Patent Description:
Illuminating sections of a light guide with LEDs leads to unwanted light bleeding to other parts of the light guide. Furthermore, LEDs are placed at a large distance from the area that couples out light from this LED due to a spike in intensity close to the LED, in a range of <NUM>-<NUM>. In order to avoid this spike being visible in the lit area the distance is increased which results in unwanted areal increase of the overall system.

Most typical methods to achieve homogeneity is to either have a large spacing or to have a lot of light diffusion and/or absorption, such that the brightness of light emitting by the light guide is considerably reduced. For neighboring icons that are at close proximity, typical light guides have no solution to reduce the cross talk between these icons to a few % or even <NUM>%. As such, turning on one icon will lead to unwanted light emission from the other icon. Moreover, light guides can be shaped such that light is spread more effectively than would be obtained by only creating an emitting area far away from the LED, <NUM>-<NUM> at the least, where the light is more homogenous. But in some cases this distance is far too large. <CIT> concerns an illuminating device and display device having the same. The device includes a light-beam direction conversion portion with two reflecting surfaces provided in a light guide plate so that an end of each of the reflecting surfaces is brought into contact with a light input surface of the light guide plate. <CIT> concerns a planar light source unit. A transparent planar light leading plate is provided adjacent to a light source, and a hole is formed in the light leading plate at a position opposite to the light source. The hole has an inverted triangular shape, opposite sides of the hole are provided for reflecting light beams emitted from the light source. <CIT> concerns a surface lighting system and display device using same. A light diffusing hole (which is a through hole or a recessed hole) is formed at a light guide in a light guide plate.

The invention proposes an optical design feature that improves the homogeneity of the illuminating section and reduces the distance of the LED to this section.

In one example an air pocket is provided at the LED that provides refraction of light at the interface with the light guide.

The proposed design provides significant improvement to the homogeneity. Instead of using <NUM>-<NUM> spacing between the LED and light emitting section, a distance can be reduced to smaller than <NUM>, possibly even ~<NUM>. The light guide may contain a slight air pocket at the LED to provide refraction.

In this way light radiated by LEDs display is homogenous already close to the LED; where it is typically extremely inhomogeneous.

Sections of different optical density of the same material type are fused together to form the appropriate light guide shape. In this way the display has a transparent portion and a border portion that form a single integrated stack of two or more segmented and complementary shaped layers.

Light bleeding may be reduced by creating the light guide out of opaque and transparent sections formed by thermoplastic polyurethane (TPU) material that is fused into a single layer, e.g. by a high temperature step, such as high pressure lamination, and/or providing a cover layer. The light guide is provided as a closed section where light is trapped until it couples out. In the current invention the piece can be fully flexible, containing all elements for an efficient light guide and openings to create any appearance as is desired. This element can be easily integrated into or onto a 3D pre-formed rigid or semi-rigid element, prior or post forming.

By using multiple high temperature TPU's to form a single layer light can be fully blocked between neighboring sections, even with a spacing between transparent sections that is smaller than <NUM>.

In <FIG> an embodiment is shown wherein a display <NUM> is formed of light guides <NUM> and LED devices <NUM>. In more detail a light guide <NUM> is shown having a incoupling face <NUM> for receiving one or more LED devices <NUM> having a principal light emitting direction for defining a light path traveling away from the incoupling face <NUM> to an outcoupling face <NUM> defining the icon, slit or picture.

The light guide <NUM> has side border portions <NUM> reflecting and/or blocking light from the LED <NUM> in a direction sideways from the principal light emitting direction L.

In more detail <FIG> shows that the light guide <NUM> is provided with a transparent portion <NUM> comprising a light homogenization zone <NUM> with an apex facing the incoupling face <NUM> extending along the LED device <NUM>. The shape of the light homogenization zone is such that a central apex is formed and side portions with interfaces oriented away from the LED device. The homogenization zone <NUM> is close to the side face <NUM>, in particular has a distance (measured from the apex) less than a length of the LED device <NUM> measured alongside its light emitting face. The homogenization zone <NUM> extends along the light emitting direction L over about a length of the LED device <NUM>. In the example of <FIG> the homogenization structure <NUM> is a single triangular cavity; although it could be multiple cavities forming a triangular homogenization structure <NUM> e.g. having one or more triangular or rounded triangular shapes. The edges of the homogenization structure <NUM> may further be roughened to improve light diffusion and light mixing in case of using RGB side LEDs.

