WO2008081376A2

WO2008081376A2 - Lighting device with a plurality of oled units

Info

Publication number: WO2008081376A2
Application number: PCT/IB2007/055206
Authority: WO
Inventors: Dietrich Bertram; Lingli Wang; Marc W. G. Ponjee
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2007-01-03
Filing date: 2007-12-18
Publication date: 2008-07-10
Also published as: WO2008081376A3; TW200836340A

Abstract

It is described a lamp (6) with a 3D illuminating area (7). The lamp (6) comprises a plurality of organic light emitting diode (OLED) units (1) and each OLED unit (1) comprises a light emitting region (8-12) to form a part of the illuminating area (7). The lamp (6) enables a desired light distribution (beam shaping) and is preferably configured as a high brightness light sources and light sources with increased lifetime and improved co lor mixing. The configuration with a plurality of OLED units (1) offers design freedom and provides integrated light sources. Further, the invention may reduce the well known heat problem.

Description

LIGHTING DEVICE WITH A PLURALITY OF OLED UNITS

FIELD OF INVENTION

The present invention relates to the use of organic light emitting diodes (OLED) for illumination, preferably for direct illumination. More particularly, the present invention relates to a lighting device comprising a plurality of OLED units. ART BACKGROUND

OLEDs typically consist of one or more organic layers, of which at least one can emit light and which are sandwiched between electrodes on substrates. One of the deficiencies in using OLEDs for general illumination may be the non-directed out coupling of light (a diffused light). Therefore, using OLEDs may not be efficient in many applications, such as local illumination: spot lighting, ceiling lighting, table lighting, desk lighting, task lighting, etc.

The second problem of OLEDs may be caused by their limited lifetime: as a function of time, the luminance decreases at a constant driving current. Moreover, the OLEDs degrade faster at higher current densities (i.e. higher luminance). At present, even at relatively low luminance levels, the lifetime of OLEDs is insufficient to enter the lighting market. In addition, the differential aging of Red Green Blue (RGB) OLEDs causes color-shifts over time.

Thirdly, color mixing still represents a problem in OLEDs. One option is to make a patterned lamp with Red, Green and Blue monochromic OLEDs positioned laterally. However, efficient color mixing restrict the 'pattern'-sizes, and, thus, the complexity of the backplane. Although it is also possible to stack the monochromic OLEDs, this may be cost-ineffective. The problems mentioned above are well-known in the field of organic solid state lighting. US 7 108 392 B2 provides a description for a flat panel light emitting unit for use in a tiled flat panel lighting system. The unit comprises a light emitting region and at least two pairs of first and second electrical contacts which are accessible externally to the unit. In one embodiment of US 7 108 392 B2, several light emitting units are interconnected at an angle to each other, so that the light emitting units do not lie in a plane. However, direct or spot lighting is not possible with the shown or described embodiments.

EP 1 367 675 Bl shows a lighting apparatus with a single OLED unit on a socket. A plurality of OLED units is not shown.

There may be a need for a lighting device that may enable the realization of OLED-based lighting units with directed light distribution, high brightness, and color mixing. Furthermore, there may be a need for improving the overall system efficacy. SUMMARY OF THE INVENTION This need may be met by the subject matter according to the independent claim. Advantageous embodiments of the present invention are described by the dependent claims. Each individual OLED unit will be driven preferably at the minimum required voltage The invention allows the adjustment of the color point of the OLED lamp assembly, adding to this light sourcea degree of freedom for the user. The invention may be used to produce light sources using 3D spatial configurations of OLEDs units. For instance, one can put rigid OLED segments in non- planar geometries, or, according to an aspect of the invention, fold/bend/position OLEDs in 3D configurations.

