A LED filament lamp

Abstract

A LED filament lamp (1) comprising a plurality of elongated LED filaments (2) adapted for, in operation, emitting LED filament light (16), and a solid, transparent, elongated rod-shaped element (3) comprising a plurality of elongated cavities (4), wherein at least one elongated LED filament (21-24) of the plurality of elongated LED filaments (2) is arranged in each elongated cavity (41-44) of the plurality of elongated cavities (4), each elongated cavity (41-44) of the plurality of elongated cavities (4) comprising an angular cross-sectional shape comprising at least three facets (61-64), each two converging facets of the at least three facets (61-64) forming a corner (51-55), each elongated cavity (41-44) of the plurality of elongated cavities (4) being arranged such that mutually adjacent elongated cavities (41, 42) are in contact at most by a respective corner (54, 55), and mutually adjacent facets (65, 66) of mutually adjacent elongated cavities (4) extend in an angle, α, with one another, the angle, α, fulfilling the relation α ≥ 2*arcsin(n0 / n1), where n0 is the refractive index of the medium present in each elongated cavity of the plurality of elongated cavities (4) and n1 is the refractive index of the material of the solid, transparent, elongated rod-shaped element (3).

Description

[0001] A LED FILAMENT LAMP

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a LED filament lamp comprising a plurality of elongated LED filaments adapted for, in operation, emitting LED filament light.

[0004] BACKGROUND OF THE INVENTION

[0005] LED filaments are attractive and widely used because of their high efficacy and are therefore particularly used in energy class A lighting products providing more than 210 Im / W. Currently, there is a strong wish to apply LED filaments in combination with other LEDs (e.g., RGB LEDs) in LED applications such as (smart) LED bulbs (HUE products), TLEDs and lighting for office and retail.

[0006] There is a continuous drive to improve the system efficacy (Im / W) of LED based systems. A relatively new LED type is the LED filament which is frequently and exclusively used in LED lamps (“bulbs”). A LED filament is a long rod-shaped emitter (typical length 30-50 mm, diameter: 1-3 mm) which emits light over the whole surface area (comparable to a fluorescent tube). A LED filament may be composed of a linear array of blue LED dies on a substrate, covered with a layer of blue light converting material (“phosphor”). This specific construction results in LED filaments with a high efficacy of up to around 230 Im / W.

[0007] More generally, a LED filament is providing LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, wherein L > 5W. The LED filament may be arranged in a straight configuration or in a non-straight configuration such as for example a curved configuration, a 2D / 3D spiral, or a helix. Preferably, the LEDs are arranged on an elongated carrier like for instance a carrier, that may be rigid (made from, e.g., a polymer, glass, quartz, metal, or sapphire) or flexible (e.g., made of a polymer or metal, e.g., a film or foil).

[0008] In case the carrier comprises a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The carrier may be reflective or light transmissive, such as translucent and preferably transparent. As used herein, the terms carrier and elongated carrier may be used interchangeably, such that the elongated carrier may also simply be denoted carrier.

[0009] The LED filament may comprise an encapsulant at least partly covering at least part of the plurality of LEDs. The encapsulant may also at least partly cover at least one of the first major surface and second major surface. The encapsulant may be a polymer material which may be flexible such as for example a silicone. Further, the LEDs may be arranged for emitting LED light, e.g., of different colors or spectrums. The encapsulant may comprise a luminescent material that is configured to convert at least a part of the LED light into converted light. The luminescent material may be a phosphor such as an inorganic phosphor and / or quantum dots or rods (QDs).

[0010] The LED filament may comprise multiple sub-filaments.

[0011] US 8,066,419 B2 discloses a lighting device. The lighting device comprises a light guide plate, and at least one array of light emitting diodes (LEDs), which LEDs are accommodated in holes arranged in the light guide plate, wherein each hole has: at least two side facets through which light from the LEDs is to be laterally coupled into the light guide plate, and at least one comer formed by two converging side facets of the at least two side facets.

[0012] A typical LED filament light bulb uses 2-12 filaments which is a large total phosphor area. The large phosphor area implies that blue light, emitted by a single filament, can be absorbed, and converted to yellow light by all neighboring filaments (especially important when the filaments are closely together). In this process, also absorption without conversion may occur. Another problem arises when the filaments are combined with additional RGB light emitting LED packages in e.g., a smart, color tunable bulb. In this case, blue light from the RGB LED packages is partially converted at the large phosphor surface of the filaments. The result is that the bulb cannot produce a saturated blue color. Yet, another problem arises when light interacts with wires, cables, PCB’s, etc. These interactions create optical losses and should be avoided.

[0013] Still further, close-packed LED filaments in, e.g., a LED light bulb gives efficacy loss and shift in color point because of the optical interaction between the filaments.

