Light emitting diode (LED) based lighting systems

Abstract

A lighting system comprises at least one excitation source (5), preferably an LED, operable to generate and radiate excitation radiation of a first wavelength (λ.sub.1); a shade (4) configured to at least in part surround the at least one source (5) and remotely located thereto; and at least one phosphor (16) provided in or on at least a part of the shade (4), wherein the phosphor (16) emits radiation of a different wavelength in response to incident excitation radiation. The phosphor can be provided on a part of an outer or inner surface of the shade. Alternatively, or in addition, the phosphor is incorporated within the shade. The lighting system finds particular application as a hanging, a desk, a floor standing, a wall mountable, a spot, an outdoor or an accent lighting fixture.

Claims

1. A lighting system comprising: at least one blue emitting light emitting diode (LED) configured to emit blue excitation light having a wavelength ranging from 420 nm to 470 nm; an optical enclosure having a curved surface that at least in part defines a volume in which the at least one LED is located, wherein the optical enclosure is light transmissive and the blue excitation light travels a distance of at least one centimeter in free space from the at least one LED to an inner surface of the optical enclosure; and a first phosphor incorporated in and dispersed throughout the optical enclosure; wherein the first phosphor emits light of a different wavelength in response to incident excitation light, and wherein an emission product of the lighting system comprises combined light from the LED and the first phosphor that passes through the optical enclosure.

2. The lighting system of claim 1, and further comprising a second phosphor wherein the second phosphor is provided as a mixture with the first phosphor and the mixture incorporated in and dispersed throughout the optical enclosure.

3. The lighting system of claim 1, wherein the optical enclosure comprises a hollow cylinder.

4. The lighting system of claim 1, wherein the optical enclosure comprises a spherical shell.

5. The lighting system of claim 1, wherein the optical enclosure comprises a paraboloidal shell.

6. The lighting system of claim 1, wherein the optical enclosure further comprises a surface topology to aid coupling of excitation light into the optical enclosure.

7. The lighting system of claim 6, wherein the surface topology comprises grooves.

8. The lighting system of claim 6, wherein the surface topology comprises ribs.

9. The lighting system of claim 6, wherein the surface topology comprises a surface roughening.

10. The lighting system of claim 1, and further comprising a reflector configured to direct excitation light towards the optical enclosure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the present invention is better understood embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic cross-sectional representation of a lighting system in accordance with the present invention which comprises an outdoor lighting fixture;

(3) FIGS. 2a to 2c are schematic representations of optical enclosures arrangements, shades, for use in the lighting fixture of FIG. 1;

(4) FIG. 3 is a schematic cross-sectional representation of a lighting system in accordance with the present invention which comprises a hanging, or pendant, lighting fixture;

(5) FIG. 4 is a schematic cross-sectional representation of a lighting system in accordance with the present invention which comprises a wall, or sconce, lighting fixture; and

(6) FIG. 5 is a partial cross-sectional perspective representation of a lighting system in accordance with the present invention which comprises a wall, or bulkhead, lighting fixture.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring to FIG. 1 there is shown a schematic cross-sectional representation of a lighting system in accordance with the present invention which comprises an outdoor lighting fixture or solar powered garden lantern 1. The lantern 1 is generally cylindrical in form and comprises a circular base 2, a circular top 3, a translucent hollow cylindrical shade 4 disposed between the base and top and a radiation source 5 mounted within the volume defined by the shade 4 in conjunction with the base 2 and top 3. A spike 6 is secured to on an underside of the base 2 enabling the lantern 1 to be installed by inserting the spike 6 into the ground 7. In the embodiment illustrated the spike 6 is removeably secured to the base 2 by a threaded stud 8 enabling the lantern 1 to be secured to fixtures other than the spike such as a wall bracket etc.

(8) In an outer surface of the top 3 there is provided a solar cell, photovoltaic cell, 9 for operating the lantern from incident ambient light 10. Housed within the top 3 there is a control/drive circuit 11 for operating the lantern 1 and a rechargeable battery 12 for powering the lantern in low ambient light levels. An ambient light sensor (not shown) is provided within the solar cell 9 and is configured to detect when the incident ambient light 10 falls below a predetermined threshold at which point the circuit 11 activates the lantern. The circuit 11 is configured to recharge the battery 12 from the solar cell 9 when the ambient light is above a threshold level.

