Light guide device

Abstract

A light guide device and a method of manufacturing a light guide device is disclosed. The light device comprises a first film and a second film. The light guide device further comprises a frame config

Description

Light guide devices typically combine a light guide with a light source, enabling efficient light distribution for a wide range of applications. Light guide devices are particularly useful in applications requiring uniform illumination, such as display backlighting. A light guide device operates in the following manner. The light guide receives light emitted by the light source and guides it through the light guide. This process relies on the principle of total internal reflection, where light is confined within the light guide due to the angle of incidence and differences in the refractive indices between the materials. When the light is directed to a wall of the light guide at an angle greater than the critical angle, the light is reflected off the light guide's walls rather than escaping. In this way, the light travels through the light guide device via multiple reflections off the walls of the light guide. The light is directed out of the device through an output surface, and often further optical features are required to control the direction and spread of the light output from the light guide device. Such optical features may include reflective coatings, diffusers, surface patterns, prisms and lenses which can be used individually or in combination to optimise the direction, intensity, and or spread of the emitted light. Typically, the light source used within a light guide device is a light-emitting diode, though other types of light sources may also be used depending on the specific requirements of the application. The light guides are generally composed of transmissive optical materials, such as polymers or glass. Polymers are more commonly used in the art due to their flexibility, ease of manufacturing, and cost-effectiveness when compared to glass, making them suitable for applications in compact and portable devices, including displays, backlighting, and automotive lighting. Despite the well-known advantages of polymer based light guides devices, there is an ongoing need for optimised solutions that reduce costs, reduce weight, and improve the overall performance of the light guide device. As display technology advances, the demand for light guide devices that are both efficient and affordable continues to rise. Furthermore, the environmental impact of employing polymer materials is a growing concern and as such there is an increasing demand for alternative light guide devices that combine sustainability with cost-effectiveness. Such alternative light guide devices must still meet essential design requirements, such as providing uniform light distribution and maintaining thin profiles to remain suitable for use within a wide variety of applications. As a result, there is a significant interest in the development of light guide devices that provide sustainability and cost-effectiveness, without compromising performance. Examples of systems and methods known in the art include Japanese Patent Publication Number JPH 07191221 A, US Patent Number US 7,226,200 B2, US Patent Publication Number US2010 / 0139165 A1, US Patent Number Publication Number US 2015 / 0131317 A1 and Korean Patent Publication Number KR 20160089686 A. Summary of Invention It is an object of an aspect of the present invention to provide a light guide that obviates or mitigates one or more drawbacks or disadvantages of the prior art. Further aims and objects of the invention will become apparent from reading the following description. According to a first aspect of the invention there is provided a light guide device comprising: a first film and a second film; a frame configured to maintain a predetermined separation distance between the first film and the second film thus providing an interior volume between the first film and the second film; and a light source located within the interior volume; wherein the first film comprises a first array of prisms and is transmissive at a wavelength of the light emitted by the light source; and wherein the first film and the second film are configured to redirect the light emitted by the light source within the interior volume. The light guide device of the present invention offers several advantages. The light guide device reduces the amount of material required to manufacture the device, by replacing the usual solid polymer light guide with a light guide device comprising an interior volume between a first and a second film. The first film and the second film are separated by a frame, which provides structural support and maintains a predetermined separation distance between the first film and the second film. The incorporation of an interior volume within the light guide device reduces the amount of material and plastic required, leading to several advantages over known prior art devices. The reduction in materials leads to a light guide device that is lighter and has a lower associated cost. Furthermore, the reduced materials and plastic also provides a light guide device with improved sustainability, addressing a growing concern across all industries. Preferably the first film comprises an output surface of the light guide device. The second film may comprise a reflective surface which is reflective at the wavelength of the light emitted by the light source. The reflective surface may comprise a specular reflector. Most preferably the second film comprises a second array of prisms and is transmissive at the wavelength of the light emitted by the light source. Preferably the interior volume is bordered by one or more reflectors. Preferably the reflectors are non-specular reflectors. The one or more reflectors may be attached to the frame. Optionally, one or more edges of the frame may comprise a reflective coating. Preferably the light guide device comprises one or more reflective features located on the first film and or the second film. The reflective features may comprise a non-specular reflective feature, for example a white printed ink dot. The reflective features act to reduce hot spots and recycle light that would otherwise not be coupled into the light guide. Preferably the light guide device comprises one or more extraction features located on the first and or second film. The extraction features may comprise a non-specular reflective feature or a white printed dot pattern. The extraction features may be spatially distributed across the second film. The extraction features extract light out of the light guide device through the output surface. The first film and or second film may comprise a thickness in the range of 0.1 mm to 1 mm. Preferably, the first film and or second film comprise a thickness of 0.5 mm. Most preferably, each prism within the first array of prisms and or second array of prisms comprise a base that is oriented towards the interior volume, and an apex that comprises the output surface of the light guide device. Preferably the first and second array of prisms comprise an array of triangular prisms. Preferably, the first array of