WO2005026611A2

WO2005026611A2 - Improvements in and relating to backlit displays

Info

Publication number: WO2005026611A2
Application number: PCT/GB2004/003971
Authority: WO
Inventors: Owen Michael Gerard O'neill; Howell John Griffiths; Christopher John Ferrari; Michael John Hanney
Original assignee: Ambisol Signage And Lighting Limited
Priority date: 2003-09-18
Filing date: 2004-09-17
Publication date: 2005-03-24
Also published as: GB2423183A; GB0321836D0; WO2005026611A3; GB0607613D0

Abstract

A light guide (30) for use with a backlit display (100), and a method of manufacturing the same is disclosed. The light guide (30) has an array of light control features (32) mechanically machined into its surface during manufacture to scatter light within the light guide (30) so that it passes out of the light guide (30) to illuminate the backlit display (100). Light is introduced to the light guide (30) from light boxes (50) containing light sources. Each light source is joined to a coupling element (52) to increase efficiency of light entry into the light guide (30) and to increase the amount of light directed toward the light control features (32).

Description

IMPROVEMENTS IN AND RELATING TO BACKLIT DISPLAYS

Field of the Invention

The present invention relates to backlit displays, light guides suitable for use with backlit displays, and to methods of manufacturing light guides for use with backlit displays. The present invention further relates to optical coupling elements for use with backlit displays, and to light boxes comprising optical coupling elements.

Background to the Invention

Backlit displays using light emitting diodes (LEDs) or other light sources to illuminate a liquid crystal display area are well known in the field of mobile electronic devices, and provide energy efficient illumination for the liquid crystal display area. Such displays can be found on many mobile phones, for example.

However, a problem arises in that the injection moulding, laser etching and/or chemical etching techniques used to manufacture light control patterns on light guides for such displays are difficult to adapt to large scale displays, meaning that the technology has only limited applications .

Furthermore, the LEDs or other light sources used in known displays are typically butted up to the edge of the light guide, or alternatively light input features such as lenses are moulded into the light guide to couple light output from the light sources into the light guide. The first of these techniques may not enable efficient optical coupling. The second of these techniques may be difficult to adapt to large scale displays and is relatively inflexible, as the input lens features can not be moved or easily adapted to suit the requirements of a particular display and each different design requires its own expensive light guide mould.

It is an aim of preferred embodiments of the present invention to overcome at least one problem associated with the prior art, whether referred to herein, or otherwise.

Summary of the Invention

In a first aspect, the present invention provides a method of manufacturing a light guide suitable for use with a backlit display, the method comprising the steps of: (a) providing a substantially transparent material sheet; and, (b) mechanically machining at least one light control feature on the material sheet .

Suitably, the material sheet provided in step (a) comprises a plastics material. Suitably, the material sheet provided in step (a) comprises either acrylic or polycarbonate .

Suitably, the material sheet provided in step (a) comprises a first side that is longer than 20 centimetres. Preferably, the first side is longer than 40 centimetres. More preferably, the first side is longer than 60 centimetres. Most preferably, the first side is longer than 1 metre . Suitably, the material sheet provided in step (a) comprises a second side that is longer than 20 centimetres. Preferably, the second side is longer than 60 centimetres. More preferably, the second side is longer than 1 metre. Most preferably, the first side is longer than 3 metres.

Suitably, the first and second sides are shorter than 20 metres. Preferably, the first and second sides are shorter than 10 metres.

In a particularly preferred embodiment the material sheet is substantially rectangular and comprises first sides of approximately 1 metre, and second sides of approximately 3 metres.

Suitably, the material sheet provided in step (a) is more than 5mm thick. Suitably, the material sheet provided in step (b) is more than 10mm thick. Suitably, the material sheet provided in step (a) is less than 50mm thick. In a particularly preferred embodiment the material sheet provided in step (a) is approximately 8mm thick.

Suitably, the step (b) comprises mechanically machining a plurality of light control features on the material sheet. Suitably, the step (b) comprises mechanically machining an array of light control features on the material sheet.

Suitably, the array of light control features has a variable spatial density of light control features across the material sheet . Suitably, the light control features comprise at least one of a substantially cylindrical recess, a substantially hemispherical recesses, a recesses comprising a section of a substantially spherical shell, a recesses comprising a substantially cylindrical portion with a section of a substantially spherical shell appended thereto, a channel, or a triangular recess.

Suitably, the mechanical machining of step (b) comprises at least one of drilling, mechanically etching, blasting and/or routing.

