GB2492761A

GB2492761A - Lighting assembly circuit board attached to a heat sink

Info

Publication number: GB2492761A
Application number: GB1111725.6A
Authority: GB
Inventors: Lawrence Mark Fagg; Neill Allan Richardson
Original assignee: VISION ENGINEERING FAR EAST Ltd
Current assignee: VISION ENGINEERING FAR EAST Ltd
Priority date: 2011-07-08
Filing date: 2011-07-08
Publication date: 2013-01-16
Also published as: GB201111725D0

Abstract

A lighting assembly 1 for a street light has a plurality of lighting elements such as LEDs connected to a circuit board 3, the circuit board being removably attached to a heat sink. The circuit board may be in thermal communication with the heat sink and attached by a fixing element such as a screw that extends through an aperture in the circuit board. The circuit board and the fixing element may be electrically insulated from the heat sink by an insulating locating element 12 configured to receive the fixing element. The locating element may be located in a recess in the heat sink. There may be an electrically insulating silicone layer 15â between the heat sink and the circuit board. The heat sink may have a curved surface and thermally conductive projections, pads and vanes. An electrical connector connects the circuit board to a street light power supply.

Description

Lighting Assembly

Field of the Invention

The invention relates generally to a lighting assembly. In particular, the invention relates to an energy efficient lighting assembly for street lighting. The invention further relates to a street light and a street light electrical connector.

Background to the Invention

Conventional streetlights utilise halogen, high pressure sodium vapour or fluorescent lighting. In order to produce the required illumination using these types of lighting, a great deal of energy is consumed, and thus they are not environmentally friendly.

Light emitting diodes (LEDs) consume less electricity and would therefore be a more environmentally friendly lighting source. They also provide the advantage that no lead or mercury is used in LED lighting. However, for street lighting, there are a number of requirements that must be satisfied to ensure quality and safety.

For example, a number of street lighting quality standards exist in the UK in respect of illumination, light distribution and safety -for example protection against electrical surge or lightening strike under BSEN 60001.

In order to produce sufficient illumination from a street light having LEDs as the sole lighting source, a great number of LEDs are necessary.

One of the problems in providing lighting having a number of lighting elements such as LEDs, is that a large amount of heat is generated. This can lead to a reduction in the working life of the LEDs and deterioration of other components of the fitting.

In prior art LED lighting designs, LEDs are arranged close together in squares on a flat printed circuit board (PCB). This often results in excess heat and interference from neighboring components. This means that frequent replacement and repair is necessary.

Furthermore, while many prior art designs can flood a space with light, they are not able to meet the horizontal light distribution requirements necessary for compliance with road lighting classifications.

It would be desirable to provide an improved lighting assembly.

Summary of the Invention

One aspect of the invention provides a lighting assembly as claimed in Claim 1.

Another aspect of the invention provides a street light as claimed in Claim 24.

Another aspect of the invention provides a kit of parts for a street light as claimed in Claim 25.

Another aspect of the invention provides an electrical connector as claimed in Claim 27.

Yet another aspect of the invention provides a street light comprising a detachable connector as claimed in Claim 28.

Yet another aspect of the invention provides method of fitting a street light assembly or a component thereof as claimed in Claim 29.

One aspect of the invention provides a lighting assembly for a street light complising a plurality of lighting elements connected to a circuit board, the circuit board being removably attached to a heat sink.

Preferably, the circuit board is removably attached to the heat sink by at least one fixing element extending through an aperture in the circuit board.

Advantageously, the circuit board is electrically insulated from the heat sink.

This protects the components from electrical surge and lightning strike and prevents the heat sink from becoming electrically charged.

Advantageously, the circuit board is in thermal communication with the heat sink.

This facilitates transfer of heat away from the circuit board and LEDs to prevent damage! reduced efficiency.

Preferably, the at least one fixing element is electrically insulated from the circuit board.

In a preferred embodiment, the at least one fixing element is electrically insulated from the circuit board by an electrically insulative locating element configured to receive the at least one fixing element.

This allows the fixing element to pass through and hold together components of the assembly without transferring electrical charge from the circuit.