prisms and or the second array of prisms comprise a height of 0.17 mm, and a centre to centre spacing of 0.35 mm between adjacent prisms. The frame may comprise a thickness in the range of 1 to 10 mm. The frame may comprise a thickness in the range of 1 to 5 mm. Preferably the frame comprises a thickness of 3 mm. The predetermined separation distance between the first film and the second film may comprise a value in the range of 1 mm to 5 mm. Preferably the predetermined separation distance between the first film and the second film is 3 mm. Preferably the interior volume comprises air. Optionally the interior volume may comprise nitrogen. The frame may be configured to form two or more interior subvolumes between the first film and the second film, wherein the frame separates adjacent interior subvolumes. The light guide device may comprise two or more light sources. Preferably, at least one of the light sources is located within each interior subvolume. Preferably the frame is configured to form a regular two dimensional array of two or more interior subvolumes. Alternatively, the frame is configured to form an irregular two dimensional array of two or more interior subvolumes. Optionally the frame is configured to form a one dimensional array of two or more interior subvolumes. Providing an array of two or more interior subvolumes between the first and second film, each comprising a light source, results in a light guide device with individual light guide units. These individual light guide units provide for a modular configuration that allows for greater flexibility in the design and size of the light guide device. The array of two or more interior subvolumes provided by the frame can be adapted to a variety of sizes and applications. Preferably the frame comprises a cuboid structure. Optionally the frame comprises a hexagonal or honeycomb structure. Optionally, the frame may be non-planer. The frame may comprise a plastic material. Preferably the light source comprises a light emitting diode and a printed circuit board for controlling the light emitting diode. Preferably the printed circuit board is attached to at least one edge of the frame. According to a second aspect of the invention, there is a method of manufacturing a light guide device comprising: providing a first film and a second film; arranging a frame to maintain a predetermined separation distance between the first film and the second film such that an interior volume is provided between the first film and the second film; locating a light source within the interior volume; configuring the first film to comprise a first array of prims, wherein the first film is transmissive at the wavelength of the light emitted by the light source; and configuring the first film and the second film to redirect the light emitted by the light source within the interior volume. Embodiments of the second aspect of the present invention may comprise features to implement the preferred or optional features of the first aspect of the present invention or vice versa. Brief Description of Drawings There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which: Figure 1 presents (a) a side view and (b) a front view of a light guide device in accordance with an embodiment of the present invention; Figure 2 presents a top view of a light guide device in accordance with an alternative embodiment of the present invention; Figure 3 presents (a) a side view and (b) a front view of a light guide device in accordance with an alternative embodiment of the present invention; and Figure 4 presents (a) a side view and (b) a top view of a light guide device in accordance with an alternative embodiment of the present invention. In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawings are not necessarily to scale, and the proportions of certain parts have been exaggerated to better illustrate details and features of embodiments of the invention. Detailed Description Figure 1 presents (a) a side view and (b) a front view of a light guide device, as generally depicted by the reference numeral 1, in accordance with an embodiment of the present invention. Axes are included for reference, where the height of the light guide device 1 is along the z axis, the length is along the y axis, and the width is along the x axis. The light guide device 1 comprises a first film 2 and a second film 3, where the first film 2 defines the output surface 4 of the light guide device 1. The first film 2 of the light guide device 1 is transmissive at the wavelength of light emitted by a light source 7 and comprises a first array of prisms 2a to guide light within the light guide device 1. The second film 3 is reflective at the wavelength of the light emitted by the light source 7. In particular, the second film 3 comprises a specular reflective surface which acts to confine and guide light within the light guide device 1. The light guide device 1 further comprises a frame 5 to provide structural support for the first film 2 and the second film 3. It should be noted that in Figures 1 (a) and 1 (b), a side section and an end section, respectively, of the frame 5 have been omitted to assist with clarity of understanding of the described embodiment. The frame 5 is also configured to maintain a predetermined separation distance between the first film 2 and the second 3 film. Furthermore, the frame 5 creates an interior volume 6 between the first film 2 and the second film 3. In the present embodiment, the interior volume comprises air. However, gases, such as nitrogen (N2), may be used as an alternative. The frame 5 of Figure 1 comprises a cuboid structure and is made from plastic. However, the frame 5 may comprise any appropriate alternative structure e.g. a hexagonal structure, as long as it provides the required structural support and maintains the fixed distance between the first film 2 and the second film 3. The frame may also be constructed from alternative materials. A light source 7 is provided within the interior volume 6 of the light guide device 1. The light source 7 is configured to emit light into the interior volume 6. In Figure 1, the light source 7 comprises a light emitting diode (LED) 8 and a printed circuit board (PCB) 9 for controlling the operation of the LED 8. The PCB 9 is fixed or attached to the frame 5 along at least one edge of the frame 5. In Figure 1, the first 2 and second 3 films each comprise a thickness of about 0.5 mm, along the z axis. The thickness of the first 2 and the second 3 films along the z axis could alternatively have a value in the range of 0.1 mm to 1 mm. Due to the thin profile of the first 2 and the second 3 films, the frame 5 is required to maintain the fixed separation distance between them. The first array of prisms 2a of the first film 2 comprises a series of prisms designed to reflect light within the light guide device 1. While the prisms of Figure 1 are triangular in shape, alternative prismatic forms (e.g. trapezoidal prisms) may alternatively be used. The first array of prisms 2a extend along the length (i.e. the y axis) of the light guide device 1. In Figure 1, the orientation of the first array of prisms 2a ensures that the base of the prisms are oriented