A LED filament

Abstract

A light emitting diode, LED, filament (1) configured to, in an on-state, emit LED filament light (2) and comprising: an elongated carrier (3) comprising a first major surface (31) and a second major surface (32), an array of a plurality of LEDs (4) configured to, in an on-state, emit LED light (41) and being arranged on the first major surface (31), an elongated light-converting encapsulant (5) at least partly enclosing the plurality of LEDs (4), at least partly covering the elongated carrier (3), and comprising a luminescent material (52) configured to at least partly convert the LED light (41) into converted light (43), and a transparent layer (6) at least partially covering the elongated light-converting encapsulant (5), and comprising a third major surface (61) and a fourth major surface (62). The transparent layer (6) comprises a reflective pattern (7), the reflective pattern (7) comprising a plurality of first reflective elements (71) arranged on or at the third major surface (61), and a plurality of second reflective elements (72) arranged on or at the fourth major surface (62). The reflective pattern (7) is configured to (i) hide the elongated light-converting encapsulant (5) as perceived by a viewer (8), and (ii) to provide openings (73) configured to transmit the LED filament light (2).

Description

[0001] A LED FILAMENT

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a light emitting diode, LED, filament configured to, in an on-state, emit LED filament light. The invention further relates to a lamp and a luminaire comprising such a LED filament.

[0004] BACKGROUND OF THE INVENTION

[0005] Recent market research shows customers desire hiding the yellow-orange color appearance of LED filaments. With significant marketing effort, companies are introducing white LED filaments in which a white layer is covering the light converting encapsulant of LED filaments.

[0006] 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 or in 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).

[0007] In case the elongated carrier comprises a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The elongated carrier may be reflective or light transmissive, such as translucent and preferably transparent.

[0008] 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 2022 / 0186889 Al discloses a LED filament which comprises an elongated substrate and a plurality of LEDs. The LED filament further comprises an at least in part light-transmissive encapsulation which encapsulate the plurality of LEDs and at least partially encapsulates the substrate, and a plurality of at least partially light-reflective particles which are arranged on an outer surface of the encapsulation.

[0012] However, the white layer in white LED filaments decreases the efficiency dramatically due light trapping, i.e., light-absorption on the white pigment due to many reflections. In order to get a good hiding function, a thick white layer with a high concentration of white particles is needed. The reflectivity of said white particles is typically about 90%. By having many reflections, a significant part of the LED filament light is lost.

[0013] It is thus desired to improve the optical performance (such as light quality and correlated color temperature, CCT, control and so forth), the efficiency (less light lost), and / or the appearance (such as light mixing) of LED filaments.

[0014] US 2024 / 218987 provides a LED filament elongating along an axis, A, comprising array (s) of a plurality of LEDs arranged to emit LED light, and an encapsulant enclosing the array(s) of the LEDs, wherein the encapsulant comprises a light-transmissive material. The LED filament further comprises an elongated reflector having a first reflectivity, Rl, arranged to reflect the LED light, wherein the reflector, by partially enclosing a cross-section, CB, perpendicular to the axis, A, of the LED filament in a radial direction, R, partially encloses the encapsulant along the LED filament, whereby the reflector defines at least one opening along the LED filament, wherein the encapsulant is not covered by the reflector along the at least one opening.

[0015] SUMMARY OF THE INVENTION

[0016] It is an object of the invention to provide a LED filament which comprise an improved optical performance, an improved efficiency and / or an improved optical appearance.

[0017] It is a further object of the invention to provide a LED filament with one or more of a reduced loss of light, an improved light quality, an improved efficiency, an improved CCT control and an improved light mixing. According to a first aspect of the invention, this and other objects are achieved by means of a light emitting diode, LED, filament configured to, in an on-state, emit LED filament light, the LED filament comprising an elongated carrier comprising a first major surface and a second major surface opposite to the first major surface, an array of a plurality of LEDs configured to, in an on-state, emit LED light and being arranged on the first major surface of the elongated carrier. Alternatively, or additionally the LEDs may be arranged in the carrier., Further, the LED filament comprises an elongated light-converting encapsulant at least partly enclosing the plurality of LEDs and at least partly covering the elongated carrier, the elongated light-converting encapsulant comprising a luminescent material configured to at least partly convert the LED light into converted light, and a transparent layer at least partially covering the elongated light-converting encapsulant, the transparent layer comprising a third major surface and a fourth major surface opposite to the third major surface, wherein the transparent layer comprises a reflective pattern, the reflective pattern comprising a plurality of first reflective elements arranged on or at the third major surface, and a plurality of second reflective elements arranged on or at the fourth major surface, and wherein the reflective pattern is configured to (i) hide the elongated light-converting encapsulant as perceived by a viewer, and (ii) to provide openings configured to transmit the LED filament light.

[0018] Thereby, and especially by providing a reflective pattern as described above, a LED filament is obtained which comprises at least one of an improved optical performance, an improved efficiency, and an improved optical appearance. Especially, by providing a reflective pattern as described above a reduced loss of light and thus an improved efficiency is obtained.

