such as Lithium-Iodide. The functional layer may be an electro-chromic layer such as hydrogen containing WO₃, NiO, Polyanilin (PANI), Gd-Mg or magnesium-rich Ni-Mg layers, where the optical properties are changed between transparent and reflective or absorbing by an applied electrical field and/or charge injection leading to a reversible reaction between a metallic or oxidic mode (e.g WO₃) and a hydride mode (e.g H_xWO₃) or the functional layer may be an electrophoretic foil comprising cavities which contain electrophoretically mobile particles, e.g aluminum particles or TiO₂ coated particles, suspended in a liquid, e.g a non-polar organic liquid such as paraffin oil or other oils. People skilled in the art may also consider other electrically switchable functional layers (electrochromic layers, electrophoretic layers other suitable layers) according to the present invention. The switching electrodes can be made of any transparent conducting materials, for instance ITO. The reflectivity of electro-chromic layers and of electrophoretic layers in reflective mode are typically 60 - 80% and 60 - 90% of the incident visible light, respectively. The transmission in the reflective mode is below 20%, in some cases close to 0%. In the transparent mode, the reflectivity is strongly reduced, for example to values of about 20% while a transmission of up to 80% is obtainable. The same magnitude of transmission is obtained for absorbing stacks comprising electrochromic layers such as ITO-electrode / WO₃ / H⁺- polymer / PANI (= Poly- Aniline) / ITO- electrode. In the absorbing mode the transparent will be lowered down to 25%, for more preferred electrochromic layers to less than 5% transmission.

Figs.l, 2 and 3 show different embodiments of the window system according to the present invention, where (a) denotes the window system in a transparent and non-light emitting mode, (b) denotes the window system in a reflective and light-emitting mode and (c) denotes the window system in an absorbing and light- emitting mode. Another embodiment covered by the present invention, where the window system is operated with the optical element in the reflective or absorbing mode and the light-emitting element in the non-light emitting mode as well as the optical element in the transparent mode and the light-emitting element in the light emitting mode are not shown here. The window element 1, the organic light-emitting element 2 and the optical element 3 can be arranged differently. In Fig.l the window element 1 is arranged between optical element 3 and organic light-emitting element 2. In Fig.2 the optical element 3 is arranged between window element 1 and organic light-emitting element 2. In Fig.3 the organic light-emitting element 2 is arranged between optical element 3 and window element 1. In Fig. Ia, 2a, 3a, the window system is transparent to window light 4, which can be sunlight or light emitted by another light source outside the window system, for example outdoor or indoor illumination. In Fig. Ib, 2b, 3b, the window system is operated in the reflective mode (optical element 3 = reflective element 3a), preventing the transmission of an at least essential part of window light 4 through the window system. The organic-light emitting element 2 emits artificial light 51 and 52, the artificial light 51 being emitted from the OLED directly to one side of the window system and the artificial light 52 being originally emitted in the opposite direction and essentially reflected back in the other direction by the reflective element 3 enhancing the brightness of the artificial light emitted to the light-emitting side of the window system. In arrangements where the OLED 2 is arranged between window element 1 and reflective element 3a, both artificial lights 51 and 52 have to pass the window element (Fig.3). If the window element 1 is arranged between OLED 2 and reflective element 3a, only artificial light 52 has to pass the window element 1 before being reflected by the reflective element 3a. In Fig. Ic, 2c, 3c, the window system is operated in the absorbing mode (optical element 3 = absorbing element 3b), preventing the transmission of an at least essential part of window light 4 through the window system. All light emitted towards the absorbing element 3b is essentially absorbed by the absorbing element 3b. The amount of absorbed artificial light (and window light) depends on the ratio between absorption and transmission coefficients of the absorbing element 3b.

In the cases where artificial light 51 and/or 52 have to pass the window element 1, it is advantageous if the refractive indices of OLED 2 and window element 1 are adapted in order to minimize the amount of light being reflected back at the interface between window element 1 and OLED element 2 due to total refection. The adjustment of the refractive indices may be achieved by introducing additional transparent layers with refractive indices between the refractive indices of both elements 1 and 3. Fig 4 shows an embodiment of the window system according to the present invention, where the window element 1 is arranged between optical element 3 and OLED 2. The two latter elements are equipped with two electrodes 32 and 22 each. The electrodes 22 and 32 are connected via electrical connections 220 and 320 to power supplies 62 and 63 applying operating voltages U_L1 and U_L2 to the OLED 2 and operating voltages U_R1 and U_R2 to the optical element 3 in order to enable the emission of light and to switch between the reflective or absorbing mode and the transparent mode, respectively. The functional layers are denoted as 21 (light emitting layer, OLED 2) and 31 (reflective/transparent layer or absorbing/transparent layer of optical element 3). In an advantageous embodiment, both power supplies are controlled by a window control unit 6 in order to switch the optical element 3 to the reflective or absorbing mode (U_R2) when the OLED light emission is switched on (U_L2) and correspondingly to switch the optical element 3 to the transparent mode (U_RO when the OLED light emission is switched off (U_L1; in common cases U_L1 = 0), according to the operating method as claimed in the present invention.

