WO2011023927A1

WO2011023927A1 - Luminaire

Info

Publication number: WO2011023927A1
Application number: PCT/GB2010/001441
Authority: WO
Inventors: Nigel Savage; Chris Harris Marsh
Original assignee: Ocean-Led Ltd
Priority date: 2009-08-28
Filing date: 2010-07-30
Publication date: 2011-03-03
Also published as: GB2473185A; GB2473185B; GB0915122D0

Abstract

A luminaire for providing general illumination and incorporating light-emitting diodes and optical elements comprises only two basic elements. The first element is a printed circuit board (1) on one side of which is mounted LEDs (2) together with other circuit elements including a microprocessor (11) holding a control program for the LEDs and a constant current controller for the LEDS. The circuit board also serves as a heat sink, transferring heat from the other face of the board. The second element is a moulded plastic part (5) that serves not only to protect the circuit board and the components, but also is shaped so that optical elements are included as part of the structure. Both the circuit board and the moulded plastic part can be manufactured and assembled cost effectively, providing a low cost luminaire. Additional decorative and optical features (8), (9) and (10) can be added in a straightforward way.

Description

LUMINAIRE

TECHNICAL FIELD

The technical field of this invention is solid-state lighting, and in particular the use of light-emitting diodes (LEDs) to provide a lighting fixture that is energy efficient, readily controllable, easy and economical to manufacture and which has a very thin physical profile.

BACKGROUND

The development of the technology of light-emitting diodes based on gallium, aluminium and indium nitrides has now reached the stage where white light sources based on these materials are more efficient that almost any other light sources. In particular, white light, usually but not necessarily based on the use of a blue (450 to 470nm) LED together with a phosphor that is excited by the blue and has a broad emission centred in the range 550 to 600nm, can now be produced with an efficiency greater than that of incandescent or fluorescent sources. The efficiency is generally described in terms of the output light energy, expressed in lumens to take account of the physical response of the human eye, relative to the input electrical energy. Typically an incandescent lamp will have an efficiency of 15 lumens/W and a compact fluorescent 60 lumens/W, in comparison to the best commercial white LEDs that are now achieving 130 lumens/W, and still improving.

This advantage in efficiency is supplemented by other major advantages. Unlike all fluorescent tubes the LED lights do not contain mercury, an environmental hazard, and do not require a ballast system to generate the electrical discharge and potentially cause electrical interference. The reliability is much better than that of other sources of light, with expected lifetimes of 50,000 hours or more, in comparison to the lifetimes of incandescent lights, which can be as low as 1,000 hours, or compact fluorescent lights with lifetimes of typically 5,000 hours. LED lights do not require a glass envelope and so in general are much more robust.

The technical development of LED lamps has triggered a major effort to use these light sources to produce efficient light sources and luminaires. The main technical problems can be classified into three groups: i. Thermal management. Unlike incandescent and in particular fluorescent tubes the heat dissipation in an LED is concentrated into a very small volume, and must be removed efficiently if it is not to cause degradation. The problems are magnified because a plastic (silicone or epoxy) encapsulation is usually used around the phosphor and the semiconductor chip for protection and to enhance light extraction. Heat can be removed efficiently from the active region of the semiconductor into the body of the LED lamp, but heat transfer from the luminaire to air by means of free convection is an inefficient process, and is usually the limiting factor in the operation of the light. ii. Optical design. Almost all commercial white LEDs are packaged in such a way that they act as Lambertian emitters, with the intensity of the light varying as the cosine of the angle from the normal. For a focussed beam a collimating lens is therefore needed. Moreover, a single LED can provide typically 200 lumens of light, in comparison to 1,000 lumens from a typical incandescent bulb or a compact fluorescent light. A practical light must therefore contain a number of LEDs. Controlling the light, and superposing the light from a number of LEDs involves careful optical design and can often lead to significant reductions of efficiency. iii. Cost. The major limitation on the widespread adoption of solid state light sources is cost. To some extent this is a reflection of the relative immaturity of the technology, but the high cost also results from the need to satisfy both thermal and optical design constraints.

Most of the LED luminaires that have been developed to date have attempted to provide a light fitting or lamp that can be used as a direct replacement for existing incandescent or fluorescent lights. Although this approach may lead to slightly earlier adoption of solid-state lighting, it does not build on the major strengths of LEDs. In particular, the attempt to provide a "retro-fit" solution does not provide the most cost- efficient solution.