[0019] The LED filament light may be white light having a correlated color temperature in a range from 1700K to 6500K, or in a range from 1700K to 3000K, and a CRI of at least 70, or at least 80.

[0020] The plurality of first reflective elements and the plurality of second reflective elements may be configured to provide a coverage of the elongated light-converting encapsulant of at least 70%, at least 80%, at least 85%, or at least 90%, e.g., 100%.

[0021] The coverage may, e.g., be measured perpendicularly to the length axis of the LED filament. Thereby a LED filament with a further improved efficiency is provided for.

[0022] The plurality of first reflective elements and the plurality of second reflective elements may be configured to any one of (i) forming no mutual overlap, O, and (ii) forming a mutual overlap, O, the overlap being at most 30 % of an area of the respective first and second reflective element.

[0023] Thereby a LED filament with a particularly high efficiency is provided for. The plurality of first reflective elements and the plurality of second reflective elements may be configured to any one of (i) providing a coverage of the elongated lightconverting encapsulant of 100%, and (ii) A) forming no mutual overlap, O, or B) forming a mutual overlap, O, the overlap being at most 10 % of an area of the respective first and second reflective element.

[0024] Thereby, an optimized efficiency of the LED filament is obtained.

[0025] The plurality of first reflective elements may be arranged (i) on a side of the third major surface facing away from the array of the plurality of LEDs, (ii) on a side of the third major surface facing towards the array of the plurality of LEDs, or (iii) embedded in the third major surface.

[0026] Alternatively, or additionally, the plurality of second reflective elements may be arranged are arranged (i) on a side of the fourth major surface facing away from the array of the plurality of LEDs, (ii) on a side of the fourth major surface facing towards the array of the plurality of LEDs, or (iii) embedded in the fourth major surface.

[0027] Alternatively, or additionally, the plurality of second reflective elements may be arranged (i) on a surface of the elongated light-converting encapsulant opposite to the array of the plurality of LEDs, or (ii) at a distance, Y, from the elongated light-converting encapsulant, wherein Y < 0.5 mm.

[0028] Thereby a LED filament with a further improved appearance and efficiency is provided for. One or more of the following may apply: (i) one or both of the third major surface and the fourth major surface of the transparent layer is arranged obliquely with respect to a light exit surface of the LEDs of the array of a plurality of LEDs, (ii) one or both of the third major surface and the fourth major surface of the transparent layer is arranged in an angle with respect to the light exit surface of the LEDs of the array of a plurality of LEDs, such as for example an angle being between 5 and 45 degrees or between 10 and 40 degrees, (iii) the plurality of first reflective elements and / or the plurality of second reflective elements are arranged obliquely with respect to a light exit surface of the LEDs of the array of a plurality of LEDs, and (iv) the reflective pattern is arranged in an angle with respect to the light exit surface of the LEDs of the array of a plurality of LEDs, such as for example an angle being between 5 and 45 degrees or between 10 and 40 degrees.. Thereby the exiting of light through the transparent layer is improved. In other words, an improved light extraction is obtained.

[0029] One or more of the following may apply: (i) the plurality of first reflective elements are arranged in any one of a regular pattern and a checkered pattern, and (ii) the plurality of second reflective elements are arranged in any one of a regular pattern and a checkered pattern.

[0030] Thereby a LED filament with a further improved appearance is provided for since different patterns may be obtained in this way.

[0031] The reflective pattern may comprise a reflectivity, R, being more than or equal to 90%, or at least 92%.

[0032] Simulations have shown that this very high reflectivity is needed to make the proposed LED filament efficient. The reason is that the proposed LED filament results in multiple reflections of light at the reflective pattern. Because in each reflection some light is lost, the reflectivity should be very high.

[0033] The absorption, A, of the reflective pattern may be A < 2 % or A < 1 %.

[0034] The reflective pattern may be diffuse reflective.

[0035] The effect is that light which impinges on the diffuse reflective pattern becomes redirected into various different angles and thus allows high transmission of light while providing a good hiding appearance.

[0036] The transparent layer comprises a thickness, T, which may be in a range from 0.2 mm to 2 mm.

[0037] The choice of such a thickness of the transparent layer bas been shown to obtain an optimum compromise between keeping the LED filament slim (i.e. small thickness) and allowing sufficient light transmission (i.e. large thickness).

[0038] One or more of the following may apply: (i) the reflective elements of the plurality of first reflective elements and the reflective elements of the plurality of second reflective elements, respectively, comprise an aspect ratio defined as the ratio of a length, L, of the reflective element to a height, Hl and H2, respectively, of the reflective element, wherein the aspect ratio is at least 5 or at least 10, and (ii) the reflective elements of the plurality of first reflective elements and the reflective elements of the plurality of second reflective elements, respectively, comprise a longest dimension being in the range of 0.2 mm to 1 mm and a height, Hl and H2, respectively, being in a range from 0.02 mm and 0.2 mm.

