GB2518355A

GB2518355A - Improvements in or relating to a lighting apparatus

Info

Publication number: GB2518355A
Application number: GB1315725.0A
Authority: GB
Inventors: Dan Harrison; Tom Lee
Original assignee: MHA LIGHTING HOLDINGS Ltd
Current assignee: MHA LIGHTING HOLDINGS Ltd
Priority date: 2013-09-04
Filing date: 2013-09-04
Publication date: 2015-03-25
Anticipated expiration: 2033-09-04
Also published as: GB2518355B; WO2015033087A1; GB201315725D0

Abstract

A lighting apparatus 10 comprises a waveguide 18 and a lighting device 28 at an end of the waveguide. The waveguide 18 is capable of sustaining total internal reflectance and has a printed reflector 26 on its surface to reflect light from the waveguide. The lighting device 28 has at least one LED 15 to emit light into the end (39, Fig. 2) of the waveguide 18. A gap (38, Fig. 2) is provided between the LED 15 and the end 39 of the waveguide 18.

Description

Improvements in or Relatinu to a Liuhtinp Apparatus

Technical Field

The invention relates to a lighting apparatus for illumination purposes, and to improvements in or relating thereto.

Background

It is known to provide a lighting apparatus comprising several LEDs which are embedded along the length of a clear acrylic rod having a reflective strip. The reflective strip is a sticker that is along the length of the rod, which is typically applied by hand during manufacture. In operation of the lighting apparatus most of the light from the LEDs passes into the rod, and is totally internally reflected within the rod before being reflected out of the rod when it encounters the reflective strip. Such a lighting apparatus may be used as a replacement for a fluorescent tube or an incandescent bulb to provide illumination.

In the known lighting apparatus pairs of LEDs are located in radial bores in the rod.

Typically four pairs of LEDs are provided in a rod of about 60cm in length such that there are eight LEDs in total. Typically the LEDs are mounted onto a surface of a circuit board facing away from the circuit board, and each pair of LEDs requires a driver.

Where additional pairs of LEDs are used, for example in rods which are longer than 60cm, additional pairs of LEDs and additional drivers may also be required.

Light Emitting Diode (LED) technology has developed in recent years so that they can now operate with a higher power output. Typically an array of LEDs is provided in the form of a Chip on a Board (COB) with the array having a phosphor coating. Such COB LEDs produce more heat than conventional LEDs.

The known lighting apparatus may have several problems. Providing the pairs of LEDs in radial bores in the rod may result in light leakage because not all of the light enters the rod. This may result in a less efficient operation of the apparatus. Furthermore, heat from the LEDs may build up in the rod in the region around the radial bores, which may also reduce the efficiency of operation of the apparatus. The build up of heat is generally unwanted because it may cause damage to the rod in the region near to the LEDs. The management of heat produced by the LEDs becomes more important when contemplating the use of higher power COB LEDs.

t5 Furthermore, when a higher power output of light is required additional pairs of LEDs are required in the known lighting apparatus. This requires additional LED drivers, which adds to the cost and complexity of the apparatus. In addition, applying the sticker for the reflector of the rod may be slow and labour intensive.

It is broadly an object of the present invention to address one or more of the above mentioned disadvantages of the previonsly known lighting apparatus.

Summary

What is required is a lighting device which may reduce or minimise at least some of the above-mentioned problems.

According to a first aspect of the invention, there is provided a lighting apparatus for illumination, comprising a waveguide and a lighting device at an end of the waveguide, the waveguide being capable of sustaining total internal reflectance and having a reflector at or near a surface thereof to reflect light from the waveguide, the lighting dcvice having at least one Light Emitting Diode (LED) to emit light into the end of the waveguide, wherein a gap is provided between the at least one LED and the end of the wavegui de.

Such an apparatus provides the advantage that there is an improved thermal management of heat that is generated by the LED because there is no physical contact between the LED and the end of the waveguide. Such an improved thermal management may avoid hot spots at or near the end of the waveguide which may reduce light losses.

