BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a known white LED as already described;
FIGS. 2 to 7 are schematic representations of LED lighting arrangements in accordance with the invention; and
FIG. 8 is a schematic representation of a method of fabricating an optical component for an LED lighting arrangement in accordance with the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
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.
Referring to FIG. 2 there is shown a LED lighting arrangement 20 in accordance with the invention. The LED lighting arrangement 20 is for generating light of a selected color for example white light. The lighting arrangement comprises a LED chip 22, preferably a Gallium Nitride chip, which is operable to produce light, radiation, preferably of wavelength in a range 300 to 500 nm. The LED chip 22 is mounted inside a stainless steel enclosure or reflection cup 24 which has metallic silver deposited on its inner surface to reflect light towards the output of the lighting arrangement. A convex lens 26 is provided to focus light output from the arrangement. In the example illustrated the lens 26 is substantially hemispherical in form. The lens 26 can be made of a plastics material such as polycarbonates or glass such as silica based glass or any material substantially transparent to the wavelengths of light generated by the LED chip 22.
In the embodiment in FIG. 2 the lens 26 has a planar, substantially flat, surface 28 onto which there is provided a layer of phosphor 30 before the lens is mounted to the enclosure 22. The phosphor 30 preferably comprises a photoluminescent material having a formula A2SiO4:Eu2+D where A is a divalent metal selected from the group comprising Sr (Strontium), Ca (Calcium), Ba (Barium), Mg (Magnesium), Zn (Zinc) and Cd (Cadmium) and D is a dopant selected from the group comprising F (Fluorine), Cl (Chlorine), Br (Bromine), I (Iodine), P (Phosphorous), S (Sulfur) and N (Nitrogen) as disclosed in our co-pending patent application U.S. 2006/0028122 the content of which is hereby incorporated by way of reference thereto. The phosphor which is in the form of a powder is mixed with an adhesive material such as epoxy or a silicone resin, or a transparent polymer material and the mixture is then applied to the surface of the lens to provide the phosphor layer 30. The mixture can be applied by painting, dropping or spraying or other deposition techniques which will be readily apparent to those skilled in the art. Moreover the phosphor mixture preferably further includes a light diffusing material such as titanium oxide, silica or alumina to ensure a more uniform light output.
The color of light emitted from the lighting arrangement can be controlled by appropriate selection of the phosphor composition as well as the thickness of the phosphor layer which will determine the proportion of output light originating from the phosphor. To ensure a uniform output color the phosphor layer is preferably of uniform thickness and has a typical thickness in a range 20 to 500 μm.
An advantage of the lighting arrangement of the invention is that no phosphor need be incorporated within the encapsulation materials in the LED package. Moreover the color of the light output by the arrangement can be readily changed by providing a different lens having an appropriate phosphor layer. This enables large scale production of a common laser package. Moreover such a lens provides direct color conversion in an LED lighting arrangement.
Referring to FIG. 3 there is shown an LED lighting arrangement in accordance with a further embodiment in which the phosphor 30 is provided as a layer on the outer convex surface 32 of the lens 26. In this embodiment the lens 26 is dome shaped in form.
FIG. 4 shows an LED lighting arrangement in accordance with a further embodiment in which the lens 26 comprises a substantially hemispherical shell and the phosphor 30 is provided on the inner surface 34 of the lens 26. An advantage of providing the phosphor on the inner surface is that the lens 26 then provides environmental protection for the LED and phosphor. Alternatively the phosphor can be applied as a layer of the outer surface of the lens 26 (not shown).
FIG. 5 illustrates an LED arrangement in which the lens 26, optical component, comprises a substantially spherical shell and the phosphor 30 is deposited as a layer on at least a part of the inner 36 or outer spherical 38 surfaces and the LED chip 22 is mounted within the spherical shell. To ensure uniform emission of radiation a plurality of LED chips are advantageously incorporated in which the chip are oriented such that they each emit light in differing directions. Such a form is preferred as a light source for replacing existing incandescent light sources (light bulbs).
Referring to FIG. 6 there is shown a further arrangement in which the optical component 26 comprises a hollow cylindrical form and the phosphor is applied to the inner 40 or outer 42 curved surfaces. In such an arrangement the laser chip preferably comprises a linear array of laser chips that are arranged along the axis of the cylinder. Alternatively the lens 26 can comprise a solid cylinder (not shown).
FIG. 7 shows an LED arrangement in which the optical component comprise a solid substantially spherical lens 26 and the phosphor is provided on at least a part of the spherical surface 44. In a preferred arrangement, as illustrated, the phosphor is applied to only a portion of the surface, which surface is then mounted within the volume defined by the enclosure. By mounting the lens 26 in this way this provides environmental protection of the phosphor 30.
Referring to FIG. 8 there is shown a preferred method of fabricating lenses in accordance with the invention. An array of lenses 46 is provided in which the lenses have a common planar surface 48 onto which the phosphor 30 is provided. In the example illustrated the lenses 36 are substantially hemispherical in form. After the phosphor has been deposited the lenses can be separated and mounted to the LED assemblies. Such a method is found to be particularly advantageous for mass production of the optical components.
It will be appreciated that the present invention is not restricted to the specific embodiments described and that modifications can be made which are within the scope of the invention. For example although in the foregoing description reference is made to a lens the phosphor can be deposited onto other optical components such as for example a window through which light passes though is not necessarily focused or directed or a waveguide which guides, directs, light. Moreover the optical component can have many forms which will be readily apparent to those skilled in the art.
It will be appreciated that the phosphor and LED chip can be selected depending on the intended application to provide light of a desired color. It is also envisaged to provide two or more phosphor materials to achieve the desired color, spectral content, of emitted light. The different phosphors can be provided by mixing the powdered material and incorporating them within a single layer or alternatively by providing multiple layers of different phosphors.
Examples of preferred phosphors are:
- YAG-based phosphors which comprising a photoluminescent material having a formula (YA)3(AlB)5(OC)12:Ce3+ where A is a trivalent metal selected from the group comprising Gd (Gadolinium), Tb (Terbium), La (Lanthanum), Sm (Samarium) or divalent metal ions such as Sr (Strontium), Ca (Calcium), Ba (Barium), Mg (Magnesium), Zn (Zinc) and Cd (Cadmium), B comprising Si (Silicon), B (Boron), P (phosphorous), and Ga (Gadolinium) and C is a dopant selected from the group comprising F (Fluorine), Cl (Chlorine), Br (Bromine), I (Iodine), P (phosphorous), S (Sulfur) and N (Nitrogen);
- orange-red silicate-based phosphors of general formula (SrM1)3Si(OD)5:Eu where M1 is selected from the group comprising Ba, Ca, Mg, Zn . . . and D is selected from the group comprising F, Cl, S, and N (such a phosphor can be used for emitting light in a wavelength range from green to yellow (580 to 630 nm));
red silicon nitride based phosphors of general formula of (SrM1)Si5N8 where M1 is selected from the group comprising Sr, Ca, Mg, and Zn;
- red sulfate based phosphors having a general formula (SrM1)S where M1 is selected from the group comprising Ca, Ba, and Mg; and
green sulfate based phosphors having a general formula (SrM1)(GaM2)2S4:Eu where M1 is selected from the group comprising Ca, Ba, and Mg, and where M2 is selected from the group comprising Al and In.
In addition to providing an LED lighting arrangement the invention further provides a novel optical component and method of fabrication thereof.
In a further embodiment it is also envisaged to incorporate the phosphor within material comprising the optical component. Moreover the phosphor can be provided as a layer on the encapsulating material.
Patent Application
20080029720