towards the interior volume 6, while the apex of the prisms comprise the output surface 4 of the light guide device 1. The specific orientation of the first array of prisms 2a is essential for achieving the desired light reflection within the interior volume 6 of the light guide device 1. As stated above, the first film 2 comprises a thickness of 0.5 mm. The prims of the first array of prisms 2a comprise a height of 0.17 mm and a centre to centre spacing of 0.35 mm between adjacent prisms. Note that alternative dimensions for the first array of prisms 2a can be provided depending on the specific requirements. The frame 5 of the light guide device 1 comprises a height of 3 mm, along the z axis. The height of the frame 5 also determines the separation between the first 2 and second 3 films, and hence the size of the interior volume 6 within the light guide device 1. Alternatively, the frame 5 height could be a value in the range of 1 mm to 10 mm. However, for many applications, a thinner light guide device 1 is preferred to enhance compactness and efficiency and minimise the weight of the light guide device 1. For the light guide device 1 depicted in Figure 1, the overall thickness of the entire device is approximately 4 mm (along the z-axis). The overall thickness for the light guide device 1 depends on the specific structure of the frame 5, the selected height for the frame 5 and the thickness of the first 2 and second 3 films. When the light guide device 1 is operational, the light source 7 emits light and the emitted light enters the interior volume 6 of the light guide device 1. Light that is directed towards the first 2 and or second 3 films at various angles may be reflected off their surfaces, guiding the light within the interior volume 6 of light guide device 1. The angle of incidence of the light on the first film 2 determines whether light will undergo total internal reflection (TIR) or exit through the output surface 4. If the angle of incidence is not suitable for TIR, the light is transmitted through the output surface 4. In this way the first film 2 and the second film 3 confine and redirect the light within the interior volume 6 of the light guide device 1. The light guide device 1 of the present invention offers several advantages over those known in the art. In particular, the present invention uses fewer materials compared to known light guide devices, resulting in a more cost efficient solution. This is due to the design of the light guide device 1, which uses thin films of material separated by an interior volume. The reduction in the materials required for the light guide device not only lowers production costs but also reduces the environmental impact of the light guide device. Furthermore, using less materials significantly reduces the weight of the light guide device compared to traditional light guides. The light guide device 1 still has a similar lightguiding function to polymer light guides, where the above mentioned advantages do not adversely affect the efficiency or performance of the light guide device 1. The light guide device 1 of Figure 1 provides a thin profile (e.g. <4mm), which allows for a compact device, while providing a cost-effective and sustainable solution for lighting and display technologies. Figure 2 presents a top view a light guide device 10 in accordance with an alternative embodiment of the present invention. For ease of understanding, the first film 2 has been omitted to assist with clarity of understanding of the described embodiment. The light guide device 10, is similar to the light guide device 1 of Figure 1, and comprises a first film 2, a second film 3, and a light source 7 located within an interior volume 6 of the light guide device 10. The light guide device 10 of Figure 2 however comprises a reflective frame 11, i.e. a reflective frame 11 comprising a reflective surface at the wavelength of the light emitted by the light source 7. Therefore, in addition to serving as a structural component that maintains the separation distance between the first 2 and the second 3 films, the reflective frame 11 also enhances the efficiency of the light guide device 10. Specifically, light that strikes the reflective frame 11 is reflected back into the interior volume 6, rather than escaping the light guide device 10, helping to keep more light confined within the light guide device 10 and reducing losses. In order to increase the internal scattering of the light, and hence the uniformity of light emitted from the output surface 4, it is preferable for the reflective frame 11 to comprise non-specular reflective surfaces. In Figure 2, the reflective frame 11 comprises four reflective edges, effectively bordering the interior volume 6 with four reflective surfaces. However, the number of reflective edges of the frame can be adjusted depending on design requirements. The reflective frame 11 could have as few as one reflective side, or all sides can feature reflective surfaces. Alternatively, the reflective frame 11 itself may be non-reflective (as shown in Figure 1) with a separate reflective element positioned along one or more sides of the frame to achieve similar optical effects e.g. a reflective coating. Figure 3 presents (a) a side view and (b) a front view of a light guide device 12 in accordance with an alternative embodiment of the present invention. It should again be noted that in Figures 3(a) and 3(b), a side section and an end section, respectively, of the reflective frame 11 have been omitted to assist with clarity of understanding of the described embodiment. The light guide device 12 again comprises a first film 2, a second film 3, a frame 11 and a light source 7 located within the interior volume 6 of the light guide device 12. As shown in Figure 3(b), both the first 2 and second 3 films are transmissive at the wavelength of the light emitted by the light source 7. Both the first 2 and second 3 films also comprise an array of prisms, 2a and 3a, to guide light within the light guide device 12. Providing the second array of prisms 3a on the second film 3 acts to reflect and guide the light emitted by the light source 7, providing better confinement within the light guide device 12. This improves the overall efficiency of the light guide device 12. The light guide device further comprises a reflective feature 13 positioned on the first film 2 and an extraction feature 14 positioned on the second film 3, where both the reflective feature and the extraction feature are located within the interior volume 6 of the light guide device 12. The reflective feature 13 acts as a hot spot reducing feature and preferably comprises a non-specular reflector. The reflective feature 13 may comprise a white printed ink dot. The reflective feature 13 is located close to the light source 7 and acts to recycle light that would otherwise not be coupled into the interior volume 6 of the light guide device 12. This reduces the appearance of hot spots which would otherwise interfere with the homogeneity or uniformity of the light output through the output surface 4. Note that while only one reflective feature 13 is depicted in Figure 3, more reflective features may be provided on the first 2 