Whereas light is emitted into an end of the waveguide it will be appreciated that this may include light being emitted into an edge of the waveguide. The gap is sufficiently large to reduce or avoid overheating of the waveguide, but sufficiently small so that light from the LED couples effectively to the waveguide. Such a gap may utilise the physical principle that a suitably small gap between the LED and the waveguide substantially eliminates or avoids light loss so that a large majority, i.e. substantially all, of the light from the LED passes into the waveguide. Such arrangements provide for improved photometric efficiency and thermal management efficiency. It will be appreciated that the gap is an air gap. A further advantage is that fewer drivers may be required to operate the apparatus when a plurality of LEDs are used which may be due to the improved efficiency of operation. The apparatus may permit the use of drivers to be used with a lower power when compared to the prior art, which may be more cost effective.

Preferably the lighting device includes a circuit board and the at least one LED is mounted to it, the circuit board being a Fibre Reinforced PCB or a flexible PCB.

Preferably the lighting dcvicc includes a metal backed circuit board comprising a substrate layer and a metal layer, the at least one LED being mounted to the metal backed circuit board so that the at least one LED is embedded within it and faces the end of the waveguide. Such an arrangement may provide an improved dissipation of heat because it is conducted away from the at least one LED by the metal backed circuit board. t5

Preferably the metal layer is closest to the end of the waveguide. Such an arrangement may further assist with thermal management and may reduce heat building up in the waveguide.

Preferably the at least one LED is mounted on an LED circuit board which is mounted to the substrate layer, the metal backed circnit board having a throngh hole, and the at least one LED being arrange to be within the through hole. Such an arrangement has the advantage that light from the LED passes through the hole, and that light from the LED is confined between the metal layer and the end of the waveguide, and is guided into the wavegui de.

Preferably the at least one LED is provided in a first recess of the metal layer, the first recess at least partially providing the gap. Preferably the end of the waveguide is in contact with the metal layer, the first recess wholly providing the gap. The metal layer provides the combined advantages of a thermal path for heat to transfer away from the LED and waveguide, whilst also reflecting light from the LED into the waveguide which may assist with substantially climinating or reducing light loss. Furthermore, such an arrangement may provide a more accurate way to set the dimension of the gap.

Preferably the lighting device has an end cap comprising a planar part with a hole in it, and with a collar around the hole, the hole being aligned with the at least one LED, and the waveguide being located in the collar. Such a collar provides the advantage of substantially blocking direct light from the LED that might otherwise exit the waveguide.

In one embodiment a portion of the lighting device is provided to space the end of the waveguide from the at least one LED when the end of the waveguide abuts the portion, said space at least partially providing the gap.

Preferably the portion of the lighting device is part of the end cap. Preferably the portion is a rib of an internal surface of the collar. Such an arrangement provides a combined use for the end cap to provide the gap and to substantially block direct light from the LED that might otherwise exit the waveguide.

Preferably the lighting apparatus frirther includes a heat sink for dissipating heat produced by the at least one LED. The heat sink has the advantage of assisting with removal or dissipation of heat produced by the LED.

Preferably the heat sink is provided in contact with the metal backed circuit board. Such an arrangement provides an improved thermal coupling between the LED and the heat sink.

Preferably the heat sink has a second recess and the LED circuit board is located within the recess. Preferably the second recess contains a phase change material which is dependent on temperature. Preferably the LED circuit board is in contact with a floor of the second recess. Such arrangements may assist with thermal coupling between the heat sink and the LED.

In one embodiment the lighting device comprises a sandwich structure including the end cap, the metal backed circuit board and the heat sink.

The lighting apparatus may inchide a phirality of lighting devices. Preferably said plurality of lighting devices includes a lighting device at another end of the waveguide.

Preferably the reflector comprises ink that is printed onto a surface of the waveguide.

