Addressing in LED filament

Abstract

A LED filament (1) comprises an elongated carrier (20), a two-dimensional array of a plurality of LEDs (32), a first elongated encapsulant (50) and a matrix driving circuit (40). The two-dimensional array comprises N≥2 rows (36) of LEDs and M≥10 columns (34) of LEDs. The first elongated encapsulant covers the plurality of LEDs and comprises a luminescent material and / or a light scattering material to convert LED light into converted light and / or scatter LED light into scattered light, forming the LED filament light. The matrix driving circuit comprises rows and columns of LED electrodes and a plurality of LED switches (46) connected to the LED electrodes. Each LED being switched by a respective LED switch. The LED filament light is white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 70.

Description

[0001] Addressing in LED filament

[0002] FIELD OF THE INVENTION

[0003] The present invention generally relates to light emitting diode, LED, filaments. More specifically, the present invention is related to arrangements for addressing of LED filaments and luminaire devices comprising such arrangements.

[0004] BACKGROUND OF THE INVENTION

[0005] The use of light emitting diodes (LED) for illumination purposes continues to attract attention. A trend in lighting is LED filament lamps. An LED filament lamp is an LED lamp which is designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of lightemitting diodes. Compared to incandescent lamps, fluorescent lamps, neon tube lamps, etc., LEDs provide numerous advantages such as a longer operational life, a reduced power consumption, and an increased efficiency related to the ratio between light energy and heat energy. In particular, LED filament lamps are highly appreciated as they are very decorative.

[0006] Due to the advantageous aspects of the use of LEDs, the interest has rapidly increased to replace conventional light sources with LEDs in many lighting arrangements. It will be appreciated that this replacement, also called retrofitting, is appreciated and desired by users who wish to have the look of an incandescent bulb. The light source replacement (retrofitting) is often performed by removing the conventional light source(s) from the luminaire (e.g. a lamp holder) of the lighting arrangement and attaching the LEDs, LED arrangement(s) or LED device(s) into the luminaire. One of these concepts is based on LED filaments which are placed in a bulb, as the appearance of lamps of this kind are appreciated as they are highly decorative.

[0007] Hence, it is an object of the present invention to overcome at least some complexity and / or operational issues regarding efficiency characteristics and / or safety. It is desired to improve the performance, functionality and / or appearance of LED filament lamps.

[0008] US 2022 / 390074 discloses a LED filament lamp which provides LED filament lamp light. The LED filament comprises a first linear array of LEDs and a second linear array of LEDs, and a carrier. The first linear array of LEDs are arranged on a first surface of the carrier and includes only first LEDs which are configured to emit first white light. The second linear array of LEDs are arranged on a second surface of the carrier, opposite to said first surface, and includes only second LEDs which are configured to emit color controllable light. The LED filament light comprises the first white light and / or the color controllable light.

[0009] SUMMARY OF THE INVENTION

[0010] It is of interest to combine the advantageous properties of LEDs with respect to energy efficiency with light distribution functionality and / or aesthetics appearance.

[0011] This and other objects are achieved by providing a LED filament having the features in the independent claims, respectively. Preferred embodiments are defined in the dependent claims.

[0012] Hence, according to a first aspect of the present invention, there is provided a LED filament, configured to emit, in operation, LED filament light. The LED filament comprises an elongated carrier, a two-dimensional array of a plurality of LEDs, a first elongated encapsulant and a matrix driving circuit. The two-dimensional array of a plurality of LEDs is arranged on or in a first major surface of the elongated carrier. This first major surface is as usual the top surface of the carrier on or in which the LEDs are arranged or mounted. Opposite to the ‘top’ surface the carrier is the ‘bottom’ surface, referred to as second major surface. The ‘top’ and ‘bottom’ surface are connected by the sides surfaces. The plurality of LEDs are configured to, in operation, emit LED light. The two-dimensional array comprises N rows of LEDs and M columns of LEDs, wherein N > 2 and M > 10, and wherein the N rows of LEDs extend along an elongation direction of the elongated carrier. The first elongated encapsulant covers the plurality of LEDs and at least part of the first major surface. The first elongated encapsulant comprises a first luminescent material and / or a first light scattering material. The first luminescent material is configured to at least partly convert LED light into first converted light. The first light scattering material is configured to scatter at least part of the LED light into first scattered light. The matrix driving circuit comprising X rows of LED electrodes, Y column of LED electrodes and a plurality of Z LED switches. Each LED switch of the plurality of LED switches is electrically connected to at least one row LED electrode and at least one column LED electrode. Each LED of the plurality of LEDs is electrically connected to a LED switch of the plurality of LED switches. The LED filament light comprises the first converted light and / or the first scattered light. The LED filament light may be white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 70, but it also may be colored light.

