FIELD OF THE INVENTION

The invention relates to a lighting device for use in an automotive environment for generating a homogenous light distribution. The lighting device comprises a substrate in which quantum dots are comprised, and where the quantum dots are excitable by electronic or optical means.

BACKGROUND OF THE INVENTION

In modern day vehicle lighting devices are not only used for illuminating the street, or for illuminating the passenger cabin, but also in the exterior rear view mirrors, e.g. for visually indicating a blind spot to the driver, or as additional direction indicators supplementing the direction indicators at the front and rear side of the vehicle. Also, in the automotive industry the visual appearance of lighting systems becomes ever more important.

The lighting devices that are used in the rear view mirrors are commonly arranged in a manner so that they radiate light away from the mirror. The lighting devices that are, for example, used as additional directional indicators are usually installed in the mirrors such that the transparent light cover of the lighting device follows the shape of the exterior surface of the exterior rear view mirror. Most of the exterior rear view mirrors that are used today are not perfectly square boxes, but rather have non-planar, i.e. three dimensional geometries. Therefore, the lighting devices must also have a corresponding three dimensional geometry. The transparent light cover is usually arranged on a place on or in the mirror which faces the direction of travel. The International regulations require only a certain intensity to the rear in the angular region between 5° and 60° horizontally, and -15° to 15 vertically, where 0° is facing horizontally opposite to the direction of travel. Also, the cover might extend around the whole side of the exterior rear view mirror to achieve a better illumination and visibility of the lighting devices, for example also from a position lateral to the vehicle actuator and/or the rear view mirror. For example, US 6,152,587 A shows and describes an exterior rear view mirror having auxiliary lighting devices installed. Most prior art lighting devices use LED technology, or use conventional light bulbs. However, these prior art lighting devices emit light in a rather non-uniform manner. Also, the lighting devices that are used in the prior art, for example OLEDs (organic LEDs) have limited luminance, brightness and durability.

Therefore, the invention aims at providing an improved lighting device for generating a homogenous light distribution which is also more durable and has a higher luminance.

SUMMARY OF THE INVENTION

The invention provides a lighting device installed in a vehicle for optimized light distribution, the lighting device comprises a substrate comprising quantum dots which are adapted to emit light. The substrate could be any transparent and/or translucent dielectric material such as for example Polymethyl Methacrylate, PMMA, or Polycarbonate. Also, silicone or germanium could be used as substrate material or the substrate could be a composite material having dielectric properties and which could be based on PMMA or Polycarbonate. The substrate can essentially extend over a large area while one dimension can be just a few micrometers. The substrate comprises quantum dots, also referred to as semiconductor nanocrystals. Essentially, these semiconductor nanocrystals are material particles that have at least one dimension smaller than 100 nanometers. Quantum dots have the property that they start to emit light at specific wavelengths, i.e. colors when they are being energized. For example, quantum dots convert light to longer wavelengths and scatter it out in a homogenous manner. Therefore, quantum dots can be incorporated into the substrate. The dimension of the quantum dots can be chosen depending on the desired wavelength.

Since quantum dots are both photo-active and electro-active, these dots can be energized with light or electricity. There are different suitable processes how the quantum dots can be incorporated into the substrate. For example, quantum dots can be integrated by growing a semiconductor heterostructure in the substrate. The quantum dots may be alternatively or in addition further assembled to the substrate by phase separation and/or contact printing. In the substrate, the quantum dots are densely packed and are essentially uniform in size and shape so that a homogenous light distribution can be achieved. Moreover, the substrate may contain quantum dots only at certain positions in order to generate a customized luminance pattern. In addition, a change of size and/or shape and/or density of the quantum dots can be used to generate a light output varying in color and/or brightness.

In one example, the substrate has a shape that is essentially non-planar. Here, the term ^on- planar" is used to refer to any shape in which the substrate material is not being disposed in one spatial plane. Advantageously, the substrate can be shaped to correspond to the geometry of the component on which it will be arranged. For example, the substrate could be curved so that the geometry of the substrate corresponds to the curvature of that part of the rear view mirror on which it will be arranged.