[0014] It is therefore desired to provide a LED filament lamp with a high density of LED filament light sources with which a compact optical solution for placing filaments and other LEDs close to each other without interaction / crosstalk between the sources may be obtained. SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to overcome this problem, and to provide a LED filament lamp with a high density of LED filament light sources with which a compact optical solution for placing filaments and other LEDs close to each other without interaction / crosstalk between the sources may be obtained.

[0016] According to a first aspect of the invention, this and other objects are achieved by means of a LED filament lamp comprising a plurality of elongated LED filaments adapted for, in operation, emitting LED filament light, and at least one solid, transparent, elongated rod-shaped element comprising a plurality of elongated cavities, where at least one elongated LED filament of the plurality of elongated LED filaments is arranged in each elongated cavity of the plurality of elongated cavities, where each elongated cavity of the plurality of elongated cavities comprises a convex angular cross-sectional shape comprising at least three facets, each two converging facets of the at least three facets forming a corner, where each elongated cavity of the plurality of elongated cavities is arranged such that mutually adjacent elongated cavities are in contact at most by a respective corner, and where mutually adjacent facets of mutually adjacent elongated cavities extend in an angle, a, with one another, the angle, a, fulfilling the relation a > 2*arcsin(l / n), where n is the refractive index of the material of the solid, transparent, elongated rod-shaped element.

[0017] Thereby, and especially by ensuring that each elongated cavity of the plurality of elongated cavities is arranged such that mutually adjacent elongated cavities are in contact at most by a respective corner, and particularly that mutually adjacent facets of mutually adjacent elongated cavities extend in an angle, a, with one another, the angle, a, fulfilling the relation a > 2*arcsin(n0 / nl), where nO is the refractive index of a medium present in each elongated cavity of the plurality of elongated cavities and nl is the refractive index of the material of the solid, transparent, elongated rod-shaped element, a LED filament lamp with a high density of LED filament light sources with which a compact optical solution for placing filaments and other LEDs close to each other without or with only very little interaction / crosstalk between the sources is provided.

[0018] The solid, transparent, elongated rod-shaped element further comprises an outer circumference, and mutually opposite sides or side segments of the outer circumference may be provided with a plurality of prism elements.

[0019] Thereby, a LED filament lamp which further exhibits a high optical efficiency is provided for. The angular cross-sectional shape of each elongated cavity of the plurality of elongated cavities may be square or rectangular with a width, a, and a length, b, and the cross-sectional shape of the prism elements of the plurality of prism elements may be that of a right angled triangle with legs of different lengths, where the angle, (|>, between the longest leg and a hypothenuse is defined as (|) = arctan(a / b), and where the angle, P, between the shortest leg and the hypothenuse is defined as P = 90 - (|).

[0020] Additionally, the prism elements of the plurality of prism elements may comprise a height, h, defined as h = b * sin(4>).

[0021] Such a choice of prism element geometry has proven to result in a LED filament lamp with a particularly high optical efficiency.

[0022] The angular cross-sectional shape of each elongated cavity of the plurality of elongated cavities may be square or rectangular with a diameter, LI, and the cross-sectional shape of the prism elements of the plurality of prism elements is that of a right angled triangle with a hypothenuse having a length, L2, and L2 is smaller than LI.

[0023] Choosing L2 to be smaller, and possibly even much smaller, than LI results in a LED filament lamp having a flat and compact structure while also having a particularly high optical efficiency.

[0024] LI may be in the range of 1 - 5 mm, and L2 may be in the range of 10 - 500 pm.

[0025] Such a choice of dimensions has proven to result in a LED filament lamp with a particularly high optical efficiency.

[0026] The angular cross-sectional shape of each elongated cavity of the plurality of elongated cavities may be any one of polygonal, triangular, square, hexagonal and rectangular.

[0027] Such a choice of shape of the elongated cavities has proven to result in a LED filament lamp with a particularly low crosstalk between the elongated cavities.

[0028] The solid, transparent, elongated rod-shaped element may comprise a cross- sectional shape being round or rectangular or square or elliptical, or circular, or polygonal or regular polygonal, or irregular.

[0029] Thereby, and depending on the cross-sectional shape chosen for the rodshaped element, it becomes possible to provide LED filament lamps according to the present invention with a variety of intensity distributions while still avoiding interaction / crosstalk between the sources. A gap may be provided between at least one of the elongated LED filaments and at least one of the facets of the elongated cavity in which the said elongated LED filament is arranged.

[0030] Thereby, a LED filament lamp with a particularly low crosstalk between the elongated cavities is provided for.

[0031] Each elongated cavity of the plurality of elongated cavities may be arranged such that mutually adjacent elongated cavities are in contact by a respective corner of the at least three respective corners.

[0032] Thereby, a LED filament lamp is provided with which the space occupied by each elongated cavity is minimized.

[0033] A gap may be provided between at least two mutually adjacent elongated cavities.