[0013] This aspect of the present invention is advantageous in that the two- dimensional array of the plurality of LEDs may be controlled in an efficient manner in dependence of the geometrical shape in order to give required emission in different directions within a user product. The present invention is thereby advantageous concerning both for energy efficiency and light distribution possibilities.

[0014] According to one embodiment of the present invention, the matrix driving circuit is an active matrix driving circuit. Each LED switch of the plurality of Z LED switches comprises a transistor and a capacitor. By this, the LED filament is configured to actively maintain a LED in an on-state while other LEDs are being addressed.

[0015] According to one embodiment of the present invention, M > 20N, preferably M > 30N, more preferably M > 40N and most preferably M > 50N. The two-dimensional array has thereby a high aspect ratio. In particular embodiments, aspect ratios of 9: 100 or higher are feasible. The LED filament may thereby be given a shape resembling incandescent lamps.

[0016] According to one embodiment of the present invention, N may be at least 5, preferably at least 8, more preferably at least 10, most preferably at least 12.

[0017] According to one embodiment of the present invention, the elongated carrier is a light transmissive carrier e.g. translucent such as transparent. The LED filament further comprises a second elongated encapsulant covering at least part of a second major surface of the elongated carrier. The second major surface is opposite to the first major surface. The second elongated encapsulant comprises a second luminescent material and / or a second light scattering material. The second elongated encapsulant is configured to at least partly convert LED light and / or first converted light into second converted light. The second light scattering material is configured to scatter at least part of the LED light and / or the first scattered light into second scattered light. The LED filament light comprises the second converted light and / or the second scattered light. In this way, spottiness may be reduced.

[0018] According to one further embodiment of the present invention, there are three options for modifying the different light properties. One or more of these options can be applied. In a first option, the first luminescent material has a first concentration in the first elongated encapsulant, and the second luminescent material has a second concentration, different from the first concentration, in the second elongated encapsulant. In a second option, the first luminescent material is a first phosphor type, and the second luminescent material is a second phosphor type, different from the first phosphor type. In a third option the first elongated encapsulant has a first thickness, and the second elongated encapsulant has a second thickness, different from the first thickness. This gives various possibilities to vary the light properties between the two encapsulants.

[0019] According to one embodiment of the present invention, there are two options for combining encapsulants and LEDs. In a first option, the first elongated encapsulant comprises the first luminescent material, and the plurality of LEDs comprises blue LEDs configured to, in operation, emit blue light having a peak emission wavelength in a wavelength range of 430-470 nm. In a second option, the first elongated encapsulant comprises the first light scattering material, and the plurality of LEDs comprises red LEDs configured to, in operation, emit red light having a peak emission wavelength in a wavelength range of 600-690 nm, green LEDs configured to, in operation, emit green light having a peak emission wavelength in a wavelength range of 500-590 nm and blue LEDs configured to in operation, emit blue light having a peak emission wavelength in a wavelength range of 430-490 nm.

[0020] According to another embodiment of the present invention, the first elongated encapsulant comprising the first luminescent material, and the plurality of LEDs comprises red LEDs configured to emit, in operation, red light having a peak emission wavelength in a wavelength range of 600-690 nm and blue LEDs configured to emit, in operation, blue light having a peak emission wavelength in a wavelength range of 430-490 nm, but where the LED filament is free from green LEDs configured to emit, in operation, green light having a peak emission wavelength in wavelength range of 500-590 nm. These options make advantageous use of the properties of the LEDs. The combination of blue LEDs and first luminescent material may provide white light especially white light having a correlated color temperature in a range from 3300K to 2000K. By combining the latter combination with red LEDs emitting red light, the correlated color temperature of the LED filament light can be varied e.g. from a higher correlated color temperature to a lower correlated color temperature (e.g. a correlated color temperature difference of at least 500K may be obtained.

