GB2568862A

GB2568862A - A waveguide and lighting device comprising the waveguide

Info

Publication number: GB2568862A
Application number: GB1716337.9A
Authority: GB
Inventors: Wilfred James Halton Luke; Kit Buchanan William
Original assignee: Waveguide Lighting Ltd
Current assignee: Waveguide Lighting Ltd
Priority date: 2017-10-06
Filing date: 2017-10-06
Publication date: 2019-06-05
Also published as: GB201716337D0

Abstract

A waveguide for use as a lighting device, comprising a transparent material 20 along which light travels by total internal reflection, and an interior channel 30 that is inside of the transparent material and that runs along a length, preferably the whole length, of the waveguide. The interior channel 30 comprises a reflective material 35 to reflect light out of the waveguide. The interior channel 30 may be aligned with the central axis of the waveguide and may be cylindrical in shape, the transparent material can be acrylic and may also have a circular, or oval cross section, and can be 3 or 5 times the diameter of the interior channel. The reflective material can be formed as a surface or coating on the interior channel. There can be a lamp or LED (10, fig 1) providing light to the waveguide, which can emit light in all directions.

Description

A WAVEGUIDE AND LIGHTING DEVICE COMPRISING THE WAVEGUIDE

DESCRIPTION

The present invention relates to a waveguide, in particular to a waveguide that can be used to emit light in a lighting device.

BACKGROUND OF THE INVENTION

In recent years, Light Emitting Diode (LED) technology has developed to the point where it can start to replace conventional incandescent and strip lighting. One of the problems in adapting LEDs to emulate known strip lighting is that LED’s are typically point light sources which do not emit light over large areas, like the phosphors in conventional strip lights can.

It is known to solve this problem by providing a length of transparent material that defines a waveguide. Then, light from an LED can be emitted into an end of the waveguide, and the light will travel along the waveguide by total internal reflection, in a similar manner to light inside of an optical cable. A reflective material can be formed on a surface of the waveguide to disrupt the total internal reflection and cause the light to be emitted from the waveguide. For example, a known waveguide of that type is described in GB 2,398,372. However, whilst the reflective material is effective in reflecting light out of the waveguide, it prevents light from exiting the waveguide on the surfaces of the waveguide where the reflective material is present.

It is therefore an object of the invention to provide an improved waveguide.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a waveguide comprising a transparent material along which light travels by total internal reflection, wherein the waveguide comprises an interior channel that is inside of the transparent material and that runs along a length of the waveguide, and wherein the interior channel comprises a reflective material which reflects light out of the waveguide.

Since the reflective material is provided inside an interior channel of the transparent material, the reflective material does not block light from exiting the exterior surfaces of the transparent material. Accordingly, greater control can be exerted over the directions in which the waveguide emits light, and the waveguide can be configured to emit light a full 360 degrees around the length of the waveguide.

The transparent material carries light along the waveguide by total internal reflection, and may consist of a single block of transparent material. The light is transmitted through the transparent material, and internally reflects at the exterior surfaces of the transparent material. The light that reflects off the reflective material inside the interior channel does not internally reflect when it reaches the exterior surface of the transparent material, but instead passes through the exterior surface and out of the waveguide.

Preferably, the interior channel is aligned with a central axis of the waveguide, to aid in distributing light more evenly around the full circumference of the waveguide. The interior channel and the reflective material within it may run along the full length of the transparent material so that light is emitted along the full length of the waveguide.

The transparent material may comprise an interior surface that adjoins the interior channel, so the transparent material itself defines the interior channel. The transparent material may comprise an exterior surface that defines an exterior of the waveguide through which light is emitted.

The reflective material is preferably at a boundary between the interior channel and the transparent material, for example so that the reflective material contacts the transparent material and light does not have to pass through any intermediate materials.