The invention described here is a novel approach to the design and manufacture of a solid-state luminaire based on LEDs, in which the three design constraints described above are treated within an integrated approach to provide a cost efficient solution to luminaire design. Moreover according to the invention each luminaire unit preferably includes a programmable microprocessor which can be flash programmed in order to provide a range of novel and advantageous characteristics for the luminaire.

THE INVENTION

The invention provides a luminaire as described in claim 1 herein. The major innovative feature of the luminaire of the invention is that it comprises only two essential elements (other elements being optional). The first essential element is a printed circuit board on which is mounted the array of LEDs together with other circuit elements for sensing and control. The circuit board itself serves as a heat sink, but that heat dissipation characteristic may be augmented by the incorporation of one or more heat sinks mounted on the circuit board, preferably on its face remote from the mounted LEDs. The second essential element is a one-piece moulded plastic optical element that serves not only to protect the circuit board and the components, but also is shaped so that it includes an integrally moulded collimator portion for each of the LEDs in the array. Each collimator portion collimates and directs the light output from its associated LED by total internal reflection. It will be clear to those skilled in the art that both the circuit board and the moulded plastic part can be manufactured and assembled cost effectively. The two basic elements are simply attached together to form the complete luminaire in its simplest form.

The solid state circuit elements mounted on the printed circuit board together form a constant current controller for the LEDs. Most current proposals for LED luminaires require the luminaire to be used in conjunction with a constant current power source, but it has been found according to the invention that all of the necessary circuit elements can be mounted on the same printed circuit board as that which mounts the LEDs, without making the luminaire unduly bulky and without presenting any heat dissipation problems. Indeed the luminaire according to the invention can be made so thin that it has the visual appearance of a recessed ceiling light fitting even though it is in fact surface mounted.

An optional but highly innovative aspect of the luminaire according to the invention is that the printed circuit board of each individual luminaire also mounts a microprocessor which has a control program for the LEDs held in flash programmable non-volatile memory. The control that can be exerted can be a control over the illumination provided by each LED in the array, such as a dimming control; or a diagnostic control to record in random access memory a history of the use of the luminaire. Consider first the dimming control. LEDs reach their maximum light output in extremely short start-up times, which lends itself to a pulse-width modulation of the total light output. Switching the LEDs ON and OFF over a very high frequency cycle time of, for example, 26 to 27 kilohertz avoids audio noise associated with the high frequency switching, and the imposition of a pulse width modulation control over that switching cycle permits the microprocessor to control the total intensity of the illumination provided by the luminaire without affecting the colour temperature of the illumination at all. The dimming potential can be utilised in many ways. If the printed circuit board mounts elements which monitor the surface temperature of the circuit board, then an excessive monitored temperature can cause the microprocessor to reduce the power consumption of the LEDs, for example by varying the mark space ratio of the pulse width modulation to dim the LEDs until the monitored temperature is restored to a predetermined safe level. Alternatively the mark space ratio can be factory-set to achieve a predetermined level of illumination, so that essentially the same luminaire can be set to a high illumination level or to a night-light 'glow' merely by inputting the appropriate program into the non-volatile memory of the microprocessor after assembly of the luminaire. A most innovative and unique dimmable characteristic can be achieved according to the invention, however, by a different programming of the microprocessor. Most dimmable lighting units require a 3-wire input: two wires for the power supply and the third for a signal setting the level of illumination. A luminaire according to the invention can be fully dimmable with only a 2-wire input, being the power input. The advantage is that such a luminaire can be connected to any conventional ON/OFF light switch such as a rocker switch, and that switch can be used for the dimming control. The dimming works as follows. Electrical components attached to the printed circuit board monitor the ON/OFF timing of the power voltage as applied through the light switch. The microprocessor is programmed to recognize when the monitored timing goes through an ON-OFF-ON cycle within a first predetermined time period, for example ON- OFF-ON within one second. On recognition of that first predetermined time period, the program converts to a pulse-width modulated cycle which cycles the intensity of the illumination through a regularly increasing and decreasing cycle, such as a sine wave pattern of increasing and decreasing intensity. When the user finds that the current intensity of illumination is exactly that which is required, he or she turns the light switch OFF, which again is monitored by the microprocessor with the result that when the luminaire is again turned ON, that current level of illumination is maintained. The luminaire remains at the same user-set level of illumination until the user again cycles the ON/OFF switch through an ON-OFF-ON cycle within the given predetermined time period, which is effective to commence a new dimming selection cycle. One advantageous variant of this control is that if the program cycles through a certain number of cycles of the above sine wave, for example three cycles, without the user making the selection by turning the power supply OFF, the assumption is that the user did not intend to enter the dimming setting mode, and the program reverts to providing the full illumination of the LED array.

