Filament-Based Solid-State Lighting Devices

Abstract

A lighting device 1 is disclosed, comprising a transparent housing 3 and a filament 10 within the transparent housing. The filament comprises a transparent substrate 20 supporting a plurality of solid state lighting elements 30, and a phosphor-containing resin coating 40 surrounding the filament. The resin coating includes at least one region 42 through which light generated by the solid state lighting elements that is not converted by the phosphor escapes, and the transparent housing supports, for each of said regions of the resin coating, a further phosphor layer 7 covering a portion of the transparent housing, each further phosphor layer being arranged to receive the unconverted light that escapes from at least one of said regions. Also disclosed is a method of manufacturing such a lighting device.

Description

[Technical field]

[0001] The present invention relates to a lighting device comprising a transmissive housing, a filament within the transmissive housing, the filament including a transmissive substrate supporting a plurality of solid state lighting elements, and a phosphor-containing resin coating surrounding the filament.

[0002] The invention further relates to a method for manufacturing such a lighting device. [Background technology]

[0003] Solid state lighting devices, such as lighting devices based on light emitting diodes (LEDs), are rapidly replacing other forms of lighting devices, such as incandescent, halogen, fluorescent, etc., due to the superior lifetime, robustness, and energy efficiency of solid state lighting devices. Despite the clear advantages of solid state lighting devices over other types of lighting devices, several challenges remain to be overcome before solid state lighting devices can gain widespread acceptance as a replacement for such other types of lighting devices.

[0004] It is not easy to manufacture a solid-state lighting device that emulates the appearance and luminous output of a conventional lighting device, such as a filament-based lighting device. For this purpose, solid-state lighting devices have been manufactured in which a plurality of solid-state lighting elements, such as LEDs, are mounted on an elongated support that mimics a filament. For example, WO 2020 / 069723(A1) discloses a linear LED light source comprising a plurality of LED units that are conductively connected to a metallic support frame, the metallic support frame being configured to act as a supply conductor through which power for driving the LED units can be supplied to the LED units.

[0005] Such filament assemblies may be coated with a phosphor-containing resin coating, whereby the light generated by the LED, for example blue light, may be spectrally converted by phosphor particles in the resin to generate, for example, white light. As known per se, the color temperature of the white light thus generated may be controlled by the composition and amount of phosphor in the resin. In such filament assemblies, the elongated support is typically made of a light-transmitting material so that light can exit the filament from substantially any part of the resin surface, thereby emulating the full 360° emission distribution of conventional filament-based incandescent lighting devices. However, even if such an emission distribution can be successfully emulated to a large extent, it remains difficult to achieve uniformity of the spectral composition of the light emitted from the surface of the resin surrounding the elongated support supporting the solid-state lighting element. Such differences may be very noticeable, for example, when the light is projected onto a surface or onto a moving observer, who receives luminous output emitted from different areas of the resin surface as the observer moves relative to the lighting device. In particular, when such luminous output is projected onto a surface, such as a work surface, the spectral variations in the projected luminous output can become quite distracting to individuals needing adequate lighting to perform specific tasks.

[0006] One particular solution to this problem would be to provide a diffusive coating on the light-transmitting housing of the filament assembly. For example, US Patent Application Publication No. 2018 / 0299080(A1) discloses an LED lamp comprising a substrate, an LED light source in optical communication with the housing of the LED lamp, a diffusive coating applied to the housing, and a luminescent coating at least partially disposed on the diffusive coating. The luminescent coating is between the LED light source and the diffusive coating. The luminescent coating has a composition that is selected to achieve a particular color temperature according to the characteristics of the LED light source. However, such a solution significantly reduces the luminous efficiency of the lighting device, resulting in a loss of luminescent power. This is undesirable, for example, from the perspective of achieving compliance with energy efficiency regulations, which typically require that a minimum amount of lumens be generated per watt. For example, for a (tubular) lighting device to achieve Class A certification in the European Union, it needs to achieve a luminous output of more than 210 lm / W, which is difficult to achieve, especially when light losses occur in the transparent housing due to, for example, the presence of a diffusing layer. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention seeks to provide a lighting device that addresses at least some of the aforementioned problems, the lighting device comprising a transmissive housing and a filament within the transmissive housing having a transmissive substrate supporting a plurality of solid state lighting elements.

