WO2007107903A1

WO2007107903A1 - Led-based lighting device with colour control

Info

Publication number: WO2007107903A1
Application number: PCT/IB2007/050769
Authority: WO
Inventors: Marc W. G. Ponjee; Herbert Lifka; Lucas J. M. Schlangen; Patrick J. Baesjou
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-03-23
Filing date: 2007-03-08
Publication date: 2007-09-27

Abstract

A colour tunable lighting device (100) comprising a LED (102) is disclosed. The device comprises at least one tunable optical component (104) capable of controlling the optical appearance of the lighting device. The LED may be an OLED or an inorganic LED that preferably emits white light . The turnable optical component (104) can be an electrophoretic, electrochronic or electrowetting device, for example, which can be electrically controlled so as to change the spectrum of the white light emitted by the LED (102) .

Description

LED-based lighting device with colour control

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a lighting device based on light emitting diodes (LED) comprising tunable optical component.

BACKGROUND ART

Customizable (e.g. brightness, color, light distribution) light sources are becoming increasingly important, as these offer flexibility in functional use and design, even for the end-customer. For professional applications efficiency is of prime importance. The developments in solid-state lighting offer us two general light sources to achieve these goals: inorganic light-emitting diodes (LEDs) and organic LEDs (OLEDs). In general, solid-state light sources (so far only inorganic LEDs) are important on the market, which will also be true with OLEDs in the future.

OLEDs are ideal light sources for area illumination. Product trends envisioned are e.g. a light-mosaic with medium to large tiles or decorative lighting devices with patterned surface. It is desirable to provide an affordable light source from the roll, customizable in shape, color and size. Inorganic LED is well known in the art.

Well-known bottlenecks in the application of LEDs for general illumination purposes are color mixing and color stability. Prior art solutions put restrictions on the complexity of the back plane and LED processing, thereby increasing the costs of a color tunable LED-based lighting device. Point sources, like inorganic LEDs, are more suited for color mixing than larger area (typically OLED) light sources. One option for color mixing is to make a patterned OLED lamp with several emitting elements positioned laterally, of which at least two emit a different color. WO99/66483 discloses such a display device comprising a light switching unit with an array of pixels each operable to vary the transmission of light there through; and backlights having several series of organic light-emissive material with different emission colors. This display device is however expensive due to more than one color light source and it is difficult to use multiple series of light-emissive material for large area lighting systems. Although it is possible to stack monochromic OLEDs to improve color mixing, this is also cost ineffective due to the increase in the number of deposition steps.

SUMMARY OF THE INVENTION The present invention is based on the understanding that various optical switches may be combined with LEDs in order to control the intensity, color and angular distribution of the LED.

An object of the present invention is to comprise various optical switches in an LED-based lighting device in order to control the intensity, color, angular distribution and the lifetime of transparent and reflective OLEDs, and inorganic LEDs.

This object is according to a first aspect of the present invention achieved by a color tunable lighting device based on a LED comprising at least one tunable optical component capable of controlling the optical appearance of the lighting device.

The LED may be a white-emitting LED, or a LED with any given or desired spectral distribution.

According to the present invention "white-emitting" means emission of white light, and "LED" means inorganic or organic LEDs, "OLED" means an OLED light source that may be based on light-emitting polymers (poly LED) or based on light-emitting small molecules (smOLED), preferably emitting white light, but may also emit colored light, "inorganic LED" means a light source based on light-emitting inorganic material.

The LED light source may consist of one light-emitting element or a plurality of light-emitting elements, which may be laterally pixilated or/and stacked on top of one another where applicable. According to the present invention the wording "optical appearance" means how the emitted light is perceived by a viewer. The present invention enables the realization of color tunable LED-based lighting devices without color-mixing problems encountered in prior art solutions. Secondly, the thus created color tunable lighting device may have a high color rendition index (CRI), as a white-emitting LED may be used as the light source. Thirdly, the present invention comprising one or more tunable optical component may be used to obtain high color stability by correcting for the aging of the LED light source overtime.

