GB2505214A

GB2505214A - Luminaire

Info

Publication number: GB2505214A
Application number: GB1215007.4A
Authority: GB
Inventors: Mike Allcock
Original assignee: FW Thorpe PLC
Current assignee: FW Thorpe PLC
Priority date: 2012-08-23
Filing date: 2012-08-23
Publication date: 2014-02-26
Also published as: GB201215007D0

Abstract

A luminaire 10 comprises a housing 12 including a plurality of lighting elements 14 arranged around the periphery of the housing. Each lighting element comprises an LED light source 16 and a phosphor screen (18, Fig. 3). The phosphor screen 18 is spaced from the LED light source 16 and is illuminated by the LED light source to provide the light output of the luminaire. The LED light sources 16 generate blue light which is absorbed by the phosphor in the screen 18, and is re-emitted at a lower frequency to more closely resemble daylight.

Description

Improvements in or relating to luminaires The present invention relates to improvements in or relating to luminaires.

S

It is becoming increasingly common for luminaires to be based on LED technology.

Examples include ceiling luminaires for room lighting, such as in offices or shops. These ceiling luminaires may be fined in suspended ceilings, for example, in place of ceiling tiles or panels. It is important to consider the quality of light produced by luminaires, since overall light levels must be adequate for the area being illuminated, whereas lighting which is harsh or significantly different in colour to daylight, may be unacceptable for many users.

Examples of the present invention provide a luminaire comprising: a housing; and a plurality of lighting elements arranged within the housing; wherein each lighting element comprises: an LED light source; and a phosphor screen spaced from the LED light source and illuminated, in use, by the LED light source to provide the light output of the luminaire.

At least one of the lighting elements may have an LED light source which comprises a single LED. A plurality of the lighting elements may each have an LED light source which comprises a single LED. Substantially all of the lighting elements may each comprise a single LED.

The luminaire may further comprise a circuit board carrying the LEDs of more than one of the lighting elements. The population density of LEDs on the circuit board may be sufficiently low for the circuit board to act as a heatsink for the LED5, there being no heatsink structure provided otherwise within each of the lighting elements. The circuit board may be in thermal contact with a panel of the housing, the panel being thermally conductive to convey heat away from the circuit board.

The lighting elements may be arrayed around a middle region of the luminaire. The s lighting elements may be arranged around the periphery of the luminaire. The luminaire may have a polygonal outline, there being a line of lighting elements arranged along at least one side of the outline. There may be a line of lighting elements arranged along each side of the outline. The luminaire may have a square outline.

The lighting elements may be arrayed around a region of the luminaire which houses control apparatus and/or, power supply apparatus for the lighting elements.

The housing may further comprise louvre elements associated with the lighting elements and which, in use, provide limits to the angle at which light leaves the is luminaire.

Examples of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a perspective view showing the lower, exposed face of a luminaire; Fig. 2 is a plan view of the luminaire, from below; Fig. 3 is an enlarged section at the line 3 -3 in Fig. 2; Fig. 4 is a perspective view of a circuit board and lighting elements of the luminaire of Fig. 1; and Fig. 5 is an enlarged, partial perspective view of the luminaire, partly in section.

Overview The drawings illustrate a luminaire 10. The luminaire 10 is intended for use as a ceiling luminaire to be installed horizontally in a ceiling, such as a suspended ceiling. The face illustrated in Fig. 2 will be lowermost and exposed to provide illumination to the room below. The luminaire 10 comprises a housing 12 and a plurality of lighting elements 14.

The lighting elements 14 are arranged within the housing 12, as will be described. Each lighting element 14 comprises an LED light source indicated generally at 16 (see Fig. 3, for example) and a phosphor screen 18. The phosphor screen 18 is spaced from the LED light source 16 and is illuminated, in use, by the LED light source 16. The phosphor screen 18 provides the light output of the luminaire 10.

The LED light sources 16 may generate blue light which is absorbed by the phosphors in the screen 18, and re-emitted at lower frequency, more closely resembling daylight.

LiQhtinp elements Fig. 3 shows one of the lighting elements 14 in section. The source 16 is based on a single LED 20, which is a single blue LED, in this example. The LED 20 is mounted on a circuit board 22 through which the LED 20 is provided with power. The LED 20 is in thermal contact with the circuit board 22.

The lighting element 14 includes a generally conical reflector 24 having a narrow end at which the LED is received through an aperture of appropriate size, and a wide end at which the phosphor screen 18 is positioned. The concave face of the reflector 24 is finished to be highly reflective so that when the LED 20 is operating, during use, the light output of the LED 20 is reflected toward the phosphor screen 18. Likewise, any light leaving the phosphor screen 18 in a direction toward the reflector 24, and arising from the phosphorescent action of the screen 1 8, will be reflected back toward the screen 18.