[0021] According to one embodiment of the present invention, each LED of the plurality of LEDs comprises a die having a surface area. The surface area has a largest spatial extent that is less than or equal to 100 micrometers. Utilizing micro-LEDs enables an increased diversity of the light properties over the surfaces of the LED filament. According to one embodiment of the present invention, the first major surface of the elongated carrier has a carrier surface area. The carrier surface area comprises a covered surface area being covered by the plurality of LEDs and the plurality of Z LED switches (and the X row LED electrodes and the Y column LED electrodes), and an uncovered surface area. The uncovered surface area is in a range of (50% to 90% or) 55% to 85% of the carrier surface area. The obtained effect is high reflection or high transmission of LED light and / or first converted / scattered light by the elongated carrier. In case the elongated carrier is reflective, its uncovered surface area has a higher reflectivity than the covered surface area, and thus a higher percentage of uncovered surface area results in a LED filament having a higher efficiency (due to less absorption). In case the elongated carrier is light-transmissive (e.g. translucent such as transparent), a higher percentage of uncovered surface area results in more transmission of LED light and / or first converted / scattered light through said elongated carrier, thus the ratio between the LED filament light emitted in a direction away from the first major surface and the LED filament light emitted in a direction away from the second major surface is lower. The latter is preferred because the omnidirectional light distribution is improved.

[0022] According to one embodiment of the present invention, the elongated carrier has a 3D spiral-shape, preferably having at least 2 loops or at least 3 loops.

[0023] According to a second aspect of the present invention, there is provided a LED filament arrangement. The LED filament arrangement comprises a LED filament according to the first aspect and a driver. The driver comprises a source driver and a gate driver. The driver is configured for switching the plurality of Z LED switches and powering the plurality of LEDs.

[0024] According to one embodiment of the present invention, the driver and LED filament are configured to generate pixelated LED filament light. The pixelated LED filament light is at least one of the following: (i) a gradient in intensity over the elongation direction of the elongated carrier, (ii) a gradient in correlated color temperature over the elongation direction of the elongated carrier, (iii) a text, logo or picture over the elongation direction of the elongated carrier. Such embodiments utilizes the elongated shape of the LED filament for providing visible effects. Preferably, the pixelated LED filament light may be varied as function of time. More preferably, the gradient in intensity over the elongation direction of the elongated carrier, the gradient in correlated color temperature over the elongation direction of the elongated carrier and / or the text, logo or picture over the elongation direction of the elongated carrier may be varied as function of time. According to one embodiment of the present invention, the driver and LED filament are configured to generate pixelated LED filament light, wherein the pixelated LED filament light may be changed from first pixelated LED filament light into second pixelated LED filament different from the first pixelated LED filament light.

[0025] According to one embodiment of the present invention, the LED filament arrangement further comprises a multichannel connector and the driver is connected to the LED filament using the multichannel connector. The LED filament further comprises electrically conductive pads wherein the multichannel connector is connecting the LED filament at the electrically conductive pads. Preferably, the electrically conductive pads are arranged at an elongated side of the LED filament. This is an advantageous practical solution, utilizing the elongated shape.

[0026] According to one embodiment of the present invention, the driver is arranged on the elongated carrier. Preferably, the driver is arranged at an outer end of the elongated carrier. This has the advantage of enabling the LED filament to be narrow.

[0027] According to a third aspect of the present invention, there is provided a LED filament lamp. The LED filament lamp comprises a LED filament according to the first aspect or a LED filament arrangement according to the second aspect. The LED filament lamp further comprises a light-transmissive tube or a light-transmissive envelope, and a connector. The light-transmissive tube or the light-transmissive envelope encloses the LED filament, at least partly. The connector is provided for electrically and mechanically connecting the LED filament lamp to a socket of a luminaire.

