GB2372879A

GB2372879A - A side emission LED for use in reflector based light device

Info

Publication number: GB2372879A
Application number: GB0117222A
Authority: GB
Inventors: William J Williams
Original assignee: WJW Ltd
Current assignee: WJW Ltd
Priority date: 2001-07-14
Filing date: 2001-07-14
Publication date: 2002-09-04
Anticipated expiration: 2021-07-14
Also published as: GB2372879B; GB0117222D0

Abstract

An LED for use in a reflector based light device comprises two leads (10, 15) wherein lead (15) has a head portion comprising a reflective cavity (14) with a light emitting die (13) therein. The side portions of the cavity are removed in the X axis direction such that light from the die may be emitted outwards from the sides of the head as well as upwards from the head. This enables the LED to be used in a reflector based device as the light passing from the sides of the LED head allow focussing of the light beam from the reflector. The LED may be used in array and one side of the exposed cavity sides may be covered with a reflective material to direct more light to one side.

Description

AN LED FOR USE IN REFLECTOR-BASED LIGHT DEVICES TECHNICAL FIELD The present invention relates to an LED or LEDs for use in reflector-based light devices.

BACKGROUND AND PRIOR ART Light sources whose dimensions are sufficiently small to enable a high degree of coherence and produce a wide solid angle light flux distribution are useful in a broad range of applications.

When such light sources are moved along the principle optical axis of a concave reflector they can produce a variable vergence light beam (i. e. focusable). Devices such as torches or other light emitting devices often contain such a light source and a parabolic reflector arrangement. This arrangement is both a simple and optically efficient way of producing a beam of light focusable from wide to spot. On purely optical grounds incandescent filament bulbs are particularly suitable as the light source since they have a high degree of coherence and also emit light evenly over a very wide solid angle, enabling efficient use of the reflector.

There are however numerous disadvantages of using filament bulbs: Filament bulbs have a limited life and as a consequence such devices are typically designed to allow the insertion of replaceable bulbs at periodic intervals by allowing separation of the device followed by reassembly. Filament bulbs get hot during use which is due to their inherent luminous inefficiency. Therefore such devices are typically designed bonded to a metal, or other heat conducting material or casing to act as a heat sink. Large amounts of infrared radiation is emitted in addition to useful visible light. Due to the low luminous efficiency of filament bulbs they consume a high quantity of electrical power. Thus for the device to be useful in a portable mode of operation, large batteries are needed.

The spectral light distribution of a filament bulb has a low colour-temperature (i. e. yellowy light). Some devices incorporate a colour-correction filter to alter the light distribution. This is required to provide an improved colourrendering-index factor, which is beneficial for analysis of biological tissues or other detailed tasks. The filament is surrounded by a fragile glass envelope. The operator must be very careful to avoid touching the glass, as grease from the fingers can cause cracks to develop on the glass envelope contributing to degradation and ultimately reducing the life of the bulb.

All of these problems may be overcome by the use of discreteleaded and surface mount device (SMD) Light Emitting Diode technology (LEDs), which have been used in focusable light emitting devices. LEDs have a long life, emit small amounts of infrared, have much reduced power requirements, have an ideal colour temperature (white types), and possess considerable physical toughness.

LEDs whilst having above advantages when compared to filament bulbs, unfortunately suffer from several disadvantages when used as the light source in reflector-based devices: Discrete-leaded types are typically available in 3 and 5mm packages with a variety of encapsulating optics designs. In a

2 'flat top design'the light source point area is small-0. 75mm2 (a moderate degree of coherence) but the widest solid angle light flux distribution is usually limited to at most-180 degrees. Accordingly poor use is made of reflector and corresponding poor Ifocusabilityl results. Depending on the type and manufacturer, in'narrow angle designs'an image of the light-emitting die is projected, this is seen as an uneven (often ringed) distribution of light. Large size of imaged light source via encapsulating optics produces an extended object, accordingly'focusability'is poor. SMD types are small in physical size but have even larger luminous source sizes than discrete-leaded types due to the package itself acting as a secondary emitter, again poor Ifocusabilityl results. Lensed SMD types also suffer from limited light flux distribution.

For certain tasks, such LEDs when compared to filament bulbs (e. g. a headtorch) are much less effective due to their reduced light output. When such LEDs are packed together to increase the light output there is a corresponding increase in the light emitting area (LEA) which in turn reduces the'focusability'.