[0039] Thereby a LED filament with a further improved performance, especially in terms of light quality, and appearance, especially in terms of light mixing, is provided for. The reflective pattern may comprise one or more of TiCE, BaSCU, AI2O3, ZrCh, and combinations thereof.

[0040] Such materials have been proved to be particularly suitable for the reflective elements, especially to provide the reflective elements with a suitable reflectivity.

[0041] One or both of the transparent layer and the reflective pattern may be applied by a depositing technique, by transfer by stamper, by offset printing, or by providing a substrate or a foil comprising the plurality of first reflective elements and the plurality of second reflective elements and place the substrate or foil around the elongated lightconverting encapsulant of the LED filament.

[0042] Thereby, the LED filament with the transparent layer and reflective elements may be manufactured in a particularly efficient and straight-forward manner.

[0043] The plurality of second reflective elements may be arranged in a distance, Y, from the elongated light-converting encapsulant, the plurality of first reflective elements may be arranged in a distance, X, from the plurality of second reflective elements, and X and Y may be chosen to fulfill the relation Y < 0.8 X.

[0044] Thereby, an improved transmission of light is obtained.

[0045] The plurality of first reflective elements comprise a length, LI, which may be in the range of 0.2 mm to 1 mm.

[0046] Alternatively, or additionally, the plurality of second reflective elements comprise a length, L2, which may be in the range of 0.2 mm to 1 mm.

[0047] Alternatively, or additionally, an aspect ratio between a length, LI, of the plurality of first reflective elements and a mutual overlap, O, between the plurality of first reflective elements and the plurality of second reflective elements defined as Ll / O may be in the range of 10 to 50.

[0048] Alternatively, or additionally, a shortest distance, Y, between the plurality of second reflective elements and the elongated light-converting encapsulant may be in the range of 0.06 mm to 0.6 mm.

[0049] Alternatively, or additionally, a shortest distance, X, between the plurality of first reflective elements and the plurality of second reflective elements may be in the range of 0.2 mm to 1 mm.

[0050] Thereby a LED filament with one or both of a further improved performance, especially in terms of light quality, and a further improved appearance, especially in terms of light mixing, is provided for. The transparent layer may fully cover the elongated light-converting encapsulant.

[0051] Thereby a LED filament with a uniform look in an off-state and with an uniform light output in an on-state is provided for.

[0052] The invention further relates to a LED filament lamp comprising a LED filament according to the invention.

[0053] The LED filament lamp may further comprise a light transmissive envelope at least partly enclosing the LED filament and a base for electrically and mechanically connecting the LED filament lamp to a socket or a socket of a luminaire.

[0054] The invention still further relates to a luminaire comprising a LED filament lamp according to the invention.

[0055] The invention still further relates to a luminaire comprising a LED filament according to the invention.

[0056] It is noted that the invention relates to all possible combinations of features recited in the claims.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] 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.

[0059] Fig. 1 shows a longitudinal cross-sectional view of a section of a light emitting diode, LED, filament according to the invention and comprising a transparent layer with a reflective pattern.

[0060] Fig. 2 shows a top view of the LED filament according to claim 1.

[0061] Fig. 3 shows a transversal cross-sectional view of another LED filament according to the invention.

[0062] Figs. 4 to 8 show longitudinal cross-sectional views of different variants of a transparent layer with a reflective pattern of a LED filament according to the invention.

[0063] Figs. 9 and 10 show a respective section of the transparent layer with a reflective pattern according to Fig. 8.

[0064] Fig. 11 is a graph illustrating the amount of light escaping the transparent layer without touching the reflective pattern from an area A shown in Fig. 10 as a function of a distance Y shown in Fig. 10.

[0065] Fig. 12 is a graph illustrating the amount of light escaping the transparent layer without touching the reflective pattern from an area B shown in Fig. 9 as a function of a distance Y calculated for different values of a distance X, both distances being shown in Fig.

[0066] 9.

[0067] Fig. 13 is a graph illustrating the total amount of light escaping the transparent layer without touching the reflective pattern from areas A and B as a function of a distance Y calculated for different values of a distance X.

[0068] Fig. 14 shows a schematical side view of a lamp comprising a LED filament according to the invention.

[0069] Fig. 15 shows a schematical side view of a luminaire comprising a lamp and a LED filament according to the invention.

[0070] 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.

[0071] DETAILED DESCRIPTION

[0072] 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.

[0073] Fig. 1 shows a longitudinal cross-sectional view of a section of a light emitting diode, LED, filament 1 according to the invention, and Fig. 2 shows a top view of the LED filament 1.

[0074] The light emitting diode, LED, filament 1 is configured to, in an on-state, emit LED filament light 2. Generally, and irrespective of the embodiment, the LED filament 1 comprises an elongated carrier 3, an array of a plurality of LEDs 4, an elongated lightconverting encapsulant 5, and a longitudinal axis LX.

[0075] The elongated carrier 3 comprises a first major surface 31 and a second major surface 32 opposite to the first major surface 31. The elongated carrier 3 may be a substrate such as a printed circuit board (PCB) configured to provide the plurality of LEDs 4 with electrical power.