The invention may advantageously enable to make a desired light distribution (beam shaping), high brightness light sources, and light sources with increased lifetime and improved color mixing. It may offer design freedom and enables integrated light sources. Further, the invention may reduce the well-known heat problem. According to an aspect of the invention, for color feedback, at least one detector can be placed inside the lighting device. This offers a cost-reduction with respect to the integration of detector(s) in the OLED substrate which can be provided for exclusive applications according to another aspect of the present invention. Although the invention is applicable for OLED technology in general, it is ideal to provide lights sources based on the proposed invention using OLED strips. According to a first aspect of the invention there is provided a lighting device, wherein the light emitting region of each OLED unit is of pre-determined size and shape, preferably strip-shaped, and is positioned at a pre-defined place of the illuminating area.

According to another aspect of the present invention, the OLED units have monochromic and/or white colors with different color temperatures. The shapes and colors of the OLED units can be used to tune color mixing, luminance, and directionality of the emitted light. According to a further aspect of the invention, the illuminating area forms a volume with an output surface area; wherein a cross-section of the output surface area is smaller than the light emitting region. The light output (luminance) depends on the shape of the structure, i.e. the output surface area versus the interior volume or illuminating area, i.e. the interior surface area, besides the intrinsic luminance offered by the light emitting regions of the OLED units.

By folding a large OLED surface into a volume with a small output surface area, a luminance higher than intrinsically possible with flat OLED units can be obtained. One OLED surface-to-output surface area-ratio can be in a range from 2 to 3 or 3 to 5. Similarly, one can reason that a suitable shape reduces the requirements on the intrinsic luminance of the OLEDs in order to obtain a certain output luminance, and therefore increases the device lifetime. Moreover, the requirements on the heat sink will be lower.

According to a further aspect of the invention there is provided an optical structure, preferably overlapping the cross-section, at least partially. The optical structure in the form of a lens or a translucent or opaque plate of glass is useful for controlling a desired or pre-defined beam shape and/or for a better color mixing result. According to a further aspect of the invention, for extending the general lifetime of the lighting device, there is provided that each OLED is driven at a pre- defined voltage, preferably at a minimum required voltage.

In a preferred embodiment of the invention, the lighting device further comprises at least one detector for detecting the color distribution of at least one OLED unit. Generally, the detector is placed in the volume formed by the illuminating area or, in other words, inside the lamp. Alternatively, the detector is one of the layers of the OLED unit.

In another embodiment of the present invention, only OLED units of the same color are connected in a serial connection. This embodiment provides to impress a different required minimum voltage for each assembly of OLED units with the same color and thus increases the lifetime of the OLED units. In the following, there will be described exemplary embodiments of the present invention. It has to be pointed out that of course any combination of features relating to different subject matters is also possible.

It has to be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments have been described with reference to device type claims, whereas another embodiment has been described with reference to a method type claim. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination of features belonging to one type of subject matter also any combination of features relating to different subject matters, in particular of features of the device type claims and of features of the method type claim, is considered to be disclosed with this application.

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodiment, but to which the invention is not limited.

On the basis of the above given and the following explanation of the method for driving a lighting device, a skilled person will be able to translate the steps of the method into a computer program for carrying out the method. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a plurality of OLED units; Figure 2 shows a schematic view of a side-section of a lighting device according to the invention; Figure 3 shows a lighting device in different views, made of faceted

OLED units;

Figure 4 shows a first luminous intensity distribution of an OLED spot lamp with OLEDs of the same brightness;

Figure 5 shows a second luminous intensity distribution of an

OLED spot lamp with OLEDs of different brightness; Figure 6 shows OLED lamps with and without an optical structure;

Figure 7 shows a linear OLED lamp and Figure 8 shows a tile made of OLED stripes.

DETAILED DESCRIPTION

The illustration in the drawing is schematic. It is noted that in different figures similar or identical elements are provided with the same reference signs.

Figure 1 shows a lighting device with OLED units 1. The OLED units 1 have monochromic colors or white OLEDs with different color temperatures. The shown four OLED units 1 are formed as OLED strips with the colors top down blue 2, red 3, green 4 and amber 5. These OLED units 1 can be folded, bend or positioned into different 3D shapes, such as a "spot lamp" shape, as shown in Fig. 2 and Fig. 3, or other lamp forms as shown in Fig. 6, Fig. 7 or Fig. 8. OLED units conventionally have a (metallic) reflector on the side opposite to that through which light is emitted. The shape of the light source (like that in Fig. 2) can be used to tune color mixing, luminance and directionality of the emitted light. Fig. 2 shows a lighting device 6 with one non-planar illuminating area 7.