[0028] Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] 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.

[0031] Fig. 1 schematically illustrates parts of a LED filament according to an exemplifying embodiment of the present invention,

[0032] Fig. 2 schematically illustrates a matrix driving circuit for a LED filament according to an exemplifying embodiment of the present invention, Figs. 3A-B schematically illustrates cross-sectional views of LED filaments with an encapsulant according to exemplifying embodiments of the present invention,

[0033] Fig. 4 schematically illustrates emission spectra for different LEDs,

[0034] Figs. 5A-B schematically illustrates cross-sectional views of LED filaments with double encapsulants according to exemplifying embodiments of the present invention,

[0035] Fig. 6 schematically illustrates a LED filament arrangement according to an exemplifying embodiment of the present invention,

[0036] Fig. 7 illustrates covered and non-covered surface areas of a LED filament according to exemplifying embodiments of the present invention,

[0037] Figs. 8A-B schematically illustrates geometrical shapes of LED filaments according to exemplifying embodiments of the present invention,

[0038] Figs. 9A-C schematically illustrates pixelated LED according to exemplifying embodiments of the present invention, and

[0039] Fig. 10 schematically illustrates a LED filament lamp according to an exemplifying embodiment of the present invention.

[0040] DETAILED DESCRIPTION

[0041] In order to provide attractive decorative lighting elongated filaments are advantageous. This shape enables the visible conditions to be modified along the filament according to different requests. A single row of LEDs may give possibilities to give a modified light appearance along the row, but is still somewhat limited. It is instead proposed to use display technology and matrix addressing of LEDs in a LED filament for decorative lighting.

[0042] Figure 1 illustrates schematically a LED filament 10, configured to emit, in operation, LED filament light. The LED filament 10 comprises an elongated carrier 20, and a two-dimensional array 30 of a plurality of LEDs 32. The plurality of LEDs 32 are configured to, in operation, emit LED light, The two-dimensional array 30 is arranged on a first major surface 21 of the elongated carrier 20. The two-dimensional array 30 comprises N rows of LEDs 36 and M columns of LEDs 34, wherein N > 2 and M > 10. The N rows of LEDs 36 extend along an elongation direction 25 of the elongated carrier 20.

[0043] In a preferred embodiment M > 20N, preferably M > 3 ON, more preferably M > 40N and most preferably M > 50N. This gives an elongated LED filament 10 shape, which opens up for many different adaptations of light properties along this elongated structure. This geometry is in great contrast to a display, a LED filament has a much higher aspect ratio. Whereas displays typically have an aspect ratio of about 3:4, LED filaments have an aspect ratio of 1 : 100 and a width W <4mm.

[0044] The LED filament 10 further comprises a matrix driving circuit 40. The matrix driving circuit 40 comprises a plurality of Z LED switches 46.

[0045] The LED filament 10 further comprises a first elongated encapsulant 50 covering the plurality of LEDs 32 and at least part of the first major surface 21. The first elongated encapsulant 50 comprises one or both of a first luminescent material and a first light scattering material. The first luminescent material is configured to at least partly convert LED light into first converted light. The first luminescent material may comprise e.g. a green-yellow phosphor and red phosphor. The first light scattering material is configured to scatter at least part of the LED light into first scattered light. The LED filament light comprises the first converted light and / or the first scattered light. The LED filament light is white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 70.

[0046] Figure 2 schematically illustrates an embodiment of a matrix driving circuit 40 more in detail. The matrix driving circuit 40 comprising X row LED electrodes 44, Y column LED electrodes 45 and a plurality of Z LED switches 46. Each LED switch 47 of the plurality of LED switches 46 is electrically connected to at least one row LED electrode 44 and at least one column LED electrode 45. Each LED 31 of the plurality of LEDs 32 is electrically connected to a LED switch 47 of the plurality of LED switches 46.