The diagnostic control provided by the microprocessor may be any of a range of diagnostics. The microprocessor preferably is connected to random access memory which permits the recordal of the operating characteristics of the luminaire such as an hour counter (to record the total number of hours during which the luminaire has been switched ON), a record of the last time the printed circuit board overheated, or the last time an overvoltage was detected. Such a diagnostic record is a very valuable tool in the long term improvement of the efficiency and reliability of LED based luminaires, and is not available in any luminaires currently proposed for commercial development.

DRAWINGS

One detailed embodiment of the invention is described below with reference to the following Figures.

Figure 1 shows the schematic cross-section through a luminaire according to the invention.

Figure 2 shows a plan view of the printed circuit board of Figure 1 with only LEDs attached. Figure 3 shows a plan view of the printed circuit board of Figure 1 but with both

LEDs and other electrical components attached.

Figure 4 is an exploded three-dimensional view of elements of the luminaire of Figure

1 .

Figure 5 is an exploded three-dimensional view of the complete luminaire of Figure 1.

In this embodiment the circuit board is a metal-cored printed circuit board (pcb) with six high power LEDs (2) mounted on the underside of the circuit board (1) in Figure 1. The high thermal conductivity of the pcb means that the temperature is almost uniform across the pcb, so that heat transfer from the upper face (in Figure 1 ) of the circuit board is as efficient as possible. If this design is implemented using the most recent generation of high-efficiency high brightness LEDs then cooling from a single face is easily sufficient to maintain the temperature of the board at an appropriate level and hence maintain the junction temperature of the LEDs well below the maximum specified in an LED manufacturer's data sheet.

With earlier generations of less efficient LEDs a much larger surface area was required in order to maintain the LEDs at a safe operating temperature, giving a luminaire with a high height to diameter ratio. In the implementation shown schematically in Figure 1 and in exploded three dimensional view in Figure 5, an extremely low profile (the ratio of height to diameter) is achieved by use of the pcb as the heat sink and heat transfer medium. In this implementation six LEDs were used, but if many more LEDs were used on a pcb of similar area additional heat sinks could be used thermally attached to the upper surface of the pcb as is well known in the art.

In Figure 1 the connection to the circuit board is made by means of insulated wires (3) passing through the centre of the circuit board and through a grommet (4) that forms a seal to prevent entry of gas or liquid. Other possibilities can be envisaged, such as the use of a ceramic circuit board with tracks formed on one face, and connection made to the other by means of conducting through vias, as is well known to those skilled in the art.

Figure 2 illustrates only the LEDs mounted on the pcb, but in practice those LEDs must be driven by a constant current source. According to the invention the pcb carries in addition to the LEDs a range of other circuit components including integrated circuits and passive components as shown in Figure 3, which together form the constant current circuit for the LEDs. These additional components add a negligible extra heat load, but enable much greater functionality to be achieved. The constant current circuit is such that the current passing through the LEDs is independent of the DC voltage supplied through the wires (3). Typically the supply voltage could be in the range of 10 to 250 volts AC or DC, but a more usual specification would be for the constant current circuit to operate at supply voltages of 10 to 50 or 15 to 30 volts DC. In this way a single design of luminaire can be used directly in different applications where supply voltages may be different.

One important circuit components that is mounted on the pcb according to the invention is a microprocessor chip (1 1) having a control program for the LEDs held in a flash programmable non-volatile memory. The microprocessor provides the luminaire of the invention with the capacity to achieve a wide range of different functions.

For example the microprocessor may provide a dimming function, responsive either to a signal sent down a signal wire (not shown) in addition to the power wires (3) or to a signal sent down the power wires (3) themselves, or to a signal sent from a remote controller such as an infrared control unit. If the power wires (3) are used as the signal source, then the microprocessor is preferably programmed to monitor the ON/OFF timing of the associated rocker switch in the manner described above.