In addition, the present invention enables tuning the color of the LED-based lighting device under ambient lighting conditions. This offers great design flexibility, such as (i) color tunability of the lighting device in the OFF-state, (ii) the virtual disappearance of the lighting device in the surroundings, e.g. background (hidden lamp),

(iii) mixing of incoming ambient light and emitted light, which provides low power options for decorative or functional lighting, for instance in the case OLED-based lighting devices are integrated in windows. According to the present invention the wording "OFF-state" means a non-emissive state of the LED, consequently "ON-state" or "ON" means wherein the LED is in an emissive state. According to the present invention the wording "virtual disappearance" means making a light source virtually disappear with respect to their surroundings, so as not to be perceived by a viewer, e.g. transparent light sources, such as transparent OLEDs. In the present invention the expression device and component is used interchangeably, and may have one or a plurality of functionalities.

Depending on the embodiment, the proposed invention offers a low cost solution to realize a color tunable LED-based lighting device wherein;

(i) the LED light source only has to emit a single spectral distribution, i.e. there is no need to deposit different light-emitting materials, and there is no need to deposit these in pixels or stacks,

(ii) no special components, e.g. diffusers, are needed to obtain a satisfactorily color mixing,

(iii) the costs of the proposed transmissive and reflective components may be relatively low, considering the possibility for low cost manufacturing, e.g. roll-to-roll, of optically active components, such as for example electrophoretic foils, which are being developed for large area, low cost display purposes.

In one embodiment the tunable optical component is a color tunable transmissive device, which may be placed in a light path of the LED, e.g. laminated on an LED, with or without an air gap.

In one embodiment a color tunable OLED-based lighting device, wherein an OLED is arranged to emit light towards one first direction, wherein the color tunable reflective device is placed at a side of the OLED being opposite to said first direction, is provided, e.g. said OLED and said color tunable reflective device are laminated together in the device, with or without an air gap.

In one embodiment at least one color tunable transmissive device and at least one color tunable reflective device are comprised in the color tunable OLED-based lighting device. In one embodiment the color tunable LED-based lighting device comprises a light sensing device, which may be capable of counter affect aging of the white emitting LED lighting device and where optionally the light sensing device, in combination with at least one tunable optical component is capable of daylight modification. In the above-mentioned embodiments the OLED may be transparent.

In embodiments where a non-transparent LED is applicable, an organic or inorganic LED may be used.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

Fig. 1 is a schematic representation of a color tunable LED-based lighting device based on a LED, in ON-state, comprising a tunable transmissive device.

Fig. 2 is a schematic representation of a color tunable lighting device based on a LED, in OFF-state, comprising a tunable transmissive device.

Fig. 3 is a schematic representation of a color tunable lighting device based on an OLED, in ON-state, comprising a tunable reflective device.

Fig. 4 is a schematic representation of a color tunable lighting device based on a ..n_ OLED, in OFF-state, comprising a tunable reflective device. Fig. 5 is a schematic representation of a color tunable lighting device based on a transparent OLED, in ON-state, comprising a tunable transmissive device.

Fig. 6 is a schematic representation of a color tunable lighting device based on a transparent OLED, in OFF-state, comprising a tunable transmissive device.

Fig. 7 is a schematic representation of a color tunable lighting device based on a transparent OLED, in ON-state, comprising a tunable transmissive device and a reflective device.

Fig. 8 is a schematic representation of a color tunable lighting device based on a transparent OLED, in OFF-state, comprising a tunable transmissive device and a reflective device.

Fig. 9 is a schematic representation of the use of a sensor(s) in combination w iitthh feedback control of the LED and/or optical switch in a color tunable lighting device based on an O ^"LLEEDD..