and or second 3 film. The extraction feature 14 is a non-specular reflector feature and may comprise a printed white dot pattern. The extraction feature 14 acts to extract light out of the light guide device 12 via the output surface 4 and therefore helps to deliver a homogeneous surface distribution. In Figure 3, only one extraction feature 14 is provided within the light guide device 12. However, as will be appreciated by the skilled person, two or more extraction features 14 may be provided and may be spatially distributed across the light guide device 12. In Figure 3, the second film 3 comprises a first surface 15 and a second surface 16. The extraction feature 14 is positioned on the second surface 16 and therefore is located within the interior volume 6 of the light guide device 12. However, as the second film 3 is transmissive at the wavelength of the light emitted by the light source 7, the extraction feature may alternatively be positioned on the first surface 15 of the second film 3. In a similar manner, the reflective feature 13 may alternatively be positioned on the output surface 4 of the light guide device 12. Figure 4 presents (a) a side view and (b) a top view a light guide device 17 in accordance with an alternative embodiment of the present invention. Some elements of these representations of the light guide device 17 have again been omitted for ease of understanding of this embodiment. In Figure 4, a frame 18 is arranged to create a regular two dimensional array of three by three interior subvolumes 6a to 6i, with each interior subvolume 6a to 6i comprising a corresponding light source 7a to 7i. Each interior subvolume 6a to 6i is separated from adjacent interior subvolumes 6a to 6i by the frame 18. In particular, the frame 18 surrounds each interior subvolume 6a to 6i to provide individual light guide units 19 within the light guide device 17. It will be appreciated by the skilled person that the light guide device 17 may comprise a larger or smaller array of interior subvolumes 6 than depicted in Figure 4, to either reduce or increase the number of light guide units 19. The light guide device 17 may alternatively be provided as a one dimensional array of interior subvolumes 6. Furthermore, the light guide device 17 may alternatively comprise an irregular two dimensional array. The array of interior subvolumes 6 can be assembled in any desired geometry which can be provided by the structure of the frame 18. The frame 18 in Figure 4 is a cuboid structure. However, the frame 18 may comprise any appropriate structure for providing an array of interior subvolumes 6 and for maintaining the predetermined separation distance between the first film 2 and the second film 3. For example, the frame 18 could alternatively comprise a honeycomb structure e.g. a hexagonal lattice structure. The light guide device 17 of Figure 4, comprises individual light guide units 19 having a structure of the type presented in Figure 1. However, as will be appreciated by the skilled person, each individual light guide unit 19a to 19i could instead comprise the structure of any of the light guide devices 1, 10 or 12 as described with reference to Figures 1 to 3, or any combination thereof. The design of the light guide device 17 of Figure 4 provides individual segmented light guide units 19a to 19i. These light guide units 19 can be tiled over a larger surface area than could be achieved by a single light guide. The modular configuration allows for greater flexibility in design, enabling the creation of light guide devices 17 that can be adapted to a variety of sizes and applications, where the modular configuration relies on the specific structure of the frame 18. By providing interior subvolumes 6a to 6i within the light guide device 17, the amount of materials required for manufacturing the light guide device 17 of Figure 4 is reduced. This results in a reduction in both the overall weight of the light guide device 17 and the cost of production. Such an arrangement of light guides units 19a to 19i is suitable for integration within a 2D array LED matrix, such as a low-resolution LED display. This offers several advantages as previously outlined, including a reduced overall thickness compared to traditional top emitting LED boards. However, it should be noted that in cases where the spacing between each light guide unit 19 is significantly larger than the dimensions of the light sources 7, the presence of light guide units and thin prism films may not result in a reduction in the overall thickness of the LED matrix. In alternative embodiments, the frame may be non-planer e.g. may define a curved device. For example, the parts of the frame or alternatively the entire frame could be designed to follow a concave or convex curvature, depending on the intended application. A curved device may be beneficial in applications where the light guide device or other components need to conform to specific shapes or contours. In summary, the present invention provides an alternative light guide device to those known in the art. The light guide device significantly reduces the amount of plastic required for its construction, when compared to traditional polymer light guides. This reduction arises due to the provision of an interior volume within the structure of the light guide device, where the interior volume separates two thin films. The frame ensures that the separation distance between the first and second film remains fixed. The light guide device offers several advantages due to its reduced materials: it is lighter, more cost-effective, and has a smaller environmental footprint compared to traditional light guide devices, whilst still maintaining a thin and efficient design. A light guide device and a method of manufacturing a light guide device is disclosed. The light device comprises a first film and a second film. The light guide device further comprises a frame configured to maintain a predetermined separation distance between the first film and the second film. The separation distance between the first film and the second film provides an interior volume within the light guide device, where a light source is located within the interior volume. The first film is transmissive at the wavelength of the light emitted by the light source and comprises a first array of prisms. The first and the second film are configured to redirect light emitted by the light source within the interior volume. The present invention provides a light guide device comprising fewer materials, reducing the weight and cost of the light guide device and providing improved sustainability. Throughout the specification, unless the context demands otherwise, the terms “comprise” or “include”, or variations such as “comprises” or “comprising”, “includes” or “including” will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. Furthermore, unless the context clearly demands otherwise, the term “or” will be interpreted as being inclusive not exclusive. Furthermore, reference to any prior art in the description should not be taken as an indication that the prior art forms part of the common general knowledge. The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

