GB2517064A

GB2517064A - Improved lighting unit

Info

Publication number: GB2517064A
Application number: GB1410729.6A
Authority: GB
Inventors: Andrew Johnson
Original assignee: Aurora Ltd
Current assignee: Aurora Ltd
Priority date: 2013-06-14
Filing date: 2014-06-17
Publication date: 2015-02-11
Anticipated expiration: 2034-06-17
Also published as: GB201410729D0; GB2517064B

Abstract

A downlight 2 comprising a casing, an LED light source 6 incorporating one or more LEDs mounted on a circuit board 8 incorporating an integrated circuit 80 including an LED driver, a lens 26, a lens holder 24 and a heat sink 10. The lens 26 incorporates one or more frustoconical sections about a light entering section, and these have a densely distributed network of convex facets for emission of multipoint lights. The heat sink may preferably have a plurality of fins to dissipate the heat away from the lighting unit.

Description

A

Improved Lighting Unit

Field of the invention

The present invention relates to an improved lighting unit, in particular, an improved construction for a downlight utilising an LED integrated light source.

Background to the invention

Downlight fittings or downlighters are a form of lighting unit becoming more and more widely used as light sources in domestic and commercial environments. They are particularly neat and unobtrusive in their appearance, since almost the entire downlight fitting is concealed behind a ceiling or other suitable panel or surface, whilst giving out a pleasing light. However, downlights suffer from a number of conflicting requirements.

To generate sufficient brightness a high power LED lighting engine is required, typically running from a low voltage or mains voltage. It is common to run such LED light engines using a separate, external driver connected to an upper end of the downlight. It will be appreciated that the space available behind the ceiling or other suitable panel or surface must also be sufficient to accommodate such a driver. It will also be appreciated that commercially there is a need to provide ever brighter lighting using an LED light source.

However, working against this requirement, is a desire for the light emitted not create a high degree of glare. To this end, LED downlights are fitted with an LED integrated light source lens. An LED integrated light source lens of the known kind, comprising a light entering section in the shape of hole and of a light emitting section in the shape of a cup, has smooth surfaces on both the light entering and emitting sections. This has as a disadvantage that light utilisation efficiency of the LED light engine is very poor. As a result, to effectively manage the light emitted by a brighter LED light engine, the lenses are required to be thicker between the light entering and emitting sections and therefore require a correspondingly longer downlight. A further disadvantage of such integrated LED light source lenses is that this arrangement creates luminous spots with obvious colour aberration, that is to say the colour rendering index is adversely affected.

Due to this requirement, that the greater the brightness of the light produced by the LED light engine the greater the height of the lens required to reduce the glare, LED downlights cannot be used in similar applications to downlights incorporating a halogen light source having similar brightness, as the LED downlights are too tong for such applications.

In addition, LED light engines for LED downlights generate significant amounts of heat. It is important to prevent overheating of the lighting element, and the associated control circuits, since overheating will have obvious detrimental effects on the light output and service life of these components. Indeed, excessive temperatures will cause electronic components to fail leading to premature failure of the lighting unit. To this end it is known to provide LED lighting units with cooling means in the form of a heat sink or cooling fan to draw heat away from the lighting element to the rear of the lighting unit where ventilation openings are provided. In the case of fire rated downlights, the lighting unit will act as a fire barrier and the ventilation openings will be adapted to be closed in the event of fire, for example due to the expansion of intumescent material.

However, such heat control or thermal management comes at a cost due to the requirement to utilise a heat sink having large dimensions.

In particular, such heat sinks extend into the available space behind the ceiling or other suitable panel or surface. In some instances the space available means that known downlighters having the desired brightness are unsuitable for use since there is not sufficient space either to fit the downlight or to provide sufficient ventilation space behind the downlight. In addition the construction of such a large heat sink is costly to manufacture, not least due to the materials used.

In addition, known arrangements of lighting unit, despite the use of large heat sinks, suffer inefficiencies in transfer of heat to the heat sink. This inefficiency in heat management, reduces the life of the LED light engine and so the LED downlight unit.

Nevertheless as noted above there is a desire for an LED downlight providing low glare but high brightness, comparable with a halogen downlight of corresponding brightness. However, as noted the requirement for a high brightness LED, increases the heat generated and places demands on the requirement for effective heat management. These conflicting requirements make LED downlights unsuitable for many applications where halogen downlights are currently used.