Fig. 10 is a schematic representation of a color tunable lighting device based OLED comprising a patterned/roughened reflective device. Fig. 11 is a schematic representation of a color tunable lighting device based on an OLED comprising a reflective device with diffuse optical properties.

Fig. 12 is a schematic representation of a color tunable lighting device based on an OLED comprising a transmissive device with diffuse optical properties. Fig. 13 is a schematic representation of a color tunable lighting device based on an OLED comprising a patterned/roughened transmissive device.

Fig. 14 illustrates a typical in-plane switching electrophoretic cell.

Fig. 15 is a schematic representation of a bottom emission OLED device.

Fig. 16 is a schematic representation of a top emission OLED device. Fig. 17 is a schematic representation of a transparent OLED device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

OLEDs typically consist of one or more organic layers, based on small molecules, and/or polymers, of which at least one can emit light, sandwiched between electrodes (anode and cathode) on substrate. Additional layers, for instance to encapsulate the OLED, may be present. Light generated in the organic stack can leave the device towards the viewer via the substrate, so-called bottom emission OLEDs, or via the top, so-called top emission OLEDs. Fig. 15 illustrates a bottom emission OLED device 160, comprising a reflective cathode 162, e.g. made of aluminum; organic light emitting layer(s) 164; a transparent anode 166, e.g. made of Indium Tin oxide (ITO) film; and a transparent substrate 168, e.g. made of glass or plastic comprising water barrier. Fig. 16 illustrates a top emission OLED device 170, comprising a transparent cathode 172, e.g. made of thin silver; organic light emitting layer(s) 174; a reflective anode 176, e.g. made of thick silver; and a bottom substrate 178, e.g. made of glass, plastic, metal etc. Bottom emission devices require the use of a transparent substrate and transparent bottom electrode, whereas top emission devices require the use of a transparent top electrode. Also transparent OLEDs, i.e. transparent substrate and transparent electrodes, may be realized, an example thereof is illustrated in Fig. 17, which illustrates a transparent OLED device 180, comprising a transparent cathode 182, e.g. made of thin silver; organic light emitting layer(s) 184; a reflective anode 186, e.g. made of thick silver; and a transparent substrate 188, e.g. made of glass or plastic comprising water barrier. Transparent light sources, such as those based on transparent OLEDs, offer the option to integrate light sources into windows or make light sources virtually disappear with respect to their surroundings, e.g. background. Electrophoresis is used in various electronic-paper displays. In these displays electrophoresis is used to control the distribution of charged pigment particles to set the optical appearance of a pixel. Electrical fields along the substrate and perpendicular to the substrate may be used to precisely control the position of the particles within the pixel volume. Due to particle-particle and particle-surface interactions, i.e. sticking, bistability is possible in electrophoretic devices. This basically means that the position of the particles is not affected when the applied potential difference is removed. A potential difference needs to be applied before the particles change positions.

In one concept, where the distribution of charged pigment particles in an oil- like liquid is controlled by means of electrodes on the carrier substrate, the substrate may be placed on an optional white reflector. When the white reflector is omitted, this pixel can switch from e.g. a black to a transparent state. By employing in-plane electric fields, an example of which may be seen in Fig 14, using appropriate electrode layouts, the charged pigment particles can be moved laterally into or out of the visible part of the pixel as disclosed in US2003/0035198. In case the particles are moved out of the visible part of the pixel, the pixel is in the transparent state. Now the particles are accumulated near the pixel wall and may be hidden from the viewer by means of a black mask. When the particles are moved into the viewing area the pixel turns black. Greyscales may be set by adjusting the driving signals on the electrodes. Other pigment colors than black may be used to yield color- changing layers. Such a layer could switch from red to transparent. Pixels that allow for more advanced color mixing need more than one kind of particle. Light scattering or reflecting particles are used e.g. in the above-mentioned concept. Non (back)scattering particles may also be used to achieve a transparent optical effect. The scattering/reflecting properties of the pixel may be controlled by means of electrophoresis. Other principles that allow for colour switching layers are dielectrophoresis, magnetophoresis, electrochromism effects or color mixing display concepts.