[0008] The present invention further seeks to provide a method for manufacturing such a lighting device. [Means for solving the problem]

[0009] According to an embodiment of an aspect of the present invention, there is provided a lighting device comprising: a transparent housing; a filament in the transparent housing, the filament including a transparent substrate supporting a plurality of solid state lighting elements; and a phosphor-containing resin coating surrounding the filament, the resin coating including at least one region having a reduced thickness that allows light generated by the solid state lighting elements not converted by the phosphor to leak out, the transparent housing supporting further phosphor layers covering a portion of the transparent housing, the further phosphor layers being optically aligned with each of the regions of the resin coating having a reduced thickness, each further phosphor layer being positioned to receive the unconverted light leaking from at least one of the aforementioned regions. The present invention is based on the insight that variations in the spectral composition of the luminous output of a filament with a solid state lighting element are caused by variations in the thickness of the phosphor-containing resin coating surrounding the transparent substrate supporting the solid state lighting elements, e.g., LEDs. Therefore, by providing an additional phosphor layer on the housing for each region in the phosphor-containing resin coating having a reduced thickness, such additional phosphor being optically aligned with such region of the phosphor-containing resin coating having a reduced thickness, the spectral uniformity of the luminous output of the lighting device can be improved, while the remainder of the filament housing remains transparent, thereby improving the luminous efficiency of the lighting device, since light losses such as those caused by a diffusing layer are avoided due to the absence of such a diffusing layer covering the entire surface of the housing.

[0010] For example, the transmissive substrate may include a mounting surface supporting at least some of the solid state lighting elements and a pair of side surfaces on either side of the mounting surface, each of the side surfaces being covered by one of the above-mentioned regions of the resin coating. The phosphor-containing resin coating may have a reduced thickness over the side surfaces of the transmissive substrate such that light emitted through the regions of the phosphor-containing resin coating over those side surfaces has a different spectral composition than light emitted through other regions of the phosphor-containing resin coating, e.g., regions covering the mounting surface of the transmissive substrate, and this difference in spectral composition is compensated for by an additional phosphor layer on the housing as described above.

[0011] The transparent substrate may include a single mounting surface, i.e. the solid state lighting elements may be mounted only on a single surface of the transparent surface. In such a scenario, the solid state lighting elements may be dual-emissive, such that they are configured to emit light towards the transparent substrate as well as away from the transparent substrate. This has the advantage that thermal management of the filament can be achieved to a large extent in a simple manner, while achieving an emission distribution that closely emulates a full 360° emission distribution. Alternatively, the transparent substrate may further include a further mounting surface opposite the aforementioned mounting surface, with the side extending between the mounting surface and the further mounting surface, and the solid state lighting elements may be distributed across the mounting surface and the further mounting surface.

[0012] The transparent substrate may be made of any suitable material, in a particular embodiment it is a sapphire substrate, although alternative materials such as a transparent ceramic material or a flexible polymer material such as polyimide are equally viable.

[0013] Each further phosphor layer is preferably arranged on an inner surface of the transmissive housing, e.g. to protect the further phosphor layer from accidental damage, e.g. by scratching, etc. Alternatively, each further phosphor layer may be arranged on an outer surface of the transmissive housing, which has the advantage that the further phosphor layer can be applied to the housing in a particularly simple manner.

[0014] The transmissive housing may be made of any suitable transmissive material. For example, the transmissive housing may be a transparent housing made of glass or plastic. In a particular set of embodiments, the transmissive housing is shaped as a tubular body, and for example, the lighting device may be a tubular LED (TLED) device that produces a luminous output of at least 210 lm / W. In this particular set of embodiments, the transmissive housing may include a pair of additional phosphor layers, each extending along the tubular body and having a radial width in the range of 60-90°, such that 50-67% of the surface of the transmissive housing remains uncovered by the additional phosphor layers, which ensures that the lighting device can achieve excellent luminous output efficiency.

[0015] The lighting device may comprise a plurality of filaments extending within the tubular body, and a pair of electrode rails extending within the tubular body, with each filament conductively connected to a respective one of the electrode rails by a corresponding support arm extending between the filament and one of the electrode rails. This allows the filaments to be connected in parallel, which limits resistance along the chain of filaments, and therefore ensures that the filaments can be driven by a sufficiently compact driver that can be mounted within the lighting device, for example within an end cap of the lighting device.

[0016] Where the tubular body is a plastic body, the plastic body may include a pair of channels in its inner surface, each extending along the tubular body to accommodate one of the electrode rails, ensuring that the filament assembly is securely mounted within the tubular body, thereby providing a particularly robust lighting device.

[0017] Alternatively, the filament may extend along the tubular body, i.e., substantially along the entire length of the tubular body, in which case the lighting device may further comprise a driver at a first end of the tubular body having a first connection to a first terminal portion of the filament proximate the first end and a second connection to a second terminal portion of the filament proximate a second end of the tubular body opposite the first end, for electrically connecting the filament to the driver. In this case, the lighting device may further comprise a support structure extending from the second terminal portion of the filament to the second end of the tubular body for fixing the filament within the tubular body.