[0034] Thereby, it becomes possible to provide LED filament lamps according to the present invention with a variety of asymmetric or non-constant intensity distributions, at least in one plane, while still avoiding interaction / crosstalk between the sources. Such intensity distributions may be of use especially in applications where it is desired to illuminate a defined area, while other adjacent areas should not be illuminated.

[0035] The elongated cavities of the plurality of elongated cavities may all comprise the same cross-sectional size.

[0036] Thereby, it becomes possible to provide LED filament lamps according to the present invention with an intensity distribution being highly symmetric or constant, at least in one plane, while still avoiding interaction / crosstalk between the sources. Such intensity distributions may be of use especially in applications where it is desired to evenly illuminate a defined area.

[0037] Alternatively, the elongated cavities of the plurality of elongated cavities may comprise at least two mutually different cross-sectional sizes.

[0038] Thereby, it becomes possible to provide LED filament lamps according to the present invention with a variety of intensity distributions while still avoiding interaction / crosstalk between the sources.

[0039] Only one elongated LED filament of the plurality of elongated LED filaments may be arranged in each elongated cavity of the plurality of elongated cavities.

[0040] Thereby, a LED filament lamp with a particularly high optical efficiency is provided for. The LED filament lamp may further comprise at least one further elongated cavity, the further elongated cavity comprising electronic components.

[0041] Thereby, the electronic components, which may be electronic components necessary for driving and controlling the LED lamp and the LED lamp light, may be arranged in such a way that the fact that there is no or very little crosstalk between the cavities is exploited to ensure that the electronic components do not influence the path of the light emitted by the plurality of LED filaments. Also, it is ensured that the light emitted by the plurality of LED filaments will not effect, such as heat up, the electronic components.

[0042] At least one of the elongated LED filaments of the plurality of elongated LED filaments may be an elongated LED filament adapted for, in operation, emitting blue LED filament light.

[0043] Thereby, a LED filament lamp is obtained in which the light from the LED filament adapted for, in operation, emitting blue LED filament light is not able to excite the phosphors of the neighboring LED filaments adapted for, in operation, emitting white, particularly warm white, light.

[0044] The material of the solid, transparent, elongated rod-shaped element may be chosen from the group comprising PMMA, polycarbonate, glass, quartz glass, and sapphire / TGA (AI2O3).

[0045] Thereby, the solid, transparent, elongated rod-shaped element in itself has very little effect on the resulting LED filament light, especially in terms of very low light losses taking place in the solid, transparent, elongated rod-shaped element.

[0046] The cross-sectional shape of each elongated LED filament of the plurality of elongated LED filaments may be any one of circular, oval, rectangular with or without rounded comers and square with or without rounded corners.

[0047] The invention further relates to a luminaire comprising a LED filament lamp according to the invention.

[0048] It is noted that the invention relates to all possible combinations of features recited in the claims.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0051] Fig. 1 shows a cross-sectional, schematic view of a LED filament lamp according to the invention. Fig. 2 shows a perspective view of a LED filament lamp according to Fig. 1.

[0052] Fig. 3 shows a cross-sectional, schematic view of an exemplary LED filament.

[0053] Fig. 4 shows a cross-sectional, schematic view of a LED filament lamp according to Fig. 1 with a central LED filament being turned on and showing a ray trace simulation.

[0054] Fig. 5 shows a cross-sectional, schematic view of a LED filament lamp according to Fig. 1 with an outer LED filament being turned on and showing a ray trace simulation.

[0055] Fig. 6 shows an intensity distribution diagram of the light emitted by a LED filament lamp according to Fig. 1.

[0056] Fig. 7 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0057] Fig. 8 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0058] Fig. 9 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0059] Fig. 10 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0060] Fig. 11 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0061] Figs. 12 and 13 show cross-sectional, schematic views of another LED filament lamp according to the invention.

[0062] Fig. 14 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0063] Fig. 15 shows a cross-sectional, schematic view of another LED filament lamp according to the invention.

[0064] Fig. 16 shows a luminaire comprising a LED filament lamp according to the invention.

[0065] As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

[0066] DETAILED DESCRIPTION The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0067] Fig. 1 shows a cross-sectional, schematic view of a LED filament lamp 1 according to the invention. Fig. 2 shows a perspective view of a LED filament lamp 1 according to Fig. 1.

[0068] Generally, and irrespective of the invention, the LED filament lamp 1 comprises a plurality of elongated LED filaments 2 and at least one solid, transparent, elongated rod-shaped element 3.

[0069] The plurality of elongated LED filaments 2 are adapted for, in operation, emitting LED filament light 16 (cf. Figs. 4 and 5). The plurality of elongated LED filaments 2 comprises at least two LED filaments 21-24. In the embodiment shown in Fig. 1, three LED filaments 21-23 are provided. Referring also to Fig. 3, each LED filament 2 comprises a light-transmissive elongated carrier 201 and a plurality of LEDs 200.