Even if future generations of individual LEDs have sufficient light output, the design of the light emitting region itself, and the integrated encapsulating optics, direct the light flux to give a directional beam of light thus making poor use of any reflector.

To utilise the advantages of LEDs for use in a reflector-based light emitting device both the'focusability'and reduced light output problems need to be solved.

SUMMARY OF INVENTION The present inventor has surprisingly found that a new design of LED with a small light emitting area provides a high degree of coherence and a wide solid angle light flux distribution that may also be efficiently packed into an array of such LEDs.

Furthermore this new design will be future scalable as any future technology developments in a individual LED can always be implemented in a multi-LED design, thus always having a greater light output whilst maintaining good Ifocusabilityl.

In a first aspect, the invention provides an LED for use in reflector-based light devices which comprises two connection leads, a light-emitting die and optionally phosphors, characterised in that one of the connection leads comprises a head, the top surface of which has a cavity which is also open to two opposing sides of the head, the light-emitting die being mounted within the cavity, whereby the light flux distribution is emitted continuously and: (a) at least 20% is emitted in more than 180 degrees in the x-z plane; and (b) at least 80% is emitted in less than 180 degrees in the y-z plane; wherein the x axis passes through the geometric centre of the cavity but not through the body of the head; the y axis, perpendicular to the x axis, passes through the geometric centre of the cavity and through the body of the head; the z axis being perpendicular to both the x and y axes.

A second aspect of the invention provides an array of LEDs, as defined above, for use in reflector-based light sources.

A third aspect of the invention provides a reflector-based light source comprising at least one LED as defined above.

A fourth aspect of the invention provides an LED-based bulb comprising an LED, or an array of LEDs, as defined above characterised in that it is also physically and electrically connected to a container. A fifth aspect of the invention provides a process of making an LED as defined above, characterised in that the sides of a full reflector dish leaded-LED are removed, exposing the cavity to the sides of the head.

DETAILED DESCRIPTION The LED In order to achieve a high degree of'focusability'and also maintain a high degree of coherence, it is important that light is emitted over a wide solid angle and also that the size of the emitting source is small in size. Hence the LED according to the invention comprises two connection leads, a lightemitting die and optionally phosphors, characterised in that one of the connection leads comprises a head, the top surface of which has a cavity which is also open to two opposing sides of the head, the light-emitting die being mounted within the cavity.

The x axis is defined as being that which passes through the geometric centre of the cavity but not through the body of the head, and thus passing entirely through the cavity and through the openings in the sides of the head. The y axis, being perpendicular to the x axis, also passes through the geometric centre of the cavity but through the physical body of the head.

The z axis is perpendicular to both the x and y axes, and thus extends out of the cavity on the top surface and through the body of the head. The x-z plane is that plane which passes through the geometric centre of the cavity and exists in the x and y axis directions, but not in the z direction. The x-y and y-z planes are similarly defined.

This arrangement accordingly allows light to be emitted from the light-emitting die in more than 180 degrees in the x-z plane whilst in the y-z plane the majority of the light is emitted in less than 180 degrees. Thus at least 20% is emitted in more than 180 degrees in the x-z plane and at least 80% is emitted in less than 180 degrees in the y-z plane. Preferably at least 30%, more preferably at least 40% of the light is emitted in more than 180 degrees in the x-z plane.

Thus in the x-z plane there are two lobes surrounding the LED, and light is emitted'backwards', unlike in the prior art. Due to the position of the light emitting die and the presence of a section of a reflector dish beneath the die, light is still emitted mainly forwards but certainly less than in prior art.

Hence according to the invention an even, wide solid angle light flux distribution occurs.

In order for the LEDs to be efficiently packed, and for manufacturing simplicity, it is preferred that the geometry of the head is such that it has two pairs of parallel sides in the x-y plane. To improve Ifocusabilityl the shortest side should be as short as possible, and is preferably less than 0.8 mm, more preferably less than 0.6 mm and most preferably less than 0.4 mm.

As described above the cavity is shaped so that it is open to two opposing sides of the head as well as the top surface.

Hence a particularly appropriate shape is based on toroidal geometry and for simplicity and efficiency, a cylindrical shape is preferred.