Suitably, the step (b) comprises the sub-steps: (bl) forming a recess; and (b2) applying a surface finish to the recess.

Suitably, the material sheet provided in step (a) comprises uniform optical properties at the edges thereof. Suitably, the material sheet provided in step (a) does not comprise light input features at the edges thereof.

In a second aspect, the present invention provides a light guide suitable for use in a backlit display, the light guide comprising a substantially transparent material sheet having at least one light control feature mechanically machined thereon.

Suitably, the light guide is manufactured in accordance with the method of the first aspect of the invention.

In a third aspect, the present invention provides an optical coupling element suitable for use with a back lit display, the coupling element comprising a light reception portion suitable for receiving light incident thereon from a light source, and a beam shaping portion arranged to produce a fan shaped output beam for coupling into a light guide of a backlit display.

Suitably, the optical coupling element is arranged to internally reflect light received at the light reception portion to produce the fan shaped output beam.

Suitably, the fan shaped output beam comprises a first divergence in a first plane, and a second, greater, divergence in a second plane.

Suitably, the beam shaping portion comprises a section of increasing cross sectional area, and a section of decreasing cross sectional area.

In a fourth aspect, the present invention provides a light box suitable for use with a backlit display, the light box comprising a housing, a light source and an optical coupling element.

Suitably, the optical coupling element is in accordance with the third aspect of the invention.

Suitably, the light source comprises an LED.

Suitably, the housing comprises at least one reflective internal surface. Suitably, the reflective internal surface of the housing comprises greater than 50% of the internal surface area of the housing. Preferably, the reflective internal surface of the housing comprises greater than 75% of the internal surface area of the housing. More preferably, reflective internal surface of the housing comprises greater than 90% of the internal surface area of the housing. Most preferably, the reflective internal surface of the housing comprises substantially all the internal surface area of the housing. Suitably, the reflective internal surface comprises a white surface, and/or a polished surface.

Suitably, the housing is arranged to be attached to a light guide of a backlit display. Suitably, the coupling elements are arranged in use to abut an edge of a light guide of a backlit display. Suitably, the housing is shaped to conform to an edge of a light guide of a backlit display.

Suitably, the light box comprises plurality of light sources and a plurality of optical coupling elements.

In a fifth aspect, the present invention provides a backlit display comprising a light source coupled to a light guide using an optical coupling.

Suitably, the light source comprises the light box of the fourth aspect of the invention.

In a sixth aspect, the present invention provides a backlit display comprising a first edge having at least one light source arranged adjacent thereto, and a second, substantially free edge.

In a seventh aspect, the present invention provides a display apparatus comprising a plurality of backlit displays according to the fifth aspect of the present invention arranged with the respective second edges adjacent to one another to form a composite display.

In an eighth aspect, the present invention provides a method of manufacturing a light guide suitable for use with a backlit display, the method comprising the steps of: (a) providing a substantially transparent material sheet; (b) mechanically machining a mask; (c) arranging the mask with the material sheet, and (d) forming at least one light control feature on the material sheet through the mask.

Suitably, the step (c) comprises releasably coupling the mask to the material sheet. Suitably, the step (d) comprises a chemical etching process. Suitably, the step (d) comprises a blasting process.

Suitably, the light guide produced is substantially in accordance with that described in relation to the first aspect of the present invention.

Brief Introduction to the Drawings

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 shows an exploded perspective view of a backlit display according to a first embodiment of the present invention;

Figure 2 shows a plan view of the light guide shown in Figure 1 ;

Figure 3 shows a perspective view of a coupling element suitable for use in the backlit display of Figure 1 ;

Figure 4 shows a first cross sectional view of the coupling element of Figure 3 about a lateral plane;

Figure 5 shows a second cross sectional view of the coupling element of Figure 3 about a frontal plane;

Figure 6 shows an example ray tracing for the cross section shown in Figure 4; and

Figure 7 shows an example ray tracing for the cross section shown in Figure 5.

Detailed Description of Preferred Embodiments

Figure 1 shows an exploded perspective view of a backlit display 100 according to a first embodiment of the present invention. The display 100 is built up in a series of layers and comprises a support 10, a reflector 20, a light guide 30, a graphic mask 40 and light boxes 50. The display 100 can be used as an illuminated sign by incorporation of suitable opaque and light transmitting regions on the graphic mask 40, with typical dimensions of approximately 1 metre wide by 3 metres long. In use light emitted from light sources in the light boxes 50 is coupled into the light guide 30. Light passing through the light guide 30 is scattered by light control features of the light guide 30, and passes out through the graphic mask 40 either directly, following further scattering at one or more light control features, and/or following reflection by the reflector 20.