[0018] According to an embodiment in accordance with another aspect of the invention, there is provided a method of manufacturing a lighting device comprising the steps of: providing a transmissive substrate; mounting a plurality of solid state lighting elements on the transmissive substrate to create a filament; surrounding the filament with a phosphor-containing resin coating, the resin coating including at least one region having a reduced thickness that allows light generated by the solid state lighting element that is not converted by the phosphor to leak out; providing a transmissive housing for the filament; forming an additional phosphor layer on a portion of the transmissive housing for each of the regions of the resin coating having a reduced thickness; and mounting the filament in the transmissive housing by optically aligning each of the regions of the resin coating having a reduced thickness with one of the additional phosphor layers, whereby each of the additional phosphor layers is positioned to receive unconverted light that leaks out from the region of the resin coating that is aligned with the additional phosphor layer. Lighting devices produced in this manner benefit from having improved luminous efficiency due to the use of a transmissive housing, and reduced variation in the spectral output of the light emitting device due to the presence of one or more additional phosphor layers on the transmissive housing to convert light generated by the solid state lighting element that is not converted by the phosphor-containing resin layer surrounding the filament.

[0019] Preferably, the transmissive housing is shaped as a tubular body, each of the further phosphor layers extending along the tubular body, and the method further comprises forming a filament assembly by mounting a plurality of filaments to a pair of electrode rails such that corresponding regions of each filament that leak light generated by the solid state lighting element not converted by the phosphor are aligned with one another, each filament being conductively connected to each of the electrode rails by a corresponding support arm extending between one of the electrode rails and the filament, and mounting the filaments in the transmissive housing comprises mounting the filament assembly in the tubular body such that the electrode rails extend along the tubular body. This has the advantage that each filament can be driven in parallel, making it easier to achieve a desired luminous output, e.g. a uniform luminous output, along the tubular housing, and fixing the electrode rails in or against the tubular housing further provides a particularly robust filament assembly in the tubular body.

[0020] Alternatively, the transmissive housing is shaped as a tubular body, each of the additional phosphor layers extending along the tubular body, the method further comprising forming a first connection between the driver and a first terminal portion of the filament, and forming a second connection between the driver and a second terminal portion of the filament opposite the first terminal portion, mounting the filament within the transmissive housing comprises mounting the filament such that the driver is located at the first end of the tubular body and the second terminal portion of the filament is located adjacent to the second end of the tubular body opposite the first end, and the method further comprises mounting a support structure between the second terminal portion of the filament and the second end of the tubular body. In this manner, a robust assembly of a single elongated filament within the tubular housing can be achieved.

[0021] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0022] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Figure 1] 1 shows a schematic cross-sectional view of a resin coated filament. [Diagram 2] 1 illustrates a schematic cross-sectional view of a lighting device according to one embodiment; [Diagram 3] 1 shows a schematic perspective view of a lighting device according to another embodiment; [Figure 4] 4 shows a schematic cross-sectional view of the lighting device of FIG. 3; [Diagram 5] 4 shows a schematic perspective view of the lighting device of FIG. 3; [Figure 6] 1A-1C are schematic illustrations of cross-sectional views of lighting devices according to at least some embodiments. [Figure 7] 7 shows a schematic perspective view of the lighting device of FIG. 6; [Figure 8] 1A-1C are schematic diagrams illustrating cross-sectional views of lighting device designs according to at least some embodiments. [Figure 9] 1A-1C are schematic illustrations of cross-sectional views of lighting devices according to at least some alternative embodiments; [Figure 10] 1A-1C are schematic diagrams illustrating exploded views of lighting devices according to at least some embodiments. [Figure 11] 3 shows a schematic cross-sectional view of a lighting device according to yet another embodiment; [Figure 12] 4 is a flow chart of an exemplary method of assembling an exemplary lighting device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will now be described with reference to the figures.

[0024] It should be understood that the detailed description and specific examples, while illustrating exemplary embodiments of the devices, systems, and methods, are intended for illustrative purposes only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are only schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to denote the same or similar parts.

[0025] FIG. 1 shows a schematic diagram of an example of a filament 10 that may be used in various embodiments of the lighting device of the present invention. The filament 10 comprises a transparent substrate 20 for supporting one or more solid state lighting elements 30. The transparent substrate 20 may be, for example, a transparent sapphire substrate or a transparent ceramic substrate if a relatively rigid filament 10 is required, or a polymer substrate such as a polyimide substrate if the filament 10 is required to be more flexible. The solid state lighting elements 30 may take any suitable shape or form, for example, one or more LEDs, such as blue-emitting LEDs. The solid state lighting elements 30 may be mounted on a single major surface 22 of the transparent substrate 20, in which case the solid state lighting elements 30 preferably emit light from at least two emission surfaces, for example, toward and away from the mounting surface 22 of the transparent substrate 20, to provide a filament 10 that exhibits an emission distribution that emulates the emission distribution of an incandescent light bulb filament. Alternatively, a further major surface 26 of the transmissive substrate 20, opposite major surface 22, may also support one or more solid state lighting elements 30 (not shown) to achieve a desired emission distribution of the filament 10. In this case, the solid state lighting elements 30 may emit light from only a single surface, e.g., in a direction away from the surface to which they are attached.

