A LED filament

Abstract

A light emitting diode, LED, filament (1) configured to provide, in an on-state, LED filament light (2), and comprising an elongated carrier (3) comprising a longitudinal direction (LD), and a two-dimensional array of a plurality of LEDs (4) arranged on a first major surface (31) of the elongated carrier (3), and configured to, in operation, emit LED light (41). The two-dimensional array of a plurality of LEDs (4) comprises N rows of LEDs 5 and M columns of LEDs, where N ≥ 6 and M ≥ 50, and where the N rows of LEDs extend along the longitudinal direction (LD) of the elongated carrier. The two-dimensional array of a plurality of LEDs (4) has an outline having an outline width, W, and an outline length, L, W being in a range from 1 to 6 mm and L being at least 25 mm, and an aspect ratio is defined as L / W is at least 10. The plurality of LEDs comprises a plurality of X direct-emitting red LEDs 10 (4a), each comprising a red die (42a) having a first die surface area, SA1, a plurality of Y direct-emitting green LEDs (4b), each comprising a green die (42b) having a second die surface area, SA2, and a plurality of Z direct-emitting blue LEDs (4c), each comprising a blue die (42c) having a third die surface area, SA3. A coverage of the plurality of LEDs defined as the ratio of the total surface area of the red dies (42a), the green dies (42b) and the 15 blue dies (42c) to the surface area being enclosed by the outline of the two-dimensional array of a plurality of LEDs (4) is in a range from 10 to 40 %. The first die surface area, SA1, the second die surface area, SA2, and the third die surface area, SA3, each have a largest spatial extent, SE, that is less than or equal to 100 micrometers.

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] As used herein, the term “blue light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 420 nm to 490 nm.

[0005] As used herein, the term “green light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 490 nm to 570 nm.

[0006] As used herein, the term “amber light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 570 nm to 620 nm.

[0007] As used herein, the term “red light” is intended to refer to light with a peak wavelength falling within the wavelength interval of 620 to 750 nm.

[0008] BACKGROUND OF THE INVENTION

[0009] 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).

[0010] 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. Alternatively, or additionally, the LEDs may be arranged in the carrier. The elongated carrier may be reflective or light transmissive, such as translucent and preferably transparent.

[0011] In embodiments, the elongated carrier may have a silver or grey appearance.

[0012] As used herein, the terms carrier and elongated carrier may be used interchangeably, such that the elongated carrier may also simply be denoted carrier. 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).

[0013] The LED filament may comprise multiple sub-filaments.

[0014] US 2022 / 0082214 Al discloses a lamp with a tunable white LED filament adapted to emit white light and a RGB LED filament, where the RGB LED filament comprises a plurality of groups, each group comprising a red LED, a green LED and a blue LED, where the tunable white LED filament of the at least one tunable white LED filament comprises first LEDs having a first pre-set correlated color temperature and second LEDs having a second pre-set correlated color temperature lower than the first pre-set correlated color temperature, the first and second pre-set correlated color temperatures defining a subrange of a correlated color temperature range of the color tunable filament lamp, and where the color tunable filament lamp is configured to use the first LEDs and the second LEDs but not the at least one RGB LED filament for target points in the sub-range.

[0015] Hiding the phosphor appearance of such LED filaments is desired. Therefore, phosphor converted LED filaments (pc-LED filaments) covered by a white coating have been proposed. It is nevertheless still desired to improve the appearance and / or efficiency of white LED filaments.

[0016] SUMMARY OF THE INVENTION

[0017] It is an object of the present invention to overcome this problem, and to provide a white LED filament with an improved appearance and / or efficiency.