[0047] Typically, the number of row LED electrodes 44 corresponds to the number N of rows of LEDs 36, and the number of column LED electrodes 45 corresponds to the number M columns of LEDs 34. However, this is not a necessity and other relations between rows of LED electrodes 44 and rows of LEDs 36 may be used as well as other relations between columns of LED electrodes 45 and columns of LEDs 43. Row LED electrodes 44 are often also referred to as gate electrodes and column LED electrodes 45 are often referred to as source electrodes.

[0048] The matrix driving circuit 40 may in a general case be a passive or an active matrix driving circuit 41. The particular embodiment illustrated in Figure 2 shows the matrix driving circuit 40 being an active matrix driving circuit 41. Each LED switch 47 of the plurality of Z LED switches 46 comprises a transistor 48 and a capacitor 49. Active matrix driving of LEDs is done by delivering voltage / current pulses to individual LEDs 31 which are placed on an active matrix substrate. In this way, the LED filament becomes configured to actively maintain a LED in an on-state while other LEDs are being addressed. The active- matrix design is preferred, since it is more beneficial for power consumption, cost and visual image quality (e.g. brightness) compared to a passive-matrix design in which pixels are only activated during a short period.

[0049] The use of micro-LEDs is preferred and gives advantages in reducing spottiness and enabling more diversative light properties over the surface of the LED filament. In such embodiments, it is preferred that each LED 31 of the plurality of LEDs 32 comprises a die having a surface area. The surface area has a largest spatial extent that is less than or equal to 100 micrometers. MicroLEDs are currently applied in e.g. displays, which have completely differing demands of control.

[0050] The encapsulant may be advantageous in several respects. It reduces the spottiness of the original LED light. It can also be used for modifying the light leaving the LED filament. Figure 3 A illustrates schematically a cross-section of an embodiment of a LED filament 10 having an encapsulant 50 comprising a first luminescent material 51. The first luminescent material 51 is in the figure for illustration purposes illustrated as a concentrated volume, however, in reality, the first luminescent material 51 is spread throughout the entire encapsulant 50. A LED 31 emits, when operated, LED light 60. This LED light 60 has a certain wavelength distribution depending on the type of LED. The LED light 60 interacts with the luminescent material 51, resulting in that LED light 60 is at least partly converted into first converted light 61. The LED filament light 65 leaving encapsulant 50 of the LED filament 10 thereby at least party comprises first converted light 61.

[0051] In a particular embodiment, the plurality of LEDs comprises blue LEDs 31 configured to, in operation, emit blue light having a peak emission wavelength in a wavelength range of 430-470 nm.

[0052] LED colors are typically categorized in terms of blue, green and red. Figure 4 schematically illustrates emission spectra from three different LEDs. A first LED, referred to as a blue LED, emits light with a peak emission wavelength I in the wavelength range of 430-490 nm. A second LED, referred to as a green LED, emits light with a peak emission wavelength X2 in the wavelength range of 500-590 nm. A third LED, referred to as a red LED, emits light with a peak emission wavelength X3 in the wavelength range of 600-690 nm. By combining such LEDs, different light properties can be obtained.

[0053] Optionally, next to red, green and blue LEDs, extreme-warm white phosphor converted pixels may be added. The extreme-warm white pixels may have a correlated color temperature of e.g. <2300K. This may be achieved using blue LEDs covered with a green- yellow and red phosphor. Such design may provide white light having a CRI of at least 80 especially at least 90.

[0054] LED filaments may comprise red, green and blue pixels, but there might also be additional pixels for white light. A LED filament may also comprise red, blue and white pixels for black body sweeping. It is possible to have cold white (CW) 6000K, normal white (NW) 4000K warm white (WW) 2000K LEDs for black body sweeping. A combination of these is also possible.

[0055] In another particular embodiment, with reference to Figure 3 A, the plurality of LEDs comprises red LEDs configured to emit, in operation, red light having a peak emission wavelength X3 in a wavelength range of 600-690 nm and blue LEDs configured to emit, in operation, blue light having a peak emission wavelength / J in a wavelength range of 430- 490 nm. However, in this embodiment, the LED filament is free from green LEDs configured to emit, in operation, green light having a peak emission wavelength X2 in wavelength range of 500-590 nm.