In a preferred embodiment, the fixing element is an acrylic T-piece!top hat bush.

Acrylic is a good conductor of heat but not electricity and therefore thermal transfer occurs but electrical conduction is inhibited.

The at least one locating element may be mounted in a recess in the heat sink.

Advantageously, the at least one fixing element is in thermal communication with the heat sink.

This provides the advantage that the fixing element may assist in thermal transfer to the heat sink.

In a preferred embodiment, the locating element extends through an aperture in a thermally conductive and electrically insulative layer between the heat sink and the circuit board.

Preferably, the layer comprises silicone.

Silicone is thermally conductive yet electrically insulating. Therefore this provides the advantage that heat from the PCB is conducted to the heat sink but electricity is not.

The silicone layer may have apertures through which locating elements extend.

A second silicone layer may be included in the assembly on the side of the PCB on which the lighting elements are mounted. In this case, the second silicone layer may have apertures through which the lighting elements project.

In one embodiment the layer may envelop the PCB.

The assembly may further include a fascia plate.

In one embodiment, the heat sink comprises a curved inner surface.

The inner surface of the heat sink is the surface adjacent the PCB.

Preferably, the curvature of the inner surface of the heat sink is around 4 degrees.

Advantageously, attachment of the circuit board to the curved surface of the heat sink causes corresponding curvature of the circuit board.

In use at least one of the lighting elements may be oriented at substantially 0 degrees to vertical axis of the lighting assembly and at least one of the lighting elements may be oriented at around 4 degrees to the vertical axis of the assembly.

This provides the advantage that when attached to the heat sink, the PCB adopts a curved configuration such that the direction of the projection of light from each LED varies depending on its position on the curve.

Preferably, the outer surface of the heat sink comprises thermally conductive projections.

Preferably, the inner surface of the heat sink comprises thermally conductive vanes.

In a preferred embodiment, the inner surface of the heat sink comprises thermally conductive heat pads at positions corresponding to the positions of the lighting elements.

The heat pads provide large surface areas adjacent the LED5 to absorb and conduct heat from the LEDs. The vanes and fins are arranged to provide a high level of thermal transfer.

The at least one fixing element may comprise a screw.

Alternatively, or in addition, other well known fixing elements suitable for connecting the assembly may be used.

The lighting elements may comprise LEDs.

Alternatively the lighting element may comprise other light sources that are known to generate substantial heat.

Preferably, the lighting elements are positioned in a non-linear arrangement.

This provides that each lighting element is spaced from the others to avoid areas of excess heat.

Preferably the lighting assembly further comprises at least one lens.

Lenses may be mounted over LEDs and/or as a fascia bowl lens.

In one embodiment the lighting assembly comprises a detachable connector for connecting an electrical supply to the circuit board.

The lighting assembly may further comprise an external housing and/or a street light connector arm and/or a street light spigot mount.

S

Another aspect of the invention provides a street light comprising the lighting assembly of the invention.

Another aspect of the invention provides a kit of parts for a street light comprising a plurality of lighting elements, a circuit board, a least one fixing element for removably fixing the circuit board to a heat sink and at least one electrically insulative locating element for locating the at least one fixing element and circuit board in position on a heat sink.

Preferably the circuit board has apertures for locating the locating elements/fixing elements in position.

This provides the advantage that one or more circuit boards may be repeatably replaced at the same position on a heat sink.

The kit of pads may further comprise an electrical connector for releasably coupling the circuit board to a street light power supply.

The kit of parts may further comprise electrically insulative, thermally conductive layers.

The kit of pads may further comprise a heat sink.

Another aspect of the invention provides an electrical connector for a street light comprising first and second electrically conductive elements, the first electrically conductive element being removably connectable to a circuit board and the second electrically conductive element being removably connectable to a street light power supply.

Another aspect of the invention provides a street light comprising an electrical connector.

Another aspect of the invention provides method of fitting a lighting assembly or a component thereof to a street light, comprising the steps of: electrically isolating a lighting assembly from a street light power supply; removably attaching a circuit board to a street light heat sink in the street light.

The method may further comprise removably attaching at least one electrically insulative, thermally conductive layer to a surface of the circuit board..