In general LEDs may be used to generate light of all visible colors. However, when the colour saturation of generated illuminating light is too high, this results in undesired effects on the perception of the illuminated environment, as many parts/items will hardly reflect the light. Hence, for illumination applications the use of colour mixing and saturated Red, Green and Blue LED materials (as developed for displays) are unfavorable, because this results in lighting devices with a low colour rendition index (CRI). Therefore white-emitting OLED elements are attractive for general illumination purposes due to their white light emission over a wide spectrum, i.e. not too saturated. With reference to Fig. 1 and Fig 2 which schematically illustrate a colour tunable lighting device 100, 200 based on a LED 102, 202, comprising a tunable transmissive device 104, 204, and for the case of an OLED a reflector electrode 106, 206 is used, the reflector may be the reflective electrode commonly present in either a bottom-emission or top-emission OLED, or a separate reflector and in the case of an inorganic LED, the function of a reflector is inherent. Fig. 1 illustrates the colour tunable lighting device 100 based on a LED 102 in an emissive state, i.e. ON-state, and Fig. 2 illustrates the colour tunable lighting device 200 based on a LED 202 in a non emissive state, i.e. OFF-state. Fig. 2 also illustrates incoming light, e.g. from the sun 208 and/or ambient light 208. Figs. 3 and Fig. 4 schematically illustrate a colour tunable lighting device 300,

400 based on a transparent OLED 302, 402 comprising and a tunable reflective device 304, 404,. Fig. 3 illustrates the colour tunable lighting device 300 based on a transparent OLED 302 in an emissive state, i.e. ON-state, and Fig. 4 illustrates the colour tunable lighting device 400 based on a transparent OLED 402 in a non emissive state, i.e. OFF-state. Fig. 4 also illustrates incoming light, e.g. from the sun 408 and/or ambient light 408.

Figs. 5 and Fig. 6 schematically illustrate a colour tunable lighting device 500, 600 based on a transparent OLED 502, 602 comprising a tunable transmissive device 504, 604. Fig. 5 illustrates the colour tunable lighting device 500 based on a transparent OLED 502 in an emissive state, i.e. ON-state, and Fig. 6 illustrates the colour tunable lighting device 600 based on a transparent OLED 602 in a non emissive state, i.e. OFF-state. Fig. 6 also illustrates incoming light, e.g. from the sun 608, 610 and/or ambient light 608, 610.

Figs. 7 and Fig. 8 schematically illustrate a colour tunable lighting device 700, 800 based on a transparent transparent OLED 702, 802, comprising a tunable transmissive device 706, 806 and a reflective device 704, 804. Fig. 7 illustrates the colour tunable lighting device 700 in an emissive state, i.e. ON-state, and Fig. 8 illustrates the colour tunable lighting device 800 in a non emissive state, i.e. OFF-state. Fig. 8 also illustrates incoming light, e.g. from the sun 808 and/or ambient light 808.

Fig. 9 schematically illustrates a colour tunable lighting device 900 based on a LED 902, comprising a tunable optical component 904, such as a reflective device or transmissive device; and one or more sensors 906, which sensor(s) 906 may be used in combination with a multiplexer 908, the optical properties are compared to optical properties collected earlier in time, in a comparator 910. The outcome of the comparison in the comparator 910 may be used to adjust said OLED 902 and/or said tunable optical component 904. Preferably a correcting means 912 may be used. Figs. 10 and Fig. 11 schematically illustrate a colour tunable lighting device 110, 120 based on an OLED 112, 122 and a tunable reflective device 114, 124. The reflective device may be patterned/roughened 114 or may possess diffuse optical properties 126.