The lowermost layer of the display 100 is the support 10. The support 10 comprises a box made from of sheet material to which higher layers and the light boxes 50 are coupled.

The support 10 comprises a substantially planar central section 12, with edges 14 along its length and sectional edges 16 partly along its width. The support 10 provides mechanical strength and rigidity to the assembled display

100, and typically may comprise a metallic material such as aluminium.

The reflector 20 is intended to catch any light which is scattered down from the light guide 30 in a direction away from the graphic mask 40. Light incident on the reflector

20 is reflected back toward the light guide 30 and the graphic mask 40. The reflector 20 comprises a reflective surface 22 that may comprise a white painted surface, or a polished metal surface. An example material suitable for use in the reflector 20 is aluminium with a highly polished and anodised surface. Such a material is commercially available and offers an optical reflectivity of over 90%. An increase in reflectivity at the reflective surface 22 increases the overall light output of the display 100, as will be discussed in more detail below. In other embodiments of the invention the reflector 20 may be omitted and the reflective surface formed 22 on the support 10.

The light guide 30 is arranged to receive incident light from the light boxes 50 and operate on this light such that it is transmitted across the display 100 and out through the graphic mask 40. To date, techniques for producing light guides for backlit displays have been unable to produce devices with external dimensions greater than a few tens of centimetres. The light guide 30 is formed from a prefabricated acrylic sheet and is mechanically machined to produce suitable optical characteristics. The light guide 30 can typically be 5- 10mm thick. The light guide is machined to comprise at least one of light control feature arranged to scatter light incident thereon from light sources in the light boxes 50. Other suitable substantially transparent colourless or coloured plastic sheet materials could also be used, for example polycarbonate.

The light boxes 50 comprise light sources, typically light emitting diodes (LEDs) . Light emitted from the light sources enters the light guide 30 along its edges. Light within the light guide 30 is scattered by the light control features, resulting in the light being directed from the light guide 30 and towards and through the graphic mask 40. The light control features will now be described in more detail, with reference to Figure 2.

Figure 2 shows a plan view of the light guide 30, including a plurality of light control features 32. The light control features 32 comprise light scattering sites mechanically machined into the plane of the material that makes up the light guide 30. The light control features 32 comprise indentations formed by drilling and/or routing. The light control features 32 introduce material-air interfaces and air-material interfaces into the path of light from the light boxes 50. The path of light incident on the light control features is altered by virtue of internal reflection and refraction at the interfaces. The distribution of light control features 32 over the extent of the light guide 30 can be varied to produce different amounts of scattering over the area, and consequently vary the light output from the light guide 30.

Suitably, open ends of light control features are positioned adjacent to the reflector 20 in the assembled display 100. As well as offering suitable optical characteristics this serves to prevent the light control features from collecting dust or other dirt.

The example distribution shown in Figure 2 is arranged to produce substantially even light output across the whole area of the light guide. This is achieved by machining a relatively low spatial density of light control features 32 proximate to the edges of the light guide 30 adjacent to the light boxes 50, and machining a relatively higher spatial density of light control features 32 toward the central area of the light guide 30. Other spatial distributions of light control features 32 can be envisaged to produce other intensity patterns for the light output from the light guide 30.

The light control features 32 can comprise a range of profiles. For example, good light scattering can be achieved by drilling substantially cylindrical recesses into the light guide 30. Other suitable profiles include substantially hemispherical recesses, recesses comprising sections of a substantially spherical shell, or recesses comprising a substantially cylindrical portion with a section of a substantially spherical shell appended thereto. The optical scattering properties can be varied by adjusting the dimensions of the light control features, for example the diameter, depth or alignment of the recesses can be varied. Other light control features having non-circular cross sections are possible, but may be more difficult to machine, and may produce uneven scattering effects.

In addition to using an array of individual point scattering light control features 32, it is possible for larger features to be mechanically machined into the light guide 30, for example line scattering features comprising a channel, or other two dimensional features. One example of a two dimensional scattering feature is an elongate triangular cut out that tapers from a point proximate to a light source to a base region proximate to the centre of a light guide to increase scattering at the central region of the light guide. The triangular cut out may be used alone, or with one or more further light control features.

The surface finish of the light control features 32 affects their light scattering characteristics. For example, the light control features may be machined by grit, sand or bead blasting techniques. In addition to the formation of the light control features using blasting, blasting may be used to impart a desired surface finish on light control features already present on a light guide.