Brief Description of the Drawings

In the drawings, which illustrate the preferred embodiments of the invention by way of

example only:

Figure 1 a shows a perspective views of the lighting assembly of the invention Figure lb shows a plan view of the lighting assembly of the invention Figure 2a shows a perspective view of the heat sink of the invention Figure 2b shows a perspective view of the heat sink of the invention Figure 3 shows a plan view of the printed circuit board assembly of the invention.

Figure 4 shows a cross sectional view of the lighting assembly of the invention Figure 5 shows an exploded view of the lighting assembly of the invention.

Figures 6 and 7 show exploded views of the street light electrical connector of the invention.

Detailed Description of the Preferred Embodiments

As illustrated in Figures la and ib, a lighting assembly 1 comprises LEDs 2, mounted on a printed circuit board (PCB) 3. In order to prevent overheating of the PCB 3 and LEDs 2, the assembly further includes a heat sink 4, which draws heat away from the LED and PCB components.

A lens 5 is mounted over each LED 2, which focuses light emitted from the LED.

Preferably, the lenses 5 function to diffract light emitted from LEDs such that light is emitted from each LED 2 through an angle of around 120 degrees.

In one embodiment, the assembly 1 may include a lens 5 that extends over more than one LED. Alternatively or in addition, a large fascia bowl lens 6 may be mounted over the base of the apparatus 1.

Figures 2a and 2b, show the heat sink 4 in more detail.

The heat sink 4 is made from a thermally conductive material, such as aluminium, and facilitates transfer of heat to air surrounding the lighting apparatus 1.

Figure 2a shows the outer surface 7 of the heat sink 4, which has fins 8 arranged to dissipate heat.

Figure 2b illustrates the inner surface 9 of the heat sink 4. The inner surface 9 has vanes 10 running parallel along the inner surface 9 at positions corresponding to the outer fins 8. Conduction of thermal energy occurs through the vanes 10 to the tins 8 and into the air surrounding the assembly 1.

This arrangement draws heat away from the PCB 3 and also facilitates even distribution of heat throughout the entire PCB. The inner 10 extend along the same diagonal routes on the inner surface 9 as the tins 8 on the outer surface 7, to allow maximum heat transference.

Referring to Figures 2a, 2b and 3, LED5 2 in the centre of the PCB 3 run at increased heat (due to the proximity of neighboring LEDs), the heat sink fins 8 are therefore larger in size towards the centre of the assembly 1 than those closer to the periphery of the assembly. This has the effect of creating a thermal management system for each LED, to balance heat dissipation perfectly and create a uniform environment for the PCB. Uniformity of thermal management is useful for establishing uniformity of LED lifespan i.e. ensuring all LEDs in the fitting run at equal performance levels.

As shown in Figure 2b, the inner surface 9 of the heat sink 4, has a network of conductive vanes 10, most of which extend diagonally along the length of the inner surface 9, parallel to the outer fins 8. Other vanes 10 extend diagonally across the inner surface 9 and intersect the parallel vanes 10.

The intersecting vanes 10' are in direct communication with LED backing pads 17 and are the initial conductors of heat from the LEDs. The LED backing pads 17 are substantially flat areas on the aluminium heat sink 4, at positions corresponding to the positions of LEDs 2 on the POB 3.

The inner surface 9 of the heat sink 4 further comprises recesses 11 configured to receive locators 12 for securing the elements of the assembly 1 together.

The locators 12 may be top hat bush type fixings, such as acrylic T-piece locators.

The locators 12 are held in the recesses 11 and receive screws (not shown), which pass through the apertures 14 in the PCB 3. The screws are preferably zinc plated screws.

The screw fit between each locator 12 and screw, ensures efficiency of thermal transfer to the heat sink 4. The locators 12 are preferably acrylic material and are therefore thermally conductive yet electrically insulative.

Metal screws can be screwed through the locators 12 into the heat sink 4, and yet are electrically isolated from the PCB 3 by the locators 12.

Location of the screws in the locators 12 and the positions of the apertures 14 with respect to the LEDs 2 on the PCB 3 ensures that each LED 2 is positioned over a heat pad 17 and this situated for optimum operation.