The reflective material may reflect light out of the waveguide in directions extending over substantially 360 degrees transverse to the length of the waveguide, for example the reflective material may have a circular or oval crosssection. The reflective material may reflect light out of the waveguide so that the light has a uniform intensity over the 360 degrees of light emission transverse to the length of the waveguide, for example both the exterior surface of the transparent material and the reflective material facing the transparent material may have circular cross sections transverse to the length of the waveguide.

To aid even distribution of light, the interior channel may have a circular or oval cross section, and the reflective material may have a circular or oval crosssection, respectively.

The reflective material may be formed as a coating on an interior surface of the transparent material that adjoins the interior channel, to help ensure that there is no intervening medium through which the light has to pass between the transparent material and the reflective material. Alternatively, the reflective material may be formed as a rod having a reflective surface, wherein the rod is inserted into the interior channel. The rod may be in the shape of a cylinder.

The interior channel is preferable formed as a circular hole through the transparent material, for example the hole could be drilled along the central axis of the transparent material.

The transparent material may be in the shape of a cylinder to help give an even distribution of light around the axis of the transparent material and waveguide. There are several types of materials that could be used as the transparent material, as will be apparent to those skilled in the art. For example, the transparent material could be an acrylic material. Preferably, the transparent material has a uniform cross section along its length, for example it may be formed as an extrusion of a plastics material.

Preferably, a diameter of the transparent material is at least three times a diameter of the interior channel, more preferably at least five times the diameter of the interior channel, so that there is a sufficient thickness of transparent material for the light to be internally reflected along the transparent material. Otherwise, too much light may be emitted near an end of the waveguide where light is injected into the waveguide, and the intensity of light emitted may noticeably dim along the length of the waveguide.

According to a second aspect of the invention, there is provided a lighting device comprising the waveguide of the first aspect, and a lamp mounted adjacent an end of the waveguide, the lamp for emitting light into the end of the waveguide. Preferably, the lamp is an LED lamp.

According to a third aspect of the invention, there is provided a method of forming a waveguide, comprising forming a solid body of transparent material with an interior channel aligned parallel to a central axis of the solid body, and incorporating a reflective material in the hole. Preferably, the solid body of transparent material has a uniform cross-section all along the central axis. The central axis is preferably aligned with a length of the waveguide, the waveguide carrying the light along the length of the waveguide by total internal reflection. The method may be used to form the waveguide of the first aspect of the invention.

The interior channel may for example be formed by drilling a hole into the transparent material, the hole constituting the interior channel. Alternatively, the interior channel could be integrally formed with the solid body, for example if the solid body and its interior channel are formed as an extrusion, or by moulding.

The method may comprise filling the interior channel with a liquid reflective material, for example a reflective white paint, so the paint cures on the interior surfaces of the transparent material that define the interior channel. Or, a reflective rod such as a reflective cylinder could be incorporated into the hole, for example by co-extruding the solid body and reflective rod together with one another, or inserting the reflective rod into the interior channel after the solid body has been formed, preferably with a refractive index matching material between the transparent material and the reflective material to help prevent total internal reflection from occurring at the interior surfaces of the transparent material that define the interior channel.

DETAILED DESCRIPTION

Embodiments of the invention will now be described by way of non-limiting example only and with reference to the accompanying drawings, in which:

Fig. 1 shows a schematic cross-sectional diagram of a lighting device according to an embodiment of the invention;

Fig. 2 shows another schematic cross-sectional diagram, taken along XS1 marked on Fig 1; and

Fig. 3 shows another schematic cross-sectional diagram, according to a further embodiment of the invention.

The figures are not to scale, and same or similar reference signs denote same or similar features.

The schematic diagram of Fig. 1 shows a cross-section taken along the length of a lighting device 1. The lighting device comprises a waveguide 15, formed by a cylindrical body of transparent material 20. Two end caps 5 are mounted at opposite ends 22 and 24 of the cylindrical body of transparent material 20. Each end cap 5 has sides 12 extending outwardly from a main body 10, the sides forming a circular cup into which an end of the transparent material 20 can be inserted.