[0070] The plurality of LEDs 200 are arranged on the first major surface 206 of the carrier 201. The plurality of LEDs 200 may, for instance, comprise RGB LEDs optionally combined with warm white and / or cold white LEDs. At least one of the elongated LED filaments 2 may be adapted for, in operation, emitting blue LED filament light, that is, may comprise blue LEDs.

[0071] The LED filament 2 may further comprise a first elongated encapsulant 202. The first elongated encapsulant 202 is arranged to cover the plurality of LEDs 200. The first elongated encapsulant 202 may comprise a first luminescent material 204. The first luminescent material 204 is configured to at least partly convert first LED light emitted by the plurality of LEDs 200 into first converted light. Alternatively, or additionally, the first elongated encapsulant 202 may comprise a first light scattering material 205. The first light scattering material 205 is configured to at least partly scatter first LED light emitted by said plurality of LEDs 200 into first scattered light.

[0072] The LED filament 2 may further comprise a second encapsulant 203. The second encapsulant 203 is arranged on a second major surface 207 of the carrier 201. The second encapsulant 203 may be the same as or different from the first encapsulant 202. The second encapsulant 203 may comprise a second luminescent material (not shown). The second luminescent material is configured to at least partly convert first LED light emitted by the plurality of LEDs into second converted light. Alternatively, or additionally, the second encapsulant 203 may comprise a second light scattering material (not shown). The second light scattering material is configured to at least partly scatter first LED light emitted by said plurality of LEDs 200 into second scattered light.

[0073] Referring again to Figs. 1 and 2, the solid, transparent, elongated rod-shaped element 3 comprises a plurality of elongated cavities 4. The plurality of elongated cavities 4 comprises at least two elongated cavities 41-44. In the embodiment shown in Fig. 1, three elongated cavities 41-43 are provided. At least one elongated LED filament 21-24 of the plurality of elongated LED filaments is arranged in each elongated cavity 41-44 of the plurality of elongated cavities 4. In the embodiment shown in Fig. 1, precisely one elongated LED filament 21-23 is arranged in each elongated cavity 41-43.

[0074] Optionally, a gap 11 may be provided between at least one of the elongated LED filaments, cf. LED filament 23 in Fig. 1, and at least one of the facets of the elongated cavity, cf. elongated cavity 43 in Fig. 1, in which the said elongated LED filament 23 is arranged. The gap 11 may be provided between one or more of the facets and the elongated LED filament. The gap 11 may be provided on all sides of the elongated LED filament, or around only part of the circumference of the elongated LED filament. The gap 11 may be provided over the whole length of the elongated LED filament, or over a part of the length of elongated LED filament.

[0075] The solid, transparent, elongated rod-shaped element 3 may for instance be made of PMMA, polycarbonate, glass, quartz glass, or sapphire / TGA (AI2O3). The rodshaped element 3 may be composed of two parts as indicated by either of the two dotted lines DI and D2. Thereby, the rod-shaped element 3 may easily be made by, for instance, injection molding.

[0076] Each elongated cavity 41-43 of the plurality of elongated cavities 4 comprises an angular cross-sectional shape comprising at least three facets 61-64. The angular cross- sectional shape of each elongated cavity 41-43 may be convex or concave. The angular cross- sectional shape of each elongated cavity 41-43 may be polygonal such as for instance be any one of triangular (cf. Fig. 14), hexagonal (cf. Fig. 15), square, and rectangular. In the embodiment shown in Fig. 1, the angular cross-sectional shape of each cavity 41-43 is square, and the elongated cavities 41-43 all comprise the same cross-sectional size. The elongated cavities 41-43 may further all comprise the same cross-sectional size over their whole length. Each two converging facets of a single cavity (or in other words each two facets of a single cavity coming together from different directions so as eventually to meet, also referred to as (a pair of) mutually adjacent facts, e.g., facets 61 and 64 of cavity 41) of the at least three facets form a corner 51-55. In the embodiment shown in Fig. 1, each cavity 41-43 thus comprises four facets 51-54 and four corners 61-64.

[0077] Each elongated cavity 41-43 is arranged such that mutually adjacent elongated cavities 41, 42 are in contact only by a respective corner 54, 55. Mutually adjacent facets (e.g., facets 65 and 66) of mutually adjacent elongated cavities 4 extend in an angle, a, with one another. The angle, a, is generally chosen to fulfill the relation a > 2*arcsin(n0 / nl), where nO is the refractive index of a medium present in each elongated cavity of the plurality of elongated cavities 4 and n is the refractive index of the material of the solid, transparent, elongated rod-shaped element 3. In a case where the medium present in each elongated cavity of the plurality of elongated cavities 4 is air, particularly atmospheric air, nO is equal to 1, and then the angle, a, is chosen to fulfill the relation a > 2*arcsin(l / n). However, it is also feasible that each elongated cavity of the plurality of elongated cavities 4 may be filled with another medium than atmospheric air, such as for instance an inert gas, in which case nO is different from 1, depending on the medium chosen.