The graphic mask 40 comprises a stretched vinyl sheet, and can be printed to include various opaque and/or translucent regions. Other opaque, transparent and/or translucent masks of plastics or other materials can be used. The configuration of the graphic mask 40, the light control features 32 of the light guide 30 and the light emitted from the light boxes 50 combine to provide the overall output from the display 100. This can be for signage or other display purposes. In certain embodiments the graphic mask 40 may comprise regions of switchable optical transmissivity, for example provided using a liquid crystal device.

The light boxes 50 comprise a plurality of LEDs therein. The number of LEDs within each light box 50, and the output characteristics of the LEDs can be varied to suit various display requirements. Typically, white light LEDs can be used, allowing multicoloured graphic masks 40 to produce a desired display output. However, red, green and blue LEDs can be used to provide a range of output colours by mixing these three optical primary colours.

The light boxes 50 are designed to enable light from LED light sources to be efficiently coupled into the light guide 30. Etching or moulding light collection features into the edges of large, display light guides is difficult to achieve, and does not allow flexibility in the number or position of light sources. By using coupling elements as light input enhancers the display 100 is easy to produce and can be easily modified to cater for a range of desired display properties.

Figures 3 to 7 show a coupling element 52 comprising a light reception portion 54 and a beam shaping portion 56. Light is collected from an LED source positioned adjacent to the light reception portion 54 and is internally reflected at the interface of the beam shaping portion 56 and air giving the ray paths shown in Figures 6 and 7. The output of the coupling element 52 comprises a fan shaped beam, with light incident on the light guide 30 predominantly within the critical angle of the plastic-air interface at the surface of the light guide 30. This ensures that the majority of the light from the LED positioned adjacent to the coupling element is coupled into the light guide 30. Furthermore, the output of the coupling element 52 is predominantly aligned at an angle to the plane of the light guide, such that multiple internal reflections within the light guide 30 are produced. This increases the amount of light that intercepts the light control features 32.

Light boxes 50 can be positioned along one or more edges of the light guide 30. In the display 100 each light box comprises twelve LEDs, with each LED having a coupling element 52 associated therewith. The light boxes 50 provide a mechanical support for the LEDs and the coupling elements 52 and also hold the wiring and/or circuit boards associated with the LEDs. To increase the coupling of light from the LEDs into the light guide 30 the light boxes 50 may comprise a reflective internal finish, such as a painted white finish or a polished surface. In this way, light which is not initially coupled into the light guide 30 has a second chance to enter the light guide 30.

As previously mentioned, the display 100 is can be readily manufactured to comprise an area of 1 metre by 3 metres. Larger displays can be easily built up by assembling a plurality of displays 100 side by side. Displays 100 can be positioned in direct contact along their long sides. For example, four displays 100 can be assembled side by side to produce a single 4 metre by 3 metre sign.

The display 100 comprises twelve LEDs in each light box 50, which when driven at the nominal rated current of 350mA produce an average illumination of 12 candelas per square metre. In this arrangement, the power consumption of the display is less than one quarter of a comparable electroluminescent display. A comparable electroluminescent display may also only provide approximately half the display brightness. The energy efficiency of LED light sources makes the display 100 suitable for use with sustainable energy sources such as solar and/or wind generators.

The backlit display can be formed in any suitable shape, for example square, rectangular, circular or other irregular forms. Similarly, the light boxes may be linear or non-linear.

The small size, efficiency and reliability of LEDs makes them particularly suited to use in displays as described, other light sources such as incandescent bulbs, fluorescent tubes, electroluminescent elements etc. may also be used. Furthermore, light sources may be provided at one of the sides of the light guide or at more than one side of the light guide. In certain circumstances it may be desirable to provide light sources at all edges of the light guide.

As an alternative to the method of manufacturing a light guide a mechanically machined a mask can be used as part of a chemical etching and/or blasting technique for forming the light control features.

The mask can be drilled, mechanically etched, blasted and/or routed, and reused a number of times to reduce the machining overheads associated with display production.

Thus, a backlit display has been described that is suitable for use in signage and other similar applications, and is relatively compact in the out of plane dimension. The display offers high brightness, high energy efficiency and extremely low maintenance. The display is simple to manufacture, and offers a great degree of flexibility in the optical output.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS :

1. A method of manufacturing a light guide suitable for use with a backlit display, the method comprising the steps of: (a) providing a substantially transparent material sheet; and, (b) mechanically machining at least one light control feature on the material sheet.