Fig.5 shows another embodiment, where the optical element 3 and the organic light-emitting element (OLED) 2 are arranged directly on top of each other. To reduce the number of layers within the layer stack of reflective and organic light emitting elements, one of the electrodes 32a of the layer stack of the optical element 3 simultaneously serves as one of the electrodes 22a of the layer stack of the organic light-emitting element 2. For instance, the voltage of the simultaneously used electrode 22a = 32a may by at ground level (=0V) and the two other electrodes 32b and 22b may be at the corresponding operating voltages of optical element 3 and OLED 2. The window element, indicated in Fig.5 by dashed lines, is either on top of the OLED 2 or on top of the optical element 3. In another embodiment where optical element 3 and the organic light-emitting element (OLED) 2 are arranged directly on top of each other, the formally simultaneously used electrode 22a, 32a is separated into two sub electrodes 22a and 32a with a barrier layer in between, e.g. a SiO₂ layer. This has the advantage, that the barrier layer avoids ion migration from the functional layer of the optical element into the OLED. The strength of the migration depends on the polarity of both elements, i.e. whether the simultaneously used electrode is the anode or the cathode of the OLED.

In a window system 10, the area sizes of optical elements 3 may be larger than the area sizes of the organic-light emitting elements 2, as shown in Fig.6. One window system 10 may comprise one or more organic light-emitting elements 2 of the same or different shape and size, as shown in Fig.6. For example, one of the OLEDs 2 may be additionally equipped with optical structures to emit a focused or aligned light beam in order to spotlight an object, e.g. a part of a table etc. As shown in Fig.7, the area size of the organic light-emitting element 2 may exceed the area size of the optical element 3. As a result of this embodiment, the window system 10 will emit artificial light 51 to both sides of the window system 10 in the areas of the window system 10 where no optical element 3 is present (here in the area close to the edge of the window system as an example). This effect can be used to simultaneously illuminate one side of the window system 10 with high brightness

(artificial light 51 and 52, larger emitting area), e.g. for room illumination purposes, and the other side of the window system with low brightness (artificial light 51, smaller emitting area), e.g. for corridor illumination etc. where no bright light is required. The brightness levels on both sides can be adapted by a suitable ratio of the area sizes of optical and organic light-emitting elements. Skilled people may choose other geometrical ratios between optical and organic light-emitting elements depending on the individual application.

In the embodiment as shown in fig.8, the window system 10 additionally comprises a light- scattering element 7 arranged at the interface between window system 10 and the environment. The light- scattering element 7 may be used to enhance the light out-coupling efficiency of the window system 10. The light- scattering element 7 may be electrically switchable with an operating voltage Us₁, Us₂ between a scattering mode (Us₂) and a transparent mode (Us₁). The modes of the light scattering element 7 may be also controlled by the power control unit 6 also controlling the voltages applied to optical element (here: reflective element 3b) and organic light-emitting element 2. In alternative embodiments, the elements 2, 3 and 7 may be controlled and switched separately. Electrically switchable elements 7 are commercially available. People skilled in the art will select suitable scattering elements 7 comprising materials/layers suitable to be operated within the above described window system 10. The optical element shown in Fig.8 is an reflective element 3b, but in other embodiments it could also be an absorbing element 3b instead of an reflective element 3a.

In another embodiment as shown in Fig.9, a building system 11 comprises a multitude of window systems 10, which are controlled by a building control unit 111. The building control unit 111 may comprise one or more window control units to apply the desired voltages to switch the individual window systems 10 to the desired mode. Alternatively, the building control unit may transmit the desired mode to the window systems 10, which each comprise a separate window control unit 6. The building system may be adapted to operate window systems 10 in a number of rooms, on a floor, in a complete building, a building facade or to operate more than one building.

One example of the inventive window system: Layer / thickness: window pane, e.g. glass pane

ITO layer, 120nm electrochromic layer / stack (transparent / reflective or absorbing)

ITO layer, 120nm SiO2 barrier layer, lOOnm ITO layer, 120nm n-doped layer electron transport layer organic green light emitting layer organic red light emitting layer hole transport layer charge generation layer electron transport layer organic blue light emitting layer hole transport layer hole injection layer ITO layer, 120nm