The heat sink 4 is attached to the FCB 3 in such a way as to ensure each LED 2 is in thermal communication with a heat pad 17. The heat pads 14 utilize the aluminium vanes 10, 10' to distribute heat evenly throughout the assembly. This provides an efficient heat dissipation method and does not require the use of permanent fixtures such as glue, heat sink paste or adhesive heat transfer tape.

The PCB 3 is shown in further detail in Figure 3.

The PCB 3 is insulated by aluminium plates, sealed and powder coated. The apertures 14 are pre-tooled, so that the PCB 3 can be secured to the assembly 1 with no drilling or copper ribbon interference.

High power LEDs are suitable for use with the assembly 1, and these can have a lifespan of upto 100,000 hours, in an ideal environment. In a preferred embodiment, the LEDs are high power chip LEDs. In order to allow the LEDs 2 to perform to their optimal potential in the assembly 1, the heat sink 4 dissipates the heat generated by the high power LEDs, which could otherwise affect their performance and lifespan.

The LEDs 2 are supported and wired in series through the PCB 3 with copper ribbon technology. In manufacture otthe assembly 1, each LED 2 is numbered for wiring by a series reference numerals before being attached to the PCB 3 using an isolated soldering chamber to ensure a precise, secure and consistent fitment. To avoid human error, there is no hand soldering at any stage in the production process.

In use, the photometric footprint created by the assembly 1 remains the same shape throughout the range, with an increase in lumen intensity only apparent as wattage is increased. The spacing between the LEDs 2, the manner in which they are attached to the PCB 3 and the curvature of the inner surface 9 (surfaces of vanes 10, 10') all contribute to this consistency.

LEDs 2 are attached to the PCB 3 using a digital solder isolation chamber. This method reduces tolerance (+ or -mm) between LEDs significantly. Each LED 2 is kept within a tolerance of ÷ or -0.2mm, an extremely accurate standard. This standard is further enhanced by the ow tolerance of the PCB. By fixing the board with t pieces and locators, tolerance is reduced to just + or -0.8mm.

Combined, these low tolerance ratings keep inconsistency in production to a bare minimum and provide better correlation in readings from luminaire plotting computer programs and reality test site scenarios. This data compares favourably to conventional, high-pressure sodium luminaires.

Prior art luminaire arrangements often contain a screw in lamp with a glass angle tolerance of + or-6mm and an inner arc tube tolerance of + or-3mm. This is before taking in to account unattainable tolerances in the ceramic lamp holder and the plastic parts holding the lamp holder in place. Photometric data over 100 such fittings will differ almost every time. This means that computer lighting software is highly inefficient when it comes to calculating road projects. The end result is a classification failure i.e. photometric data produced by computer lighting software, is not consistent with photometric data in reality.

Unlike conventional LED lighting designs, where LEDs are arranged close together in squares on a flat PCB, the present assembly 1 provides a non-linear arrangement of LEDs, giving each LED 2 a discrete platform on which to perform. This allows the LEDs 2 to distribute light (as well as excess heat) with minimum interference from neighbouring components.

Prior art arrangements may flood a space with light, but are unable to meet horizontal light distribution requirements. Each LED 2 of the present invention radiates light over an angle of around 120 degrees. Each LED is also able to generate a minimum of 116 lumens per Watt.

The inner surface 9 of the heat sink 4, which comprises vanes 10,10', has a slightly convex profile, which in a preferred embodiment has a curvature of around 4 degrees.

When the PCB 3 is screwed to the heat sink 4, the PCB 3 adopts a gently curved configuration defined by the profile of the heat sink 4, such that the LEDs 2 in the centre of the PCB 3 ( at 0° to the vertical axis Y of the assembly 1, or substantially flat) are able to provide good downward light output up their 120° limit. LEDs 2 operating on the outer edges of the PCB board (+ or-4° to the vertical axis Y) are able to project some light horizontally, away from the photometric centre of the assembly 1.

LED5 mounted between the centre and outer edges of the PCB 3 act as luminance aids, giving the light distribution an even curve with excellent average luminosity. Not only does this system meet street light classifications, it allows LEDs to run at a safe, stable temperature and cuts down on unnecessary wattage from boost or partnering LEDs.