Figs. 12 and 13 schematically illustrate a colour tunable lighting device 130, 140 based on an OLED 132, 142 and a tunable transmissive device 134, 144 and a reflector 136, 146, which may be the electrode of the OLED. The transmissive device may be patterned/roughened 144 or may possess diffuse optical properties 138.

Fig. 14 illustrates a non-limiting example of a typical in-plane switching electrophoretic cell 150 comprising a top layer 151, cell walls 153 and a bottom substrate 157. The electrophoretic cell contains a transparent fluid 152, which fluid comprises charged pigment particles 154. The electrophoretic cell also comprises in-plane side electrodes 155 and in-plane center electrode 156, located between the in-plane side electrodes 155. Several different electrode layouts are possible.

An embodiment of the present invention is a colour tunable lighting device based on a LED, comprising at least one tunable optical component capable of controlling the optical appearance of the lighting device, where the tunable optical component may be a transmissive component and/or a reflective component. The transmissive and/or reflective component(s) may be positioned in the light path of the LED with an air gap between the LED and the component(s). In that case optical losses, e.g. total internal reflection, occur due to the interface between LED and air and the interface between a component and air.

Therefore, a component preferably is placed in optical contact with the LED light source, e.g. laminated on top. This is particularly advantageous in case the component has diffusive optical properties or a patterned/roughened surface. In that case light can be extracted from the LED, which would otherwise be trapped in the LED light source due to total internal reflection (TIR). The embodiments shown in Fig. 10-11 further improves light extraction from the colour tunable lighting device by reducing optical losses, i.e. reducing the probability for total internal reflection. The embodiment schematically shown in Fig. 11 , shows a preferred embodiment wherein the reflective device additionally comprise diffuse optical properties. The embodiment schematically shown in Fig. 10, shows a preferred embodiment wherein the reflective device is patterned/roughened. According to the present invention patterned means the use of a controlled way to define a structure, e.g. stamping/photolithography. According to the present invention roughened means a locally more uncontrolled way to define a structure, e.g. sand blasting is one method to roughen a structure. Furthermore the colour tunable device may comprise a transparent OLED arranged to emit light towards one first direction, wherein a reflective component(s) is placed at a side of the OLED being opposite to said first direction. Additionally said tunable optical component may be based on electrophoresis, e.g. in-plane switching electrophoresis; dielectrophoresis; electro wetting; magnetophoresis or electrochromism. An embodiment of the present intention is a reflective OLED where a colour tunable transmissive component is placed in front of an OLED. The spectrum of light emitted by the OLED is changed when passing through this transmissive component, causing the viewer to experience a tunable colour different than emitted by the OLED, as is shown in the embodiment schematically illustrated in Fig. 1. Such a transmissive component may be, but is not limited to, a tunable colour filter that absorbs specific wavelengths, e.g. based on electrophoretic principles, or a tunable luminescent component that emits a spectrum different than the incident spectrum coming from the OLED, e.g. based on fluorescent or phosphorescent principles. Depending on the properties of the transmissive component, the method allows the lighting device to emit saturated colors. The same method may be used to tune the colour of reflected incident ambient light, as is shown in the embodiment schematically illustrated in Fig. 2. The spectrum of incident ambient light is changed when passing through the transmissive component, reflected on the backside of the OLED, either via a reflective electrode or via a reflector at the back of a transparent OLED, possibly changed again when passing through the transmissive component, causing the viewer to experience a tunable colour different than that of the incident ambient light, as is shown in the embodiments schematically illustrated in Fig. 1-4.

The OLED light source in a preferred embodiment is non-transparent, e.g. bottom emission or top emission, and comprises a reflective electrode and transparent electrode, such that the transparent electrode is positioned in between the reflective electrode and the tunable transmissive component.