(9) A respective reflector 13, 14 is provided on the upper and lower surfaces of the base 2 and top 3 to increase the brightness of light 15 generated by the lantern. On an inner curved surface of the shade 4 a layer of phosphor 16 is provided. As is known a phosphor is a photo luminescent material which generates radiation, typically light, when subjected to excitation radiation of a selected wavelength or range of wavelengths. In the embodiment illustrated the excitation radiation source 5 comprises a light emitting diode (LED) or an array of LEDs which is operable to generate excitation radiation of wavelength λ.sub.1 in a range 300 to 350 nm (ultra violet) or greater than 350 nm, typically in a range 420 nm to 470 nm (blue). Any appropriate phosphor can be used such as for example orthosilicate, silicate and aluminate materials. It is preferable to use an LED 5 which emits blue light rather than U.V. to lessen any likelihood of damage to a user's eye and degradation of the shade material which is conveniently made of a plastics material.

(10) In the context of the present invention a shade is defined as an optical enclosure which at least partially encloses the light source and is located remotely thereto and can be substantially transparent, translucent or opaque. The radiation source 5 is located remote to the surface of the shade 4 (in particular is located remotely to the phosphor) such that excitation energy emitted by the source is radiated, that is propagates in free-space (that is it is not guided by an optical medium), a distance of at least one centimeter from the excitation source to the shade (phosphor). Where the lantern is required to generate white light 15, a yellow (650 nm) emissive phosphor 16 is provided. The phosphor which typically comprises a fine powder can be coated on the shade by painting or other deposition techniques as part of an epoxy resin or silicone or other binder material. The thickness of the phosphor layer 16 and concentration of the phosphor powder within the binder determines the color of light emitted by the lantern. In an alternative arrangement, the phosphor can be incorporated into a polymer material or silicone and fabricated as a flexible sheet, which is then inserted inside of the shade. It will be appreciated that the color of light 15 emitted by the lantern can be controlled by appropriate selection of the phosphor composition.

(11) Referring to FIGS. 2a to 2c there are shown schematic representations of alternative shade arrangements 4, for use in the lantern of FIG. 1. Each of the shade arrangements illustrated are hollow cylindrical in form though it will be appreciated that the can take any form such as polygonal and multi-faceted forms. FIG. 2a shows a shade in which the phosphor 16 is provided as a layer on the inner curved surface of the shade 4. The shade can be fabricated from any translucent or transparent material such as glass or a plastics material. FIG. 2b shows a shade in which the phosphor 16 is provided on an outer curved surface of the shade 4. Advantageously the inner curved surface of the shade includes some form of surface topology, such as longitudinal ribs/grooves 17 or a roughing of the surface to assist coupling of light from the LED into the shade to thereby maximize light output from the lantern. Moreover, such a surface topology can alternatively or in addition be applied to the outer surface of the shade irrespective of where the phosphor is provided. FIG. 2c illustrates a shade 4 in which the phosphor is integrally incorporated in (dispersed throughout) the shade material during fabrication of the shade. Typically the shade in such an arrangement comprises a plastics material.

(12) Referring to FIG. 3 there is shown a schematic cross-sectional representation of a lighting system in accordance with the present invention which comprises a hanging, or pendant, lighting fixture 18. Throughout this specification the same reference numerals are used to denote like parts.

(13) The hanging fixture 18 is suspended by a cable 19 which is secured to the shade 4 by a threaded mount 20. The mount 20 can include a cable clamp (not shown) for maintaining a fixed relation between the cable 19 and mount 20. In the embodiment illustrated the phosphor 16 is provided on an inner surface of the shade 4 which is made of a translucent material. As illustrated the LED 5 can be directly connected to the cable 19 or a connector arrangement can be provided as part of the mount. A parabolic reflector 21 is provided in one of two alternative arrangements indicated as 21a and 21b in FIG. 3, the latter of which the reflector is indicated by a broken line. In the first arrangement the reflector 21a is provided below the LED 5 and is arranged to reflect emitted radiation from the LED towards the shade 4 and thereby prevent direct emission of radiation from the LED. Such an arrangement is particularly advantageous to ensure a uniform color of emitted radiation 22 from the lighting fixture. Moreover, when a U.V. emitting LED is used, the reflector further prevents damage to a user's eye and eliminates the need for a U.V. filter across the open end of the shade. In the second arrangement the reflector 21b is provided above the LED 5 and is arranged to reflect radiation from the open end of the lighting fixture.