[0078] The solid, transparent, elongated rod-shaped element 3 further comprises an outer circumference 7. The solid, transparent, elongated rod-shaped element 3 comprises a cross-sectional shape which may be round or rectangular or square or elliptical or circular or polygonal or regular polygonal or irregular. More generally, the cross-sectional shape of the rod-shaped element 3 may be formed or chosen to achieve a specific far-field intensity distribution. In the example of Figs. 1 and 2, a square cross-sectional shape of the rod-shaped element 3 is used.

[0079] Fig. 4 shows a cross-sectional, schematic view of the LED filament lamp 1 according to Fig. 1 with a central LED filament 22 being turned on, while the outer LED filaments 21 and 23 are turned off. Fig. 4 further illustrates a ray trace simulation of that situation. As may be seen, all rays of LED light 17 emitted by the LEDs of the central LED filament 22 avoid entering the neighboring cavities in which the outer LED filaments 21 and 23 are arranged. More particularly, the rays of LED light 17 incident on facets of the neighboring cavities, in which the outer LED filaments 21 and 23 are arranged, are reflected back off the facets. Eventually the rays of LED light 17 exit the rod-shaped element 3 at the outer circumference 7 and are emitted as LED filament light 16.

[0080] Fig. 5 shows a cross-sectional, schematic view of a LED filament lamp according to Fig. 1 with an outer LED filament 23 being turned on, while the opposite outer LED filament 21 and the central LED filament 22 are turned off. Fig. 5 further illustrates a ray trace simulation of that situation. As may be seen, all rays of LED light 17 emitted by the LEDs of the outer LED filament 23 avoid entering the neighboring cavities in which the LED filaments 21 and 22 are arranged. More particularly, the rays of LED light 17 incident on facets of the neighboring cavities, in which the LED filaments 21 and 22 are arranged, are reflected back off the facets. Eventually the rays of LED light 17 exit the rod-shaped element 3 at the outer circumference 7 and are emitted as LED filament light 16.

[0081] Thus, in both cases interaction or crosstalk between the respective LED filaments are seen to be effectively avoided. It is noted that the simulations in Figs. 4 and 5 were made without taking Fresnel reflections at the interface between the rod-shaped element 3 and the surrounding air into account. If taking said Fresnel reflections into account, there is a very small interaction between two neighboring sources. A clear indicator is the optical efficiency of the system. If assuming that all three LED filaments 21-23 are 100 % absorbing and have the same flux and spectral properties, and not taking said Fresnel reflections into account, the optical efficiency of the system is 100 %. The optical efficiency is 90.5 % when said Fresnel reflections are taken into account.

[0082] Fig. 6 shows an intensity distribution diagram of the light emitted by a LED filament lamp 1 according to Figs. 1 and 2. The diagram shows the intensity distribution 13 in the XY-plane and the intensity distribution 14 in the YZ-plane. As may be seen square cross-sectional shape of the rod-shaped element 3 used yields an almost constant intensity profile 14 in the YZ-plane.

[0083] Fig. 7 shows a cross-sectional, schematic view of another embodiment of a LED filament lamp 100 according to the invention. The LED filament lamp 100 shown in Fig. 7 differs from that described above in relation to Figs. 1 and 2 in virtue of the following features.

[0084] The LED filament lamp 100 comprises four elongated cavities 41-44 and four LED filaments 21-24. While the cavities 41-43 of the LED filament lamp 1 according to Fig. 1 are arranged on one line, the cavities 41-44 of the LED filament lamp 100 are arranged such that one cavity 44 is displaced sideways with respect to the remaining three cavities 41- 43.

[0085] When turned on, LED filament 22 has no interaction with LED filaments 21, 23 and 24. When LED filament 22 is a LED filament adapted for emitting blue light (or comprises a linear array of SMD LEDs), and LED filaments 21, 23, and 24 are LED filaments emitting warm white light (e.g., 4000K), the light emitted by LED filament 22 is not able to excite the phosphors of LED filaments 21, 23 and 24. There will however be a very limited interaction between LED filament 21 and 24 and between LED filament 23 and 24.

[0086] Fig. 8 shows a cross-sectional, schematic view of another embodiment of a LED filament lamp 101 according to the invention, where the LED filaments are not shown for simplicity. The LED filament lamp 101 shown in Fig. 8 differs from those described above in relation to Figs. 1, 2 and 7 in virtue of the following features.

[0087] The LED filament lamp 101 illustrates that generally the elongated cavities 41-43 may generally comprise at least two different cross-sectional sizes. In the embodiment shown, the elongated cavity 42 comprises a larger cross-sectional size as compared to the elongated cavities 41 and 43.