[0056] Figure 3B illustrates schematically a cross-section of an embodiment of a LED filament 10 having an encapsulant 50 comprising a first scattering material 52. The first scattering material 52 is in the figure for illustration purposes illustrated as a concentrated volume, however, in reality, the first scattering material 52 is spread throughout the entire encapsulant 50. A LED 31 emits, when operated, LED light 60. This LED light 60 has a certain wavelength distribution depending on the type of LED. The LED light 60 interacts with the scattering material 52, resulting in that LED light 60 is at least partly scattered into first scattered light 62. The LED filament light 65 leaving encapsulant 50 of the LED filament 10 thereby at least party comprises first scattered light 62. In a particular embodiment, the plurality of LEDs comprises red LEDs 31 configured to, in operation, emit red light having a peak emission wavelength X3 in a wavelength range of 600-690 nm, green LEDs configured to, in operation, emit green light having a peak emission wavelength X2 in a wavelength range of 500-590 nm and blue LEDs configured to in operation, emit blue light having a peak emission wavelength / J in a wavelength range of 430-490 nm.

[0057] Further possibilities to modify the light properties are enabled if the elongated carrier 20 is a light transmissive carrier 23. Figure 5 A illustrates one such embodiment of a LED filament. The light may then travel between the two sides of the LED filament 10 and interact with more than one type of encapsulant. In this embodiment, except for the first encapsulant 50 comprising the first luminescent material 51 on the first major surface 21 of the elongated carrier 20, there is also a second elongated encapsulant 50’ covering at least part of a second major surface 22 of the elongated carrier 20. The major surface 22 is opposite to the first major surface 21. In this embodiment, the second elongated encapsulant 50’ further comprises a second luminescent material 51’ configured to at least partly convert LED light 60 and / or first converted light 61 into second converted light 61’. The second luminescent material may in a particular embodiment comprise a green-yellow phosphor and red phosphor. The LED filament light 65 leaving second encapsulant 50’ of the LED filament 10 thereby at least party comprises second converted light 61’. Analogously, but not explicitly illustrated, LED light 60 may first be converted by the second luminescent material 51’ and then by the first luminescent material 51, so as to give LED filament light 65 leaving first encapsulant 50 of the LED filament 10 at least party comprising second converted light 61’.

[0058] Figure 5B illustrates another embodiment of a LED filament 10 having a light transmissive carrier 23. In this embodiment, except for the first encapsulant 50 comprising the first scattering material 52 on the first major surface 21 of the elongated carrier 20, there is also a second elongated encapsulant 50’ covering at least part of a second major surface 22 of the elongated carrier 20. The major surface 22 is opposite to the first major surface 21. In this embodiment, the second elongated encapsulant 50’ further comprises a second scattering material 52’ configured to at least partly scatter LED light 60 and / or first scattered light 62 into second scattered light 62’. The LED filament light 65 leaving second encapsulant 50’ of the LED filament 10 thereby at least party comprises second scattered light 62’. Analogously, but not explicitly illustrated, LED light 60 may first be converted by the second scattering material 52’ and then by the first scattering material 52, so as to give LED filament light 65 leaving first encapsulant 50 of the LED filament 10 at least party comprising second scattered light 62’.

[0059] It is also possible with further combinations, for instance having scattering material on one side and luminescent material on the other. In a general embodiment for light transmissive carriers 23, the LED filament 10 further comprises a second elongated encapsulant 50’ covering at least part of a second major surface 22, opposite to the first major surface 21, of the elongated carrier 20. The second elongated encapsulant 50’ comprises at least one of a second luminescent material 51 ’ configured to at least partly convert LED light 60 and / or first converted light 61 into second converted light 61’ and a second light scattering material 52’ configured to scatter at least part of the LED light 60 and / or the first scattered light 62 into second scattered light 62’, wherein the LED filament light 65 comprises the second converted light 61’ and / or the second scattered light 62’.

[0060] The provision of LEDs on a light transmissive, e.g. transparent, preferably flexible, elongated carrier thus gives various opportunities to adapt the light properties and to reduce spottiness. This is e.g. not of interest in e.g. applications concerning displays.