[0026] The transparent support 20 supporting the solid state lighting elements 30 is typically surrounded by a resin 40 that contains a phosphor, e.g., in the form of particles suspended in the resin, which converts the light emitted by the solid state lighting elements 30 into light having a different spectral composition. For example, the phosphor may convert the light emitted by the solid state lighting elements 30 into white light having a particular color temperature, which may be controlled by the chemical composition of the phosphor. Any suitable phosphor may be used for this purpose. For example, one or more phosphors that convert blue light into yellow / green light, such as YAGaG:Ce, LuAGaG:Ce, or A3B5O4 may be used. 12 Garnets such as CaAlSiN3:Ce (where A represents a chemical element such as Y, Lu, or La, and B represents a chemical element such as Al, Ga, or Fe), as well as phosphors that convert blue light to orange / red light, for example aluminonitridosilicates, or calsin phosphors, for example CaAlSiN3:Eu phosphor, or nitridosilicates, may be used for this purpose, but it should be understood that the invention is not limited to these exemplary phosphors and phosphors having any suitable composition may be used. The resin may be any suitable transparent resin, preferably a transparent resin. Examples of suitable resins include ethyl- and phenyl-type silicones. Other suitable resins will be readily apparent to those skilled in the art.

[0027] A problem associated with surrounding the transmissive substrate 20 with a resin coating 40 is that the thickness of the resin coating 40 around the transmissive substrate 20 is not constant. As shown in FIG. 1, the resin coating 40 typically has a thickness r1 and a thickness r2 on the major surfaces 22 and 26, respectively, while the resin coating 40 has a significantly smaller thickness r3 on the side 24 of the transmissive substrate 20, which extends between the opposing major surfaces 22 and 26. This reduced thickness r3, which is typically a function of the thickness d of the transmissive substrate 20, is due to the fact that when coating the transmissive substrate 20 supporting the solid state lighting elements 30, it is difficult to achieve the same thickness of the resin coating 40 on the side 24 as compared to the major surfaces 22, 26. As a result, light emitted by the solid state lighting elements 30, traveling through the transmissive substrate 20, and exiting the substrate through the side 24 will typically exit the filament 10 through a window 42 defined by a dashed line extending from the side 24. As this light passes through the relatively thin layer of resin coating 40, there is not enough phosphor in the path of the light rays through this portion of the resin coating 40, and therefore at least a portion of the light rays thus exiting the filament 10 will be unconverted, i.e., will have its original spectral composition as produced by the solid state lighting element 30. This can therefore result in spatial variations in the spectral composition of the luminous output produced by the filament 10.

[0028] Such spatial variations may be compensated for by diffusing the luminous output, for example by mounting the filament 10 in a diffusing housing. However, this causes light losses and therefore impairs the optical efficiency of the lighting device including the filament 10. On the other hand, if a transmissive housing is used with the filament 10, the optical efficiency of the lighting device is improved, at the cost of producing a luminous output with spatial variations in its spectral composition. According to the teachings of the present invention, there is provided a lighting device 1, such as the lighting device 1 shown diagrammatically in FIG. 2, in which the housing 3 is made of an optically transparent material, such as glass or an optically transparent polymer, and the housing 3 supports on one of its surfaces, i.e. on the inner or outer surface of the housing 3, a further phosphor layer 7, which is optically aligned with the emission window 42, such that unconverted light exiting a filament 10 mounted in a fitting or end cap 5 of the lighting device 1 is converted by the further phosphor layer 7 to improve the uniformity of the spectral composition of the light emitted from the lighting device 1 and also improve the perceived light efficiency of the lighting device 1, since the human eye is less sensitive to blue light, e.g. light having a wavelength of 400-450 nm, than to yellow-green light, e.g. light having a wavelength of 500-550 nm, and therefore the luminous flux as perceived by the sensitivity of the human eye is increased by the further phosphor layer 7.