[0088] Furthermore, a gap 12 is provided between at least two mutually adjacent elongated cavities, in the embodiment shown between elongated cavities 42 and 43.

[0089] Fig. 9 shows a cross-sectional, schematic view of another embodiment of a LED filament lamp 102 according to the invention. The LED filament lamp 102 shown in Fig. 9 differs from those described above in relation to Figs. 1, 2, 7 and 8 in virtue of the following features.

[0090] The LED filament lamp 101 illustrates that the elongated cavities 41-43 may generally comprise at least two different cross-sectional shapes. In the embodiment shown, the elongated cavity 42 comprises a cross-sectional shape being rectangular, while the elongated cavities 41 and 43 comprise a cross-sectional shape being square.

[0091] The LED filament lamp 101 further illustrates that one or more elongated cavities, here the elongated cavity 42, may comprise more than one, here two, LED filaments 22 and 22’.

[0092] Fig. 10 shows a cross-sectional, schematic view of another embodiment of a LED filament lamp 103 according to the invention. The LED filament lamp 103 shown in Fig. 10 differs from those described above in relation to Figs. 1, 2 and 7 to 9 in virtue of the following features.

[0093] The LED filament lamp 103 illustrates that one or more further elongated cavities 45 may be provided. In the embodiment shown in Fig. 10, one further elongated cavity 45 is provided. The further elongated cavity 45 may be used to house electronic components 15 of the LED filament lamp 103. In that way interaction or crosstalk between light emitted by the LED filaments 21 and 22 and the electronic components 15 may be effectively avoided. The electronic components 15 may for instance be wiring 152 for supplying electrical energy to the LED filaments 21 and 22 and a controller 151 for controlling the LED filaments 21 and 22, and in particular parameters related to the LED filament light emitted by the LED filaments 21 and 22.

[0094] The LED filament lamp 103 further illustrates that generally the LED filaments 21, 22 may generally comprise at least two different cross-sectional shapes. In the embodiment shown, the LED filament 21 comprises a cross-sectional shape being circular, while the LED filament 22 comprise a cross-sectional shape being oval or elliptic. Fig. 11 shows a cross-sectional, schematic view of another embodiment of a LED filament lamp 104 according to the invention. The LED filament lamp 104 shown in Fig. 11 differs from those described above in relation to Figs. 1, 2 and 7-10 in virtue of the following features.

[0095] The LED filament lamp 104 show in Fig. 11 comprises an array of 3x3 solid, transparent, elongated rod-shaped elements 3a, 3b, 3c and 3d. The rod-shaped elements 3d are massive elongated rod-shaped elements 3d without any cavities of LED filaments. The rod-shaped elements 3a, 3b and 3c each comprise four elongated cavities 4a, 4b and 4c, respectively and four LED filaments 2a, 2b and 2c, respectively, each arranged on one line. The four elongated cavities 4a and 4c, respectively and the four LED filaments 2a and 2c, respectively, are arranged on a respective line extending parallel to one another. The four elongated cavities 4b and the four LED filaments 2b are arranged on a line being rotated by ninety degrees with respect to the four elongated cavities 4a and 4c, respectively and the four LED filaments 2a and 2c, respectively. To form an overall elongated rod-shaped element with a square cross sectional shape, the three elongated rod-shaped elements 3a, 3b and 3c are arranged or sandwiched between six elongated rod-shaped elements 3d, three on each side.

[0096] Furthermore, the respective elongated rod-shaped elements 3a, 3b, 3c and 3d may be separated from one another by an air gap such that they are not in optical contact with one another. This air gap may be less than 10 pm wide.

[0097] Figs. 12 and 13 shows cross-sectional, schematic views of another embodiment of a LED filament lamp 105 according to the invention. The LED filament lamp 105 shown in Figs. 12 and 13 differs from those described above in relation to Figs. 1, 2 and 7-11 in virtue of the following features.

[0098] The LED filament lamp 105 comprises an optical element 8. The optical element 8 is arranged on the outer circumference 7 of the rod-shaped element 3. More particularly, the optical element 8 is arranged on mutually opposite sides 71, 72 or side segments of the outer circumference 7 of the rod-shaped element 3. The general purpose of the optical element 8 is to restore or improve the optical efficiency of the LED filament lamp 105.

[0099] The rod-shaped element 3 of the LED filament lamp 105 may be composed of two parts 31 and 32. Thereby, the rod-shaped element 3 may easily be made by, for instance, injection molding.

[0100] As shown the optical element 8 comprises a plurality of prism elements 81, 82. Furthermore, the angular cross-sectional shape of each elongated cavity 41 of the plurality of elongated cavities 4 is square or - as shown in Fig. 12 and 13 - rectangular with a width, a, and a length, b. Each elongated cavity 41 of the plurality of elongated cavities 4 further comprises a diameter LI.