It is an advantage of the present invention in that it provides a lighting unit enabling the utilisation of a higher brightness LED light engine without adversely affecting the length of the LED downlight.

Further advantages of the present invention will be apparent from

the following description.

Summary of the invention

According to the present invention a downlight comprises a casing, an LED light source incorporating one or more LEDs mounted on a circuit board incorporating an integrated circuit driver, a lens incorporating one or more frustoconical sections about a light entering section, the or each frustoconical section being provided with a densely distributed network of convex facets, a lens holder and a heat sink.

Preferably, the heat sink is provided in thermal contact with a rear side of the circuit board.

Preferably, the heat sink incorporates fins. Preferably, the heat sink is substantially cylindrical in cross-section. More preferably, the heat sink is substantially circular cylindrical in cross-section. This has as an advantage that a conventional finned aluminium extrusion may be used for the heat sink.

Preferably, the circuit board comprises an aluminium base provided with an aluminium oxide layer. This has as an advantage that heat generated by the LED light source is quickly dissipated.

Preferably the lens is further provided with a network of refractive surfaces on a light emitting section of the lens.

Preferably the number of frustoconical portions of the lens corresponds to the number of LEDs mounted on the circuit board.

Brief description of the drawings

The invention will now be described, by way of example only, in relation to the attached Figures, in which Figure 1 shows a side view of a lighting unit illustrating an embodiment of the present invention; Figure 2 shows a sectional view of the lighting unit of Figure 1; Figure 3 shows a side view of a lens utilised in the present invention; Figure 4 shows a sectional view of the lens shown in Figure 2; Figure 5 shows a view from below of the lens of Figure 1; and Figure 6 shows a section along line A-A of Figure 2.

Description of the preferred embodiments

Referring first to Figure 1, an embodiment of a downlight unit 2 in accordance with the present invention is shown. The downlight unit 2 comprises an LED light source 6 mounted to a circuit board 8, for example a printed circuit board, the circuit board including control circuitry for the light source 6, a heat sink 10 connected to a cylindrical casing, the heat sink 10 being provided to a rear side of the circuit board 8 and a lens arrangement located at a front side of the circuit board.

The term "cylindrical casing" means conforming approximately to the shape of a hollow cylinder. It will be understood that a misshapen cylinder will work equally well. Similarly, while the embodiments show a generally circular cylindrical tubular body other sections may be used with amendment to the sectional shape of other components.

The LED light source preferably comprises one or more LEDs.

The heat sink 10 is formed from any suitable material, preferably cast aluminium. The heat sink 10 comprises at a lower end an outer annular portion for location against an upper portion of the cylindrical casing. The annular portion surrounds an end face. In the illustrated embodiment the end face is proud of the annular portion.

The cylindrical casing comprises a mounting ring 14. The mounting ring 14 comprises a side wall having a lower peripheral annular flange extending outwardly from a bottom end of the side wall and an upper peripheral annular flange extending inwardly from an upper end of the side wall. The mounting ring 14 is formed from any suitable material, preferably steel.

The upper peripheral flange locates against the annular portion of the heat sink and surrounds the end face of the heat sink.

A first ring or washer 16 of silicon is conveniently provided on the upper surface of the lower peripheral flange. In use, the ring or washer 16 butts up against a rim of an aperture into which the downlight is fitted.

A bracket 18 incorporating spring biased members or clips 20 is located about the heat sink 10. The spring biased members or clips are adapted to secure the lighting unit in a recess in a known manner. The bracket 18 is secured to the upper peripheral flange of the mounting ring 14 in a suitable fashion, for example by screw fasteners 22.

The lens arrangement comprises a lens holder 24 and a lens 26.

The lens holder 24 may be of any suitable material, for example a polycarbonate. The lens may be of any suitable material, for example polymethylmethacrylate. The lens 26 is retained in position relative to the light source 6 by the lens holder 24. The lens holder 24 comprises a ring or washer having a support structure for engaging and securing the lens 26 to the lens holder 24, as well as an inwardly directed finger or fingers 28. The lens holder 24 is secured at its periphery to the upper peripheral flange of the mounting ring 14 in a suitable fashion, for example by utilising the screw fasteners 22 securing the bracket 18 to the mounting ring 14.

An example lens is shown in more detail with reference to Figures 3 and 4. The lens 26 can be seen to comprise a substantially solid body having a generally conical or frusto-conical portion provided with a flange 112 extending thereabout providing a circular periphery to the lens. The side of the flange from which the conical or frusto-conical portion extends will be referred to as the bottom or rear side and reference to an upper side', a front side', above' or below' should be interpreted accordingly.