A temperature sensor can be included on the pcb, together with control circuitry that reduces the current supplied to the LEDs if the temperature increases beyond safe limits as specified in the manufacturer's data sheet.

The circuitry mounted on the PCB can have supply voltage monitoring and diagnostic functionality, such that action can be taken to ensure correct any operation which if continued may result in damage, and can also provide status indicators, giving a visual indication if the temperature is too high or if the supply voltage is outside the allowed ranges. A motion sensor can be mounted on the pcb, either to illuminate the LCDs for a predefined period when movement is detected in the vicinity of the luminaire or to change the illumination from a stand-by low level illumination to a full power illumination.

The pcb is covered by a plastic part (5), formed for example from polycarbonate using techniques such as injection moulding well known to those in the field. The moulding (5) performs a multiplicity of functions, and this is a key innovative step. In addition to providing a cover for the pcb, the moulding is shaped to provide optical elements (6), one for each LED on the pcb, and to hold these optical elements in precise alignment with the LEDs. The shape of each optical element is designed so that it provides a lens or collimator (6) coupled closely to each LED, and changes the Lambertian light emission from the LEDs into the desired pattern of illumination. By 'lens' it is intended to identify a shaped reflector with typically a silvered reflective surface; and by 'collimator' it is intended to identify a shaped optical element which provides a collimated beam of light by total internal reflection. For example, each lens or collimator can be manufactured to have a collimating form to produce a beam of light with an angular spread which may be selected from near parallel to a divergence of nearly 180°. Beams with a divergence of 178° are attainable, although the demand is most likely to be for a narrow angular spread.

Plastic part (5) is shaped to have an integral ring (7) that meets the pcb (1) both to locate the two components securely in the correct relative positions, and also to provide a seal between the two. This seal can be formed using an appropriate silicone or a rubber seal or gasket. The two components can be held in position by a number of means including the use of screws through the pcb into the plastic moulding, adhesive, or locating clips. The innovative design allows the luminaire to be sealed effectively and so to have good ingress protection (IP) up to IP66, corresponding to external use on a boat, and much better than required for normal outdoor use.

A further key innovative step in this invention relates to the design that allows the circuit board (1) and the moulding (5) each to be manufactured separately in a cost effective way. The LEDs and other electrical components can be assembled on the pcb using automated techniques similar to those used, for example, in the mobile phone industry by sub-contractors not skilled in luminaire design. Similarly the plastic part (5) can be moulded as a single entity even though it has multiple functions. The design of the two parts provides precise location when they are brought together, so that no complex alignment of the lenses and the LEDs is necessary. An outer periphery of the optical moulding (5) surrounding the integrally mounded lenses or collimators (6) may be rendered opaque to conceal any of the additional circuit components of Figure 3; or alternatively may be moulded as an annular array of prisms or lenses so that the precise nature of the components cannot be identified by simple observation though the moulding (5).

Additional functionality of the luminaire of the illustrated embodiment is provided by the bezel (9) shown in Figures 1 and 5. This serves not only a decorative function, but can be used if desired also to locate a range of additional optical elements such as filters, lenses and anti-glare elements exemplified by the parts marked (8) and (10) in Figures 1 and 5. (8) is an anti-glare panel which is preferably a disc of folded plastic strips adhered together to form a honeycomb of apertures through which the light passes. As an example the anti-glare element is shown in exploded three-dimensional view in Figure 4. It is held in place by a screen (10) which may itself be a moulded polycarbonate protective screen or a colour filter screen.

The use of a colour filter screen is of particular value in connection with a luminaire according to the invention. One specific form of filter (10) which may be used in the luminaire is a colour-correcting filter. In general to achieve a luminaire with a high efficiency it is preferable to use a commercial LED with a relatively high colour temperature of above 6000K. For many applications the light emitted from such LEDs is considered to be too "cold", by which is meant that the blue component of the light is too obvious. The use of a colour correcting filter can be used to reduce the blue component and to give a "warmer" light with a colour temperature of 4000K or below, which is more acceptable in many applications. Although commercial LEDs with colour temperatures in this range are available, a higher efficiency is obtained through the use of high-efficiency high-colour-temperature LEDs with a colour correcting filter. A further advantage is that a single design of luminaire can be used with different colour-correcting filters to give any desired colour temperature. As is well known in the art, similar filters can also be used to change the tint of the emitted light.