[0076] The array of a plurality of LEDs 4 is configured to, in an on-state, emit LED light 41. The array of a plurality of LEDs 4 is arranged on the first major surface 31 of the elongated carrier 3. The LEDs of the array of a plurality of LEDs 4 may be any suitable type of LEDs, such as LEDs configured to emit white light, green light, red light, or blue light.

[0077] Generally, and irrespective of the embodiment, the elongated light-converting encapsulant 5 encloses the plurality of LEDs 4 at least partly. Generally, and irrespective of the embodiment, the elongated light-converting encapsulant 5 further covers the elongated carrier 3, and particularly the first major surface 31, at least partly. As shown in Fig. 1, the elongated light-converting encapsulant 5 encloses the plurality of LEDs 4 fully. The elongated light-converting encapsulant 5 may also cover the elongated carrier 3 fully as is illustrated by the LED filament 100 shown in Fig. 3. The elongated light-converting encapsulant 5 may also cover the second major surface 32, at least partly. The elongated light-converting encapsulant 5 is configured to convert at least a part of the LED light 41 into converted light 43. The elongated light-converting encapsulant 5 comprises a luminescent material 52. The LED filament light 2 may thus comprise LED light 41 and converted light 43 or only converted light 43. The elongated light-converting encapsulant 5 comprises an outer surface 51 facing away from the array of a plurality of LEDs 4. The elongated lightconverting encapsulant 5 may consist of a plurality of light-converting encapsulant parts. The plurality of light-converting encapsulant parts may have the same properties or two or more different properties. The elongated light-converting encapsulant 5 may comprise an elongated light-converting encapsulant pattern.

[0078] The LED filament 1 further comprises a transparent layer 6. The transparent layer 6 is arranged on the elongated light-converting encapsulant 5, and more particularly on the outer surface 51 of the elongated light-converting encapsulant 5. As shown in Fig. 1, the transparent layer 6 covers the elongated light-converting encapsulant 5 at least partially. The transparent layer 6 may also cover the elongated light-converting encapsulant 5 fully as is illustrated by the LED filament 100 shown in Fig. 3. The transparent layer 6 comprises a third major surface 61 and a fourth major surface 62 opposite to the third major surface 61. The fourth major surface 62 and the outer surface 51 of the elongated light-converting encapsulant 5 are arranged abutting one another. The transparent layer 6 further comprises a thickness T. The thickness T may be in a range from 0.2 mm to 2 mm. The transparent layer 6 may be applied by a depositing technique, such as chemical vapor deposition, CVD, or physical vapor deposition, PVD. Alternatively, the transparent layer 6 may be applied by transfer by stamper. Alternatively, the transparent layer 6 may be applied by offset printing. Alternatively, the transparent layer 6 may be applied by providing a substrate or a foil comprising the plurality of first reflective elements 71 and the plurality of second reflective elements 72 and placing the substrate or foil around the elongated light-converting encapsulant 5 of the LED filament 1.

[0079] Referring now also to Fig. 2, the transparent layer 6 comprises a reflective pattern 7. The reflective pattern 7 comprises a plurality of first reflective elements 71 and a plurality of second reflective elements 72. The plurality of first reflective elements 71 are arranged on or at the third major surface 61. The plurality of second reflective elements 72 are arranged on or at the fourth major surface 62. The reflective pattern 7 is configured to hide the elongated light-converting encapsulant 5 as perceived by a viewer 8 looking at the LED filament 1, especially when looking in the direction perpendicular to the LED filament 1. The transparent layer 6, and thus also the reflective pattern 7, comprise a length LTL (cf. Fig. 2) less than or equal to a length of the LED filament 1. The transparent layer 6, and thus also the reflective pattern 7, comprise a width WTL (cf. Fig. 2) being less than or equal to a width of the LED filament 1.

[0080] The reflective pattern 7 is arranged such that openings 73 configured to transmit light, especially the LED filament light 2, are provided. More particularly, the plurality of first reflective elements 71 and the plurality of second reflective elements 72 are arranged in such a way with respect to one another that openings 73 configured to transmit light are provided. Thereby some light rays 63 of LED light 41 and / or converted light 43 incident at the transparent layer 6 will be transmitted through the openings 63, and some light rays 64 of LED light 41 and / or converted light 43 incident at the transparent layer 6 will be reflected off of the plurality of first reflective elements 71 and / or the plurality of second reflective elements 72. Both light rays 63 and 64 will eventually leave the transparent layer 6 at the third major surface 61 to be emitted as LED filament light 2. In this way ambient light is reflected by the transparent layer 6. That is, the fraction of ambient light reflected by the plurality of first reflective elements 71 and the plurality of second reflective elements 72 (and not being converted by the luminescent material 52) is much higher than the fraction of ambient light reaching the elongated light-converting encapsulant 5 and, e.g., being converted by the luminescent material 52. The ratio between these two said fractions of ambient light may be at least 5. The plurality of first reflective elements 71 and the plurality of second reflective elements 72 are generally arranged and configured to provide a coverage of the elongated light-converting encapsulant 5 of at least 70 %. However, the plurality of first reflective elements 71 and the plurality of second reflective elements 72 may be arranged and configured to provide a coverage of the elongated light-converting encapsulant 5 of at least 80 %, at least 90 % or even 100 %. As shown in Fig. 1, the plurality of first reflective elements 71 are arranged on a side of the third major surface 61 facing towards the array of the plurality of LEDs 4. Alternatively, or additionally, the plurality of first reflective elements 71 may be arranged on a side of the third major surface 61 facing away from the array of the plurality of LEDs 4 (cf. Fig. 4), or the plurality of first reflective elements 71 may be embedded in the third major surface 61. As shown on Fig. 1, the plurality of second reflective elements 72 are arranged on a side of the fourth major surface 62 facing away from the array of the plurality of LEDs 4. Alternatively, or additionally, the plurality of second reflective elements 72 may be arranged on a side of the fourth major surface 62 facing towards the array of the plurality of LEDs 4 (cf. Fig. 4), or the plurality of second reflective elements 72 may be embedded in the fourth major surface 62.