Each OLED unit 1 of the lighting device 6 comprises a light emitting region 8 to 12 to form the illuminating area 7. The OLED units 1 with the regions 8 to 11 provide a wall 13 of the lighting device. The OLED unit 1 with region 12 provides the bottom 14 of the lighting device 6. Further, an optical structure 15 is shown overlapping a cross- section 16 of an output surface area 16 of the lighting device. The optical structure 15 could be used for beam manipulating. The output surface area 17 is more than three times smaller than the illuminating area 7. The red OLED units with light emitting regions 10 and 12 emit red light and are connected in a serial connection. The lighting device further comprises at least one detector 18 with a reflector 19. The detector 18 detects the color distribution of at least one OLED unit 1 and is placed in the volume formed by the illuminating area 7, in other words, inside the spot lamp.

Fig. 3 shows a lighting device, more precisely a spot lamp made of faceted and/or segments of OLED units on the reflector wall and bottom.

Fig. 4 and 5 shows different luminous intensity distributions of the spot lamp of Fig. 3. According to Fig. 4, all OLED units of the spot lamp have the same brightness. According to Fig. 5, an OLED unit with a high brightness is placed at the bottom 14, and lower brightness OLED units are placed as a reflector at the coniform wall 13 of the spot lamp.

Besides the discussed spot lamp embodiment, OLED units can be folded, bent, positioned into different shapes, such as a 'TL shape'(see Fig. 6a and 6b), a 'linear lamp shape' (see Fig. 7) or a 'tile shape' (see Fig. 8) and other shapes according to the invention. All embodiments of Fig. 6 to 8 provide OLED strips as OLED units 1. Fig. 6 b shows another optical structure 15 that overlaps a part of the output surface area 17. It should be noted that the term "comprising" does not exclude other elements or steps and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

CLAIMS:

1. A lighting device (6) with at least one non-planar illuminating area (7), the lighting device (6) comprising a plurality of organic light emitting diode (OLED) units (1); wherein each OLED unit (1) comprises a light emitting region (8-12) to form a part of the illuminating area (7).

2. The lighting device (6) of claim 1, wherein the light emitting region (8- 12) of each OLED unit (1) is of pre-determined size and shape, preferably strip-shaped, and is positioned at a pre-defined place of the illuminating area (7).

3. The lighting device (6) of claim 1, wherein OLED units (1) have monochromic and/or white colors (2-5) with different color temperatures.

4. The lighting device (6) of claim 1, wherein the illuminating area (7) forms a volume with the output surface area (17); wherein a cross-section (16) of the output surface area (17) is smaller than the light emitting regions (8-12).

5. The lighting device (6) of claim 1, further comprising an optical structure (15), wherein the optical structure (15) preferably overlaps the cross section (16), at least partially.

6. The lighting device (6) of claim 1, wherein light is continuously emittable over the illuminating area (7) of the lighting device (6).

7. The lighting device (6) of claim 1, wherein the OLED units (1) are folded, bent and/or arranged to form the illuminating area (7) with its light emitting regions (8-12).

8. The lighting device (6) of claim 1, wherein each OLED unit (1) is driven at a pre-defined voltage, preferably at a minimum required voltage.

9. The lighting device (6) of claim 1, further comprising at least one detector (18) detecting the color distribution of at least one OLED unit (1), wherein the detector (18) is one of the layers of the OLED unit (1), or is placed in the volume formed by the illuminating area (7).

10. The lighting device (6) of claim 1, wherein only OLED units (1) of the same color (2-5) are connected in a serial connection.

11. A method for driving a lighting device (6) of claim 1 , comprising the steps of detecting the color distribution of at least one OLED unit (1); o driving each OLED unit (1) at a pre-defined and/or changeable voltage, preferably at a minimum required voltage.