[0018] 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 provide, in an on-state, LED filament light, the LED filament comprising an elongated carrier comprising a first major surface, a second major surface opposite to the first major surface, and a longitudinal direction, and a two-dimensional array of a plurality of LEDs arranged on the first major surface of the elongated carrier or in the carrier, and configured to, in operation, emit LED light, wherein the two-dimensional array of a plurality of LEDs comprises N rows of LEDs and M columns of LEDs, wherein N > 6 and M > 50, and wherein the N rows of LEDs extend along the longitudinal direction of the elongated carrier, wherein the two-dimensional array of a plurality of LEDs has an outline having an outline width, W, and an outline length, L, wherein W is in a range from 1 to 6 mm and L is at least 25 mm, and wherein an aspect ratio defined as L V is at least 10, wherein the plurality of LEDs of the two-dimensional array of a plurality of LEDs comprises a plurality of X direct-emitting red LEDs, each comprising a red die having a first die surface area, SAI, configured to emit, in operation, red LED light, a plurality of Y direct-emitting green LEDs, each comprising a green die having a second die surface area, SA2, configured to emit, in operation, green LED light and a plurality of Z direct-emitting blue LEDs, each comprising a blue die having a third die surface area, SA3, configured to emit, in operation, blue LED light, X, Y and Z being integers, wherein a coverage of the plurality of LEDs of the two-dimensional array of a plurality of LEDs defined as the ratio of the total surface area of the red dies, the green dies and the blue dies to the surface area being enclosed by the outline of the two-dimensional array of a plurality of LEDs is in a range from 10 to 40 %, and wherein the first die surface area, SAI, has a first largest spatial extent, SEI, that is less than or equal to 100 micrometers, wherein the second die surface area, SA2, has a second largest spatial extent, SE2, that is less than or equal to 100 micrometers, and wherein the third die surface area, SA3, has a third largest spatial extent, SE3, that is less than or equal to 100 micrometers, and wherein in an operational mode the LED filament light is white light.

[0019] By using a LED filament with such red, green and blue LEDs arranged in a two-dimensional array on an elongated carrier as described above, the LED filament will be provided with a silver appearance in the off-state as a relatively low portion of the first major surface of the elongated carrier is covered by LEDs. Furthermore, as efficient direct-emitting and small LEDs are used, such a LED filament also has an improved efficiency.

[0020] The outline length, L, may be at least 30 mm, at least 40 mm or at least 50 mm.

[0021] The first, second and / or third spatial extent may be less than or equal to 90, less than or equal to 80, or less than or equal to 60.

[0022] Thereby the silver appearance of the LED filament in the off-state is improved further.

[0023] The red, green and blue LEDs in the array of LEDs may be arranged such that each red LED is arranged adjacent to at least one or at least two green LEDs and / or at least one or at least two blue LEDs, each green LED is arranged adjacent to at least one or at least two red LEDs and / or at least one or at least two blue LEDs, and each blue LED is arranged adjacent to at least one or at least two green LEDs and / or at least one or at least two red LEDs.

[0024] The LED filament may comprise a translucent encapsulant at least partly enclosing the two-dimensional array of a plurality of LEDs, and at least partly covering the first major surface of the elongated carrier, wherein the LED filament has, in an off-state of the LED filament, a silver or grey appearance.

[0025] Thereby, the silver appearance of the LED filament in the off-state is improved.

[0026] The LED filament may be free from a luminescent material.

[0027] Ensuring that the LED filament does not comprise any luminescent material further improves the silver appearance of the LED filament in the off-state.

[0028] The encapsulant may be transparent and configured to refract or diffract at least a part of the LED light into redirected light, the LED filament light comprising the redirected light.

[0029] Thereby, a LED filament providing a more uniform LED filament light is provided for.

[0030] The elongated carrier may be light-transmissive or transparent.

[0031] Thereby light losses, which may otherwise occur by absorption in the carrier is avoided, which in turn increases the efficiency of the LED filament.

[0032] The LED filament light comprises a first light component having a first intensity, II, and emitted in a first direction away from the first major surface, and a second light component having a second intensity, 12, and emitted in a second direction opposite to the first direction, wherein the ratio between the first intensity of the light component and the second intensity of the second light component may be in a range of 4 to 20, or in a range of 4 to 15, or in a range of 10 to 20, or in a range of 8 to 16.

[0033] Thereby, a LED filament with an improved efficiency is provided for.