<FIG> shows that the side border portions are provided by a non-transparent material <NUM> that is formed contiguously and complementary to the light guide <NUM>. White TPU may be used as substrate <NUM> onto which the electrical design is printed. Alternatively, the TPU may have a white liner or the substrate may be a PEN substrate, with a white coating. Curing of this ink on this TPU is easy due to its high processing temperature of <NUM>. The white colour serves to allow reflection at the substrate interface of the generated light originating from LEDs bonded to the printed circuit. Side emitting LEDs <NUM> may be are bonded onto the Ag printed circuit with a height preferable < <NUM>, more preferably < <NUM>, etc etc. High power LEDs are preferred (output > <NUM> nits). The matrix <NUM> is may also be formed by a white TPU from which sections are cut by laser or another method. The matrix <NUM> may also be black, or a combination of black and white, depending on the design. A black TPU would serve to block light as it is fully absorbing, non- transparent. This would lead to loss of the power efficiency of the optical system but on the other hand certifies unwanted light leakage is avoided and thus lighting areas defined sharply.

When combined as in <FIG>, the display <NUM> has transparent portion <NUM> and the border portion <NUM> form a single integrated stack <NUM> of two or more segmented and complementary shaped layers. Combination can be done by separately cutting out the complementary structures, and overlaying both structures to form a single layer. After overlaying, lamination, e.g. by a cover layer (see <FIG>) can be provided to preserve an integral structure for the device <NUM>.

<FIG> shows that the light guide <NUM> is not square, or rectangular, but contains shapes that spread the light further to circumvent reduced light intensities on sides <NUM> compared to the central part of the outcoupling face <NUM>. LEDs strongly couple out at close distance, which makes it difficult to achieve homogeneous emission at this distance, and over larger areas. The light guide may be provided with a patterning on the incoupling face at the location of in-coupling to spread the light. Thus, the incoupling face may be non flat to include a cavity between the incoupling face and the LED device.

For example, the light guide <NUM> contains an air pocket <NUM> at the LED light emitting surface <NUM> that provides refraction of light at the interface with the light guide <NUM>. By these air pockets <NUM>, the length D of the LED can be limited relative to the width of the outcoupling face <NUM>, while still having its sides homogenously illuminated. A typical ratio may be a width of the outcoupling face of about <NUM>-<NUM>% of the length D of the LED. The air pockets are triangular in shape, possibly with rounded curves and a roughening on a base side of the triangular of rounded triangular shapes, that prevents color splitting. The opposite side of the incoupling face may be likewise provided with a refractive structure.

<FIG> show optical responses for some homogenization zones of various structures in light guide <NUM>. In <FIG> a base optical response is given for the light guide <NUM>, where no homogenization structure is provided. It is shown that the outcoupling face shows inhomogeneity especially near the center. In <FIG> a homogenization zone <NUM> is provided by a single cavity in the transparent portion <NUM>. It is shown that the homogeneity is improved especially towards the sides. In <FIG> an excellent homogeneity is shown for a homogenization structure in the form of perfect lenses included in the homogenization zone. This embodiment is difficult to manufacture.

<FIG> shows an exemplary top view of an icon display <NUM> on the outcoupling top face <NUM> and gradiented bottom face <NUM> with gradient pattern <NUM>. The gradient pattern is formed in a reflective surface, thus partly reflecting the light emitted from LED <NUM>. The reflective surface is usually provided by a light reflecting coating with a gradiented pattern. The pattern has a decreasing reflection away from the incoupling face <NUM>. In this example, the gradiented light reflecting pattern extends underside the outcoupling face <NUM>.

It is shown that the side faces of the LED incoupling face <NUM> and/or homogenization zone <NUM> have a roughening to prevent color splitting e.g. when using RGB LEDs. In this example, the incoupling face <NUM> receives a LED devices is a side face of a planar transparent layer. LED device <NUM> is an upstanding LEDs with a thickness corresponding to the transparent layer of light guide <NUM>. The light guide sections <NUM> may be cut from a transparent or hazy TPU and are positioned inside the border portions <NUM> of the white light guide. Separately a cover foil (PET, PEN, TPU, PVB, PC or other), optionally hazy or modified to provide light diffusion, can be printed with a reflective coating, e.g. dielectric inks with openings that allow the light to leave the light guide. Alternatively, the cover layer may be a printed coating, e.g. a coating on a TPU layer. This white dielectric reflective coating can be a cover foil aimed towards the TPU during the lamination assembly step of the transparent portion and border portion. On top of the cover foil further layers may be printed (dielectric, anti- scratch or other). Light guiding and out-coupling can be improved by applying an engraving pattern on the interior and or exterior, but may also be incorporated on the inside. This pattern may be random, but may also periodic in nature. For instance, good results can be obtained with engravings of ~<NUM> microns lines with a periodicity of <NUM> microns that were lasered into PEN and PC with a CO2 laser. In the shown example the light guide is formed by a transparent planar layer of <NUM> thickness and the incoupling face is positioned at a distance of about <NUM>-<NUM> away from the outcoupling face. The homogenization zone <NUM> is provided in a temperature resistant material so that at higher temperatures it's shape is not changed significantly.