[0081] Referring now specifically to Fig. 2, the plurality of first reflective elements 71 are arranged in a regular pattern. In the case shown, the regular pattern is a checkered pattern. Likewise, the plurality of second reflective elements 72 are arranged in a regular pattern. In the case shown, the regular pattern is a checkered pattern. Since the transparent layer 6 is transparent, a viewer 8 looking at the LED filament 1 will perceive the reflective pattern 7 as a checkered pattern comprising alternating first reflective elements 71 and second reflective elements 72 both in the width direction WX and the length direction LX of the LED filament 1.

[0082] Reference is now also made to Fig. 5. The reflective elements of the plurality of first reflective elements 71 comprise a first length LI and a first height HL The first length LI may be between 0.2 mm and 1 mm. The reflective elements of the plurality of second reflective elements 72 comprise a second length L2 and a second height H2. The second length L2 may be between 0.2 mm and 1 mm. The reflective elements of the plurality of first reflective elements 71 each comprise an aspect ratio defined as the ratio of the length LI to the height Hl of the reflective element, and the aspect ratio is at least 5 or at least 10. The reflective elements of the plurality of second reflective elements 72 each comprise an aspect ratio defined as the ratio of the length L2 to the height H2 of the reflective element, and the aspect ratio is at least 5 or at least 10. The reflective elements of the plurality of first reflective elements 71 comprise a longest dimension being in the range of 0.3 mm to 1 mm. The height Hl of the plurality of first reflective elements 71 may be in a range from 0.02 mm and 0.2 mm. The reflective elements of the plurality of second reflective elements 72 comprise a longest dimension being in the range of 0.2 mm to 1 mm. The length LI of the reflective elements of the plurality of first reflective elements 71 may be in the range of 0.2 mm to 1 mm. The length L2 of the reflective elements of the plurality of second reflective elements 72 may be in the range of 0.2 mm to 1 mm. The height H2 of the plurality of second reflective elements 72 may be in a range from 0.02 mm and 0.2 mm.

[0083] The reflective pattern 7 has a reflectivity, R, being more than or equal to 90 %. The reflective pattern 7 may be diffuse reflective. The reflective pattern 7 may comprise one or more of TiCL, BaSCU, AI2O3, ZrCL and combinations thereof. The reflective pattern 7, i.e., the plurality of first reflective elements 71 and / or the pattern of second reflective elements 72, may be white or have a white color. The reflective pattern 7 may be applied by a depositing technique, such as chemical vapor deposition, CVD, or physical vapor deposition, PVD. Alternatively, the reflective pattern 7 may be applied by transfer by stamper. Alternatively, the reflective pattern 7 may be applied by offset printing. Alternatively, the reflective pattern 7 may be applied by providing a substrate or a foil comprising the plurality of first reflective elements 71 and the plurality of second reflective elements 72 and placing the substrate or foil on the transparent layer 6, which in turn is placed around the elongated light-converting encapsulant 5 of the LED filament 1.

[0084] Referring now to Figs. 4 to 7 various optional features of the semi-reflective light-transmissive metallic layer 6 will be described.

[0085] Fig. 4 shows a cross-sectional view of a transparent layer 6 and a reflective pattern 7 of a LED filament 1 according to the invention. Here, the plurality of first reflective elements 71 and the plurality of second reflective elements 72 are arranged and configured to provide a coverage of the elongated light-converting encapsulant 5 being in the range of 95 % to 100 %. That is to cover 95 % to 100 % of the surface area of the elongated lightconverting encapsulant 5. This means essentially full coverage of the surface area of the elongated light-converting encapsulant 5. Furthermore, as indicated by the dotted line in Fig. 4, the plurality of first reflective elements 71 and the plurality of second reflective elements 72 are in this case arranged and configured to form no mutual overlap.

[0086] Fig. 5 shows a cross-sectional view of another transparent layer 600 and reflective pattern 700 of a LED filament 1 according to the invention.