An upper portion of the conical or frusto-conical portion 103 is provided with a light entering section 101 in the form of a blind recess or hole provided therein. 9.

In use, the LED light source 6 is located at the opening of the hole in the conical or fwsto-conical portion, such that the hole forms a light entering section 101 of the lens. In this embodiment the refractive surface 118 is circular in shape. In use, the refractive surface 118 creates multi-point light beams.

The external surface of the conical or frusto-conical portion is provided with a network of densely distributed convex facets 124. In use, these facets 124 create multi-point light beams.

The front of the lens is provided with a shaped recess forming a light emitting section 102 of the lens. The generally circular base 22 is provided with a network of refractive surfaces 128.

When light is emitted from the LED light source 6, light passing through the sides of the light entering section 101 will, having passed through the lens, encounter the network of convex facets 124. This causes the light at the surface to form multipoint full reflection lights directed back toward the light emitting section 102. The creation of multipoint full reflection lights decreases the glare index and increases the colour rendering index.

Light encountering the refractive surface 118 on the base of the hole is focussed on the network of refractive surfaces 128 on the light emitting section 102 of the lens. This improves light efficiency.

Light passing to the network of refractive surfaces 128 on the light emitting section 102 of the lens forms multi point refraction emitting light which decreases the glare index and increases the colour rendering index.

Referring now to Figures 5 and 6, which show further embodiments in which the lens has a central vertical axis extending generally along a line from D2 to Dl. The lens is formed from a transparent or translucent material. In the case of a transparent or translucent plastics material, the lens is preferably formed by injection moulding.

A base of the conical or frusto-conical portion 10 is provided with a recess or hole provided therein. The hole is in the form of a blind recess. As may be seen from the figures the recess is typically substantially circular in section, though other sections may be used.

The side or sides of the recess are substantially aligned with the central vertical axis of the lens.

The base of the conical or frusto-conical portion 10 is provided with two cut away portions 114 extending along a portion of a circumference of the conical or frusto-conical base portion 10 to create two tabs 116 extending in between. These cut away portions or tabs are adapted to accommodate wires supplying electricity to the LED light engine. From Figure 5, it can be seen that the tens is substantially symmetric about a central plane A-A.

In use, an LED (LED light engine) is located at the opening of the hole in the base of the conical or frusto-conical portion, such that the hole forms a light entering section 101 of the lens. The end of the blind recess or base of the hole may be provided with a refractive surface 18, for example a spotted or dimpled surface made up of a series of facets. In this embodiment the refractive surface 118 is substantially circular in shape and has a diameter D2. From Figure 5 it can be seen that this refractive surface takes the form of a plurality of substantially hexagonal convex facets formed on the surface of the base of the hole. In use, the refractive surface 18 creates multi-point light beams. In this embodiment the refractive surface 118 is located on a generally level plane, substantially perpendicular to the central vertical axis of the lens.

The external surface of the conical or frusto-conical portion 10 is provided with a network of densely distributed convex facets 124. In use, these facets 124 create multi-point light beams by total internal reflection. The facets 124 of this embodiment can be seen to be generally triangular or diamond shape in outline. The outer surface of each triangle/diamond is convex in shape, causing light rays from the LED light source to be reflected out of the front of the lens by total internal reflection. It will be appreciated that the angle of curvature of these convex reflecting facets can be varied by the designer to achieve the desired beam angle for a particular lens. For a given and fixed set of dimensions for Dl, H and D2 the beam angle of the lens can be varied between 60 degrees and 15 degrees by adjusting the angle of curvature of the reflecting facets.

It can be seen from Figures 5 and 6 that the density of facets, that is the number of facets per square centimetre on the outside of the conical part of the lens, increases towards the light entering section or the base of the lens. This, as well as the overall average density of the facets, is an important feature of this lens design. Examples for average facet densities are given in the table below. Each facet is preferably greater than 1 square millimetre in surface area.

Facets smaller than this are difficult to manufacture with the necessary degree of accuracy required to achieve the desired beam angles and optical efficiency. As a general rule, the uniformity of the light distribution of a lens according to the present invention is relative to the size of facets; the smaller facets the more uniform the light distribution.