[0061] The conversion of the LED light can be tailored to different applications by e.g. utilizing different materials in the encapsulations on the different sides of the LED filament. With reference to Figure 5 A, one possibility is that the first luminescent material 51 has a first concentration, Cl, in the first elongated encapsulant 50, and that the second luminescent material 51 ’ has a second concentration, C2, in the second elongated encapsulant 50’, and wherein these concentrations are different, i.e. C1^C2. Preferably, C1>C2, and more preferably, Cl> 1.2*C2.

[0062] Another possibility is that the first luminescent material 51 is of a first phosphor type, Pl, and that the second luminescent material 51’ is of a second phosphor type P2, and where these types are different, i.e. P1^P2;

[0063] Yet another possibility is that the first luminescent material 51 has a first thickness (Tl) and that the second luminescent material 51’ has a second thickness, and where these thicknesses are different, i.e. T1^T2; Preferably, T1>T2, and more preferably, Tl> 1.2*T2.

[0064] Figure 6 illustrates schematically an embodiment of a LED filament arrangement 9. The LED filament arrangement 9 comprises a LED filament 10 according to what has been described here above. The LED filament arrangement 9 further comprises a driver 4. In the present embodiment, the driver 4 is arranged on the elongated carrier 20, preferably at an outer end 27 of the elongated carrier 20. The driver 4 may in alternative embodiments be provided at other positions at the elongated carrier 20 or externally to the the elongated carrier 20.

[0065] The driver comprises a source driver 5 and a gate driver 6. The driver 4 is configured for switching the plurality of Z LED switches 46 and powering the plurality of LEDs 32. For placing driver electronics, the row and the column electrodes are made to be smaller and brought together so that driver electronics can be placed onto the electrodes at the edges. The LED filament 10 may be connected to the controller 4 using a multichannel e.g. 4 pin connector. In one embodiment, the connector is arranged at an elongated side of the LED filament 10, because the width of the LED filament is too small. In an embodiment of a LED filament arrangement 9, LED filament arrangement 9 further comprises a multichannel connector 7 and wherein the driver 4 is connected to the LED filament 10 using the multichannel connector 7. The LED filament 100 further comprises electrically conductive pads wherein the multichannel connector 7 is connecting the LED filament 10 at electrically conductive pads 8. Preferably, the electrically conductive pads 8 are arranged at an elongated side 21 of the LED filament 10.

[0066] In the case of an elongated display, which is a preferred embodiment in the present invention, the connection conditions become somewhat special. The high aspect ratio requires more electrodes per LED switch than devices with a lower aspect ratio. If, as a nonlimiting example, dimensions of 150x5mm is used, there will be 1500x50 pixels based on led size of 100x100 micrometers. This means that if the side surface is used for placing the driver or bringing electrode lines to the bottom, this will cover up an area which may be as big as the area of the rest of the display.

[0067] In Figure 7, a schematic illustration of LED-occupied areas, i.e. covered areas, and free areas, i.e. uncovered areas of the elongated carrier 20 of a LED filament arrangement 9 is shown. The first major surface 21 of the elongated carrier 20 has a carrier surface area SI. The carrier surface area SI comprises a covered surface area S2 being covered by the plurality of LEDs and the plurality of Z LED switches and an uncovered surface area S3. In this embodiment, the uncovered surface area S3 is in a range of 55% to 85% of the carrier surface area SI.

[0068] In one embodiment, schematically illustrated in cross-section in Figure 8A, the plurality of LEDs are placed on a an elongated carrier 20 being a transparent and flexible substrate with transparent electrodes. The long edge 21 and the uncovered surface area S3 is, as illustrated, rolled inside the covered surface area S2. Alternatively, as illustrated in Fig. 8B, the uncovered surface area S3 is folded back to the covered surface area S2. The covered surface area S2 is then fully exposed to the environment, whereas the uncovered surface area S3 is folded away. Such a folding of the elongated carrier 20 using a bend in between the LED pixels and the row and the column electrodes keeps the LED filament arrangement 9 slim. The uncovered surface area S3 may furthermore physically protected by the covered surface area S2.