This may have the advantage of providing an improved speed of manufacture.

Preferably the gap is in the range 0.2mm to 1.0mm. Preferably the gap is substantially 0.4mm. Such a gap may be sufficiently large to reduce or avoid overheating of the waveguide, but sufficiently small so that light from the LED couples effectively to the waveguide.

According to a second aspect of the invention there is provided a waveguide for a lighting apparatus, the waveguide capable of sustaining total intemal reflectance and having a reflector at or near a surface thereof wherein the reflector comprises ink that is printed onto a surface of the waveguide.

Preferably the printed reflector is applicd using a stcncil.

Such a reflector may provide the advantage of providing an improved speed of manufacture.

According to a third aspect of the invention there is provided a method of applying a reflector to a waveguide for a lighting apparatus, the waveguide capable of sustaining total internal reflectance, the method including printing the reflector onto a surface of the waveguide.

B

Preferably the method further includes using ink fbr the printing. Preferably the method further includes printing the reflector using a stencil.

According to an alternative characterisation of the invention there is provided a lighting apparatus lbr illumination, comprising a waveguide and a lighting device at an end of thc waveguide, thc wavcguide bcing capable of sustaining total internal reflectance and having a reflector at or near a surfice thereof to reflect light from the waveguide, the lighting device having at least one Light Emitting Diode (LED) to emit light into the end of the waveguide, wherein the lighting device includes a metal backed circuit board comprising a substrate layer and a metal layer, the at least one LED being mounted to the metal backed circuit board so that the at least one LED is embedded within it and faces the end of the waveguide, wherein a gap is provided between the at least one LED and the end of the waveguide.

Any preferred or optional features of one aspect or characterisation of the invention may be a preferred or optional feature of other aspects or characterisations of the invention.

Brief Description of the Drawings

Other features of the invention will be apparent from the fbllowing description of preferred embodiments shown by way of example only with reference to the accompanying drawings, in wffich Figure 1 shows a perspective view of a lighting apparatus according to an embodiment of the invention; Figure 2 shows a cross scction of thc lighting apparatus shown in Figurc 1; Figure 3 shows a cross section of an alternative lighting apparatus to the arrangement shown in Figure 2; Figure 4 shows an exploded view of the lighting apparatus shown in Figure 3; Figure 5 shows a front view of the lighting device shown in Figures 1 -4; Figure 6 shows a closc up vicw of part of Figurc 3; Figure 7 shows stcps of a mcthod according to an cmbodimcnt of thc invcntion; and Figure 8 shows a cross section of an alternative lighting apparatus to the arrangcmcnt shown in Figurc 2.

Detailed Description

Figure 1 shows a perspective view of a lighting apparatus according to an embodiment of the invention, generally designated 10. The lighting apparatus 10 has a heat sink 12, a Printed Circuit Board (PCB) 14 with a Light Emitting Diode (LED) array 15, an end cap 16, and a wavcguidc 18. Thc PCB 14 may altcmativcly bc tcrmcd an LED circuit board and is substantially planar. The heat sink 12 is a substantially cuboid block of metal such as aluminium with dimensions of about 60mm by 30mm by 30mm. The heat sink 12 removes or dissipates heat produced by the LED array 15. The PCB 14 is mounted to one of the faces of the heat sink 12. The PCB 14 has a connector 17 to provide electrical connections for the LED array 15. The end cap 16 is of plastic such as nylon and has a planar part 20 with a circular hole at its centre, and has a cylindrical collar 22 around the circular hole. The collar 22 is of a material that blocks light or substantially blocks light from passing through it. The end cap 16 is mounted to the PCB 14 such that the PCB 14 is sandwiched between the planar part 20 and the heat sink 12 so that the LED array 15 is within the circular hole. Fasteners 23 are provided to hold the sandwich structure together. In another arrangement the planar part 20 is provided with locating rods (not shown) instead of the fasteners 23. The locating rods pass through respective holes in the PCB 14 and cooperate with receiving holes in the heat sink 12. Fasteners (not shown) are provided in the rear face of the heat sink 12 to engage the locating rods and to hold and compress the sandwich structure together. The fasteners 23 or locating rods assist with alignment of the heat sink 12, the PCB 14 and the end cap 16.

