WO2003098099A1

WO2003098099A1 - Light source and light guide

Info

Publication number: WO2003098099A1
Application number: PCT/AU2003/000591
Authority: WO
Inventors: Hadrian N Fraval; Hanafi R Fraval; C Jeffrey Brinker
Original assignee: Rofin Australia Pty Ltd
Current assignee: Rofin Australia Pty Ltd
Priority date: 2002-05-16
Filing date: 2003-05-16
Publication date: 2003-11-27
Anticipated expiration: 2004-11-16

Abstract

A light source and light guide (50) including: an array of light emitting diodes (56) for producing light; and a light guide (10) for positioning in proximity to the array of light emitting diodes, the light guide having an entrance end for receiving the light produced by the light emitting diodes, said light guide including: an outer body; a cladding on an internal surface of the outer body, the cladding being formed from a material having low refractive index; and a core having a refractive index greater than the cladding.

Description

LIGHT SOURCE AND LIGHT GUIDE

Field of the Invention

This invention relates to a light source and light guide for providing illumination.

Background of the Invention

Light guides are commonly used to provide illumination for a variety of different applications. Applications may vary from biological, forensic, and like applications, to aesthetic applications including signage, moving displays and the like.

Conventional systems include incandescent light sources which are located in proximity to the light guide so that light can enter the entrance aperture of the light guide and be internally reflected within the light guide, so that the light travels along the light guide and then exit the exit aperture of the light guide. In some applications, a number of such light guides can be arranged in a grid pattern and by controlling the incandescent light source, a display can be formed which can provide information such as text, moving pictures, or the like, as well as simply aesthetic color patterns.

The light guide enables the light source to be positioned at a position remote from the intended location of the illumination or display, which makes a display area formed by a number of light guides as small and compact as possible.

Incandescent light sources, or like light sources, are generally used in order to provide sufficient intensity in a relatively small area, which can thereby enter the entrance end of the light guide for transmission to the exit end. Because of the relatively high intensity of incandescent sources and their relatively small size, the numerical aperture of the light guide is not of great importance.

However, incandescent light sources do present some disadvantages including heat generation, lifetime of the light source and power consumption.

Summary of the Invention

The present invention provides a light source and light guide including: an array of light emitting diodes for producing light; and a light guide for positioning in proximity to the array of light emitting diodes, the light guide having an entrance end for receiving the light produced by the light emitting diodes, said light guide having: an outer body; a cladding on an internal surface of the outer body, the cladding being formed from a material having low refractive index; and a core having a refractive index greater than the cladding.

The inventors have found that by using the light guide described above, the numerical aperture of the light guide is significantly increased because of the cladding which has a low refractive index compared to the core. Because the numerical aperture is large, the size of the light source can also be made large without loss of light. Since the light source can be made large, the light source can be formed of a relatively large number of light emitting diodes which may, for example, number 50 to 100, and therefore provide an equivalent light output to incandescent sources. The light emitting diodes provide the advantage of considerably long lifetime, low cost and efficient electric power conversation to light output.

The use of a plurality of light emitting diodes also provides the advantage of being able to control or switch the light emitting diodes on and off as desired, thereby providing different effects along the length of the light guide, or of the light exiting an exit end of the light guide.

Furthermore, since the cladding is responsible for the internal reflection as light is transmitted along the light guide, the outer body can be made from a relatively inexpensive material, such as common plastic material, without regard to the refractive index of the body.

The cladding is formed from a material having low refractive index. Preferably, the cladding material is a fluoropolymer, such as fluorinated olefin polymer, more particularly fluorinated ethylene polymer. Alternatively, the cladding may include ionomer tubing coated with an aerogel or may be formed from an aerogel material. Aerogel materials are highly porous materials which may, for example, have a porosity in the order of 40 to over 90 volume %. Typical surface areas for aerogel materials are in the order of greater than 650m²/g and typical densities are in the order of 0.224g/cc. The invention is not, however limited to these typical values. Such materials may be prepared by a low temperature and pressure aerogel process wherein porosity is generated by dilation or spring-back of a gel during drying. Alternatively, a surfactant-templating technique may be used in which an organic silicon network is formed around an organic liquid-crystal or micellular structure, followed by removal of the template. This creates a porous silica fossil of the organic assembly. Aerogel materials include mesoporous thin-film materials of the type disclosed in "Continuous formation of supported cubic and hexagonal mesoporous films by sol-gel dip-coating" Nature, Volume 389, 25 September 1987. The contents of this article is incorporated into this specification by this reference.

Preferably, the array of diodes is moveable relative to the entrance end of the light guide, such as for adjusting receipt of the light produced by the light emitting diodes into the entrance end of the light guide.

In one embodiment the plurality of light emitting diodes are mounted on a circuit board, and the circuit board is mounted for movement relative to the entrance end of the light guide.