In another example, the substrate is a flexible substrate. Here, the term„flexible" is used to refer to a substrate that is bendable under the influence of an external force, i.e. the shape of the substrate can be altered under the influence of the external force without destroying and/or negatively influencing the integrity of the substrate. Since silicone is usually bridle, strained silicone which has larger spaces between its atoms could be used as substrate. Advantageously, this allows adjusting the shape of the substrate during mounting the lighting device to the external side mirror without doing any damage to the substrate.

In yet another example, the lighting device comprises a light source that is adapted to excite the quantum dots that are comprised within the substrate. The light source might be arranged anywhere at the substrate in such a manner that light from the light source can propagate directly into the substrate to excite the quantum dots comprised within the substrate. For example, the light of the light source might propagate in a waveguide-like structure inside the substrate, or the light might simply illuminate the surface of the substrate where the surface is not covered with the reflective layer. The light from the light source excites the quantum dots which in turn start to radiate light from the surfaces that are not covered by the reflecting layer. The quantum dots radiate light for as long as the light source is switched on. Advantageously, by absorbing and emitting light in the above described manner, the quantum dots can be used for converting the wavelength of the exciting light. For example, the quantum dots might absorb blue light or UV light from a blue LED or from a UV LED, respectively, but might emit orange light themselves. For example, the light source might be a LED lamp arranged somewhere at the substrate.

In one example, the substrate is comprised by the light source and/or arranged in a housing of the light source. Here, the term "housing" refers to the protective enclosure or casing of the light source that might consist of transparent and/or translucent material and which is essentially designed to protect the actual light source from adverse outside influences such as mechanical influences. The substrate might be arranged anywhere within the housing, e.g. within the inside perimeter of the housing and/or within the housing material itself. For example, in case the light source is a LED lamp then the substrate could be arranged within the casing of the LED, and/or on the lens of the LED and/or inside the material that is used for the lens and/or the casing.

Alternatively, in another example, the light source is part of the substrate comprising the quantum dots. Here, the light source might be a LED lamp arranged on the same substrate that also comprises the quantum dots. For example, this can be done by integrating the LED lamp in the substrate material. Advantageously, the dimensions of the lighting device can be greatly reduced. In another example, the lighting device comprises a power source that is adapted to excite the quantum dots that are comprised within the substrate. The power source might be a conventional voltage supply that is adapted to apply a voltage between the reflecting layer and the transparent layer. The supply voltage might range from one volt up to several hundreds of volts. For example, the voltage might be in the region of 1 to 20 volts or 1 to 50 volts.

In yet another example, the lighting device further comprises a reflecting layer arranged on, especially attached to the bottom side of the substrate; and/or a transparent layer arranged on, especially attached to the top side of the substrate. Here, the term "bottom side" refers to the side of the substrate that faces the component to which the reflecting layer is attached to, such as the casing of an exterior rear view mirror. The reflective layer could be, for example, a thin metalized foil that is attached to the bottom side of the substrate. Advantageously, due to the presence of the reflective layer, the light loss of the lighting device can be greatly reduced.

The transparent layer is attached opposite the reflective layer on the "top side" of the substrate. Here, the term "top side" refers to the side of the substrate that points towards the environment, or refers to the side that points away from the component on or in which it is installed. For example, the transparent layer can consist of a thin layer of plastic material which is attached to the substrate. For example, the transparent layer could be attached to the substrate by means of an adhesive, or by some other appropriate means. Advantageously, the transparent layer covers the substrate and allows the light beams which originate from the quantum dots to propagate therethrough.

In another example, the reflecting layer and/or the transparent layer have electroconductive properties, i.e. they are being conductive. For example, the reflecting layer and the transparent layer could be composed of a conductive plastic material so that these layers can conduct electricity from the power source to the substrate. In order to achieve a difference in charge between the two sides of the substrate, the two conducting layers are insulated from each other. For example, this can be done by adding a barrier layer of non-conductive material, e.g. non- conductive plastic material between the two conductive layers. Alternatively, a spatial gap can be left between the two conductive layers to insulate the two conductive layers from each other.