The waveguide 18 has a circular cross section, and is a glass rod, or a plastic rod for example nylon or acrylic. The waveguide 18 fits into the collar 22 of the end cap 16 t5 with a push fit, or interference fit in the direction shown by arrow 25. In the embodiment shown, an inner surface of the collar 22 has a circumferential rib 24 so that an end face 39 (shown in Figure 2) of the waveguide 18 abuts the rib 24 when it is fitted inside the collar 22. The rib 24 at least partially sets a gap 38 (shown Figures 2 and 3) between the end face 39 of the waveguide 18 and the LED array 15 when it is fitted inside the collar 22. The gap 38 has a dimension, for example, of between 0.2mm to 1mm, and possibly up to 2mm, and preferably 0.4mm, and reduces the risk of overheating the waveguide 18 due to heat from the LED array 15. The gap 38 is sufficiently large to reduce or avoid overheating of the waveguide 18, but sufficiently small so that light from the LED array 15 couples effectively to the waveguide 18. The gap 38 may utilise the physical principle that a suitably small gap between a light source and a waveguide 18 substantially eliminates or reduces light loss.

It will be appreciated that the collar 22 of the end cap 16 is sufficiently long so that it blocks direct light from the LED array 15 that might exit the waveguide 18.

Furthermore, the collar 22 is sufficiently long so that the angle of incidence of light on an internal surface of the waveguide 18 after the end of the collar 22 is sufficient so that total internal reflectance occurs. Such an arrangement substantially avoids direct light from the LED array 15 exiting the waveguide 18. Light for illumination purposes is arranged to exit the waveguide 18 via a reflector 26 that is printed onto a surface of the waveguide 18. The reflector 18 peniiits light to be reflected out of the waveguide 18 and also diffuses the light. The reflector 18 extends along the waveguide 18 and may be at or near the surface of the waveguide 18. The reflector 26 is ink which is applied to the waveguide 18 using a stencil. Such an arrangement permits an increased rate of waveguide 18 manufacture, for example up to 600 waveguides 18 per day, per person.

Together the heat sink 12, the PCB 14 with the LED array 15, and the end cap 16 form a lighting device 28 that can be fitted to one end of the waveguide 18. It will be appreciated that a second lighting device 28 (not shown) may be fitted to the other end of the waveguide 18 so that there are two lighting devices 28 per waveguide 18.

Figure 2 shows a cross section of the lighting apparatus 10 shown along a plane 30 in Figure 1. In Figure 2 like features to the arrangements of Figure 1 are shown with like reference numerals. In Figure 2 the heat sink 12 is shown to have a recess 32 on the face adjacent to the PCB 14. The LED array 15 is also shown in more detail whereby a board 34 is provided and the LED array 15 is mounted to it. The board 34 may alternatively be tcrmcd an LED circuit board. Such an arrangcmcnt may bc known as a Chip on Board (COB) LED array 15, which has an array of individual LEDs with a phosphor coating covering the array. The LED array 15 may have a power output in the range 4 -20 Wafts. The board 34 is mounted to the PCB 14 so that it makes electrical contact with electrical tracks on the PCB 14, which in turn is in electrical contact with the connector 17 shown in Figure 1. In Figure 2 the PCB 14 has a hole 35 in it (shown more clearly in Figure 4), and thc board 34 is mountcd to a rcar surface of thc PCB 14 so that the LED array 15 is within the hole 35 and the LED array 15 is embedded in the PCB 14. Such embedding sets the gap 38 between the LED array 15 and the end face 39 of the waveguide 18 when it is within the collar 22 of the end cap 16. The rib 24 is also shown which also sets the gap 38.

t5 The board 34 is within the recess 32 of the heat sink 12 so that there is a space 36 surrounding the board 34 within the recess 32. The space 36 is substantially filled with a phase-change material to assist with thermal coupling between the heat sink 12 and the LED array 15. When the phase-changc material is hot due to heat from the LED array 18, it liquefies. When the phase-change material cools down it solidifies. The phase-change material liquefies and solidifies depending on the temperature of the LED array 15. M improved thermal coupling is thereby provided by the phase-change material between the LED array 15 and heat sink 12.