[0029] The further phosphor layer 7 preferably has a minimum width W to ensure that a large area of ​​the housing 3 remains transparent so that the optical efficiency of the lighting device 1 is not excessively impaired by the addition of the further phosphor layer 7. The width W is preferably selected such that only the light emitted from the window 42 enters the further phosphor layer 7 to ensure that the width of the further phosphor layer remains minimal. The further phosphor layer 7 may have any suitable chemical composition. In a particular embodiment, the phosphor in the further phosphor layer 7 has the same chemical composition as the phosphor in the resin coating 40, but it is also feasible for the phosphor in the further phosphor layer 7 to have a different chemical composition than the phosphor in the resin coating 40. As will be readily understood by those skilled in the art, the thickness of the further phosphor layer 7 should preferably be selected such that all unconverted light emitted by the filament 10 is converted when passing through the further phosphor layer 7. The further phosphor layer 7 may be a resin layer in which phosphor particles are suspended. The resin layer may have the same composition as the resin coating 40 or a different composition. Naturally, other support materials for the phosphors in the further phosphor layer 7 can also be envisaged.

[0030] A particular class of lighting devices that can benefit from the teachings of the present invention are tubular lighting devices. Figure 3 shows such a lighting device 1 in a schematic manner, in which the housing 3 has a tubular body 6 with a filament 10 (not shown) extending in the elongation direction of the tubular body 6. In such a scenario, the further phosphor 7 also typically extends in the elongation direction of the tubular body 6, for example on the inner or outer surface of the tubular body 6, which may support a number of such further phosphor layers 7, typically one further phosphor layer 7 for each window 42 of the filament 10. For example, if the filament 10 comprises two such windows 42, as in the case of using a rectangular transmissive substrate 20, the two further phosphor layers 7 will extend along the elongation direction of the tubular body 6 such that each window 42 is optically aligned with one of the further phosphor layers 7. The use of a filament 10 in such a tubular lighting device 1 ensures that the lighting device is able to generate a 360° light emission distribution, in contrast to tubular lighting devices equipped with solid state lighting elements, where the solid state lighting elements are mounted on a support, which itself is mounted on a portion of the surface of the tubular body 6, thereby preventing this portion of the tubular body 6 from transmitting the light generated by the solid state lighting elements. To make such a light emission distribution more omnidirectional, the tubular body 6 typically supports a diffusing layer or the like, which, as mentioned above, reduces the optical efficiency of such a tubular lighting device.

[0031] FIG. 4 shows, in a schematic manner, one embodiment of how the filament 10 can be mounted within the transparent housing 3. The transparent housing 3 may include a pair of channels 9 in which electrode rails 62, 63 can be mounted, the electrode rails being conductively coupled to the filament 10 via support arms 64, 65, e.g., support wires, that suspend the filament 10 within the transparent housing 3. For example, each electrode rail 62, 63 may be slid into the channel 9 when mounting the filament 10 within the tubular body 6, i.e., within the transparent housing 3. This is shown more clearly in FIG. 5, which shows that the channel 9 includes a slot 99 through which the support arms 64, 65 can extend from the electrode rails 62, 63, which are embedded within the channel 9, to the filament 10. The channel 9 may be formed within the transparent housing 3 in any suitable manner. For example, if the permeable housing 3 comprises a plastic tubular body 6, the channel 9 may be formed in the plastic tubular body 6 during molding of the plastic tubular body 6.

[0032] Of course, the electrode rails 62, 63 may be attached in any suitable manner within the tubular body 6. For example, if it is more difficult to achieve such channels 9, e.g. in the case of a glass tubular body 6, the electrode rails 62, 63 may instead be glued to the inner surface of the tubular body 6. This may be achieved, for example, using a UV-activated adhesive or any other suitable type of adhesive. In the case of a UV-activated adhesive, the electrode rails 62, 63 may be coated with such an adhesive and positioned within the tubular body 6, after which the tubular body 6 is exposed to UV radiation to activate the adhesive and secure the electrode rails 62, 63 to the tubular body 6. Alternatively, at least a portion of the inner surface of the tubular body 6 may be coated with such an adhesive and activated with UV light after the electrode rails 62, 63 are positioned within the tubular body 6. Other suitable methods of fixing the electrode rails 62, 63 to the tubular body 6 will be apparent to those skilled in the art.

[0033] The filament 10 in some embodiments may be comprised of multiple filaments 10, as shown diagrammatically in Figures 6 and 7, where each filament 10 is connected to the electrode rails 62, 63 via a corresponding support arm 64, 65. For example, each filament 10 may extend between a pair of support arms 64, 65. This has several advantages. First, it allows each filament 10 to be connected in parallel to the electrode rails 62, 63, thus lowering the resistance encountered in driving the solid state lighting elements 30 along each filament 10. As a result, for example, the requirements on the drivers of the solid state lighting elements 30 are less stringent, since the voltage drop across the solid state lighting elements 30 extending along the tubular body 6 is smaller due to this parallel connection of the filaments 10. This means that the drivers can be smaller, which makes it easier to mount the drivers in the end caps of the tubular body 6. Secondly, the use of multiple smaller filaments 10, rather than a single filament 10 extending along the entirety of the tubular body 6, makes a robust lighting device 1 easier to achieve.