In one embodiment a lens is provided between the light emitting diodes and the entrance end of the light guide for focusing the light from the light emitting diodes to the entrance end of the light guide. Although the number of light emitting diodes may vary depending on the particular application and desired result, preferably the number of light emitting diodes is from 50 to 100 light emitting diodes.

The light emitting diodes may produce light of a single colour. Alternatively, the light emitting diodes may include groups of light emitting diodes for producing light of different colours.

The core of the light guide may be a liquid core. In preferred embodiments, the core is made from methacrylate material or the like, such as methyl, ethyl or butyl methacrylate. However, other materials such as gels can be used to form the core provided that they have a refractive index which is as high as possible relative to the refractive index of the cladding.

Preferably the cladding has a thickness in the order of 1 to 3 microns. With aerogel coating on ionomer tubing of less than 600nm thickness, the transmission of light in the region 500-700nm may be impaired. Uniform coatings of at least 1.2 microns have been shown to give good transmission of light in the region 400-750nm.

In one embodiment of the invention the light guide has an exit end and light is transmitted along the light guide and out the exit end with as little loss as possible.

In other embodiments, the core may be provided with scattering material, such as glass micro beads, for scattering the light as the light is transmitted along the light guide. In such cases, the light scatters out through the cladding and body prior to reaching the end of the light guide opposite the entrance end. In this embodiment, the efficiency of transmission of the light is such that light will preferably be lost progressively and evenly over the length of the light guide.

In the embodiment in which light is intended to be scattered through the cladding and the body, a second array of light emitting diodes may be provided at the end of the light guide opposite the entrance end so the light guide effectively has two entrance ends.

Brief Description of the Drawings

A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a view of a light guide in accordance with the preferred embodiment;

Figure 2 is a cross-sectional view through the light guide of Figure 1;

Figure 3 is a cross-sectional view of a light source and light guide according to the preferred embodiment;

Figure 4 is a view along the line IV-IV of Figure 3; and

Figure 5 is a view of a further embodiment of the invention.

Detailed Description of the Preferred Embodiments

With reference to Figure 1, a light guide 10 is shown which has an outer tubular body 12 of circular cross-section. The body 12 has an internal surface 14 which is coated with a cladding film or layer 18. The cladding layer 18 is formed from an aerogel material.

The light guide 10 has a central core 20 which is formed from a material which has a high refractive index compared to the cladding 18. The core 20 may be a liquid core, but most preferably, is a sold core formed from butyls material. However, other cores of high refractive index material may also be used. If a liquid core is used, the aerogel material should be hydrophobic to prevent interaction with the liquid core.

Figure 3 shows the light source and light guide according to a preferred embodiment of the invention. The light source and light guide 50 includes a housing 52 in which a circuit board 54 is mounted. The circuit board 54 carries a plurality of light emitting diodes 56 which may number in the order of 50 to 100 diodes.

Power is supplied to the circuit board 54 from a battery 58 via lead 59. The circuit board 54 may also include driver electronics for driving the diodes 56, or otherwise controlling the diodes, so the diodes are turned on to emit light in accordance with a required sequence or pattern which may be generated by a microprocessor or other controller (not shown) via bus 60.

The housing 52 has a stem 62 which has screw thread 64 and light guide 10 is inserted into the stem 62. The light guide 10 carries a nut 66 which has a screw thread 68 which screws on to the screw thread 64 to thereby securely support the light guide 10 in the housing 52.

A lens 70 is provided in the housing 52 between the light emitting diodes 56 and entrance end 72 of the light guide 10.

The lens is moveable in the direction of double-headed arrow A relative to the entrance end 72 so that light produced by the light emitting diodes 56 is focused to the entrance end 72 of the light guide 10.

The provision of the aerogel cladding which provides the reflective layer of the light guide 10, and which has a very low refractive index approaching that of air, together with the high refractive index of the core 20, produces a large numeral aperture at the entrance end 72 of the waveguide 10. Thus, the angle of the incoming light rays as shown by cone 82, can result in a high acceptance angle α of the light impinging on the cladding 18, which will still produce total internal reflection so that the light is transmitted along the light guide 10. Thus, the size of the array of light emitting diodes on the circuit board 54 can be quite large, with all of the light still being accepted within the numerical aperture and then transmitted along the lightguide 10. Thus, the large amount of light emitting diodes produces a high light intensity equivalent to a high intensity incandescent light source, without the disadvantages of the incandescent light source. Thus, the diodes provide the advantage of low cost, long lifetime and efficient electric power conversion to light output.

The light which enters the light guide 10 is totally internally reflected along the light guide 10 and therefore passes along the light guide 10 to exit end 88.

The number of light emitting diodes included in the array on the circuit board 54 will be dependent on the diameter of the light guide 10. For example, a 10mm diameter light guide 10 and a 5° divergent light emitting diode will allow more than 50 light emitting diodes to be positioned so that their light is introduced into the light guide 10.