2. The method of claim 1, wherein the material sheet provided in step (a) comprises a plastics material.

3. The method of claim 2, wherein the material sheet provided in step (a) comprises either acrylic or polycarbonate .

4. The method of any preceding claim, wherein the step (b) comprises mechanically machining a plurality of light control features on the material sheet .

5. The method of claim 4, wherein the step (b) comprises mechanically machining an array of light control features on the material sheet .

6. The method of claim 5, wherein the array of light control features has a variable spatial density of light control features across the material sheet .

7. The method of any preceding claim wherein the step (b) comprises mechanically machining the light control features comprising at least one of a substantially cylindrical recess, a substantially hemispherical recesses, a recesses comprising a section of a substantially spherical shell, a recesses comprising a substantially cylindrical portion with a section of a substantially spherical shell appended thereto, a channel, or a triangular recess .

8. The method of any preceding claim, wherein the mechanical machining of step (b) comprises at least one of drilling, mechanically etching, blasting and/or routing.

9. The method of any preceding claim, wherein the step (b) comprises the sub-steps: (bl) forming a recess; and

(b2) applying a surface finish to the recess.

10. The method of any preceding claim, wherein step (a) comprises providing a material sheet having uniform optical properties at the edges thereof.

11. The method of any preceding claim, wherein step (a) comprises providing a material sheet that does not comprise light input features at the edges thereof.

12. The method of any preceding claim, wherein the material sheet provided in step (a) comprises a first side that is longer than 20 centimetres.

13. The method of any preceding claim, wherein the material sheet provided in step (a) comprises a second side that is longer than 20 centimetres.

14. The method of any preceding claim, wherein the material sheet provided in step (a) is substantially rectangular and comprises first sides of approximately 1 metre, and second sides of approximately 3 metres.

15. The method of any preceding claim, wherein the material sheet provided in step (a) is more than 5mm thick.

16. The method of any preceding claim, wherein the material sheet provided in step (a) is approximately 8mm thick.

17. A light guide suitable for use in a backlit display, the light guide comprising a substantially transparent material sheet having at least one light control feature mechanically machined thereon.

18. An optical coupling element suitable for use with a back lit display, the coupling element comprising a light reception portion suitable for receiving light incident thereon from a light source, and a beam shaping portion arranged to produce a fan shaped output beam for coupling into a light guide of a backlit display.

19. The optical coupling element of claim 18, arranged internally to reflect light therein following reception of light at the light reception portion to thereby produce the fan shaped output beam.

20. The optical coupling element of claim 18 or 19, wherein the fan shaped output beam comprises a first divergence in a first plane, and a second, greater, divergence in a second plane.

21. The optical coupling element of any one of claims 18- 20, wherein the beam shaping portion comprises a section of increasing cross sectional area, and a section of decreasing cross sectional area.

22. A light box suitable for use with a backlit display, the light box comprising a housing, a light source and an optical coupling element.

23. The light box of claim 22, wherein the optical coupling element is that of any one of claims 18-21.

24. The light box of claim 22 or 23, wherein the light source comprises a light emitting diode (LED) .

25. The light box of claim 22, 23 or 24, wherein the housing comprises at least one reflective internal surface.

26. The light box of claim 25, wherein the reflective internal surface of the housing comprises substantially all the internal surface area of the housing.

27. The light box of any one of claims 22-26 comprising a plurality of light sources and a plurality of optical coupling elements.

28. A backlit display comprising a light source coupled to a light guide using an optical coupling.

29. The backlit display of claim 28, wherein the light source comprises the light box of any one of claims 22-27.

30. A backlit display comprising a first edge having at least one light source arranged adjacent thereto, and a second, substantially free edge.

31. A display apparatus comprising a plurality of the backlit displays of claim 28 or 29 arranged with the respective second edges adjacent to one another to form a composite display.

32. A method of manufacturing a light guide suitable for use with a backlit display, the method comprising the steps of: (a) providing a substantially transparent material sheet; (b) mechanically machining a mask; (c) arranging the mask with the material sheet, and (d) forming at least one light control feature on the material sheet through the mask.

33. The method of claim 32, wherein the mechanical machining of step (b) comprises at least one of drilling, mechanically etching, blasting and/or routing.

34. The method of claim 32 or 33, wherein the step (c) comprises releasably coupling the mask to the material sheet .

35. The method of claim 32, 33 or 34, wherein the step (d) comprises one of: a chemical etching process; and (d) comprises a blasting process.