[0087] The plurality of first reflective elements 71 and the plurality of second reflective elements 72 are in this case arranged and configured to form no mutual overlap. Furthermore, the plurality of first reflective elements 71 and the plurality of second reflective elements 72 are here arranged and configured to provide a coverage of the elongated lightconverting encapsulant 5 being in the range of 70 % to 90 %, or in the range of 70 % to 95 %. That is to cover 70 % to 90 %, or 70 % to 95 %, of the surface area of the elongated lightconverting encapsulant 5.

[0088] The plurality of first reflective elements 71 and the plurality of second reflective elements 72 are in this case arranged with a distance N between their respective end surfaces. The distance N is measured perpendicular to both end surfaces and is larger than 0. For instance, the distance N may be larger than or equal to both the height Hl of the reflective elements of the plurality of first reflective elements 71 and the height H2 of the reflective elements of the plurality of second reflective elements 72.

[0089] Fig. 6 shows a cross-sectional view of another transparent layer 601 and reflective pattern 701 of a LED filament 1 according to the invention.

[0090] The plurality of first reflective elements 71 and the plurality of second reflective elements 72 are in this case arranged and configured to form a mutual overlap O. The overlap O may be in the range of 1 % to 30 %, such as at most 10 %, or at most 30 %, of a surface area Al of the reflective elements of the plurality of first reflective elements 71 and of a surface area A2 of the reflective elements of the plurality of second reflective elements 72, respectively. Furthermore, an aspect ratio between length, LI, of the plurality of first reflective elements 71 and a mutual overlap, O, between the plurality of first reflective elements 71 and the plurality of second reflective elements 72 is defined as Ll / O. The aspect ratio Ll / O may be chosen to be in the range of 10 to 50.

[0091] Fig. 7 shows a cross-sectional view of another transparent layer 602 and reflective pattern 702 of a LED filament 1 according to the invention.

[0092] One, or as shown in Fig. 7 both, of the third major surface 61 and the fourth major surface 62 of the transparent layer 6 is arranged obliquely with respect to a light exit surface 42 of the LEDs of the array of a plurality of LEDs 4. One, or as shown in Fig. 7 both, of the third major surface 61 and the fourth major surface 62 of the transparent layer 6 is arranged in an angle with respect to the light exit surface 42 of the LEDs of the array of a plurality of LEDs 4, such as for example an angle being between 5 and 45 degrees or between 10 and 40 degrees. Additionally, or alternatively, the reflective pattern 7 is arranged obliquely with respect to the light exit surface 42 of the LEDs of the array of a plurality of LEDs 4. The reflective pattern 7 may be arranged in an angle with respect to the light exit surface 42 of the LEDs of the array of a plurality of LEDs 4, such as for example an angle being between 5 and 45 degrees or between 10 and 40 degrees.

[0093] Fig. 8 shows a cross-sectional view of another reflective pattern 703 of a LED filament 1 according to the invention. In Fig. 8, the transparent layer 6 is for simplicity not shown. Figs. 9 and 10 show a respective section of the reflective pattern 703 according to Fig. 8.

[0094] In this case, the plurality of second reflective elements 72 is arranged in a distance Y from the elongated light-converting encapsulant 5. The lowest value of the distance Y between the plurality of second reflective elements 72 and the elongated lightconverting encapsulant 5 may be chosen to be in the range of 0.06 mm to 0.6 mm. The distance Y may be chosen to be less than or equal to 0.5 mm. Likewise, the plurality of first reflective elements 71 is arranged in a distance X from the plurality of second reflective elements 72. The lowest value of the distance X between the plurality of first reflective elements 71 and the plurality of second reflective elements 72 may be chosen to be in the range of 0.2 mm to 1 mm. The distance X and the distance Y may be chosen such that Y < 0.8*X.

[0095] Figs. 11 to 13 shows graphs illustrating the performance of a transparent layer 6 with a reflective pattern 703 according to Fig. 8. Referring also to Figs. 9 and 10, calculations were made of the fraction of light escaping from two different areas A (Fig. 10) and B (Fig. 9). The areas A and B have a length L which may be expressed as a function of the distances xL and yL shown in Figs. 9 and 10, respectively, where x and y are respective numbers or fractions of numbers.

[0096] Fig. 11 is a graph illustrating the amount of light escaping the transparent layer without touching the reflective pattern from an area A shown in Fig. 10 as a function of y shown in Fig. 10. It may be seen from Fig. 11 that the amount of light escaping the transparent layer without touching the reflective pattern from an area A exhibits a maximum at around y = 0.8.

[0097] Fig. 12 is a graph illustrating the amount of light escaping the transparent layer without touching the reflective pattern from an area B shown in Fig. 9 as a function of y calculated for different values of x. It may be seen from Fig. 12 that with increasing y the fraction of light escaping from area B decreases.