[0034] The LED filament may have or comprise micro-LEDs only. It is noted that as used herein, the term “micro-LED” is intended to encompass LEDs with a largest spatial extent, SE, of equal to or less than 100 micrometer, preferably equal to or less than 80 micrometer, more preferably equal to or less than 70 micrometer, most preferably equal to or less than 60 micrometer.

[0035] By using micro LEDs, and especially relatively efficient direct-emitting micro-LEDs, the LED filament is provided with a high efficiency. Each row of the N rows may comprise a plurality of red LEDs, each row of the N rows may comprise a plurality of green LEDs, each row of the N rows may comprise a plurality of blue LEDs, each column of the M columns may comprise a plurality of red LEDs, each column of the M columns may comprise a plurality of green LEDs, and each column of the M columns may comprise a plurality blue LEDs.

[0036] More generally, the plurality of X direct-emitting red LEDs, the plurality ofY direct-emitting green LEDs, and the plurality of Z direct-emitting blue LEDs may be distributed in such a way, for instance as described in the previous paragraph, that the resulting LED filament light is white light without any color effects.

[0037] Thereby, a LED filament is provided with which color effects which may otherwise occur due to the clustering and small size of the LEDs, especially when using micro-LEDs, may be avoided.

[0038] The plurality of red LEDs in each row may be at least 3 or at least 5 red LEDs. The plurality of green LEDs in each row may be at least 3 or at least 5 green LEDs. The plurality of blue LEDs in each row may be at least 3 or at least 5 blue LEDs. The plurality of red LEDs in each column may be at least 20 or at least 30 red LEDs. The plurality of green LEDs in each column may be at least 20 or at least 30 green LEDs. The plurality of blue LEDs in each column may be at least 20 or at least 30 blue LEDs.

[0039] The LED filament light may comprise a luminous emittance, Mv, being at least 100 lumens per square centimeter or at least 200 lumens per square centimeter.

[0040] Thereby, a LED filament is provided with which pixelation which may otherwise be visible at a short distance may be avoided.

[0041] It may be ensured that the integers X, Y, and Z fulfill the relation X > 1.5*Y > 1.5*Z, or X > 2*Y > 2*Z, or X > 2.5*Y > 2.5*Z.

[0042] Thereby, a LED filament capable of providing LED filament light in the form of extreme warm white light may be obtained. This is desired in LED filament applications.

[0043] Each LED of the plurality of X direct-emitting red LEDs comprises a surface area, SAI, each LED of the plurality of Y direct-emitting green LEDs comprises a surface area, SA2, each LED of the plurality of Z direct-emitting blue LEDs comprises a surface area, SA3, and the following relation may be fulfilled: SAI > 2*SA2 > 2*SA3.

[0044] Thereby, a LED filament capable of providing LED filament light in the form of extreme warm white light, for instance in the range of 1700 K to 2700 K, may be obtained.

[0045] One or more of the following may apply:

[0046] W is in a range from 2 to 4 mm and L is at least 40 mm, the aspect ratio defined as LAV is at least 15 or at least 20, and the ratio of the total surface area of the LEDs to the surface area being enclosed by the outline is in a range from 10 to 35 %, or in a range from 15 to 40 %, or in a range from 20 to 30 %.

[0047] Thereby, a LED filament with at least one of a further improved efficiency and a further improved silver appearance in the off-state is provided for.

[0048] One or more of the following may apply:

[0049] N > 7 and M > 60 or N > 8 and M > 70, and the largest spatial extent, SE, is less than or equal to 80 micrometers or less than or equal to 60 micrometers.

[0050] Thereby, a LED filament with a further improved efficiency is provided for. The plurality of LEDs of the two-dimensional array of a plurality of LEDs may further comprise direct-emitting amber LEDs configured to emit, in operation, amber LED light.

[0051] Thereby, LED filament light in the form of white light with a color temperature suitable for mimicking the filament of an incandescent light bulb may be obtained.

[0052] The invention further relates to a LED filament arrangement comprising one or more LED filaments according to any one of the preceding claims and a controller configured to individually control the plurality of X direct-emitting red LEDs, the plurality of Y direct-emitting green LEDs, the plurality of Z direct-emitting blue LEDs, and where provided the direct-emitting amber LEDs.