1. A light guide device comprising:a first film and a second film;a frame configured to maintain a predetermined separation distance between the first film and the second film and thus providing an interior volume between the first film and the second film; anda light source located within the interior volume;wherein the first film comprises a first array of prisms and is transmissive at a wavelength of the light emitted by the light source; andwherein the first film and the second film are configured to redirect the light emitted by the light source within the interior volume.

2. A light guide device as claimed in claim 1, wherein the second film comprises a reflective surface which is reflective at the wavelength of the light emitted by the light source.

3. A light guide device as claimed in claim 1 or claim 2, wherein the second film comprises a second array of prisms and is transmissive at the wavelength of the light emitted by the light source.

4. A light guide device as claimed in claim 1 or claim 2, wherein the interior volume is bordered by one or more non-specular reflectors.

5. A light guide device as claimed in any of the preceding claims wherein one or more reflective features are located on the first film and or the second film.

6. A light guide device as claimed in any of the preceding claims wherein one or more extraction features are located on the first film and or the second film.

7. A light guide device as claimed in claim 5 or claim 6, wherein the one or more reflective and or extraction features comprises a non-specular reflective feature.

8. A light guide device as claimed in any of the preceding claims, wherein the frame is configured to form two or more interior subvolumes between the first film and the second film.

9. A light guide device as claimed in claim 8, wherein the light guide device comprises two or more light sources and wherein at least one of the light sources is located within each interior subvolume.

10. A light guide device as claimed in claim 8 or claim 9 wherein the frame is configured to form a regular two dimensional array of two or more interior subvolumes.

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