Light out-coupling layer

Fig.10 shows another embodiment of our present invention. Here, the window element 1 comprises two window panes Ia, Ib, where the organic light- emitting element 2 and the optical element 3 are arranged between the both window panes Ia, Ib on the inner surfaces of the two window panes facing together. This arrangement simultaneously serves as an encapsulation (Ia, 12, Ib, 12) for the organic light-emitting element 2, which is sensitive to moisture and oxygen. The two window panes Ia, Ib are sealed together in a gas-tight way with an appropriate seal 12 establishing a gap 13 between the window panes Ia, Ib sufficient for previously preparing optical element 3 and organic light-emitting element 2 onto the inner surfaces of window panes Ia and Ib. The optical and organic light-emitting elements may be in direct contact or may be separated by a certain gap. In alternative embodiments, such a gap may be filled with an optical coupling layer (e.g. silicon) in order to prevent undesired optical transitions between optical element 3 and organic light-emitting element 3 leading to total reflection effects. The volume between the sealed window panes Ia and Ib may be filled with dry and inert gases (e.g. noble gases or dry nitrogen) or may be evacuated to sufficient low pressures below 1 mbar enabling a good life-time performance of the organic light-emitting device. Additional getter materials to remove moisture and/or oxygen may be arranged in the neighborhood of the seals with the sealed volume for a further improved life-time performance.

By applying one or more features of the previous embodiments, either individually or in combination with each other, the resulting window systems and/or building systems operate as multi-functional light sources for general illumination purposes, spotlighting objects, light effects, light management etc. The embodiments described in the patent specification and the figures shall be considered as examples of a window system, a building system and a method of operating a window system according to the present invention. People skilled in the art will also consider alternative embodiments of the window system, building system and the method of operating the widow system, which are also covered by the claims of the present invention.

Claims

1. Window system (10) comprising a stack of elements arranged in any order: a transparent window element (1), a transparent organic light-emitting element (2) comprising at least one organic light emitting layer (21) arranged between electrodes (22) to emit artificial light

(51, 52) and a optical element (3), where the optical element (3) is a reflective element (3a) or an absorbing element (3b), comprising at least one functional layer (31) arranged between switching electrodes (32), which is electrically switchable between a transparent mode in order to enable the transmission of window light

(4) through the window system and a o reflective mode if the optical element (3) is the reflective element (3a) in order to reflect at least an essential part of the artificial light (51, 52) emitted towards the optical element (3), or o an absorbing mode if the optical element (3) is the absorbing element

(3b) in order to absorb at least an essential part of the artificial light (51, 52) emitted towards the optical element (3).

2. Window system (10) according to claim 1, characterized in that the transparent window element (1) is arranged between the optical element (3) and the organic light-emitting element (2).

3. Window system (10) according to claim 1, characterized in that the optical element (3) is arranged between the transparent window element (1) and the organic light-emitting element (2), or the organic light-emitting element (2) is arranged between the optical element (3) and the transparent window element (1).

4. Window system (10) according to claim 1, characterized in that the transparent window element comprises at least two window panes arranged with a gap between the two window panes and wherein the optical element (3) is arranged in the gap on one window pane and the organic light-emitting element (2) is arranged in the gap on the other window pane facing towards the optical element (3).

5. Window system according to claim 5, characterized in that the both window panes are sealed together in a gas-tight way in order to provide an encapsulation for the organic light-emitting element

6. Window system (10) according to any of the preceding claims 3 or 5, characterized in that one of the switching electrodes (32) of the optical element (3) simultaneously serves as an electrode (22) of the organic light-emitting element (2).

7. Window system (10) according to any of the preceding claims, characterized in that the electrodes (22, 32) of the optical element (3) and the organic light emitting element (2) are connected in such a way as to obtain either no artificial light (51, 52) in the transparent mode of the reflective element (3) or artificial light (51, 52) in the reflective mode of the reflective element (3).

8. Window system (10) according to any of the preceding claims, characterized in that the area size of the optical element (3) exceeds the area size of the organic light-emitting element (2).

9. Window system (10) according to any of claims 1 to 7, characterized in that the area size of the organic light-emitting element (2) exceeds the area size of the optical element (3).

10. Window system (10) according to any of the preceding claims, further comprising a light scattering element (7) arranged on top of the side of the organic light-emitting element (2) facing away from the optical element (3).

11. Window system (10) according to claim 10, characterized in the light scattering element (7) is switchable between a transparent mode and a light scattering mode.

12. Window system (10) according to any of the preceding claims, characterized in that the window system (10) further comprises a window control unit (6) to switch at least the transparent organic light-emitting element (2) and the optical element (3)in response to a received signal.

13. Building system (11) comprising a multitude of window systems (10) according to claim 1, characterized in that the building system (11) further comprises a building control unit (111) to switch the transparent organic light-emitting element (2) and the optical element (3) of different window systems (10) simultaneously or separately.

14. Method of operating a window system (10) according to claim 1, characterized in that the following steps: switching on the organic light emitting element (2) in order to emit artificial light (51, 52) and switching the optical element (3) to the reflective or absorbing mode are performed simultaneously.

15. Method of operating a window system according to claim 14, further comprising the steps: switching off the organic light emitting element (2), and - switching the optical element (3) to the transparent mode, which steps are performed simultaneously.