Each main body 10 comprises an LED light source, which emits light into the corresponding end of the cylindrical body of transparent material 20. Each LED light source comprises one or more LEDs, and a heatsink for dissipating excess heat. The main body 10 also comprises LED drivers for driving the LED(s), although the LED drivers could be located remotely from the main body 10 in alternate embodiments. A small gap 14 exists between the main body 10 and the cylindrical body of transparent material 20 to help prevent overheating of the cylindrical body of transparent material 20.

The main body 10 has a reflective surface 11 facing towards the corresponding end of the cylindrical body of transparent material 20, and apertures (not shown in Figs) are provided through the reflective surface to allow light to exit from the LED(s) in the main body and into the transparent material 20.

The cylindrical body of transparent material 20 has an interior channel 30 that passes through the cylindrical body of transparent material, aligned with a central axis 40 of the cylindrical body of transparent material. This can be seen in Fig. 2, which shows a cross-section through the cylindrical body of transparent material 20, taken along line XS1 marked on Fig. 1.

The cylindrical body of transparent material 20 has an exterior surface 26 which has a circular cross section, and an interior surface 28 which also has a circular cross section. Both the cross-sections of the exterior and interior surfaces 26 and 28 share the same central axis 40. The interior surface 28 defines the perimeter of the interior channel 30, which therefore also has a circular cross section.

Inside the interior channel 30, a coating of reflective material 35 is formed on the interior surface 28. The coating is applied to the interior surface 28 as a liquid, and is then allowed to cure. The cylindrical body of transparent material 20 has the same cross section along its whole length.

The cylindrical body of transparent material 20 may be formed as an extrusion or moulding. The interior channel 30 may be formed during the extrusion or moulding, or may for formed afterwards, for example by drilling.

In use, the end caps 5 each emit LED light into a respective end of the cylindrical body of transparent material 20, and the cylindrical body of transparent material 20 transmits the light towards the middle 50 of the waveguide by total internal reflection. Light that travels all the way along the waveguide from one end cap 5 to the other end cap 5, is reflected back into the waveguide by the reflective surface 11.

As the light is internally reflected along the waveguide, some of the light reflects off the reflective material 35. This changes the direction of the light, and causes it to exit the waveguide through the exterior surface 26, rather than being totally internally reflected again. Since the reflective material 35 follows the circular shape of the interior surface 28, the light intensity exiting the waveguide is consistent all the way around the circumference defined by the external surface 26.

As shown, the diameter of the transparent material across the exterior surface 26 is greater than five times the diameter of the interior channel across the interior surface 28, and so the light can travel far enough along the waveguide so that the waveguide is not noticeably dimmer at the centre 50 than at adjacent the ends 22 and 24.

A further embodiment of the invention will now be described with reference to Fig. 3, which shows an alternative cross section of the cylindrical body of transparent material 20, now labelled as 20a. The transparent material 20a can be incorporated in Fig. 1 instead of the transparent material 20. The transparent material 20a differs from the transparent material 20 in that the interior surface 28a has an oval shape, rather than a cylindrical shape. Additionally, the reflective material is an oval rod 35a, rather than a reflective coating. The oval rod 35a is present inside the interior channel 30a, and reflects light out of the waveguide through the exterior surface 26a. In this embodiment, the oval rod 35a is a solid body of opaque white plastics material, such as acrylic, however other types of reflective rod could alternatively be implemented. Both transparent material 20a and rod 35a share a common central axis 40a running along the lengths of the transparent material 20a and rod 35a.

In use, oval rod 35a reflects light out of the transparent material 20a through the exterior surface 26a. The oval shape of the rod 35a creates a variation in the intensity of the light exiting the waveguide 15a around the central axis 40a. Specifically, in the orientation shown in Fig. 3, the light intensity is higher to the left and right of the waveguide, and the light intensity is relatively lower to above and below the waveguide.