[0034] The further phosphor layer 7 is optically aligned with a window 42 on the side of the transmissive support 20 within the filament 10. It is again noted that although the further phosphor layer 7 is shown on the outer surface of the transmissive housing 3, the further phosphor layer 7 may also be located on the inner surface of the transmissive housing 3, in which case the further phosphor layer is less susceptible to accidental damage, for example by scratching the outer surface of the transmissive housing 3, although positioning the further phosphor layer 7 on the outer surface of the transmissive housing 3 may be more cost-effective if such accidental damage is of limited concern. In a particular embodiment, each of the further phosphor layers 7 covers a portion of the tubular body 6 having a radial width in the range of 60-90°. For example, Fig. 8 shows diagrammatically a cross-section of a tubular lighting device 1 in which the radial width of the further phosphor layers 7 is 60° as indicated by a pair of 30° sections on either side of the horizontal plane dividing the further phosphor layers 7, while in Fig. 9 each of the further phosphor layers 7 has a radial width of 90°. As mentioned above, the (radial) width W of each of the further phosphor layers 7 is typically selected such that all unconverted light emitted through the window 42 facing the side of the transmissive substrate 20 in the filament 10 is incident on such further phosphor layer 7, the actual width W being a function of the dimensions and positioning of the filament 10 within the transmissive housing 3, such as the thickness d of the transmissive substrate 20.

[0035] 10 shows a schematic exploded view of an exemplary tubular lighting device 1 according to the present invention. One or more filaments 10 typically extend between opposing end caps 5 mounted on opposite ends 61, 67 of a transmissive, or more preferably transparent, tubular body 6, at least one of the end caps 5 housing a driver arrangement 70 for the one or more filaments 10. Preferably, as mentioned above, when there are multiple filaments 10 in the transparent tubular housing 6, the filaments 10 are connected in parallel to electrode rails 62, 63 via support arms 64, 65, which may be mounted within channels 9 inside the tubular body 6. This reduces the voltage that the driver arrangement 70 must supply due to a smaller voltage drop across the solid state lighting element 30 on the filament 10 along the tubular body 6, thereby keeping the driver arrangement 70 compact and making it easier to mount the driver arrangement 70 within the end caps 5. It should be further noted that although the further phosphor layer 7 is shown on the outer surface of the tubular body 6, it is likewise feasible for the further phosphor layer 7 to be located on the inner surface of the tubular body 6.

[0036] 11 shows a schematic representation of an alternative embodiment of a tubular lighting device 1 of the present invention, in which a single filament 10 extends along the tubular body 6 such that a first end 11 of the single filament 10 is disposed adjacent an end portion 61 of the tubular body 6 and an opposite second end 13 of the single filament 10 is disposed adjacent an opposite end portion 67 of the tubular body 6. The filament 10 may be supported within the tubular body 6 in any suitable manner. For example, the filament 10 may be wedged between opposing end caps 5, or the filament 10 may be supported by a driver arrangement 70 at the first end 61 of the tubular body 6 and by a support member 75 extending from the end portion 13 of the filament and the end cap 5 at the opposite end 67 of the tubular body 6.

[0037] The driver arrangement 70 may be mounted in any suitable location, for example in the end cap 5 of the end portion 61 of the tubular body 6. In this embodiment, the driver arrangement 60 is electrically connected to the filament 10 via a first connection 72 at the first end 11 of the filament 10 and via a second connection 74 extending from the driver arrangement 70 to the second end 13 of the filament 10. The second connection 74 may be a separate wire or the like, or may be a conductive track running on the transparent substrate 20 of the filament 10, for example on the side surface 24 or on the main surface 26 opposite the mounting surface 22 supporting the solid-state lighting element 30. Alternatively, the conductive track may run on the inner surface of the tubular body 6, in which case the conductive track is preferably made of an optically transparent conductive material, such as indium tin oxide, so that the conductive track does not interfere with the light emission distribution of the tubular lighting device 1.

[0038] An illumination device 1 according to an embodiment of the invention may be manufactured according to a manufacturing method 100, the flow chart of which is shown in Figure 12. The method 100 starts in operation 102 with providing a transmissive substrate 20, for example a transparent sapphire substrate, a transmissive white ceramic substrate, a polymer substrate such as a polyimide substrate, etc., on which a plurality of solid state lighting elements 30 are attached in operation 104 to create a filament 10. The solid state lighting elements 30 may be attached on the transmissive substrate 20 in any suitable manner, and such attachment techniques are known per se, so that this will not be described in further detail merely for the sake of brevity.