Figure 3 shows a cross section of an alternative lighting apparatus to the arrangement shown in Figure 2. In Figure 3 like features to the arrangements of Figure 2 are shown with like reference numerals. In Figure 3 the rib 24 is omitted and the gap 38 between the end face 39 of the waveguide 18 and the LED array 15 is provided only by the LED array 15 being recessed relative to a front surface 40 (shown in Figure 4) of the PCB 14.

Such a recessed LED array 15 is provided by the thickness of the LED array 15 being less than the thickness of the PCB 14 so that when the LED array 15 is within the hole of the PCB 14 the surface of the LED array 15 is below the front surface 40 of the PCB 14. It will be appreciated that thc gap 38 may be achieved by either solely using the rib 24, or by providing a recessed LED array 15 relative to the front surface 40 of the PCB 14 (as shown in Figure 3), or by using a combination of the rib 24 and recessing the LED array 15 relative to the front surface 40 (as shown in Figure 2).

In the arrangement of Figure 3 the end face 39 of the wavcguidc 18 makes contact with t5 the front surface 40 of the PCB 14. Such an arrangement may provide a more accurate way to set the dimension of the gap 38 because the dimensions of the PCB 14, the LED array 15, and the board 34 can be accurately controlled during manufacture.

Furthermore such an arrangement traps or constrains light between the LED array 15 and the end face 39 of the waveguide 18 due to the close fitment of the end face 39 of the waveguide 18 with the front surface 40 of the PCB 14. This may assist with substantially eliminating or reducing light loss. It will be appreciated that the end face 39 is perpendicular to a longitudinal axis of the waveguide 18, and the PCB 14 is adjacent to the end face 39 so that it is substantially parallel with the end face 39 and in contact with it.

Figure 3 also shows that the recess 32 is shallower than in Figure 2 so that a rear surface 33 of the board 34 abuts a floor 37 of the recess 32. The rear surface 33 and the floor 37 are most clearly shown in Figure 4. The arrangement of Figure 3 improves the thermal coupling of the LED array 15 to the heat sink 12. In one arrangement the recess 32 has a depth which is slightly less, for example 0.15mm less, than the thickness of the board 34. This provides a close coupling between the board 34 of the LED array 15 and the heat sink 12 when the lighting device 28 is assembled, which may further improve thermal conductivity. In such an arrangcment the phase change material may be omitted from the recess 32.

Figure 4 shows an exploded view of the lighting apparatus shown in Figure 3. In Figure 4 like features to the arrangements of Figure 3 are shown with like reference numerals.

In Figure 4 a detailed view 42 of the PCB 14 is also shown. In the detailed view 42 the PCB 14 is shown to comprise a composite of a circuit board substrate layer 44 having an aluminium layer 46. Such a PCB 14 may be termed a metal backed PCB or aluminium backed PCB, or a metal backed circuit board. The substrate layer 44 is about 0.1mm thick, and thc aluminium layer 46 is about 1mm thick. The metal backcd PCB 14 provides an advantage that heat from the LED array 15 is conducted away and towards the heat sink 12. The metal backed PCB 14 also provides an advantage that light from the LED array 15 is trapped, i.e. confined, between the aluminium layer 46 and the end face 39 of the waveguide 18, and is guided into the waveguide 18. Heat that may build up in the waveguide 18 is also conducted away and towards the heat sink 12 via the aluminium layer 46 because the end face 39 is in contact with the aluminium layer 46. In effect the aluminium layer 46 provides a thermal path for heat to transfer to the heat sink 12, and also reflects light from the LED array 15 into the waveguide 18.