[0098] Fig. 13 is a graph illustrating the total amount of light escaping the transparent layer without touching the reflective pattern from areas A and B as a function of y calculated for different values of x. It may be seen from Fig. 13 that almost half of the light coming from the total LED filament 1 will be escaping without touching the reflective elements of the reflective layer 703 when x > 1 and y is in the range of 0.1 < y < 0.6. When roughly 50 % of the light escape without touching the reflective elements of the reflective layer 703, a consequence is that the other 50 % of the light is reflected back off the reflective elements of the reflective layer 703. This means that for light, especially from areas A, to escape without touching the reflective elements of the reflective layer 703, the distance y needs to be sufficiently high, and in practice needs to be y > 0.3. Combining this with the previous restriction gives 0.3 < y < 0.6. In relation to real dimensions, and if the length L of the reflective elements is in the range of 0.2 mm to 1 mm, then the distance Y from the plurality of second reflective elements 72 to the elongated light-converting encapsulant 5 should be in the range 0.06 mm < Y < 0.6 mm. This in turn means that the distance between the distance X between the plurality of first reflective elements 71 and the plurality of second reflective elements 72 should be in the range 0.2 mm < X < 1 mm.

[0099] Fig. 14 shows an exemplary lamp 300 comprising a LED filament 1, 100 according to any embodiment of the invention. In the embodiment shown, the LED filament 1, 100 comprises a substantially straight LED filament. The LED filament of such a lamp may in other embodiments be a LED filament with another shape, such as, but not limited to, spiral-shaped, helix-shaped, meandering, twisted, flat and combinations thereof.

[0100] The lamp 300 further comprises a driver or controller 305 configured for controlling the plurality of LEDs 4 of the LED filament 1, 100. The controller 305 is configured to power the plurality of LEDs 4 via electrical circuitry (not visible on the figures) of the LED filament 1, 100. The LED filament 1, 100 may also comprise a controller, which may or may not be separate from the controller 305. In other words, the controller 305 and the controller of the LED filament 1, 100 may be integrated into one and the same driver or controller, or they may be mutually separate units.

[0101] The lamp 300 further comprises an envelope 301 at least partially enveloping the at least one LED filament 1, 100. The lamp 300 further comprises a cap 303. As shown in Fig. 14, the controller 305 is arranged within the envelope 301. When comprising a cap 303, the controller 305 may also be arranged inside the cap 303 such that it is hidden from view. The lamp 300 further comprises threading 302 for connection to a socket, and a terminal 304 for connection to a source of electrical energy.

[0102] The envelope 301 of the lamp 300 may further and optionally be provided with a coating (not shown), such as a reflective coating, covering at least a part of the envelope 301.

[0103] Turning finally to Fig. 15, an exemplary luminaire in the form of a pendant 400 is shown. The pendant 400 comprises a LED filament 1, 100 according to any embodiment of the invention. The LED filament 1, 100 is as shown in Fig. 9 provided within a lamp 300 in the form of a light bulb. The LED filament 1, 100 as shown in Fig. 15 comprises a substantially straight LED filament.

[0104] As is also mentioned above, the light bulb further comprises a transparent envelope (cf. transparent envelope 301 of lamp 300) at least partially enveloping the at least one LED filament 1, 100. The transparent envelope 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 may comprise a luminescent material. The transparent envelope may be a glass envelope.

[0105] The pendant 400 further comprises a socket 401 for connecting the lamp 300, and thereby the LED filament 1, 100, to the pendant 400. The socket 401 is adapted to cooperate with the base 303 of the lamp 300. The socket 401 may comprise a threading adapted to cooperate with the threading 302 of the lamp 300. The socket 401 may comprise a terminal adapted to cooperate with the terminal 304 of the lamp 300. The pendant 400 further comprises a reflector or screen 403.

[0106] The pendant 400 may further comprise a driver 402 configured for controlling the LED filament 1, 100. The driver 402 may or may not be the same unit as the controller 305 described above. In other words, the driver 402 and the controller 305 may be integrated into one and the same driver or controller, or they may be mutually separate units. Alternatively, or additionally, the LED filament 1, 100 may also comprise a controller, which may or may not be separate from one or both of the driver 402 and the controller 305.

[0107] As shown in Fig. 15, 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.

[0108] It is noted that the pendant 400 shown in Fig. 15 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.

[0109] 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.

[0110] 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 light emitting diode, LED, filament (1) configured to, in an on-state, emit LED filament light (2), the LED filament comprising: an elongated carrier (3) comprising a first major surface (31) and a second major surface (32) opposite to the first major surface, an array of a plurality of LEDs (4) configured to, in an on-state, emit LED light (41) and being arranged on the first major surface (31) of the elongated carrier or being arranged in the carrier, an elongated light-converting encapsulant (5) at least partly enclosing the plurality of LEDs and at least partly covering the elongated carrier, the elongated lightconverting encapsulant (5) comprising a luminescent material (52) configured to at least partly convert the LED light (41) into converted light (43), and a transparent layer (6) fully covering the elongated light-converting encapsulant (5), the transparent layer (6) comprising a third major surface (61) and a fourth major surface (62) opposite to the third major surface, wherein the transparent layer (6) comprises a reflective pattern (7), the reflective pattern (7) comprising a plurality of first reflective elements (71) arranged on or at the third major surface (61), and a plurality of second reflective elements (72) arranged on or at the fourth major surface (62), and wherein the reflective pattern (7) is configured to (i) hide the elongated lightconverting encapsulant (5) as perceived by a viewer (8), and (ii) to provide openings (73) configured to transmit the LED filament light (2).