It is important to note that the lighting element 14 illustrated in Fig. 3 has an LED light source 16 which comprises only a single LED 20. A plurality of the lighting elements 14, which may be all or substantially all of the lighting elements 14 aiso each comprise only a single LED.

The LED 20 is mounted on the circuit board 22, as noted above. It can be seen from Fig. 4 that the circuit board 22 carries several lighting elements 14. Accordingly, the light sources 16 of each of the lighting elements 14, as illustrated in Fig. 4, are each mounted on the circuit board 22 and are each in thermal contact with the circuit board s 22. Noting that each lighting element 14 contains only a single LED 20, the population density of LEDs 20 on the circuit board 22 is very low. This allows the circuit board 22 to act as a heatsink for the LEDs 20. No heatsink structure is provided otherwise within any of the lighting elements 14.

The circuit board 22 is secured against a panel 26 (Fig. 3) of the housing 12, by fixings 28. The panel 26 is the back panel of the housing 12 and will be uppermost (and generally horizontal) when the luminaire lOis installed in a ceiling, as described above.

The intimate contact between the circuit board 22 and the panel 26 provides thermal contact between these components. Furthermore, the panel 26 is thermally conductive.

is For example, the panel 26 may be made of metal. Accordingly, the panel 26 can convey heat away from the circuit board and thus, in turn, away from the lighting elements 14.

Geometry of the luminaire The lighting elements 14 are arrayed around the luminaire 10, as can be seen from various drawings. In this example, a total of 20 lighting elements 14 are provided within the luminaire 10. The luminaire has a square outline, but other polygonal outlines could be chosen, such as a rectangle. In this example, a line of lighting elements 14 is arranged along each side of the square. In other examples, lighting elements 14 may be arranged along at least one side of the outline, but not along all sides. It can also be seen from the drawings that the lighting elements 14 are arrayed around the periphery of the luminaire 10. Thus, the lighting elements 14 are arrayed as a square of 20 elements 14 around the periphery of the luminaire 10. This leaves a middle region 30, containing no lighting elements 14.

Louvre elements The front face of the luminaire 10 is divided into a series of wells 32 by louvre or baffle elements 34. The louvre elements 34 divide a channel which runs generally along each side of the luminaire 10. The walls 36 of the channel provide a further louvre or baffle function. Accordingly, each well 32 is generally square in shape, when viewed from beneath, having sloping sides defined by two louvre elements 34, and two channel walls 36. Each well 32 will be downwardly directed, when the luminaire is installed. The base of each well 32 (which will be uppermost in the well 32, during use) has an aperture 38 through which the phosphor screen 18 of one of the lighting elements 14 is exposed.

Accordingly, when the luminaire 10 is installed, the arrangement illustrated in particular in Fig. 3 will be inverted as compared with that drawing and will include the panel 26 uppermost, the circuit board 22 immediately below the panel 26; the LED 20 mounted on the circuit board 22; the reflector 24 below the circuit board 22; the phosphor screen 18 below the reflector 24; and the louvres 34 and walls 36 below the phosphor screen 18.

Each circuit board 22 carries five lighting elements 14, as can be seen from Fig. 4.

Accordingly, four circuit boards 22 are used in the luminaire 10. Each circuit board 22 carries one lighting element 14 at a respective extreme corner of the luminaire 10, and the four lighting elements 14 along one of the sides extending away from the extreme corner. The lighting element 14 at the next extreme corner is carried by the next circuit board 22.

The louvre elements 34 and the walls 36 serve to baffle the light output from the phosphor screen 18, to help avoid unacceptably harsh lighting effects.

Middle region The panel 26 extends across substantially the whole area of the luminaire 10, including the middle region 30. The panel 26 is also in thermal contact with the circuit boards 22, as described above. Accordingly, the panel 26 provides a large area for disposal of waste heat. Indeed, as can be seen from Fig. 2 in particular, the area of the panel 26 is very large as compared with the area of the individual LEDs 20. It is expected that this large relative area will allow for good thermal control of the operating conditions of the LEDs 20, by allowing surplus heat to be conveyed away from the LEDs 20, through the circuit board 22 to the panel 26, for dispersal into the environment.

The middle region 30 also provides an area for housing various control apparatus and power supply apparatus, all of which is indicated generally at 40 in Fig. 5. The equipment necessary to control and power LEDs from a mains supply is known in itself and will not be further described here. Power is conveyed by the circuit boards 22 from the apparatus 40 to the lighting elements 14. It is appropriate to note that the control and supply apparatus 40 can also be placed in thermal contact with the panel 26, allowing the panel 26 to serve as a heatsink for the apparatus 40.