It will be understood that the electrical tracks from the connector 17 are provided on the substrate layer 44 so that they cooperate with electrical tracks on the LED board 34.

This means that the LED array 15 is mounted to the PCB 14 the opposite way round when compared to a typical known mounting of an LED array on a board. According to the embodiment light passes through the hole 35 in the PCB 14.

Figure 5 shows a front view of the lighting device 28 shown in Figures 1 -4. In Figure S like features to the arrangements of Figures 1 -4 are shown with like reference numerals. In Figure 5 the waveguide 18 is omitted for clarity. The cylindrical collar 22 is shown with the aluminium layer 46 being visible within it. The LED array 15 can also be seen through the hole 35 in the PCB 14. It can be seen in Figure 5 that the hole 35 has a first diameter 48, and the intemal dimension of the cylindrical collar 22 has a second diameter 50. The second diameter 50 is larger than the first diameter 48 which means that the aluminium layer 46 can be seen within the cylindrical collar 22. Such an arrangcmcnt means that the end face 39 of thc wavcguidc 18 is in contact with the aluminium layer 46, or in close proximity to it, when the waveguide 18 is fined within the collar 22 so that heat can be transferred to the heat sink 12 as shown by the arrows 52. Such an arrangement helps with heat transfer.

Figure 6 shows a close up view of part of Figure 3. In Figure 6 like features to the arrangements of Figures 1 -5 are shown with like reference numerals. In Figure 6, when the LED array 15 is switched on light may bounce off a sidewall of the aluminium layer 46 and enter the waveguide 18 as shown at 53. In this way the embedding of the LED array 15 in the aluminium layer 46 means that the aluminium layer 46 acts as a guide for the light. This means that the light has nowhere else to go other than into the waveguide 18. Figure 6 also shows that the LED array 15 is embedded in the aluminium layer 46 to set the gap 38, and that the end 39 of the waveguide l8is in contact with the aluminium layer 46.

Figure 7 shows steps of a method according to an embodiment of the invention, generally designated 60. It will be appreciated that the steps may be performed in a different order, and may not necessarily be performed in the order shown in Figure 7. In Figure 7 the method is a method of applying a reflector 26 to a waveguide 18 for a lighting apparatus 10, the waveguide 18 is capable of sustaining total internal reflectance. The method includes printing the reflector 26 onto a surface of the waveguide 18, as shown at 62. The method further includes using ink for the printing, as shown at 64. The method further includes printing the reflector 26 using a stencil, as shown at 66.

Figure 8 shows a cross section of an altemative lighting apparatus to the arrangement shown in Figure 2. In Figure 8 like features to the arrangements of Figures 1 -6 are shown with like reference numerals. In Figure 8, the hole 35 is omitted and the board 34 is mounted to the PCB 14 in a conventional manner so that it is on the surface of the PCB 14 and in contact with the aluminium layer 46. The circuit board substrate layer 44 is on direct contact with the heat sink 12. In Figure 8 the gap 38 is set by the circumferential rib 24 of the inner surface of the collar 22 so that an end face 39 of the waveguide 18 abuts the rib 24 when it is fitted inside the collar 22.

In operation, when the LED array 15 is switched on light enters the waveguide 18 as shown at 53 in Figure 3 and 6. Light emitted from the LED array 15 is directed substantially along the waveguide 18 and the light is substantially totally internally reflected within the waveguide 18. The light is totally internally reflected within the waveguide 18 until it encounters the reflector 26 where it is reflected out of the waveguide 18 to provide a diffuse beam of light for use in illumination. The distribution of the light can be controlled by modifying the reflector 26. It will be appreciated that the reflector 26 is along the length of the waveguide 18 so that light escape from the waveguide 18 along its length and where the reflector 26 is located.