In a preferred embodiment, the light source may comprise a transparent OLED with a tunable reflector positioned behind it, i.e. at the opposite site of the OLED with respect to the location of the transmissive component. The reflector is either incorporated in the substrate or a separate element, and may contain diffuse and/or specular reflective properties, as is shown in the embodiments schematically illustrated in Fig. 10 and Fig. 11. The reflector may be switch able from a reflective to transparent state, e.g. electro chromic mirror, electro chromic diffuser reflector, an in-plane switching electrophoretic pixel with white scattering particles. An embodiment of the present invention is a transparent OLED, where a colour tunable reflective component is placed behind a transparent OLED. The spectrum of light emitted by the OLED is changed when reflecting from the reflective component. The viewer experiences a superposition of reflected light and non-reflected light, and with that a tunable colour different than emitted by the OLED, as is shown in the embodiment schematically illustrated in Fig. 3. Similarly, the reflective component can change the spectrum of incident ambient light upon reflection, causing the viewer to experience a tunable colour different than that of the incident ambient light, as is shown in the embodiment schematically illustrated in Fig. 4. Such a reflective component may be, but is not limited to, a colour selective reflector, specular or diffuse e.g. based on electrophoretic principles, a reflector, diffuse or specular, in combination with a tunable colour filter that absorbs specific wavelengths, e.g. based on electrophoretic principles, or a combination of a reflector, specular or diffuse, with a tunable luminescent component that emits a spectrum different than the incident spectrum coming from the OLED, e.g. based on fluorescent or phosphorescent principles. According to the present invention specular means that the angle of reflection is the same as the angle of incoming light. According to the present invention diffuse means that the angle is randomized, e.g. particles or holes in the material may diffuse the light, as is shown in the embodiments schematically illustrated in Fig. 11 and Fig. 12.

In the latter two cases, the tunable optical component may be switch able from a transparent state to a diffuse state, either reflective, Fig. 11, or transmissive, Fig. 12, e.g. electro chromic, cholesteric LC effect, etc. In case a reflective component based on electrophoretic particles is used, preferably the particles are essentially (back)scattering. This may for instance be achieved by using particles with a size >100 nm. In case a transmissive component based on electrophoretic particles is used, the particles are preferably essentially forward scattering, i.e. essentially transparent. This may for instance be achieved by using particles with a size <100 nm. Preferably the OLED light source is transparent.

An embodiment of the present invention relates to the use of certain geometrical shape(s) which may result in fixed out coupling, i.e. determined by the geometrical shape, examples thereof is illustrated in Fig. 10 and Fig. 13. An embodiment of the present invention is a transparent OLED, where a colour tunable transmissive component is placed in front of a transparent OLED, as is shown in the embodiment schematically illustrated in Fig. 5. In this case, the spectrum of light emitted by the OLED is changed when passing through this transmissive component, causing the viewer to experience a tunable colour different than emitted by the OLED, as is shown in the embodiment schematically illustrated in Fig. 5. In this embodiment, the OLED light source can also emit light through its other side, such as also shown in Fig. 5, thus creating a dual-side emission lighting device. This light may be either unfiltered or may be filtered when passing it also through a transmissive component. Naturally, the embodiment may be extended towards those cases in which more than one transmissive component is used on a side of the OLED light source. Depending on the properties of the transmissive component(s) used, the method allows the lighting device to emit saturated colors towards the viewer through the transmissive component(s). The same method may be used to tune the colour of transmitted incident ambient light, as is shown in the embodiment schematically illustrated in Fig. 6. The spectrum of incident ambient light, from either side on the OLED, is changed when passing through the transmissive component, causing the viewer to experience a tunable colour different than that of the incident ambient light. In case a plurality of transmissive components is present, the control on colour and transmissivity of the lighting device increases. For instance, the characteristics of transmissive components present on the right- and left-hand side of the OLED may be chosen such that no ambient light at all can pass through it, i.e. it looks black, while the lighting device can still emit light when turned ON. The specifics of the transmissive components are mentioned above. The specifics of the transparent OLED light source are mentioned above.