<FIG> shows exemplary layer stacks where it is shown that the LED <NUM> is an LED that couples from the side of the light guide <NUM>. The stack <NUM> is not to scale, but merely serves to illustrate a number of optional layers. The central light guide layer <NUM> is segmented from a transparent PMMA. Layer <NUM> is the PMMA interface that is modified with a gradient engraving for enhanced light guiding. The engraved cover layer <NUM> is placed in contact with a densite white foil <NUM> that is laminated onto a bottom decorative foil <NUM>. The light guide stack is optically closed by a white coating <NUM>' and finished by scatter foil <NUM> and top foil <NUM>'.

<FIG> shows a variant wherein the side border portions and transparent portion are manufactured by injection moulding. In this example, a cover layer <NUM> is provided e.g. by a coated polycarbonate (PC) transparent front foil <NUM> of e.g. <NUM> micron. A reflective white surface <NUM> is provided by a light reflecting coating with a gradient pattern; thus covering the segmented transparent light guide stack G on the top side with a gradient pattern. The sides 104a of the reflective white coating <NUM> may be terminated by a black coating blocking light guiding in the cover foil. The PC cover foil <NUM> is further provided with a top coating 104b, 104w that is a stack of white and black ink- black on the outside. The coating <NUM> leaves the icon picture free so that the transparent polycarbonate layer shows the icon when illuminated. On the backside of the cover layer <NUM> the light guide stack G is formed by segmented light side border portions <NUM> provided by a non-transparent material that is formed contiguously and complementary to transparent portions <NUM>. The light guide <NUM> thus forms a single integrated stack of two or more segmented and complementary shaped layers <NUM> and a cover layer <NUM>.

This has as a consequence that the functional layers are provided as a stack, on top of the injected moulding part <NUM>, which serves to provide a suitable thickness. a backside layer on top of a back substrate may be provided by a TPU layer, but can also be injection moulded. Layer <NUM> is simultaneously injection moulded with complementary shaped layers <NUM>. By altering the shape from the mould at this side, the shape of layer <NUM> can be non flat, making it possible to create a non-flat reflecting surface, thereby providing potential beneficial optical effects. Layer <NUM> is a single or combination of functional and non-functional foils, being flat or containing contacts for via's or slots for backside contacting that are protected during the moulding process. It can also be imagined that functionalities, in the form of chips, sensors or devices, may be added to this part, by which the front part may be contacted or powered. Also top emitting LEDs can be added to layer <NUM>. The stack in <FIG> would be altered to injection moulded white shapes <NUM>, but having a white reflecting foil with printed circuit and components as layer <NUM>.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments.

Claim 1:
A display (<NUM>) having a display area for displaying an illuminated icon (<NUM>) or picture; the display comprising:
- a light guide having an incoupling face (<NUM>) for receiving one or more LED devices (<NUM>) having a principal light emitting direction (L) for defining a light path traveling away from the incoupling face to an outcoupling face (<NUM>) where the light couples out, the outcoupling face defining the icon or picture;
- the light guide having side border portions (<NUM>) blocking light from the one or more LED devices (<NUM>) in a direction sideways from the principal light emitting direction;
- the light guide being provided with a transparent portion (<NUM>) comprising a light homogenization zone (<NUM>) with an apex facing the incoupling face (<NUM>) extending along the one or more LED devices (<NUM>); said homogenization zone being distanced from the incoupling face by a distance measured from the apex less than a length of the one or more LED devices (<NUM>) as measured alongside its light emitting face and said homogenization zone (<NUM>) extending along the light emitting direction over a length of the one or more LED devices (<NUM>),
wherein the transparent portion (<NUM>) and the side border portions (<NUM>) are formed of two or more segmented and complementary shaped layers of different optical density and formed of the same material type that are fused to form a single layer (<NUM>).