In operation the LED array 15 generates heat. The heat sink 12 is operable to remove heat from the LED array 15. By shining the light from the LED array 15 through the hole 35 in the metal backed PCB 14 a number of advantages are provided. These advantages include confining light from the LED array 15 between the LED array 15 and the end face 39 of the wavcguide 18 so that the light has nowhere else to go other than into the waveguide 18. Additionally the metal backed PCB 14 provides a thermal path for heat to escape from the region near the end face 39 of the waveguide 18 and the LED array 15 to improve thermal dissipation. Furthermore, the arrangement of the LED array 15 being within the hole 35 provides a ready way to set the dimension of the gap 38. Such arrangements provide for improved photometric efficiency and thermal management efficiency.

It will be appreciated that the waveguide 18 may be a substantially transparent or clear solid rod such as a glass rod, an acrylic rod or a nylon rod. The waveguide 18 is able to sustain total internal reflectance of light. Alternatively the waveguide 18 may be a hollow tube. The rod or hollow tube may be curved as required for a particular lighting requirement. Alternatively the waveguide 18 may be a sheet, with the light from the LED array 15 being input to an end or an edge of the sheet. The sheet may be solid or may be hollow comprising two sheets separatcd by a small gap, and may also be curved.

In thc case of the waveguide 18 being a sheet, there may be more than one lighting device 28 on one edge of the sheet, or adjacent edges of the sheet. Whereas the waveguide 18 is described as transparent it will be understood that this may include a waveguide 18 that is slightly opaque or has a slightly opaque surface such as a matt finished surface. In the ease of the waveguide being a hollow sheet or a tube, the gap 38 is provided between an end of the hollow sheet or tube and the LED array 15.

The arrangements described herein provide an improved lighting device 28 with an improved photometric efficiency and thermal management efficiency. Such a lighting device 28 may mean that only one or two LED arrays 15 are required per waveguide 18.

For example, only one lighting device 28 may be required at one end of the waveguide 18, but another lighting device 28 may also be used at the other end of the waveguide 18. In the case of the waveguide 18 being a sheet there may be additional lighting devices 28, for example on different edges of the sheet. Since each LED array 15 requires a driver to operate, the apparatus 10 may also provide the additional advantage of requiring less drivers to operate, or permitting a lower power driver to be used when compared to the prior art, which may be more cost effective.

Whereas the term LED has been used above, it will be understood that this may include an Organic LED (OLED). The LED array 15 may also be a cluster of LEDs arranged in a geometric pattern such as a square or octagon comprising, for example, up to nine LEDs. The LED array 15, the OLEDs, or cluster of LEDs may be mounted conventionally on the PCB 14 as shown in Figure 8, i.e. so that they point away from, and shine light away from, the circuit board substratc layer 44. Alternatively, the LED array 15, the OLEDs, or cluster of LEDs may be mounted to the PCB 14 as shown in Figures 2 -5, i.e. so that they point through, and shine light though, the circuit board substrate layer 44 and the aluminium layer 46.

Whereas the PCB 14 is described above with reference to Figures 1 -6 and 8 as a metal backed PCB, in an alternative arrangement the PCB 14 may be substituted with a Fibre Reinforced (FR) PCB or a flexible PCB. In the case of the FR PCB the type of board may be FR4, which is a glass fibre reinforced PCB and has the advantage of being flame and heat resistant and may also be self extinguishing. In the case of a flexible PCB, such flexibility may improve the contact with the heat sink 12.