An external surface of the light entering section 101 can thus be seen to be provided with convex facets 124 on the reflective surface of the conical or frusto-conical portion 10 and convex facets on the refractive surface 118. Computer programs are commercially available that enable modelling of the propagation of light and optimisation of design criteria. An example of one such program is Tracepro, sold by Lambda Research Corporation of 25 Porter Road Littleton, MA 01460, USA.

Importantly, light from the LED light engine is focussed in the present lenses into a light beam between 15 degrees and 60 degrees about the central vertical axis with an efficiency of about 88% or above.

Achieving such a narrow beam angle with high efficiency and with a Dl:H ratio of 1.9 or above has not previously been possible.

As can be seen from Figure 6, the front of the lens is provided with a shaped recess. The shaped recess is in the shape of a cup, being generally concave, comprising an inclined surface 120 extending inwardly from the front face of the lens, the inclined surface 120 meeting a generally circular base 122 of the cup shape, the base 122 being substantially convex in shape. The curved convex shape is used to change the light beam angle. The generally circular base 122 is provided with a network of refractive surfaces in the form of densely distributed convex facets. The inclined surface is preferably substantially concave.

In use, the shaped recess forms a light emitting front face or section 102 of the lens. It should be emphasised that a refractive surface may be present on either the base of the light entering section 1, or on the front face of the lens, or both, as required by the desired performance characteristics of the lens.

The portion of the lens between the hole and the shaped recess forms an optical body or lens 103 positioned between the front face and the base of the lens body.

It will be understood that the light entering section 1011! the light emitting section 102 and the optical lens 103 are preferably formed as a unitary or one piece body from transparent/translucent material.

With reference to Figure 6, it can be seen that a height H can be measured between the left hand most side of the lens, that is the bottom plane of the base and the right hand most side of the lens, that is the front of the light emitting front face. Similarly, the light emitting front face or section 102 can be seen to have a cross sectional dimension, or diameter, Dl across its front. The light entering section can also be seen to include a cross sectional dimension D2. A preferred ratio for D2:H:D1 is 1:2:4. This ratio, or a ratio close to this one, provides lens having an optimum range of beam angles and is applicable to all the lenses exemplified herein.

For this embodiment, the lens includes:- (i) a lens body having a base where light from the LED light engine can enter the lens, and a light emitting front face, the lens body having a substantially frusto-conical shape having a central vertical axis extending from the base through the light emitting front face, said lens body having a height H between a bottom plane of the base and a front of the light emitting front face, and a cross-sectional dimension Dl across the front of the light emitting front face; (ii) a light entering section recessed in the base of the lens body adapted to accommodate an LED light engine, the light entering section having a cross-sectional dimension D2; (iii) the outer surface of the frusto-conical lens body between the base and the light emitting front face incorporating a plurality of densely distributed convex facets; wherein light from the LED light engine is focussed into a light beam between 15 degrees and 60 degrees about the central vertical axis, and wherein the ratio of Dl to H is equal to or greater than 1.90 and wherein D2 is no greater than 15 mm.

In summary, this aspect of the construction has a number of advantages. The densely distributed convex facets on the external surfaces of the light entering and emitting sections, cause the LED light source to emit multipoint lights, which enhances light utilisation efficiency, creates no spot lights with colour aberration, this in turn greatly improves the colour rendering index. The side of the optical lens 26 having a spotted surface, creates multi-point lights. The other side of the optical lens 26, having a curved surface, changes the light beam angle.

A further advantage is that such a lens is relatively squat in comparison to the integrated light source lenses acknowledged above.

A bezel 30 is fitted to an underside of the mounting ring 14. The bezel 30 may be of any suitable material, for example cast aluminium. The bezel 30 comprises an inner wall having an inwardly directed shoulder toward a lower end and a radially outwardly directed annular flange at the lower end. The inner wall extends within the side wall of the mounting ring 14. In use the inner wall of the bezel and the side wall of the mounting ring are provided with cooperating features, such as male and female parts of a bayonet fixing, to enable the bezel 30 to be secured to the mounting ring 14.

In use the inner shoulder supports a glass 32 located in front of the lens 26. The glass 32 is of any suitable material to allow transmission of the light emitted from the lens 26.

The enhancement of light utilisation efficiency means that the LED light source does not need to be brighter to generate a brighter light at the glass 32. This, in turn means that the there is no increased heat at the circuit board to be managed and the need for a larger heat sink is removed.

Preferably a second ring or washer 34 of silicon extends between the radially outwardly directed annular flange of the bezel 30 and the first peripheral flange of the mounting ring 14.