(14) In one embodiment, which it is intended to generate white light 22 in a downward direction and a different colored light from the shade 15, a blue LED is utilized with a yellow phosphor and the reflector arrangement 21b. Blue light generated by the LED 5 which is radiated in a downward direction in combination with yellow light generated by the phosphor 16 gives emitted radiation 22 which appears white in color to the eye. In addition light transmitted through the shade 15 will appear more yellow in color than the white light 22. The exact color of light emitted by the shade will depend on the thickness and density of the phosphor layer 16. Moreover it will be appreciated that the color of light generated by the shade can be tailored by providing one or more different color phosphors such as for example green, orange or red phosphors.

(15) In an alternative arrangement, when it is intended to generate light 15, 22 of substantially a single color, a U.V./blue LED is utilized with a yellow phosphor and the reflector arrangement 21a. U.V./blue light generated by the LED 5 which is radiated in a downward direction is reflected back toward the phosphor rather than being directly emitted by the lighting arrangement. The reflected light excites the phosphor emitting colored light 22, 15 which is emitted from the lighting arrangement.

(16) Referring to FIG. 4 there is shown a schematic cross-sectional representation of a lighting system in accordance with the present invention which comprises a wall, or sconce, lighting fixture 23. The lighting fixture 23 comprises a bracket or sconce 24 to which the shade 4 is mounted. In the embodiment illustrated the fixture is configured as an up lighting arrangement though other variants, such as down lighting or back lighting, can be readily implemented by appropriate configuration of the shade 4. As described in relation to the embodiment of FIG. 3 the lighting arrangement can be configured to emit different colored light from light transmitted through the shade and emitted from the opening of the shade. The lighting fixture can include suitable power driver circuitry to enable the fixture to be operated from a mains electricity supply.

(17) Referring to FIG. 5 there is shown a partial cross-sectional perspective representation of a lighting system in accordance with the present invention which comprises a wall mountable or ceiling mountable, lighting fixture or bulkhead light 25. The fixture comprises a circular housing 26 and detachable front plate 27 which is ring shaped. The housing 26 includes a recess 28 on its inner front face configured for receiving the shade 4 which in the embodiment illustrated comprises a circular plate. The front plate 27 is secured to the housing 26 by screw fixtures 29 and the housing 26 advantageously includes a reflective inner surface (not shown) for reflecting light towards the shade 4. The housing 26 can be made of an opaque material such as a metal or plastics material to ensure light 15 is only emitted from the shade 4. In an alternative arrangement the housing is made of a translucent/transparent material which includes a different phosphor material such that the lighting fixture 25 emits a different colored light around its periphery.

(18) It will be readily apparent to those skilled in the art that modifications can be made to the lighting arrangements disclosed without departing from the scope of the invention. For example whilst exemplary implementations in the form of a garden lantern, pendant lighting system and wall lighting systems have been described the invention can be readily applied to other lighting systems such as for example: desk, ceiling, flush, floor standing, spot, accent and up lighting fixtures.

(19) Moreover, it will be appreciated that any of the lighting fixtures can be powered by a solar cell, a battery or from a mains supply. In the case of the latter the lighting fixture advantageously further includes a power converter, such as a solid state switched mode power supply, to convert the mains electricity from 110-220 volts to a 3.3 volt 20 mA for driving the LED. In addition the lighting system advantageously further incorporates a heat sink, for example as a part of the fixture, which is in thermal communication with the LED to provide cooling of the LED. Furthermore it will be apparent to those skilled in the art that the shade can be made in any form to meet a required application such as for example: being closed in form, e.g. spherical, such as to substantially enclose the excitation source, polygonal in form or multi-faceted in form.