[0053] The invention further relates to a LED filament lamp comprising a LED filament according to the invention or a LED filament arrangement according to the invention.

[0054] 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.

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

[0056] The invention still further relates to a luminaire comprising a LED filament according to the invention or a LED filament arrangement according to the invention.

[0057] It is noted that the invention relates to all possible combinations of features recited in the claims. 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 schematic top view of a light emitting diode, LED, filament according to the invention.

[0060] Fig. 2 shows a cross-sectional side view of the LED filament according to Fig. 1.

[0061] Fig. 3 shows an enlarged view of the section III in Fig. 1.

[0062] Fig. 4 shows a top view of a section of a LED filament according to the invention and illustrating an exemplary distribution of red, green, and blue LEDs on the LED filament.

[0063] Fig. 5 shows a spectral power distribution illustrating the intensity as a function of the wavelength of LED filament light emitted by a LED filament according to the invention.

[0064] Fig. 6 shows a schematical side view of a lamp comprising a LED filament according to the invention.

[0065] Fig. 7 shows a schematical side view of a luminaire comprising a lamp and a LED filament according to the invention.

[0066] 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.

[0067] DETAILED DESCRIPTION

[0068] 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.

[0069] Referring first to Figs. 1 to 3, a light emitting diode, LED, filament 1 according to the invention is shown. Fig. 1 shows a schematic top view of the LED filament 1, and Fig. 2 shows a cross-sectional side view of the LED filament 1. Fig. 3 shows an enlarged view of a part of the LED filament 1 corresponding to the section III indicated in Fig. 1. Generally, and irrespective of the embodiment, the LED filament 1 comprises an elongated carrier 3 (cf. Figs. 1 and 2), and a two-dimensional array of a plurality of LEDs 4 (cf. Fig. 3). The LED filament 1 is configured to provide, in operation, LED filament light 2 (cf. Fig. 2). In one operational mode, the LED filament light 2 is white light.

[0070] As is best seen in Fig. 2, the elongated carrier 3 comprises a first major surface 31 and a second major 32. The second major surface 32 is opposite to the first major surface 31. The elongated carrier 3 further comprises a longitudinal direction, LD, cf. Figs. 1 and 3.

[0071] The two-dimensional array of a plurality of LEDs 4 is arranged on the first major surface 31 of the elongated carrier 3. The two-dimensional array of a plurality of LEDs 4 is configured to, in operation, emit LED light 41 (cf. Fig. 2). Referring specifically to Fig. 3, the two-dimensional array of a plurality of LEDs 4 comprises N rows of LEDs and M columns of LEDs. N and M are positive integers. N and M are chosen such that N > 6 and M > 50. Alternatively, N and M may be chosen such that, for instance, N > 7 and M > 60 or N > 8 and M > 70. The N rows of LEDs extend along the longitudinal direction, LD, of the elongated carrier 3.

[0072] The two-dimensional array of a plurality of LEDs 4 comprises an outline. The outline has an outline width, W, (cf. Fig. 2) and an outline length, L, (cf. Fig. 1). The outline width, W, is chosen to be in a range from 1 to 6 mm or in a range from 2 to 4 mm. The outline length, L, is chosen to be at least 25 mm, at least 30 mm, at least 40 mm, or at least 50 mm. An aspect ratio is defined as LAV and is chosen to be at least 10, at least 15 or at least 20.

[0073] A coverage of the plurality of LEDs of the two-dimensional array of a plurality of LEDs 4 of the LED filament 1 is defined as the ratio of the total surface area of the LEDs to the surface area being enclosed by the outline of the two-dimensional array of a plurality of LEDs 4. The coverage is in a range from 10 to 40 %, in a range from 15 to 35 % or in a range from 20 to 30 %.