[0101] The cross-sectional shape of the prism elements 81, 82 is that of a right angled triangle with a hypothenuse 10 and legs 91, 92 of different lengths. The angle, (|>, between the longest leg 92 and the hypothenuse 10 is chosen such that (|) = arctan(a / b). The angle, P, between the shortest leg 91 and the hypothenuse 10 is chosen such that as P = 90 - (|). The third angle is a right angle. The prism elements 81, 82 of the plurality of prism elements 8 further comprise a height, h, chosen such that h = b * sin(4>). Furthermore, the hypothenuse 10 comprises a length L2 which is chosen such that L2 < LI. By way of example, LI may be in the range of 1 mm - 5 mm, and L2 may be in the range of 10 pm - 500 pm.

[0102] Referring back to Figs. 4 and 5, it has been shown that the optical efficiency is 90.5 % when such an optical element 8 is provided and said Fresnel reflections are taken into account, and even 90.9 % for the specific construction shown in Figs. 12 and 13. The optical efficiency drops to 76.8 % when the optical element 8 is removed.

[0103] Turning finally to Fig. 14, an exemplary luminaire in the form of a pendant 400 is shown. The pendant 400 comprises a LED filament lamp 1; 100-105 according to any embodiment of the invention. The LED filament lamp 1; 100-105 is as shown in Fig. 14 provided in the form of a light bulb 300.

[0104] The light bulb 300 further comprises a transparent envelope 301 at least partially enveloping the at least one LED filament lamp 1; 100-105. The transparent envelope 301 may be shaped in any feasible shape, for example such as to resemble the shape of any one of a standard light bulb, a globe light bulb, a candlelight bulb, a customized light bulb and even a spiral light bulb. The transparent envelope 301 may comprises a luminescent material. The transparent envelope 301 may be a glass envelope. The light bulb 300 further comprises a base 303, such as a cap. The transparent envelope 301 is connected to or mounted on the base 303. The base 303 is configured to connect the LED filament lamp 1; 100-105 electrically and mechanically to a socket 401 of the luminaire. The transparent envelope 301 may comprise a neck, and where provided, the neck forms the part of the transparent envelope 301 that is connected or attached to the base 303.

[0105] The light bulb 300 may further comprise threading 302 for connection to a socket and a terminal 304 for connection to a source of electrical energy. The threading 302 and the terminal 304 may form part of or be provided on the base 303.

[0106] The LED filament lamp 1; 100-105 may further optionally comprise a driver or controller (cf. controller 151 in Fig. 10) configured for controlling the LED filament lamp 1; 100-105. The driver or controller 151 may be an external unit, a unit arranged within the LED filament lamp 1; 100-105 or a combination of both such units.

[0107] The pendant 400 further comprises a socket 401 for connecting the light bulb 300, and thereby the LED filament lamp 1; 100-105, to the pendant 400. The socket 401 is adapted to cooperate with the base 303 of the light bulb 300. The socket 401 may comprise a threading adapted to cooperate with the threading 302 of the light bulb 300. The socket 401 may comprise a terminal adapted to cooperate with the terminal 304 of the light bulb 300.

[0108] The pendant 400 may further comprise a driver 402 configured for controlling the LED filament lamp 1; 100-105. The driver 402 may or may not be the same unit as the controller 151 described above. In other words, the driver 402 and the controller 151 may be integrated into one and the same driver or controller, or they may be mutually separate units. The driver 402 is configured to power the plurality of LED filaments 21-24 via the electrically conducting wires of the LED filament lamp 1; 100-105. The driver 402 may further be configured for controlling at least one of the CCT of the LED filament lamp light 17 and the CRI of the LED filament lamp light 17. The driver 402 may also be configured for controlling other parameters related to the LED filament lamp light sources (that is, the plurality of LEDs 200 of the LED filaments 21-24), the plurality of LED filaments 21-24, and the LED filament light 16.

[0109] As shown in Fig. 14, the driver 402 is arranged on a reflector or screen 403 of the pendant 400. The driver may also be arranged within or incorporated into the reflector or screen 403. The pendant 400 further comprises an electrical wiring 404 for connection to a source of electricity, such as a mains. It is noted that the pendant 400 shown in Fig. 14 is only one example of a luminaire according to the invention. Any suitable type of luminaire may be envisaged, such as but not limited to, a standing luminaire, a wall hung luminaire, a chandelier, a reading luminaire, an outdoor luminaire, and a table luminaire.

[0110] A LED filament lamp 1; 100-105 may be suitable for use in a wide range of LED lighting applications. Presently, LED filaments are widely used in LED bulbs. For instance, an LED filament lamp 105 as shown in Figs. 12 and 13 may be used in LED bulbs with a high LED count and / or a very limited crosstalk. LED filament lamps 1; 100-105 according to the invention also allows to combine conventional SMD LEDs and one or more LED filaments (e.g., LED filaments can be placed on top of an array of SMD LEDs). In addition, the invention is relevant for TLED (LED replacement of fluorescent tubes), and lighting for office and retail applications.