It is usual practice to encapsulate fragile LEDs with a hard, transparent resin. According to the present invention, the light-emitting die is preferably encapsulated, more preferably having flat faces, and most preferably the top face of the encapsulation is no more than 1 mm from the top surface of the head. As an optional modification the encapsulation has a notch, which acts as a mirror which reflects additional light 'backwards'.

Since it is preferred that such LEDs may be packed closely together, in order to dissipate any heat which is developed it is preferred that the LED is surrounded by heat-conducting material. Such heat-conducting material may extend all the way to the top of the LED, up to the light emitting area.

The Tightly Packed Array The second aspect of the invention is an array of LEDs as described above. The most preferred arrangement for the array is a plurality of LEDs arranged in a row. For this purpose it is important that the LEDs are shaped with parallel sides with two short sides and two long sides. Accordingly this allows the LEDs to be closely packed and thus remain'focusable'. For efficiency it is preferred that some of the LEDs are of a type which is different to that described above. Accordingly, these so-called type (ii) LEDs have a cavity which passes through only one side of the head. These type (ii) LEDs therefore emit light biased towards one of the long sides of the LED.

Preferably, the side which the cavity does not pass through, has a reflector which is preferably thin and plane so that the overall width of the lead is the same as type (i).

It is particularly preferred that the array is such that the LED in the centre (or the two LEDs if there are an even number) stands proud of the adjacent LEDs and any further LEDs towards the outside of the row are arranged lower than the adjacent LEDs nearer the centre. Such an arrangement is referred to as a staggered array. A particularly effective form of this arrangement is where type (ii) LEDs are used with the side which the cavity passes through facing away from the LED, or LEDs, in the highest position. Alternatively the advantages of this preferred arrangement may equally be achieved when the LEDs which are not in the highest position are of type (i), and the light emitted towards the centre of the row is reflected by the adjacent LED which has mirrored sides.

An advantage of the staggered pattern in general is that it enables all sides of each LED to contribute to the flux distribution, especially'backwards', resulting in a good even flux distribution. A disadvantage is that each light emitting region of the individual LED is spatially separated from each other by a larger distance than would be the case than in a row which increases the light source area. This disadvantage is partially offset, however, by the'mirror'imaging effect by the use of type (ii) LEDs or lead reflection.

Optionally, as well as being arranged in a staggered pattern, the LEDs may be arranged in a fan-shape arrangement with space between the LEDs away from the light emitting area. The advantage of the fan shape is that it enables the LEDs to be separated giving spaces for heat-sinking. Preferably heatconducting material is between the LEDs. The heat-conducting material may be a matrix which contains metal to further increase the heat-conducting properties of heat sink. One disadvantage is that the LEDs are arranged in a curve inwards but this is again offset somewhat by the staggered pattern.

The Bulb The LEDs described above, whether alone or in an array, are intended to be used in bulbs which may subsequently be fitted in reflector-based light devices. In practice this means that the LED (s) are physically and electrically connected to a container. It is possible that such bulbs may replace filament bulbs and due to the different voltage requirements it may suitably comprise a voltage control apparatus within the container. If the supply is too high, this can be a regulator circuit or a more elaborate and efficient step down switching or transformer circuit. A voltage boost configuration may be employed if supply is too low, again this can be an step up switching type or transformer based. Any control means preferably is connected to LED (s) within the container itself.

The bulb is preferably surrounded by a shroud, preferably forming a meniscus lens. The shroud can be made of any suitable material, but preferably it is transparent. Glass has a higher heat capacity than plastic but plastic is easier to form. The shroud can be any thickness so required and if required, can have anti-reflection means on surfaces. The shroud serves the multiple functions of a transparent heat sink, protection, a holder for thumb and forefinger to grip enabling easy insertion into device and minimising the light source area due to a negative lens effect of the surface.

A method for modification As the prior art discrete type is easy to handle it is possible to remove encapsulation leaving a small amount so as to maintain patency of bond wire whilst also shaping reflector dish to become that according to the invention. This process removes metal of reflector dish and also some phosphor. Any remaining faces can then be polished. Note: if phosphor is removed then the overall light spectral distribution will be shifted to the blue end of spectrum due to dominance of blue light emitting die itself. This is undesirable, however if a rank of LED is chosen with a lot of phosphor within reflector dish before we modify (i. e. 4000-6000 K type) then any modification will not cause the colour temperature to increase too much.