[0074] Furthermore, each LED of the two-dimensional array of a plurality of LEDs 4 of the LED filament 1 comprises a surface area, SA. Referring also to Fig. 3, assuming the surface of each LED is approximately rectangular, the surface area, SA, may be defined as the product of a length, LL, of the LED and a width, WL, of the LED. The surface area, SA, comprises a largest spatial extent, SE, where the largest spatial extent, SE is less than or equal to 100 micrometers (pm). Alternatively, the largest spatial extent, SE, may be less than or equal to 90 micrometers or less than or equal to 80 micrometers, or less than or equal to 60 micrometers. At least some of the plurality of LEDs of the two-dimensional array of a plurality of LEDs 4 of the LED filament 1 may be micro-LEDs.

[0075] Referring specifically to Fig. 2 showing a cross-sectional side view of a section of a LED filament 1 according to the invention, the plurality of LEDs of the two- dimensional array of a plurality of LEDs 4 of the LED filament 1 comprises a plurality of red LEDs 4a, green LEDs 4b, and blue LEDs 4c, respectively. The plurality of LEDs of the two- dimensional array of a plurality of LEDs 4 comprises a plurality of X direct-emitting red LEDs 4a configured to emit, in operation, red LED light 41a, a plurality of Y direct-emitting green LEDs 4b configured to emit, in operation, green LED light 41b and a plurality of Z direct-emitting blue LEDs 4c configured to emit, in operation, blue LED light 41c. X, Y and Z are each a positive integer. X, Y and Z may be chosen to fulfill the relation X > 1.5*Y > 1.5*Z. Alternatively, may be chosen to fulfill the relation X > 2*Y > 2*Z, or the relation X > 2.5*Y > 2.5*Z.

[0076] The plurality of X direct-emitting red LEDs 4a, the plurality ofY direct- emitting green LEDs 4b, and the plurality of Z direct-emitting blue LEDs 4c may be distributed in such a way that the resulting LED filament light 2 is white light without any color effects. The plurality of X direct-emitting red LEDs 4a each comprise a red die 42a having a first die surface area, SAL The plurality of X direct-emitting red LEDs 4a are configured to emit, in operation, red LED light 41a. The plurality of Y direct-emitting green LEDs 4b each comprise a green die 42b having a second die surface area, SA2. The plurality of X direct-emitting green LEDs 4b are configured to emit, in operation, green LED light 41b. The plurality of Z direct-emitting blue LEDs 4c each comprise a blue die 42c having a third die surface area, SA3. The plurality of X direct-emitting blue LEDs 4c are configured to emit, in operation, blue LED light 41c. The surface areas SAI, SA2, and SA3 may be chosen such as to fulfill the relation SAI > 2*SA2 > 2*SA3. It is also feasible that the surface areas SAI, SA2, and SA3 may be chosen such as to fulfill the relation SAI > 1.5*SA2 > 1.5*SA3 or the relation SAI > SA2 > SA3. The first die surface area, SAI, has a first largest spatial extent, SEI, that is less than or equal to 100 micrometers. The second die surface area, SA2, has a second largest spatial extent, SE2, that is less than or equal to 100 micrometers. The third die surface area, SA3, has a third largest spatial extent, SE3, that is less than or equal to 100 micrometers. Alternatively, the respective largest spatial extent, SEI, SE2 and SE3, may be less than or equal to 90 micrometers or less than or equal to 80 micrometers or less than or equal to 60 micrometers. The coverage of the plurality of LEDs of the two-dimensional array of a plurality of LEDs 4 may be defined as the ratio of the total surface area of the red dies 42a, the green dies 42b and the blue dies 42c to the surface area being enclosed by the outline of the two-dimensional array of a plurality of LEDs 4. As mentioned above, the coverage is in a range from 10 to 40 %, in a range from 15 to 35 % or in a range from 20 to 30 %.

[0077] As shown in Fig. 2, the plurality of LEDs of the two-dimensional array of a plurality of LEDs 4 may further optionally comprise direct-emitting amber LEDs 4d. The direct-emitting amber LEDs 4d are configured to emit, in operation, amber LED light 4 Id. In such a case, the LED filament light 2 further comprises the amber LED light 41b.