[0111] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0112] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 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. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A LED filament lamp (1) comprising: a plurality of elongated LED filaments (2) adapted for, in operation, emitting LED filament light (16), and at least one solid, transparent, elongated rod-shaped element (3) comprising a plurality of elongated cavities (4), wherein at least one elongated LED filament (21-24) of the plurality of elongated LED filaments is at least partly or fully arranged in each elongated cavity (41-44) of the plurality of elongated cavities, wherein each elongated cavity of the plurality of elongated cavities (4) comprises a convex angular cross-sectional shape comprising at least three facets (61-64), each two converging facets of the at least three facets forming a corner (51-55), wherein each elongated cavity of the plurality of elongated cavities (4) is arranged such that mutually adjacent elongated cavities (41, 42) are in contact at most by a respective corner (54, 55), and wherein mutually adjacent facets (65, 66) of mutually adjacent elongated cavities (4) extend in an angle, a, with one another, the angle, a, fulfilling the relation a > 2*arcsin(n0 / nl), where nO is the refractive index of a medium present in each elongated cavity of the plurality of elongated cavities (4) and nl is the refractive index of the material of the solid, transparent, elongated rod-shaped element (3).

2. A LED filament lamp according to claim 1, wherein the solid, transparent, elongated rod-shaped element (3) further comprises an outer circumference (7), and wherein mutually opposite sides (71, 72) or side segments of the outer circumference are provided with a plurality of prism elements (8).

3. A LED filament lamp according to claim 2, wherein the angular cross-sectional shape of each elongated cavity of the plurality of elongated cavities (4) is square or rectangular with a width, a, and a length, b, and wherein the cross-sectional shape of the prism elements (81, 82) of the plurality of prism elements is that of a right angled triangle with legs (91, 92) of different lengths, wherethe angle, (|>, between the longest leg (92) and a hypothenuse (10) is defined as (|) = arctan(a / b), and where the angle, P, between the shortest leg (91) and the hypothenuse (10) is defined as P = 90 - (|).

4. A LED filament lamp according to claim 2 or 3, wherein the angular cross-sectional shape of each elongated cavity of the plurality of elongated cavities (4) is square or rectangular with a diameter LI, wherein the cross-sectional shape of the prism elements of the plurality of prism elements (8) is that of a right angled triangle with a hypothenuse (10) having a length L2, and whereinL2 < L1.

5. A LED filament lamp according to claim 4, wherein LI is in the range of 1 - 5 mm, and wherein L2 is in the range of 10 - 500 pm.

6. A LED filament lamp according to any one of the above claims, wherein the angular cross-sectional shape of each elongated cavity of the plurality of elongated cavities (4) is any one of polygonal, hexagonal, triangular, square, and rectangular.

7. A LED filament lamp according to any one of the above claims, wherein the solid, transparent, elongated rod-shaped element (3) comprises a cross-sectional shape being round, or rectangular, or square or elliptical, or circular, or polygonal or regular polygonal, or irregular.

8. A LED filament lamp according to any one of the above claims, wherein a gap (11) is provided between at least one of the elongated LED filaments (23) and at least one of the facets of the elongated cavity (43) in which the said elongated LED filament (23) is arranged.

9. A LED filament lamp according to any one of the above claims, wherein each elongated cavity of the plurality of elongated cavities (4) is arranged such that mutually adjacent elongated cavities (41, 42) are in contact by a respective corner (54, 55) of the at least three respective corners, or whereina gap (12) is provided between at least two mutually adjacent elongated cavities (42, 43).

10. A LED filament lamp according to any one of the above claims, wherein the elongated cavities of the plurality of elongated cavities (4) all comprise the same cross- sectional size, or wherein the elongated cavities of the plurality of elongated cavities (4) comprise at least two mutually different cross-sectional sizes.

11. A LED filament lamp according to any one of the above claims, wherein only one elongated LED filament of the plurality of elongated LED filaments (2) is arranged in each elongated cavity of the plurality of elongated cavities (4).

12. A LED filament lamp according to any one of the above claims, and comprising at least one further elongated cavity (45), the further elongated cavity comprising electronic components (15).

13. A LED filament lamp according to any one of the above claims, wherein at least one of the elongated LED filaments of the plurality of elongated LED filaments (2) is an elongated LED filament adapted for, in operation, emitting blue LED filament light.

14. A LED filament lamp according to any one of the above claims, wherein the material of the solid, transparent, elongated rod-shaped element (3) is chosen from the group comprising PMMA, polycarbonate, glass, quartz glass, and sapphire / TGA (AI2O3).

15. A luminaire (400) comprising a LED filament lamp (1) according to any one of the preceding claims.

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