EXAMPLES The invention will be now illustrated by, but in no way limited by, the following examples.

Fig 1 Top view of SMD LED.

Fig 2 Side View of SMD LED.

Fig 3 Side view of discrete-leaded LED.

Fig 4 Top view of discrete-leaded LED.

Fig 5 Side view of reflector based light source.

Fig 6 Side view of collection of LEDs.

Fig 7 Top view of collection of LEDs.

Fig 8 Close up top view of discrete-leaded LED.

Fig 9 Close up side view of discrete-leaded LED.

Fig 10 Close up top view of type (i) LED.

Fig 11 Close up top view of type (ii) LED.

Fig 12 Close up side view of type (i) or type (ii) LED.

Fig 13 Close up top view of different type (i) LEDs. Fig 14 Close up end view of different type (i) LEDs. Fig 15 Close up side view of different type (i) LEDs.

Fig 16 Flux distribution of discrete-leaded LED.

Fig 17 Flux distribution of type (i) LED.

Fig 18 Flux distribution of discrete-leaded (encap) LED.

Fig 19 Flux distribution of type (i) (encap) LED.

Fig 20 Flux distribution of type (ii) LED.

Fig 21 Flux distribution of type (ii) (encap) LED.

Fig 22 Arrangement showing'mirror'effect.

Fig 23 Arrangement showing'v'notch. Fig 24 Arrangement showing staggered and fan shapes.

Fig 25 Arrangement showing heat-conducting material.

Fig 26 New bulb.

White LEDs are described though following disclosed methods can be applied to non-white LEDs. White LEDs that are commercially available use a blue light emitting semiconductor die surrounded by phosphors contained within a cup or reflector dish. Fig 1 and 2 shows prior art top and side views of SMD LEDs with (1) light emitting region, body which acts as a secondary light source (2), electrical connection pads (3) and any encapsulating lens (4) for producing a concentrated beam.

Fig 3 shows side view of discrete-leaded LED with (5) light emitting region and (6) transparent encapsulation. Fig 4 shows top view of discrete-leaded LED; notice how light emitting semiconductor die (5) is imaged thus appearing almost the same size as the total diameter; this is due to the encapsulating lens (6).

Fig 5 shows prior art side view of reflector based light source incorporating reflector (7), bulb (8). Either the bulb or the reflector can move relative to each other to effect a change of vergence of light rays (9). Fig 6 and 7 shows prior art side and top views of collection of LEDs that may be grouped together to increase light output; but at the expense of an increase in light source area.

Fig 8 and 9 show close up top and side views of prior art discrete-leaded LEDs. In more detail the salient features of the LED. The anodic lead (10) is separated by a small gap (11) from the other lead (cathodic) (15), a bond wire (12) connects the leads to the die (13), side view shows the small drop (11) enabling wire to travel in an approximately straight minimum length line, this design ensures electrical efficiency which ultimately translates into a low failure-long life. Any phosphors (14) covering the die enable different light wavelengths to be emitted. The outer edge of the essentially circular reflector dish (16) is shown, notice how this extends past the leads themselves.

Fig 10 shows close up top view of a new type (i) LED. The cavity that is the truncated reflector dish is exposed to the side aspects of the lead (15), this enables light to be emitted in these side directions. X and Y axis are also shown. Fig 11 shows close up top view of type (ii) LED. This differs from Fig 10 in that one side of the cavity is blocked off with material (17) that preferably acts as a reflector. Fig 12 shows close up side view of type (i) or type (ii) LED. The cavity is shown exposing light emitting region (13) and (14) bounded by reflector dish (16). As an example encapsulation is shown (18) it takes the form of flat faces to avoid any optical imaging of light emitting region and it uses a small amountsufficient to cover bond wires and to protect and physically hold together constituent parts of LED. Z and Y axis are also shown. Fig 13,14 and 15 show close up top, end and side views respectively, of different type (i) LEDs. This shows that there are many different alternative shapes to the cavity shape from toridial to cylindrical through to saddle shapes, each have their own advantages and disadvantages. Such profiles can apply equally to type (ii) LEDs.