[0078] As is illustrated in Fig. 1, the LED filament 1 may form part of a LED filament arrangement 100. The LED filament arrangement 100 comprises one or more LED filaments 1 (in Fig. 1 simply one) according to the invention. The LED filament arrangement 100 further comprises a controller 6. The controller 6 is configured to individually control the plurality of X direct-emitting red LEDs 4a, the plurality of Y direct-emitting green LEDs 4b, and the plurality of Z direct-emitting blue LEDs 4c. Where direct-emitting amber LEDs 4d are provided, the controller 6 is further configured to individually control the direct-emitting amber LEDs 4d. Alternatively, or additionally, the LED filament arrangement 100 may comprise a driver. The driver may be configured to provide power and / or adapt current and / or voltage of the LED filament arrangement 100. The driver and the controller 6 may be separate units or integrated into one and the same unit. Alternatively, or additionally, the LED filament arrangement 100 may comprise an antenna for wireless control of the of the controller 6, for instance using a suitable interface.

[0079] The LED filament 1 may be free from a luminescent material. The LED filament 1 may comprise an optional encapsulant 5 as shown on Figs. 1 and 2. The encapsulant 5 at least partly encloses the two-dimensional array of a plurality of LEDs 4. The encapsulant 5 at least partly covers the first major surface 31 of the elongated carrier 3. The encapsulant 5 may be an elongated encapsulant. The encapsulant 5 may be transparent. Alternatively, or additionally, the encapsulant 5 may be configured to diffuse at least a part of the LED light 41 into diffuse light. To this end the encapsulant 5 may comprise a diffusing material or diffusing structures. Alternatively, or additionally, the encapsulant 5 may be configured to convert at least a part of the LED light 41 into converted light. To this end, the encapsulant 5 may comprise a light converting material or light converting particles, such as for instance a phosphor. In the off-state of the LED filament 1, the encapsulant has a grey or silver colored appearance. The encapsulant 5 may be transparent. The encapsulant 5 may further be configured to refract or diffract at least a part of the LED light 41 into redirected light. In such a case the LED filament light 2 comprises the redirected light. To this end the encapsulant may comprise refractive or diffractive surface structures, particles, or embedded structures.

[0080] Referring specifically to Fig. 2, the LED filament light 2 comprises a first light component 21 having a first intensity, II, and emitted in a first direction away from the first major surface 31, and a second light component 22 having a second intensity, 12, and emitted in a second direction opposite to the first direction. The ratio between the first intensity II of the first light component 21 and the second intensity 12 of the second light component 22 may be in a range of 4 to 20.

[0081] The elongated carrier 3 may be light-transmissive. The elongated carrier 3 may also be transparent. This allows for the LED filament light 2 to comprise two light components 21 and 22 as shown in Fig. 2. A first light component 21 is emitted in a first direction. The first direction is a direction away from the first major surface 31 and through the encapsulant 5. The first direction may correspond to a main emission direction of the LEDs 4. A second light component 22 is emitted in a second direction. The second direction is a direction being opposite to the first direction. The ratio between the first light component and the second light component may be chosen to be in a range of 4 to 20. The LED filament light 2 comprises a luminous emittance, Mv. The luminous emittance, Mv, may be being at least 100 lumens per square centimeter.

[0082] Fig. 4 illustrates one exemplary distribution of red LEDs 4a, green LEDs 4b, and blue LEDs 4c on the LED filament 1. In this configuration, each row of the N rows comprises a plurality of red LEDs 4a, each row of the N rows comprises a plurality of green LEDs 4b, and each row of the N rows comprises a plurality of blue LEDs 4c. Furthermore, each column of the M columns comprises a plurality of red LEDs 4a, each column of the M columns comprises a plurality of green LEDs 4b, and each column of the M columns comprises a plurality blue LEDs 4c.