The invention also relates to a rear view mirror comprising the lighting device according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The following schematic drawings show aspects of the invention for improving the understanding of the invention in connection with some exemplary illustrations, wherein

Figure 1 shows a schematic cross sectional view of a lighting device according to a first embodiment of the invention wherein the quantum dots which are comprised within the substrate are excitable by means of a light source;

Figure 2 shows a schematic cross sectional view of a lighting device according to a second embodiment of the invention wherein the quantum dots which are comprised within the substrate are excitable by means of a power source; and

Figure 3 shows a view of a lighting device according to the invention which is installed in a rear view mirror of a vehicle. DETAILED DESCRIPTION

The lighting device 1 according to a first embodiment of the invention and illustrated in figure 1 comprises a substrate 2 which comprises quantum dots 3. In figure 1 quantum dot 3 a is exemplarily shown to account for all quantum dots 3 in the substrate 2. In the example that is shown in figure 1 , the substrate 2 is bent to correspond to the surface of the component to which the lighting device 1 will be attached to. However, the skilled person would know that the substrate 2 could be also planar, i.e. the substrate 2 could be flat, so that it would extend substantially in just two dimensions while having a height of only a few micrometers itself. On the bottom side of the substrate 2, a reflective layer 4 is arranged to reflect the light originating from the quantum dots 3 towards the top side of the substrate 2. To the latter side a transparent layer 5 is attached which allows the light to pass through. However, the skilled person would understand that the two layers 4, 5 are not necessarily required for the proper functioning of the lighting device 1. Also, the skilled person would know that the reflecting layer 4 could be also arranged on the top side and the transparent layer 5 could be arranged on the bottom side, respectively. This is because the quantum dots 3 which are embedded in the substrate 2 will emit light in all directions once they get excited. In the here shown example, the quantum dots 3 can be excited by means of a light source 6 that is located at a location close to the substrate 2. Alternatively, the light source 6 could be also located on and/or within the substrate 2 (not shown in the figure).

Figure 2 shows a schematic cross sectional view of a lighting device 1 ' according to a second embodiment of the invention. Elements of the lighting device 1 ' correspond to elements of the lighting device 1, hence the same reference number is used, however having one apostrophe. The quantum dots 3' which are comprised within the substrate 2' are excitable by means of a, especially electrical, power source 7'. In the here shown example, both the reflecting layer 4' and the transparent layer 5' are composed of conductive material so that a voltage can be applied across the substrate 2' by connecting the two layers 4', 5' to the power source 7' as shown in figure 2. Since both layers 4', 5' are attached to the surface of the substrate 4', the voltage can be applied equally over the entire surface of the substrate 2'. A barrier layer of non-conductive material 8' is used to separate the two layers 4', 5' from each other. However, the skilled person would know alternative ways how the power source 7' could be connected to the substrate 2'. For example, appropriate electroconductive structures could be embedded in the substrate 2'. In the latter case layers 4', 5' would not need to possess any electroconductive properties. Thus, layers 4', 5' would not be required for the functioning of the lighting device 1 ' at all.

Figure 3 illustrates a lighting device 1 according to the invention which is installed in a rear view mirror 9 of a vehicle. Also, lighting device maybe installed in the rear view mirror 9. In the shown example, the lighting device 1, is used as an auxiliary direction indicator which is located in the rear view mirror 9 of the vehicle. As illustrated in the figure, the lighting device 1, 1 ' has a three dimensional shape that corresponds to the shape of the rear view mirror 9.

The features disclosed in the claims, the specification, and the drawings maybe essential for different embodiments of the claimed invention, both separately or in any combination with each other.

Reference Signs , 1 ' lighting device

, 2' substrate

, 3' quantum dots

a, 3a' quantum dot

, 4' reflecting layer

, 5' transparent layer

light source

' power source

' non-conductive material

rear view mirror