An embodiment of the present invention is a transparent OLED, where a colour tunable reflective component is placed behind a transparent OLED in combination with a colour tunable transmissive component placed in front of the transparent OLED, as is shown in the embodiment schematically illustrated in Fig. 7. In this case, the spectrum of light emitted by the OLED is changed when reflecting from the reflective component, and may be changed once more when passing through the transmissive component. In addition, the spectrum of light emitted by the OLED in the direction of the viewer is changed when passing through the transmissive component. The viewer experiences a superposition of reflected light and non-reflected light, and with that a tunable colour different than emitted by the OLED. Similarly, the reflective and transmissive components may change the spectrum of incident ambient light upon transmission and reflection, as is shown in the embodiment schematically illustrated in Fig. 1, causing the viewer to experience a tunable colour different than that of the incident ambient light. The characteristics of the components present on the right- and left-hand side of the OLED may be chosen such that no ambient light will reflect from the OLED, i.e. it looks black, while the lighting device can still emit light when turned ON. Generally the lighting device may be expanded to include a plurality of transmissive components in front of the OLED or in between the OLED and reflective component. The specifics of the transmissive component, the reflective component, and the transparent OLED light source are mentioned above. According to an embodiment of the present invention a colour tunable optical component, either reflective or transmissive or a plurality of reflective and transmissive components, may be used to counter affect the aging of an OLED light source. Aging is one of the well-known problems of an OLED light source and encompasses the change in the spectrum of emitted light over time. For instance, a shift of the colour coordinates of the white point over time. A colour tunable optical component may be used to correct for this by altering the spectral properties of the component such that the colour coordinates, and preferably the spectrum as well, of light emitted by the lighting-element, i.e. OLED and components, are identical to the desired values. This may be accomplished by selective reflection of ambient light, e.g. tunable reflective component, possibly in combination with a transmissive component, and selective emission of white-light emitted by the OLED via a reflective and/or transmissive component. Preferably a sensor may be included in the lighting device to sense the optical properties, e.g. colour coordinates, spectrum, luminance, etc, of emitted light over time. The sensed properties are compared, e.g. in a comparator, to the optical properties earlier in time. The outcome of the comparison is used, e.g. in an optical switch and/or an OLED, to adjust the addressing of the OLED and/or colour tunable optical components to bring about the emittance of light with constant optical properties. A single sensor or a plurality of sensors may be used. In the latter case a multiplex approach may be used. A sensor may be positioned such, that it measures the optical properties of light emitted by the OLED, or of the light emitted by the lighting device towards the viewer (or of the ambient light). The same approach may be used to have the colour tunable lighting device based on an OLED to emit light with user desired optical properties, which may be stabilized over time. In addition, this approach can also be used to measure the optical characteristics, such as colour coordinates, spectrum, luminance, etc, and wavelengths of environmental light and use that information to control the lamp settings. According to an embodiment of the present invention a colour tunable optical component, either reflective or transmissive or a plurality of reflective and transmissive components, may be used to tune the light coming from an organic-based lighting device by mixing light emitted by the OLED, i.e. generated, with ambient light, e.g. coming from the OLED. The above mentioned embodiments illustrate how the present invention may be used to tune the colour of light emitted by the lighting device in the ON-state, and ambient light coming from the OLED, either reflected or transmitted, in the OFF-state.

The inventors propose to mix ambient light with emitted light coming from the OLED when the OLED is in the ON-state. An advantage of this approach is that ambient light may be used to contribute to the colored light emitted by the lighting device. This provides a way to lower the power consumption. Moreover, it provides a way to tune the colour-tone, e.g. atmosphere, in a room to a greater extend with respect to the prior art case in which no tunable control of ambient light is possible. Preferably a sensor may be used in a closed feedback loop to control the optical properties of the light emitted by the lighting device. In addition, to the described optical switches to control the colour, a transparent-to- reflector (diffuse/specular) optical switch may be added attenuate ambient light. If required also a transparent-to-black (absorbing) optical switch may be used.