[0083] In a further example, the red LEDs 4a, green LEDs 4b and blue LEDs 4c in the array of LEDs 4 may be arranged such that each red LED 4a is arranged adjacent to at least one or at least two green LEDs 4b and / or at least one or at least two blue LEDs 4c, each green LED 4b is arranged adjacent to at least one or at least two red LEDs 4a and / or at least one or at least two blue LEDs 4c, and each blue LED 4c is arranged adjacent to at least one or at least two green LEDs 4b and / or at least one or at least two red LEDs 4a.

[0084] Referring now to Fig. 5, a graph in the form of a power distribution is shown. The graph illustrates the intensity as a function of the wavelength of LED filament light 2 emitted by a LED filament 1 with a distribution of red LEDs 4a, green LEDs 4b, and blue LEDs 4c as shown in Fig. 4.

[0085] As may be seen the LED filament light 2 thus obtained has a peak emission wavelength of slightly above 600 nm. Such a distribution results in LED filament light 2 being white light without any color effects. By using such a LED filament 1 with microLEDs, the LED filament 1 will have a silver appearance in the off-state as a relatively low portion of the first major surface of the elongated carrier is covered by LEDs 4, 4a, 4b, 4c. In addition, as efficient direct-emitting micro-LEDs are used, the LED filament has a high efficiency.

[0086] Fig. 6 shows an exemplary lamp 300 comprising a LED filament 1 according to any embodiment of the invention. In the embodiment shown, the LED filament 1 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, spiralshaped, helix-shaped, meandering, twisted, flat and combinations thereof.

[0087] The lamp 300 further comprises a driver or controller 305 configured for controlling the plurality of LEDs 4 of the LED filament 1. 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. The LED filament 1 may also form part of a LED filament arrangement 100 comprising a controller 6, which may or may not be separate from the controller 305. In other words, the controller 305 and the controller 6 may be integrated into one and the same driver or controller, or they may be mutually separate units.

[0088] The lamp 300 further comprises an envelope 301 at least partially enveloping the at least one LED filament 1. The lamp 300 further comprises a cap 303. As shown in Fig. 6, 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.

[0089] 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.

[0090] Turning finally to Fig. 7, another exemplary luminaire in the form of a pendant 400 is shown. The pendant 400 comprises a LED filament 1 according to any embodiment of the invention. The LED filament 1 is as shown in Fig. 6 provided within a lamp 300 in the form of a light bulb. The LED filament 1 as shown in Fig. 7 comprises a substantially straight LED filament.

[0091] 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. 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.

[0092] The pendant 400 further comprises a socket 401 for connecting the lamp 300, and thereby the LED filament 1, 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.

[0093] The pendant 400 may further comprise a driver 402 configured for controlling the LED filament 1. 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 may form part of a LED filament arrangement 100 comprising a controller 6, which may or may not be separate from one or both of the driver 402 and the controller 305.

[0094] As shown in Fig. 7, 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.

[0095] It is noted that the pendant 400 shown in Fig. 7 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.

[0096] 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. 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 provide, in an on-state,LED filament light (2), the LED filament comprising: an elongated carrier (3) comprising a first major surface (31), a second major (32) surface opposite to the first major surface, and a longitudinal direction (LD), and a two-dimensional array of a plurality of LEDs (4) arranged on the first major surface (31) of the elongated carrier or arranged in the carrier, and configured to, in operation, emit LED light (41), wherein the two-dimensional array of a plurality of LEDs (4) comprises N rows of LEDs and M columns of LEDs, wherein N > 6 and M > 50, and wherein the N rows of LEDs extend along the longitudinal direction (LD) of the elongated carrier; wherein the two-dimensional array of a plurality of LEDs (4) has an outline having an outline width (W) and an outline length (L) wherein W is in a range from 1 to 6 mm and L is at least 25 mm, and wherein an aspect ratio defined as LAV is at least 10, wherein the plurality of LEDs of the two-dimensional array of a plurality of LEDs (4) comprises a plurality of X direct-emitting red LEDs (4a), each comprising a red die (42a) having a first die surface area, SAI, configured to emit, in operation, red LED light (41a), a plurality of Y direct-emitting green LEDs (4b) , each comprising a green die (42b) having a second die surface area, SA2, configured to emit, in operation, green LED light (41b) and a plurality of Z direct-emitting blue LEDs (4c), each comprising a blue die (42c) having a third die surface area, SA3, configured to emit, in operation, blue LED light (41c), X, Y and Z being integers, wherein a coverage of the plurality of LEDs of the two-dimensional array of a plurality of LEDs (4) defined as the ratio of the total surface area of the red dies (42a), the green dies (42b) and the blue dies (42c) to the surface area being enclosed by the outline of the two-dimensional array of a plurality of LEDs (4) is in a range from 10 to 40 %, and wherein the first die surface area, SAI, has a first largest spatial extent, SEI, that is less than or equal to 100 micrometers, wherein the second die surface area, SA2, has a second largest spatial extent, SE2, that is less than or equal to 100 micrometers, and whereinthe third die surface area, SA3, has a third largest spatial extent, SE3, that is less than or equal to 100 micrometers; and wherein in an operational mode the LED filament light is white light.