2. A LED filament according to claim 1, wherein the plurality of first reflective elements (71) and the plurality of second reflective elements (72) are configured to providing a coverage of the elongated light-converting encapsulant (5) of at least 70%.

3. A LED filament according to claim 1 or 2, wherein the plurality of first reflective elements (71) and the plurality of second reflective elements (72) are configured to any one of:(i) forming no mutual overlap,(ii) forming a mutual overlap (O), the overlap being at most 30 % of an area of the respective first and second reflective element (71; 72).

4. A LED filament according to any one of the above claims, wherein the plurality of first reflective elements (71) and the plurality of second reflective elements (72) are configured to any one of:(i) providing a coverage of the elongated light-converting encapsulant (5) 100%, and(ii) (A) forming no mutual overlap or (B) forming a mutual overlap (O), the overlap being at most 10 % of an area of the respective first and second reflective element (71; 72).

5. A LED filament according to any one of the above claims, wherein the following applies: the plurality of first reflective elements (71) are arranged (i) on a side of the third major surface (61) facing away from the array of the plurality of LEDs (4), (ii) on a side of the third major surface (61) facing towards the array of the plurality of LEDs (4), or (iii) embedded in the third major surface (61), the plurality of second reflective elements (72) are arranged are arranged (i) on a side of the fourth major surface (62) facing away from the array of the plurality of LEDs (4), (ii) on a side of the fourth major surface (62) facing towards the array of the plurality of LEDs (4), or (iii) embedded in the fourth major surface (62), and the plurality of second reflective elements (72) are arranged (i) on a surface of the elongated light-converting encapsulant (5) opposite to the array of the plurality of LEDs (4), or (ii) at a distance (Y) from the elongated light-converting encapsulant (5), wherein Y < 0.5 mm.

6. A LED filament according to any one of the above claims, wherein one or more of the following applies: one or both of the third major surface (61) and the fourth major surface (62) of the transparent layer (6) is arranged obliquely with respect to a light exit surface (42) of the LEDs of the array of a plurality of LEDs (4), andthe plurality of first reflective elements (71) and / or the plurality of second reflective elements (72) are arranged obliquely with respect to a light exit surface (42) of the LEDs of the array of a plurality of LEDs (4).

7. A LED filament according to any one of the above claims, wherein one or more of the following applies: the plurality of first reflective elements (71) are arranged in any one of a regular pattern and a checkered pattern, and the plurality of second reflective elements (72) are arranged in any one of a regular pattern and a checkered pattern.

8. A LED filament according to any one of the above claims, wherein the reflective pattern (7) has a reflectivity, R, being more than or equal to 90 %.

9. A LED filament according to any one of the above claims, wherein the reflective pattern (7) is diffuse reflective.

10. A LED filament according to any one of the above claims, wherein the transparent layer (6) comprises a thickness (T) being in a range from 0.2 mm to 2 mm.

11. A LED filament according to any one of the above claims, wherein one or more of the following applies: the reflective elements of the plurality of first reflective elements (71) and the reflective elements of the plurality of second reflective elements (72), respectively, comprise an aspect ratio defined as the ratio of a length (L) of the reflective element to a height (Hl; H2) of the reflective element, wherein the aspect ratio is at least 5, and the reflective elements of the plurality of first reflective elements (71) and the reflective elements of the plurality of second reflective elements (72), respectively, comprise a longest dimension being in the range of 0.2 mm to 1 mm and a height (Hl; H2) being in a range from 0.02 mm and 0.2 mm.

12. A LED filament according to any one of the above claims, wherein the plurality of second reflective elements (72) are arranged in a distance (Y) from the elongated light-converting encapsulant (5), wherein the plurality of first reflective elements (71) arearranged in a distance (X) from the plurality of second reflective elements (72), and wherein Y < 0.8 X.

13. A LED filament according to any one of the above claims, wherein one or more of the following applies: the plurality of first reflective elements (71) comprise a length (LI) being in the range of 0.2 mm to 1 mm, the plurality of second reflective elements (72) comprise a length (L2) being in the range of 0.2 mm to 1 mm, an aspect ratio between a length, LI, of the plurality of first reflective elements (71) and a mutual overlap, O, between the plurality of first reflective elements (71) and the plurality of second reflective elements (72), the aspect ratio being defined as Ll / O, is in the range of 10 to 50, a shortest distance (Y) between the plurality of second reflective elements (72) and the elongated light-converting encapsulant (5) is in the range of 0.06 mm to 0.6 mm, and a shortest distance (X) between the plurality of first reflective elements (71) and the plurality of second reflective elements (72) is in the range of 0.2 mm to 1 mm.

14. A LED filament lamp (300) or a luminaire (400) comprising a LED filament (1) according to any one of the preceding claims.

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