Using 50 light emitting diodes, each with 3 candela light output, the total light entering the light guide will be 150 candela. Since the transmission of the light guide is about 80% over 1 metre length, the total energy exiting the exit end 88 of the light guide is 120 candela.

The light emitting diodes may include groups of light emitting diodes of different colour, such as 33 blue diodes, 33 red diodes, and 30 green diodes, which when turned on simultaneously, result in white light. Conversely, when the colours are turned on individually, such an arrangement will result in a monochromatic output of that colour. Alternatively, all the diodes may be diodes for producing white light.

In another embodiment, rather than providing the light guide 10 so that the light exits the exit end 88, the guide 10 may be configured so that light is scattered out through the cladding 18 and body 12 to provide an effect where light seems to come out of the tube along the length of the tube, rather than from the exit end 88. In order to achieve this effect, the core material is provided with particulate material which will scatter the light travelling along the light tube so that the light will impinge on the cladding and body at an angle where the body is able to be transmitted through the cladding and body, and therefore exit the light guide 10 through the cladding 18 and body 12.

In this embodiment the loss along the light guide 10 is preferably set such that the loss is evenly distributed along the light guide, and such that all of the light is effectively lost before the light reaches the end 88. Furthermore, in this embodiment, a second housing 52 similar to that previously described can be located at the end 88 for directing light into the end 88. In this case, light is directed into both ends 72 and 88 and is scattered out through the cladding 18 and body 12 in the manner previously described.

In this embodiment, for example, 100 light emitting diodes positioned at each end of the light guide 10 may provide for light guide 10 that is over 10 metres in length.

Figure 5 shows a second embodiment in which like reference numerals indicate like parts to those previously described.

In this embodiment the lens 70 is omitted and the circuit board 54, or an alternative support on which the diodes 56 are mounted, is generally disc-shaped or parabolic in configuration so that the diodes 56 are directed towards the entrance aperture 72 of the light guide 10 as shown in Figure 5.

In other embodiments a combination of a parabolic or disc-shaped support or circuit board 54 and a lens 70 could be utilised.

It should be understood that whilst primary applications of the preferred embodiments will be in the visible part of the electromagnetic radiation spectrum, the term light used in this specification should be understood to include both the visible part of the spectrum and non-visible part of the spectrum.

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

Claims

The claims defining the invention are as follows:

1. A light source and light guide including: an array of light emitting diodes for producing light; and a light guide for positioning in proximity to the array of light emitting diodes, the light guide having an entrance end for receiving the light produced by the light emitting diodes, said light guide including: an outer body; a cladding on an internal surface of the outer body, the cladding being formed from a material having low refractive index; and a core having a refractive index greater than the cladding.

2. A light source and light guide according to claim 1, wherein the cladding of the light guide is formed from a fluoropolymer material or ionomer tubing coated with an aerogel material.

3. A light source and light guide according to claim 2, wherein the aerogel material has a porosity of 40 volume % or more and a surface area of greater than 650m²/g.

4. A light source and light guide according to claim 2, wherein the fluoropolymer material is a fluorinated olefin polymer, preferably a fluorinated ethylene polymer.

5. A light source and light guide according to claim 1, wherein the array of diodes is moveable relative to the entrance end of the light guide.

6. A light source and light guide according to claim 5, wherein the plurality of light emitting diodes are mounted on a circuit board, and the circuit board is mounted for movement relative to the entrance end of the light guide.

7. A light source and light guide according to claim 1, wherein a lens is provided between the light emitting diodes and the entrance end of the light guide for focusing the light from the light emitting diodes to the entrance end of the light guide.

8. A light source and light guide according to claim 1, wherein the number of light emitting diodes is from 50 to 100.

9. A light source and light guide according to claim 1, wherein the light emitting diodes produce light of a single colour.

10. A light source and light guide according to claim 1, wherein the light emitting diodes include groups of light emitting diodes for producing light of different colours.

1 1. A light source and light guide according to claim 1, wherein the core of the light guide is a liquid core.

12. A light source and light guide according to claim 1, wherein the core of the light guide is a solid core formed from a methacrylate material or the like, preferably methyl, ethyl or butyl methacrylate.

13. A light source and light guide according to claim 1 , wherein the cladding has a thickness in the order of 1-3 microns.

14. A light source and light guide according to claim 1, wherein the light guide has an exit end and light is transmitted along the light guide and out the exit end.

15. A light source and light guide according to claim 1, wherein the core of the light guide is provided with a scattering material for scattering the light as the light is transmitted along the light guide such that light scatters out through the cladding and body prior to reaching an end of the light guide opposite the entrance end of the light guide.

16. A light source and light guide according to claim 15, wherein the scattering material is glass micro beads.

17. A light source and light guide according to claim 15, wherein a second array of light emitting diodes is provided at the end of the light guide opposite the entrance end.