The present invention surpasses horizontal light distribution standards requirements.

As shown in Figures 3, 4 and 5, further electrical insulation protects components of the assembly 1 from electrical surge and lightning strike and ensures compliance with EN 60001.

Thin silicone wraps or layers 15 electrically insulate the PCB 3, in order to electrically isolate the PCB 3 and LEDs 2 from surrounding metal structures, such as the heat sink 4.

An upper silicone layer 15' has apertures 18, which allow the locators 12 to extend through it to secure the whole assembly 1 together, while electrically insulating the LEDs 2 and PCB 3 from the metal heat sink 4.

The locators 12 also function to electrically insulate the PCB from the metal screws and heat sink 4.

The lower silicone layer 15" has apertures 18 through which the LEDs 2 project.

Silicone is pliable, has good electrical isolation properties but is not a thermal insulator. Importantly, is an extremely efficient conductor of heat. The silicone wrap or layers 15 is therefore thermally conductive and electrically insulative.

This heat conductor property enables the LEDs 2 to transfer heat from the PCB 3 to the inner vanes 10,10' via the heat pads 17) without surplus heat being retained in the assembly 1 and without direct contact (and thus without electrical communication) with the heat pads 17.

As the silicone is held in place by the locators 12 (T-pieces) and screws 13 (bright zinc plated (bzp) machine screws), there is no need for heat sink paste or glue, and removal of the PCB 3 for replacement or repair is simplified.

In fact, at no point during PCB removal or replacement is re-tailing, soldering or fixing to terminal blocks required. This system also eliminates the possibility of unsure or irregular connection from fitting to fitting, since the positions of the locators 12 and apertures 14 ensure correct positioning of the components.

Figure 7 shows an exploded view of a clip 16 which further assists in removal and replacement of the PCB 3.

The clip 16 is a removable plastic clip, which braces the cables at an insulated point and secures them against the PCB 3 at positive and negative connection points.

Another part 22 of the clip passes over the exposed cable tails to provide safe insulation.

Two teeth 23 pass through pre-tooled apertures 14 in the PCB body and fix with bright zinc plated screws 13 to secure the clip.

Figures 6 and 7 show two location points that pass through the PCB assembly and screw for secure fitment. The clip 16 is fully isolated to avoid electrical arc or short circuit.

The earth point is located away from the PCB 3, alongside the outer live, neutral and earth connection points for the inbound electrical feed (from the LED Driver).

The earth point connects to the aluminium body of the assembly 1 using a standard ring terminal and fastener.

As the fitting is a sealed ingress protected unit (1F67) and earth points are necessary for periodical electrical testing, keeping the earth point away from the PCB 3, helps to avoid complications.

The apparatus 1 can be easily retrofitted to existing street light housing, or the apparatus with an associated housing/outer casing (not shown) can be fitted to an existing street light connector arm or spigot mount.

Further, the electronic components of the assembly 1 are compatible and easily connectable to existing street light components and monitoring software.

The apparatus provides optimum performance levels for LED lumen output and lifespan efficiency and is able to maintain these levels using multiple LEDs having uniform performance from different mounting positions and angles.

The apparatus meets all necessary criteria in regards to UK lighting standards and replacement schemes.