In the above mentioned embodiments, given as examples within the scope of the invention, it can be readily understood by a person skilled in the art to arrange the elements in different configurations using inorganic LEDs, OLEDs, e.g. transparent and non- transparent, light sensing devices, correcting means, transmissive and reflective tunable optical components, and reflective devices to achieve the effect of the present invention.

Claims

CLAIMS:

1. A colour tunable lighting device (100, 200, 300, 400, 500, 600, 700, 800, 900, 110, 120, 130, 140) comprising a LED (102, 202, 402, 502, 602, 702, 802, 902, 112, 122, 132, 142, 160, 170, 180) comprising at least one tunable optical component (104, 204, 304, 404, 504, 604, 704, 706, 804, 806, 904, 114, 124, 134, 144) capable of controlling the optical appearance of the lighting device.

2. Colour tunable lighting device according to claim 1, wherein the LED (102, 202, 402, 502, 602, 702, 802, 902, 112, 122, 132, 142, 160, 170, 180) is a white-emitting LED.

3. Colour tunable lighting device according to claim 1 or 2, wherein the LED is an OLED.

4. Colour tunable lighting device according to claim 1, 2 or 3, wherein at least one of the at least one tunable optical component is a colour tunable transmissive device

(104, 204, 706, 806, 904, 134, 144).

5. Colour tunable lighting device according to claim 4, wherein the colour tunable transmissive device is arranged such that light from the LED passes said colour tunable transmissive device.

6. Colour tunable lighting device according to claim 1, 2 or 3, wherein the tunable optical component is a colour tunable reflective device (304, 404, 704, 804, 904, 114, 124).

7. Colour tunable lighting device according to claim 6, comprising a transparent OLED arranged to emit light towards one first direction, wherein the colour tunable reflective device is placed at a side of the transparent LED being opposite to said first direction.

8. Colour tunable lighting according to claim 6, wherein the tunable reflective device is a colour selective reflector, diffuse or specular; a reflector, diffuse or specular; in combination with a tunable colour filter; or in combination with a tunable luminescent component.

9. Colour tunable lighting device according to claim 1, 2 or 3, comprising at least one colour tunable transmissive device and at least one colour tunable reflective device.

10. Colour tunable lighting device according to any one of claims 1-9, comprising at least one light sensing device (906).

11. Colour tunable lighting device according to claim 10, comprising correcting means (912), wherein the light sensing device and the correcting means are used to correct changes in the spectrum of emitted light over time.

12. Colour tunable lighting device according to claim 10 or 11, wherein the light sensing device is arranged in a closed feedback loop.

13. Colour tunable lighting device according to claim 1, 2 or 3, wherein ambient light is mixed with light emitted by the LED.

14. Colour tunable lighting device according to claim 13, further comprising light measuring means providing a light measuring signal such that at least one tunable optical component is arranged to control said mixed ambient light and light emitted by the LED.

15. Colour tunable lighting device according to any one of claims 1-14, comprising an optical switch, wherein the optical switch attenuates ambient light.

16. Colour tunable lighting device according to any one of claims 1-15, wherein colour control of the lighting device with the LED in the OFF-state allows tuning of the optical appearance of the lighting device

17. Colour tunable lighting device according to any one of claims 1-16, wherein the OLED is transparent, enabling virtual disappearance of the lighting device in the background.

18. Colour tunable lighting device according to any one of claims 1-17, comprising an optical switch for attenuating emitted light.

19. Colour tunable lighting device according to any one of claims 1-18, wherein the tunable optical component is based on electrophoresis, dielectrophoresis, electro wetting, magnetophoresis or electrochromism.

20. Colour tunable lighting device according to claim 19, wherein the tunable optical component is based on in-plane switching electrophoresis.

21. Colour tunable lighting device according to any one of claims 1, 2, 4, 5, 10-16, or 18-20, wherein the LED is an inorganic LED (102, 202).