Operation of the luminaire When the luminaire 10 is in use, power is supplied to the LEDs 20 from the apparatus 40, resulting in the LEDs 20 creating blue light within the reflectors 24. The light from the LEDs 24 is incident on the phosphor screens 18! directly or after reflection. The phosphor screens 18 absorb the incident light and re-emit the light, which then passes through the wells 32 to leave the lurninaire 10, between the louvre elements 34 and the walls 36. Any light which the phosphor screens 18 re-emit back toward the reflector 24 will be reflected again toward the phosphor screen 18.

This arrangement is expected to exhibit a number of advantages, including the following. The use of blue LEDs 20 and remote phosphor screens 18 is expected to provide efficiency (measured by considering the light output of the lurninaire 10, and the electrical input to the apparatus 40). In particular, the efficiency is expected to be greater than for a luminaire based on white LEDs, because white LEDs must usually be accompanied by a diffuser, to avoid unacceptably harsh lighting effects. The presence of the diffuser significantly reduces the overall efficiency of the arrangement.

The LEDs 20 are arranged singly, as has been described. That is, each lighting element 14 contains only a single LED 20. This is expected to contribute to a softer lighting effect by providing a large number of single LEDs spread over a large area, i.e. relatively low intensity points of illumination, rather than using clusters of LEDs, i.e. groups of more than one LED located in a small area. Clusters of several LEDs can produce intense points of illumination, which can create harsh lighting effects.

Spreading the single LEDs over a large area also allows for easier thermal management, for example by using the large area of the panel 26, and is therefore expected to avoid any specific heatsink structures being required within the lighting elements 14, there being adequate heatsink ability provided by the combination of the is circuit boards 22 and the panel 26.

Accordingly, the luminaire 10 is expected to provide efficient lighting which provides a soft lighting effect with good thermal management of the LEDs 20, thus contributing to their longevity.

Many variations and modifications can be made to the apparatus described above, without departing from the scope of the present invention. In particular, different numbers of lighting elements 14 and LEDs 20 could be provided. Lighting elements 14 could be arrayed in different patterns to those shown and described. A middle region has been described, without lighting elements 14, but other patterns with no middle region could be used. Other types of lighting elements could be incorporated in the luminaire, in addition to the lighting elements 14. Conveniently, the other lighting elements could be in the middle region described above. Different shapes, sizes and relative shapes and sizes could be adopted for the elements described and illustrated.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims 1. A luminaire comprising: a housing; and a plurality of lighting elements arranged within the housing; wherein each lighting element comprises: an LED light source; and a phosphor screen spaced from the LED light source and illuminated, in use, by the LED light source to provide the light output of the luminaire.
2. A luminaire according to claim 1, wherein at least one of the lighting elements has an LED light source which comprises a single LED.
3. A luminaire according to claim 1 or 2, wherein a plurality of the lighting elements each has an LED light source which comprises a single LED. C')
4. A luminaire according to claim 1, 2 or 3, wherein substantially all of the lighting o elements each comprise a single LED. (0

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5. A luminaire according to any preceding claim, further comprising a circuit board carrying the LEDs of more than one of the lighting elements.
6. A luminaire according to claim 5, wherein the population density of LEDs on the circuit board is sufficiently low for the circuit board to act as a heatsink for the LEDs, there being no heatsink structure provided otherwise within each of the lighting elements.
7. A lurninaire according to claim 5 or 6, wherein the circuit board is in thermal contact with a panel of the housing, the panel being thermally conductive to convey heat away from the circuit board.
8. A luminaire according to any preceding claim, wherein the lighting elements are arrayed around a middle region of the luminaire.
9. A luminaire according to any preceding claim, wherein the lighting elements are arranged around the periphery of the luminaire.
10. A luminaire according to any preceding claim, having a polygonal outline, there being a line of lighting elements arranged along at least one side of the outline.
11. A luminaire according to claim 10, there being a line of lighting elements arranged along each side of the outline.
12. A lurninaire according to any preceding claim, having a square outline.
13. A luminaire according to any preceding claim, wherein the lighting elements are arrayed around a region of the luminaire which houses control apparatus and/or power supply apparatus for the lighting elements.
14. A luminaire according to any preceding claim, wherein the housing further comprises louvre elements associated with the lighting elements and which, in use, o provide limits to the angle at which light leaves the luminaire. (0

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15. A luminaire substantially as described above, with reference to the accompanying drawings.
16. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.