The circuit board 8 is generally circular and provided with fixtures, such as portions recessed from the circular periphery by which the circuit board may be located in position. For example the periphery of the circuit board to either side of the recessed portions serves to locate the circuit board with respect to the fasteners 22.

The circuit board includes integrated control circuitry for the light source, and as such no additional driver is required for this downlight construction. LED driving circuits utilised here can effectively avoid excessive power consumption and overheat problems when the input voltage is excessive; can effectively avoid inaccurate LED current at different input voltages; and use a splicing method to increase the power factor. In other approaches the LED driving circuit can include a holding current circuit and the driver maintains a stable input voltage VIN at low-voltage conduction angle to prevent flickering of the LED and avoid high power consumption and over-heat when the input voltage VIN is high. The LED driver can detect whether an input voltage is lower than a LED conducting voltage using an input voltage detection circuit. If it is then the charging capacitance and corresponding charging voltage will be controlled to discharge to the LEDs, so that there is still some current passing through the LEDs. This also means that flicker is improved, enhancing the illumination efficiency of the LED in every AC cycle.

The driving circuit uses switches having a reference voltage and a critical activation voltage, and also changes the connecting relation between the switches and the LEDS, which further simplifies the configuration of the driving circuit.

In practice the circuit board 8 is secured between the heat sink 10 and the lens holder 24. The end face of the heat sink 10 is in thermal contact with a rear face of the circuit board. A ring or washer 36 of a suitable fireproof material is located between the edge of the circuit board 8 and the upper peripheral flange of the mounting ring 14.

Conveniently, the circuit board is constructed as a high efficiency thermal conductive base board. In the illustrated embodiment, the circuit board comprises an aluminium material provided with a nano metal oxide coating. A suitable board comprising an aluminium substrate in which the aluminium substrate is placed in an electrolytic bath and oxidised to form an aluminium oxide layer through micro-arc oxidation is known from US 7 036 219. Suitable conductive contacts may be formed on the metal oxide layer for electrical connection of the electronic components (such as the LED light engine and the integrated circuitry). Such a construction has high efficiency thermal conductivity allowing heat generated by the LED light engine to be more effectively dissipated to the rear of the circuit board and then to a front face of the heat sink 110, such that heat is transferred by conduction directly from the circuit board 108 to the heat sink 110.

Such enhanced heat management enhances the life of the LED light engine (and so the downlight). It will be understood that other high efficiency thermal conductive base boards may be used. By way of example a ceramic material such as that marketed by Jing De Zhen Fared Technology Co as part of their radiative heat dissipation technology could be utilised.

It is an advantage of the present invention that it allows for the construction of an LED downlight of shorter length than previously known for an LED light engine of comparable brightness. This enables the LED downlight to providing a brightness associated with halogen downlights, without requiring a longer downlight and while maintaining the benefits of LED efficiency.

In an alternative embodiment (not shown), more than one LED light source may be provided on the circuit board. Where more than one LED light source is provided, the number of frustoconical portions of the lens corresponds to the number of LEDs mounted on the circuit board and in particular the light entering sections of the frustoconical portions are arranged in alignment with the respective LED light source.

Claims

CLAIMS1 A downlight comprising:- (i) a casing; (ii) an LED light source incorporating one or more LEDs mounted on a circuit board incorporating an integrated circuit driver; (iii) a lens; (iv) a lens holder; and (v) a heat sink; wherein the lens incorporates one or more frustoconical sections about a light entering section, the or each frustoconical section being provided with a densely distributed network of convex facets.
2 A downlight according to claim 1, in which the heat sink is provided in thermal contact with a rear side of the circuit board.
3 A downlight according to claim 1 or claim 2, in which the heat sink incorporates fins.
4 A downlight according to any of claims I to 3, in which the heat sink is substantially cylindrical in cross-section.
A downlight according to claim 4, in which the heat sink is substantially circular cylindrical in cross-section.
6 A downhight according to any of claims 1 to 5, in which the circuit board comprises a high efficiency thermal conductive base board.
7 A downlight according to claim 6, in which the circuit board comprises an aluminium base provided with an aluminium oxide layer.
8 A downlight according to any of claims 1 to 7, in which the lens is further provided with a network of refractive surfaces on a light emitting section of the lens.
9 A downlight according to any of claims 1 to 8, in which the number of frustoconical portions of the lens corresponds to the number of LEDs mounted on the circuit board.A downlight substantially as described herein with reference to and as illustrated in the accompanying drawings.