Fig 16 shows a representation of flux distribution of prior art discrete-leaded LED. The x-y and y-z planes are essentially the same, with vast majority of light being directed 'forwards'. Some light will be emitted along axes, indeed a very small amount will be diffracted over edges of reflector dish. Fig 17 shows flux distribution of type (i) LED. Figs 18 and 19 shows flux distribution of discrete-leaded encapsulated LED and new type (i) LED. The encapsulation especially if of

the'flat top'type will result in scattering of light, resulting in a small amount being directed'backwards'. Fig 20 shows flux distribution of type (ii) LED. In this design there is only one lobe in the x-z plane with the other half of this plane acting in the same manner as prior art. Fig 21 shows flux distribution of type (ii) encapsulated LED. Again a small

amount will be directed'backwards'.

Fig 22 shows arrangement giving'mirror'effect. When a two type (i) LEDs are placed together one higher than another light emitted in region (19) is reflected by lead (preferably tinned). The light is imaged as a virtual image from within lead itself. This effect results in a compact light source area (real or virtual). Fig 23 shows arrangement showing'v' notch.

Fig 24 shows arrangement producing staggered and fan shapes in an array. The LED is shown in (20) and spaces between LEDs in (21).

Fig 25 shows arrangement showing heat-conducting material. The LED (20) is surrounded by a matrix (21) that fills spaces between LEDs and also rises up almost completely surrounding lead. Metal fragments are shown in (22).

Fig 26 shows how array of LEDs with a heat sink applied can be mounted into container to form a replacement bulb. A shroud (24) is fitted over LED (s) (27) via a gap (26), the shroud has two surfaces outer (23) and inner (25). The heat-sink (28) also serves the function of physically securing the LED (s) both to the shroud (29) and the container (30). Also shown are optional screw threads (31). The connector (33) is shown. A control means is shown (32), which may be needed if new bulb is required as a replacement for a pre-existing device.

Claims

CLAIMS 1. An LED for use in reflector-based light devices which comprises two connection leads, a light-emitting die and optionally phosphors, characterised in that one of the connection leads comprises a head, the top surface of which has a cavity which is also open to two opposing sides of the head, the light-emitting die being mounted within the cavity, whereby the light flux distribution is emitted continuously and: (a) at least 20% is emitted in more than 180 degrees in the x-z plane; and (b) at least 80% is emitted in less than 180 degrees in the y-z plane; wherein the x axis passes through the geometric centre of the cavity but not through the body of the head; the y axis, perpendicular to the x axis, passes through the geometric centre of the cavity and through the body of the head; the z axis being perpendicular to both the x and y axes.
2. An LED according to claim 1, characterised in that at least 30%, preferably at least 40%, is emitted in more than 180 degrees in the x-z plane.
3. An LED according to claim 1 or claim 2, characterised in that the head has two pairs of parallel sides in an x-y plane.
4. An LED according to claim 3, characterised in that one pair of parallel sides are less than 0.8 mm apart, preferably less than 0.6 mm, more preferably less than 0.4 mm.
5. An LED according to any preceding claim, characterised in that the cavity is toridial, preferably substantially cylindrical.
6. An LED according to any preceding claim, characterised in that at least the light-emitting die is encapsulated, preferably having flat faces, more preferably the top face of the encapsulation is no more than lmm from the top surface of the head.
7. An LED according to claim 6, characterised in that the encapsulation has a notch.
8. An LED according to any preceding claim, characterised in that it is surrounded by heat-conducting material.
9. A tightly packed array of LEDs arranged in a row comprising (i) an LED according to any one of claims 1 to 8 and/or (ii) an LED according to any one of claims 1 to 8 but where the cavity passes through only one side of the head.
10. An array of LEDs according to claim 9, characterised in that the LEDs are in a staggered array.
11. An array of LEDs according to claim 10, characterised in that the LEDs which are not in the highest position are of type (ii) with the side which the cavity passes through facing away from the LED, or LEDs, in the highest position.

12. An array of LEDs according to claim 10, characterised in that the LEDs which are not in the highest position are of type (i) and the light emitted towards the centre of the row is reflected by the adjacent LED which has mirrored sides.

13. An array of LEDs according to any one of claims 9 to 12, characterised in that the LEDs are arranged in a fan-shape arrangement and preferably heat-conducting material is between the LEDs.

14. An LED-based bulb comprising an LED according to any one of claims 1 to 8 or an array of LEDs according to any one of claims 9 to 13 characterised in that it is also physically and electrically connected to a container.

15. An LED-based bulb according to claim 14, characterised in that it comprises a voltage control apparatus within the container.