2. A LED filament according to claim 1, wherein the LED filament (1) comprises an encapsulant (5) at least partly enclosing the two-dimensional array of a plurality of LEDs (4), and at least partly covering the first major surface (31) of the elongated carrier (3); and wherein the LED filament (1) has, in an off-state of the LED filament, a silver or grey appearance.

3. A LED filament according to claim 1 or 2, wherein the LED filament (1) is free from a luminescent material.

4. A LED filament according to claim 2 or 3, wherein the encapsulant (5) is transparent and configured to refract or diffract at least a part of the LED light (41) into redirected light, and wherein the LED filament light comprises the redirected light.

5. A LED filament according to any one of the above claims, wherein the elongated carrier (3) is light-transmissive, or transparent.

6. A LED filament according to any one of the above claims, wherein the LED filament light (2) comprises a first light component (21) having a first intensity, II, and emitted in a first direction away from the first major surface (31), and a second light component (22) having a second intensity, 12, and emitted in a second direction opposite to the first direction, and wherein the ratio between the first intensity of the first light component and the second intensity of the second light component is in a range of 4 to 20.

7. A LED filament according to any one of the above claims, wherein the LED filament only has micro-LEDs.

8. A LED filament according to any one of the above claims, wherein each row of the N rows comprises a plurality of red LEDs, wherein each row of the N rows comprises a plurality of green LEDs, wherein each row of the N rows comprises a plurality of blue LEDs, wherein each column of the M columns comprises a plurality of red LEDs, whereineach column of the M columns comprises a plurality of green LEDs, and, wherein each column of the M columns comprises a plurality blue LEDs.

9. A LED filament according to any one of the above claims, wherein the LED filament light (2) comprises a luminous emittance, Mv, being at least 100 lumens per square centimeter.

10. A LED filament according to any one of the above claims, wherein X > 1.5*Y > 1.5*Z.

11. A LED filament according to any one of the above claims, wherein SAI > 2-SA2 > 2-SA3.

12. A LED filament according to any one of the above claims, wherein the plurality of LEDs of the two-dimensional array of a plurality of LEDs (4) further comprise direct-emitting amber LEDs (4d) configured to emit, in operation, amber LED light (4 Id).

13. A LED filament arrangement, comprising one or more LED filaments according to any one of the preceding claims and a controller (6) configured to individually control the plurality of X direct-emitting red LEDs (4a), the plurality ofY direct-emitting green LEDs (4b), the plurality of Z direct-emitting blue LEDs (4c), and where provided the direct-emitting amber LEDs (4d).

14. A LED filament lamp (300) comprising a LED filament (1) according to any one of claims 1-12 or a LED filament arrangement (100) according to claim 13, and further comprising (i) a light transmissive envelope (301) at least partly enclosing the LED filament (1) and (ii) a base (303) for electrically and mechanically connecting the LED filament lamp to a socket or a socket of a luminaire.

15. A luminaire (400) comprising a LED filament lamp (300) according to claim 14, or comprising a LED filament (1) according to any one of claims 1-12, or comprising a LED filament arrangement (100) according to claim 13.

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