[0039] The filament 10 is then surrounded with a phosphor-containing resin coating 40 in operation 106, for example, by immersing the filament 10 in a bath containing the coating, or in any other suitable manner. As described in more detail above, the resin coating 40 will typically include at least one region 42, for example two regions or windows 42 facing the sidewall 24 of the transmissive substrate 20, that will allow light generated by the solid state lighting element 30 that has not been converted by the phosphor in the resin coating 40 to escape when the filament 10 is in use. A transmissive housing 3, for example a glass or plastic housing, which in a preferred embodiment may take the form of a tubular body 6, is provided in operation 108, into which the filament 10 will be attached.

[0040] The further phosphor layer 7 is formed in operation 110 on a portion of the transmissive housing 3 such that each of the regions or windows 42 of the resin coating 40 can be optically aligned with the further phosphor layer 7. For example, in the case of a bulbous transmissive housing 3, a single further phosphor layer 7 may be formed extending across the bulbous transmissive housing 3, so that a pair of opposing regions or windows 42 of the resin coating 40 can be optically aligned with different sections of the single further phosphor layer 7. Alternatively, in the case of a tubular transmissive housing 3, a pair of further phosphor layers 7 may be formed extending along the elongation direction of the tubular transmissive housing 3, so that each of the regions or windows 42 of the resin coating 40 can be optically aligned with one of the further phosphor layers 7. As will be understood from the above, the one or more further phosphor layers 7 are sized based on the dimensions of the filament 10, e.g. the thickness d of the transmissive substrate 20, and the positioning of the filament 10 within the transmissive housing 3. The further phosphor layer 7 may be formed on a section of the inner or outer surface of the transparent housing 3 in any suitable manner, for example using conventional masking techniques. For example, the tubular body 6 may be partially filled with a D-shaped plug, leaving exposed the section where the further phosphor layer 7 will be formed. The exposed section is then filled with a liquid resin containing the further phosphor until the liquid reaches the plug, after which the resin is cured (for example using hot air or UV light, depending on the type of resin) and the plug is removed from the tubular body 6, as disclosed for example in CN Patent Application Publication No. 1763890.

[0041] Finally, in operation 112, the filament 10 is mounted within the transmissive housing 3 before the method 100 ends at operation 114. In operation 112, the filament 10 may be mounted within the transmissive housing 3 by aligning each of the regions 42 of the resin coating with the further phosphor layers 7 on the transmissive housing 3 such that each of the further phosphor layers 7 is optically aligned with one or more of the regions 42 of the resin coating 40 such that the further phosphor layers 42 are positioned to receive unconverted light leaking from the regions 42 of the resin coating 40. The filament 10 may be supported by and extend from the end caps 5 into the transmissive housing 3 in the case of a bulbous transmissive housing 3.

[0042] In the case where the transmissive housing 3 is molded as the tubular body 6 such that each of the additional phosphor layers 7 extends along the tubular body, the method 100 may further include forming a filament assembly by mounting a plurality of filaments 10 on a pair of electrode rails 62, 63 such that corresponding regions 42 of each filament that leak light generated by the solid state lighting element 30 that is not converted by the phosphor are aligned with one another. Each filament 10 in this filament configuration may be conductively connected to each of the electrode rails 62, 63 by a corresponding support arm 64, 65 extending between the electrode rails 62, 63 and the filament 10. In this case, the operation 112 further includes mounting the filament assembly within the tubular body 6 such that the electrode rails 62, 63 extend along the tubular body, for example, by sliding the electrode rails 62, 63 within the channel 9 or by gluing the electrode rails 62, 63 to an inner surface of the tubular body 6 after the electrode rails 62, 63 are positioned within the tubular body 6.

[0043] Alternatively, if a single filament 10, e.g., a filament 10 extending substantially along the length of the tubular body 6, is mounted within such a tubular body 6, operation 112 of method 100 may further include forming a first connection 72 between the driver 70 and a first terminal portion 11 of the filament 10, and forming a second connection 74 between the driver 70 and a second terminal portion 13 of the filament 10 opposite the first terminal portion 11 of the filament. In this case, the step of mounting the filament 10 within the tubular body 6 may further include mounting the filament 10 such that the driver 70 is located at the first end 61 of the tubular body 6 and the second terminal portion 13 of the filament 10 is located adjacent to the second end 67 of the tubular body 10 opposite the first end 61 of the tubular body, and mounting a support structure 75 between the second terminal portion 13 of the filament 10 and the second end 67 of the tubular body 6, for example between the second terminal portion 13 of the filament 10 and the end cap 5 of the second end 67 of the tubular body 6, to stabilize the filament 10 within the tubular body 6.