16. An LED-based bulb according to claim 14 or claim 15, characterised in that the array is surrounded by a shroud, preferably forming a meniscus lens.

17. The process of making an LED according to any one of claims 1 to 8, characterised in that the sides of a full reflector dish leaded-LED are removed, exposing the cavity to the sides of the head.

18. A reflector-based light source which comprises an LED according to any one of claims 1 to 8 or an array of LEDs according to any one of claims 9 to 14.

19. A modified LED or array of LEDs substantially as herein described and illustrated in accompanying drawings. Amendments to the claims have been filed as follows CLAIMS 1. An LED for use in reflector-based light devices which comprises two connection leads, a light-emitting die, characterised in that the top surface of one of the connection leads has a cavity which is open to at least one of two opposing sides of the lead, the light-emitting die being mounted within the cavity, whereby the light flux distribution is emitted continuously and: (a) at least 20% of the light emitted in the x-z plane is emitted in more than 180 degrees; and (b) at least 80% of the light emitted in the y-z plane is emitted in less than 180 degrees; wherein the x axis passes through the geometric centre of the cavity but not through the body of the lead; the y axis, perpendicular to the x axis, passes through the geometric centre of the cavity and through the body of the lead; the z axis being perpendicular to both the x and y axes.

2. An LED according to claim 1, characterised in that at least 30% of the light emitted in the x-z plane is emitted in more than 180 degrees.

3. An LED according to claim 2, characterised in that at least 40% of the light emitted in the x-z plane is emitted in more than 180 degrees.

4. An LED according to any one of claims 1 to 3, characterised in that the top surface of the lead has two pairs of parallel sides one about the x-z plane and one about the y-z plane.

5. An LED according to claim 4, characterised in that one pair of parallel sides are less than 0.8 mm apart.

6. An LED according to any preceding claim, characterised in that the cavity is a toridial section.

7. An LED according to claim 6, characterised in that the cavity is substantially a cylindrical section.

8. An LED according to any preceding claim, characterised in that the light-emitting die is encapsulated.

9. An LED according to claim 8, having encapsulation with flat faces.

10. An LED according to claim 9, where the top face of the encapsulation is no more than lmm from the top surface of the lead. ll. An LED according to any one of claims 8 to 10, characterised in that the encapsulation has a notch.
12. An LED according to any preceding claim, characterised in that it is surrounded by heat-conducting material, which also physically secures.
13. An LED according to any preceding claim where the light emitting die is surrounded by phosphors.
14. A tightly packed array of LEDs arranged in a row comprising (i) an LED according to any one of claims 1 to 13 and/or (ii) an LED according to any one of claims 1 to 13 but where the cavity passes through only one side of the lead.
15. An array of LEDs according to claim 14, characterised in that the LEDs are in a staggered array.
16. An array of LEDs according to claim 15, characterised in that the LEDs which are not in the highest position are of type (ii) with the side which the cavity passes through facing away from the LED, or LEDs, in the highest position.
17. An array of LEDs according to claim 14 or 15, characterised in that the LEDs which are not in the highest position are of type (i) and the light emitted towards the centre of the row is reflected by the adjacent LED which has reflective sides.
18. An array of LEDs according to any one of claims 14 to 17, characterised in that the LEDs are arranged in a fan-shape arrangement.
19. An array of LEDs according to any one of claims 14 to 18, characterised in that heat-conducting material is between the LEDs which also physically secures.
20. An LED-based bulb comprising an LED according to any one of claims 1 to 13 or an array of LEDs according to any one of claims 14 to 19 characterised in that it is also physically and electrically connected to a container.
21. An LED-based bulb according to claim 20, characterised in that it comprises a voltage control apparatus within the container.
22. An LED-based bulb according to claim 20 or 21, characterised in that the array is surrounded by a shroud.
23. An LED-based bulb according to claim 22, characterised in that the shroud forms a meniscus lens.
24. The process of making an LED according to any one of claims 1 to 13, characterised in that the sides of a full reflector dish discrete-leaded LED are removed, exposing the cavity to the sides of the lead.
25. A reflector-based light source which comprises an LED according to any one of claims 1 to 13 or an array of LEDs according to any one of claims 14 to 19.
26. An LED or array of LEDs substantially as herein described and illustrated in figures 10-15,17 and 19-26.