Claims

CLAIMS1. A lighting apparatus for illumination, comprising a waveguide and a lighting device at an end of the waveguide, the waveguide being capable of sustaining total internal reflectance and having a reflector at or near a surface thereof to reflect light from the waveguide, the lighting device having at least one Light Emitting Diode (LED) to emit light into the end of the waveguide, wherein a gap is provided between the at Icast one LED and the end of the waveguide.
2. A lighting apparatus according to claim 1, wherein the lighting device includes a metal backed circuit board comprising a substrate layer and a metal layer, the at least one LED being mounted to the metal backed circuit board so that the at least one LED is embedded within it and faces the end of the waveguide.
3. A lighting apparatus according to claim 2, wherein the metal layer is closest to the end of the waveguide.
4. A lighting apparatus according to claim 2 or 3, wherein the at least one LED is mounted on an LED circuit board which is mounted to the substrate layer, the metal backed circuit board having a through hole, and the at least one LED being arrange to be within the through hole.
5. A lighting apparatus according to claim 2, 3 or 4, wherein the at least one LED is provided in a first recess of the metal layer, the first recess at least partially providing the gap.
6. A lighting apparatus according to claim 5, wherein the end of the waveguide is in contact with the metal layer, the first recess wholly providing the gap.
7. A lighting apparatus according to any preceding claim, wherein the lighting dcvicc has an cnd cap comprising a planar part with a hole in it, and with a collar around the hole, the hole being aligned with the at least one LED, and the waveguide being located in the collar.
8. A lighting apparatus according to any of claim 1 -5, wherein a portion of the lighting device is provided to space the end of the waveguide from the at least one LED t5 when the end of the waveguide abuts the portion, said space at least partially providing the gap.
9. A lighting apparatus according to claim 7 and 8, wherein the portion of the lighting device is part of the end cap.
10. A lighting apparatus according to claim 9, wherein the portion is a rib of an internal surface of the collar.
11. A lighting apparatus according to any preceding claim, and further including a heat sink for dissipating heat produced by the at least one LED.
12. A lighting apparatus according to claim 11 when dependent on claim 2, wherein the heat sink is provided in contact with the metal backed circuit board.
13. A lighting apparatus according to claim 12 when dependent on claim 4, wherein the heat sink has a second recess and the LED circuit board is located within the recess.
14. A lighting apparatus according to claim 13, wherein the second recess contains a phase change material which is dependent on temperature.
15. A lighting apparatus according to claim 13 or 14, wherein the LED circuit board is in contact with afloor of the second recess.
16. A lighting apparatus according to any of claims 11 -15 when dependent on claims 2 and 7, wherein the lighting device comprises a sandwich structure including the end cap, the metal backed circuit board and the heat sink.
17. A lighting apparatus according to any preceding claim, and further including a plurality of lighting devices.
18. A lighting apparatus according to claim 17, wherein said plurality of lighting devices includes a lighting device at another end of the waveguide.
19. A lighting apparatus according to any preceding claim, wherein the reflector comprises ink that is printed onto a surface of the waveguide.
20. A lighting apparatus according to any preceding claim, wherein the gap is in the range 0.2mm to 1.0mm.
21. A lighting apparatus according to claim 20, wherein the gap is substantially 0.4mm.
22. A lighting apparatus according to claim 1, wherein the lighting device includes a circuit board and the at least one LED is mounted to it, the circuit board being a Fibre Reinfbrced PCB or a flexible PCB.
23. A lighting apparatus as substantially described herein with reference to Figures 1 -6 and 8 of the accompanying drawings.
24. A waveguide for a lighting apparatus, the wavcguidc capable of sustaining total internal reflectance and having a reflector at or near a surfice thereof, wherein the reflector comprises ink that is printed onto a surface of the waveguide.
25. A waveguide according to claim 24, wherein the printed reflector is applied using a stencil.
26. A waveguide as substantially described herein with reference to Figure 1 of the accompanying drawings.
27. A method of applying a reflector to a waveguide for a lighting apparatus, the waveguide capable of sustaining total internal reflectance, the method including printing the reflector onto a surface of the waveguide.
28. A method according to claim 27, and further including using ink for the printing.
29. A method according to claim 27 or 28, and further including printing the reflector using a stencil.
30. A method as substantially described herein with reference to Figure 7 of the accompanying drawings.