[0044] Variations to the disclosed embodiments can be understood by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims, and can be effected in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0045] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0046] When the term "adapted to" is used in the claims or the specification, it is intended to be equivalent to the term "configured to."

[0047] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. A lighting device comprising: A transparent housing; a filament within the transmissive housing, the filament including a transmissive substrate supporting a plurality of solid state lighting elements; a phosphor-containing resin coating surrounding the filament, the resin coating including at least one region having a reduced thickness that allows light generated by the solid state lighting element that is not converted by the phosphor to leak out; an illumination device, wherein the transparent housing supports further phosphor layers covering a portion of the transparent housing and in optical alignment with each of the regions of the resin coating having the reduced thickness, each of the further phosphor layers positioned to receive unconverted light leaking from at least one of the regions, while other portions of the housing remain transparent.

2. 2. The lighting device of claim 1, wherein the transmissive substrate includes a mounting surface supporting at least some of the solid state lighting elements and a pair of side surfaces on either side of the mounting surface, each of the side surfaces being covered by one of the regions of the resin coating.

3. the transmissive substrate further includes a further mounting surface opposite the mounting surface, the side surface extending between the mounting surface and the further mounting surface; the solid state lighting elements being distributed across the mounting surface and the further mounting surface; 3. A lighting device according to claim 2.

4. The lighting device of claim 1 , wherein the transparent substrate is a sapphire substrate.

5. 10. The lighting device of claim 1, wherein each of the further phosphor layers is disposed on an inner surface or an outer surface of the transmissive housing.

6. 10. The lighting device of claim 1, wherein the transmissive housing is a transparent housing made of glass or plastic.

7. 7. The lighting device according to any one of the preceding claims, wherein the transmissive housing (10) is shaped as a tubular body.

8. 8. The lighting device of claim 7, wherein the transmissive housing comprises a pair of the further phosphor layers, each extending along the tubular body and having a radial width in the range of 60 to 90 degrees.

9. a plurality of said filaments extending within said tubular body; a pair of electrode rails extending within the tubular body, each filament being conductively connected to a respective one of the electrode rails by a corresponding support arm extending between the filament and one of the electrode rails; 9. A lighting device according to claim 7 or 8, further comprising:

10. 10. The lighting device of claim 9, wherein the tubular body is a plastic body including a pair of channels in an inner surface of the body, each of the channels extending along the tubular body and accommodating one of the electrode rails.

11. 9. A lighting device as claimed in claim 7 or 8, wherein the filament extends along the tubular body, the lighting device further comprising a driver at a first end of the tubular body, the driver having a first connection to a first terminal portion of the filament proximate the first end and a second connection to a second terminal portion of the filament proximate a second end of the tubular body opposite the first end.

12. 12. The lighting device of claim 11, further comprising a support structure extending from the second terminal portion of the filament to the second end of the tubular body.

13. 1. A method of manufacturing a lighting device, comprising the steps of: Providing a transparent substrate; mounting a plurality of solid state lighting elements on the transparent substrate to create a filament; surrounding the filament with a phosphor-containing resin coating, the resin coating including at least one region having a reduced thickness that allows light generated by the solid state lighting element that is not converted by the phosphor to leak out; providing a permeable housing for said filament; for each of the regions of the resin coating having the reduced thickness, forming a further phosphor layer on a portion of the transmissive housing, other portions of the housing remaining transmissive; and mounting the filament within the transmissive housing by optically aligning each of the regions of the resin coating having the reduced thickness with one of the further phosphor layers, whereby each of the further phosphor layers is positioned to receive unconverted light that leaks from the region of the resin coating that is aligned with the further phosphor layer.

14. The transmissive housing is shaped as a tubular body, each of the additional phosphor layers extending along the tubular body, and the method of manufacture further comprises: forming a filament assembly by mounting a plurality of the filaments to a pair of electrode rails such that corresponding regions of each of the filaments that leak light generated by the solid state lighting element that is not converted by the phosphor are aligned with one another, each filament being conductively connected to a respective one of the electrode rails by a corresponding support arm extending between the filament and one of the electrode rails; 14. The method of claim 13, wherein mounting the filament within the transmissive housing comprises mounting the filament assembly within the tubular body such that the electrode rail extends along the tubular body.

15. The transmissive housing is shaped as a tubular body, each of the additional phosphor layers extending along the tubular body, and the method further comprises: forming a first connection between a driver and a first terminal portion of the filament; forming a second connection between the driver and a second terminal portion of the filament opposite the first terminal portion; and mounting the filament within the transmissive housing includes mounting the filament such that the driver is located at a first end of the tubular body and the second terminal portion of the filament is located adjacent a second end of the tubular body opposite the first end, the method further comprising: The method of claim 13 including attaching a support structure between the second terminal portion of the filament and the second end of the tubular body.

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