Claims

<claim-text>Claims 1. A lighting assembly for a street light comprising a plurality of lighting elements connected to a circuit board, the circuit board being removably attached to a heat sink.</claim-text> <claim-text>2. A lighting assembly as claimed in Claim 1, wherein the circuit board is removably attached to the heat sink by at least one fixing element extending through an aperture in the circuit board.</claim-text> <claim-text>3. A lighting assembly as claimed in Claim 1 or 2, wherein the circuit board is electrically insulated from the heat sink.</claim-text> <claim-text>4. A lighting assembly as claimed in Claim 3 wherein the circuit board is in thermal communication with the heat sink.</claim-text> <claim-text>5. A lighting assembly as claimed in any of Claims 2 to 4, wherein the at least one fixing element is electrically insulated from the circuit board.</claim-text> <claim-text>6. A lighting assembly as claimed in Claim 5 wherein the at least one fixing element is electrically insulated from the circuit board by an electrically insulative locating element configured to receive the at least one fixing element.</claim-text> <claim-text>7. A lighting assembly as claimed in Claim 6, wherein the at least one locating element is mounted in a recess in the heat sink.</claim-text> <claim-text>8. A lighting assembly as claimed in any of claims 2 to 7, wherein the at least one fixing element is in thermal communication with the heat sink.</claim-text> <claim-text>9. A lighting assembly as claimed in any of Claims 6 to 8, the locating element extends through an aperture in a thermally conductive and electrically insulative layer between the heat sink and the circuit board.</claim-text> <claim-text>10. A lighting assembly as claimed in Claim 9, wherein the layer comprises silicone.</claim-text> <claim-text>11. A lighting assembly as claimed in any preceding claim, wherein the heat sink comprises a curved inner surface.</claim-text> <claim-text>12. A lighting assembly as claimed in Claim 11, wherein the curvature of the inner surface of the heat sink is around 4 degrees.</claim-text> <claim-text>13. A lighting assembly as claimed in Claim 11 or 12, wherein attachment of the circuit board to the curved surface of the heat sink causes corresponding curvature of the circuit board.</claim-text> <claim-text>14. A lighting assembly as claimed in Claim 13, wherein in use at least one of the lighting elements is oriented at substantially 0 degrees to vertical axis of the lighting assembly and at least one of the lighting elements is oriented at around 4 degrees from the vertical axis of the assembly.</claim-text> <claim-text>15. A lighting assembly as claimed in any preceding claim, wherein the outer surface of the heat sink comprises thermally conductive projections.</claim-text> <claim-text>16. A lighting assembly as claimed in any preceding claim, wherein the inner surface of the heat sink comprises thermally conductive vanes.</claim-text> <claim-text>17. A lighting assembly as claimed in any preceding claim wherein the inner surface of the heat sink comprises thermally conductive heat pads at positions corresponding to the positions of the lighting elements.</claim-text> <claim-text>18. A lighting assembly as claimed in any preceding claim, wherein the at least one fixing element comprises a screw.</claim-text> <claim-text>19. A lighting assembly as claimed in any preceding claim, wherein the lighting elements comprise LEDs.</claim-text> <claim-text>20. A lighting assembly as claimed in any preceding claim, wherein the lighting elements are positioned in a non-linear arrangement.</claim-text> <claim-text>21. A lighting assembly as claimed in any preceding claim, further comprising at least one lens.</claim-text> <claim-text>22. The lighting assembly as claimed in any preceding claim, further comprising a detachable connector for connecting an electrical supply to the circuit board.</claim-text> <claim-text>23. The lighting assembly as claimed in any preceding claim, further comprising an external housing and/or a street light connector arm and/or a street light spigot mount.</claim-text> <claim-text>24. A street light comprising the lighting assembly of any of claims ito 23.</claim-text> <claim-text>25. A kit of parts for a street light comprising a plurality of lighting elements, a circuit board, a least one fixing element for removably fixing the circuit board to a heat sink and at least one electrically insulative locating element for locating the at least one fixing element and circuit board in position on a heat sink.</claim-text> <claim-text>26. A kit of parts as claimed in Claim 25, further comprising an electrical connector for releasably coupling the circuit board to a street light power supply.</claim-text> <claim-text>27. An electrical connector for a street light comprising first and second electrically conductive elements, the first electrically conductive element being removably connectable to a circuit board and the second electrically conductive element being removably connectable to a street light power supply.</claim-text> <claim-text>28. A street light comprising the electrical connector of Claim 27.29. A method of fitting a lighting assembly or a component thereof to a street light, comprising the steps of: electrically isolating a lighting assembly from a street light power supply; removably attaching a circuit board to a heat sink in the street light.</claim-text> <claim-text>29. A lighting assembly substantially as shown in and described with reference to the drawings.</claim-text> <claim-text>30. A street light substantially as shown in and described with reference to the drawings.</claim-text> <claim-text>31. An electrical connector substantially as shown in and described with reference to the drawings.</claim-text>