In this embodiment, the oval rod 35a and the transparent material 20a are integrally formed with one another by co-extruding them. However, extruded materials sometimes have poorer optical qualities than moulded materials, and so the transparent material 20a and the oval rod 35a could be moulded/cast separately from one another. A liquid refractive index matching material may be poured into the interior channel 30a prior to inserting the oval rod into the interior channel, so that when the oval rod is inserted and the index matching material cures into a solid form, the index matching material helps to hold the rod in place inside the interior channel. The index matching material has a refractive index sufficiently close to the refractive index of the transparent material to prevent total internal reflection occurring at the interior surface 28a.

Many other variations of the described embodiments falling within the scope of the invention will be apparent to those skilled in the art. For example, although the interior channels 30 and 30a are aligned along the central axes 40 and 40a of the transparent material 20 and 20a in the illustrated embodiments, the interior channels 30 and 30a could be offset from the central axes 40 and 40a in alternate embodiments, to produce varying intensities of light about the central axes.

Claims

1. A waveguide comprising a transparent material along which light travels by total internal reflection, wherein the waveguide comprises an interior channel that is inside of the transparent material and that runs along a length of the waveguide, and wherein the interior channel comprises a reflective material which reflects light out of the waveguide.

2. The waveguide of claim 1, wherein the interior channel is aligned with a central axis of the waveguide.

3. The waveguide of claim 1 or 2, wherein the interior channel runs along substantially a full length of the waveguide.

4. The waveguide of claim 1, 2, or 3, wherein the transparent material comprises an interior surface that adjoins the interior channel.

5. The waveguide of any preceding claim, wherein the transparent material comprises an exterior surface that defines an exterior of the waveguide through which light is emitted.

6. The waveguide of any preceding claim, wherein the reflective material is at a boundary between the interior channel and the transparent material.

7. The waveguide of any preceding claim, wherein the reflective material reflects light out of the waveguide in directions extending over substantially 360 degrees transverse to the length of the waveguide.

8. The waveguide of any preceding claim, wherein the interior channel has a circular cross section.

9. The waveguide of any preceding claim, wherein the reflective material has a circular or oval cross-section.

10. The waveguide of any preceding claim, wherein the reflective material is formed as a coating on an interior surface of the transparent material that adjoins the interior channel.

11. The waveguide of any one of claims 1 to 9, wherein the reflective material is formed as a rod having a reflective surface, wherein the rod has been inserted into the interior channel.

12. The waveguide of any preceding claim, wherein the channel is formed as a circular hole through the transparent material.

13. The waveguide of any preceding claim, wherein the transparent material is in the shape of a cylinder.

14. The waveguide of any preceding claim, wherein the transparent material is an acrylic material.

15. The waveguide of any preceding claim, wherein a diameter of the transparent material is at least three times a diameter of the interior channel, and preferably at least five times the diameter of the interior channel.

16. A lighting device comprising the waveguide of any preceding claim and a lamp mounted adjacent an end of the waveguide, the lamp for emitting light into the end of the waveguide.

17. The lighting device of claim 1, wherein the lamp comprises one or more Light Emitting Diodes.

18. A method of forming a waveguide, comprising forming a solid body of transparent material with an interior channel aligned parallel to a central axis of the solid body, and incorporating a reflective material in the interior channel.

19. The method of claim 18, wherein the interior channel is formed by drilling a hole into the transparent material.

20. The method of claim 18 or 19, wherein the reflective material is received in the interior channel as a liquid, and cures to a solid inside the hole.

21. The method of claim 18 or 19, wherein the reflective material is a reflective rod, and the method comprises inserting the reflective rod into the hole.

22. The method of claim 21, wherein the reflective rod is inserted into the hole along with a refractive index matching material between the transparent material and the rod to prevent total internal reflection occurring at an interior surface of the transparent material defining the hole.

23. The method of claim 18, wherein the reflective material is a reflective rod, and the method comprises co-extruding the rod and the transparent material together with one another.

24. The method of claim 21,22, or 23, wherein the reflective rod is a reflective cylinder.