The bezel in this implementation is supported by the moulding (5), preferably by means of a screw thread on the outside of the moulding, and clamps the optical element against the moulding. Other forms of attachment are of course possible.

To protect the optical elements the bezel (9) is sealed against the moulding (5) by means of the O-ring gasket (12) shown in Figure 5. The bezel is also sealed against the optical element (10) by means of the sharp structure (13) shown at the inner edge of the bezel (9) in Figure 1. Other methods of sealing are of course possible. By means of these seals a luminaire containing the optical elements are also suitable for outdoor use and is can be certified to IP66.

This detailed description is by way of example only, and does not define the only way in which this invention can be implemented. Other variations on the basic innovation will be obvious to those skilled in the art.

Claims

1. A luminaire for providing general illumination, comprising an array of light- emitting diodes (LEDs) and an associated optical element, characterised in that the luminaire comprises

a printed circuit board on which are mounted:

the LEDs and

solid state circuit elements which together form a constant current controller for the LEDs; and

a one-piece moulded optical element comprising a transparent protective shield to cover and protect the whole of the printed circuit board, and having an integrally moulded lens or collimator portion for each individual one of the LEDs, the printed circuit board and the optical element being held together by means of a silicone or rubber seal to prevent ingress therebetween of gas or liquid.

2. A luminaire according to claim 1 in which the circuit board is metal-cored printed circuit board, or a circuit board formed from an electrically insulating ceramic which is a good thermal conductor of heat on which are fabricated electrically conductive metal tracks and connections for attaching the light-emitting diodes and circuit components.

3. A luminaire according to claim 2, in which the printed circuit board is formed from aluminium nitride, on which are fabricated electrically conductive metal tracks and connections for attaching the light-emitting diodes and circuit components.

4. A luminaire according to any preceding claim, further comprising a bezel mounted in front of the luminaire to cover the plastic part and to hold in place an antiglare element, optical lens, diffusing screen or filter in front of the luminaire.

5. A luminaire according to claim 4, in which the filter is a colour-correcting filter which is effective to change the colour temperature of the emitted light.

6. A luminaire according to claim 4, in which the filter is a colour correcting filter which is effective to change the tint of the emitted light.

7. A luminaire according to any preceding claim, in which the constant current controller operates irrespective of the external voltage supplied to the circuit when that external voltage is in the range 10 to 250 volts.

8. A luminaire according to claim 7, in which the constant current controller operates irrespective of the external voltage supplied to the circuit when that external voltage is in the range 10 to 50 volts.

9. A luminaire according to any of claims 1 to 8, in which the printed circuit board further mounts a microprocessor having a control program for the LEDs held in a flash programmable non-volatile memory and which controls electrical components attached to the circuit board to control the intensity of the light emitted from the luminaire.

10. A luminaire according to claim 9, having a 2-wire power input for connection to a light switch, wherein electrical components attached to the circuit board monitor the ON/OFF timing of a voltage applied to the power input through that light switch, and the microprocessor is programmed to convert to a pulse-width modulated cycle of alternate decreasing and increasing intensity of illumination of the light emitted from the luminaire when the monitored timing goes through an ON-OFF-ON cycle within a first predetermined time period and which then holds the intensity of illumination of light emitted from the luminaire at the current level for future single ON and OFF operations of the light switch when the applied voltage is turned OFF.

11. A luminaire according to claim 10, wherein the microprocessor is programmed to terminate the alternate decreasing and increasing intensity of illumination after the applied voltage has remained ON for a second predetermined time period immediately following the sensed ON-OFF-ON cycle.

12. A luminaire according to any of claims 9 to 1 1, in which the microprocessor controls electrical components attached to the circuit board which provide a circuit for sensing infra-red radiation under the luminaire and for reducing or increasing the intensity of the emitted light in response to the detection of an infra-red signal.

13. A luminaire according to any of claims 9 to 12, in which the microprocessor controls electrical components attached to the circuit board which provide a circuit for sensing an excessive temperature of the circuit board and reducing the power in the diodes to reduce such a sensed excessive temperature.

14. A luminaire according to any of claims 9 to 13, in which the microprocessor controls electrical components attached to the circuit board which provide status indicators, giving a visual indication if the temperature of the circuit board is excessive or if the supply voltage is outside a desired range.