[0069] Because LED filaments typically emit at lower correlated color temperatures than for instance in display applications, the pixels layout may also be different from the pixel layout of displays e.g. more red than green and more green than blue LEDs may be used. Furthermore, due to the elongated shape and the use for lighting purposes, various new pixelation designs are possible. In particular, when using active addressing, various effects can be created in the LED filament. In one embodiment, the driver and LED filament are configured to generate pixelated LED filament light. Different effects can be achieved. Figure 9A illustrates a diagram showing the intensity variation along an embodiment of a LED filament. In this particular example, the intensity is lower in a middle portion. In other words, there is a gradient in intensity over the elongation direction of the elongated carrier. Figure 9B illustrates a diagram showing the color temperature variation along another embodiment of a LED filament. In this particular example, the color temperature is higher at one end than at the other. In other words, there is a gradient in correlated color temperature over the elongation direction of the elongated carrier. This may be achieved e.g. by using patterned phosphor.

[0070] Figure 9C illustrates yet another embodiment of a LED filament. Here, the active addressing is used to create visibly perceived light structures along the LED filament. In this particular embodiment, selected LEDs are controlled in order to give rise to the text “TEXT”. In other words, there is a text, logo or picture over the elongation direction of the elongated carrier.

[0071] As any person skilled in the art realizes, the possibilities for varying different optical conditions and properties along the LED filament are endless.

[0072] In order to resemble an experience of an incandescent lamps with LED filament technology, some kind of curved shapes may be used. The present elongated carrier is well suited for allowing different shaping of the LED filament, e.g. in the shape of a 3D spiral. Such a spiral, in particular when the number of loops increases, gives an impression for a viewer that resembles traditional incandescent lamps. In other words, in one embodiment, the LED filament has an elongated carrier 20 that is formed as a 3D spiralshape, preferably having at least 3 loops. This may also be combined with the ability to control the LEDs, either by changing the type of LEDs along the spiral and / or by controlling them differently. For instance, for homogeneity purposes, the sequence of R-G-B-EWW LEDs may vary for neighboring rows. In other words, the pixels may shift in position for the different rows, in order to achieve a suitable mix. The controller may specially take into account the number and size of the loops used in the spiral.

[0073] Figure 10 illustrates schematically an embodiment of a LED filament lamp 1. The LED filament lamp 1 comprises a LED filament 10 or a LED filament arrangement 9 according to the discussions above. The LED filament lamp 1 further comprises a light- transmissive tube or a light-transmissive envelope 2 at least partly enclosing the LED filament 10. A connector 3 is provided for electrically and mechanically connecting the LED filament lamp 1 to a socket of a luminaire.

[0074] 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.

Claims

CLAIMS:

1. A light emitting diode, LED, filament (10), configured to emit, in operation, LED filament light (65), the LED filament (10) comprising: an elongated carrier (20); a two-dimensional array (30) of a plurality of LEDs (32) arranged on a first major surface (021) of the elongated carrier, wherein the plurality of LEDs (32) are configured to, in operation, emit LED light (60), wherein the two-dimensional array comprises N rows (36) of LEDs (31) and M columns (34) of LEDs (31), wherein N > 2 and M > 10, and wherein the N rows (36) of LEDs (31) extend along an elongation direction (25) of the elongated carrier (20); a first elongated encapsulant (50) covering said plurality of LEDs (32) and at least part of said first major surface (21), said first elongated encapsulant (50) comprising at least one of a first luminescent material (51) configured to at least partly convert LED light (60) into first converted light (61) and a first light scattering material (52) configured to scatter at least part of the LED light (60) into first scattered light (62); a matrix driving circuit (40) comprising X row LED electrodes (44), Y column LED electrodes (45) and a plurality of Z LED switches (46), each LED switch (47) of the plurality of LED switches (46) is electrically connected to at least one row LED electrode (44) and at least one column LED electrode (45), each LED (31) of the plurality of LEDs (32) is electrically connected to a LED switch (47) of the plurality of LED switches (46); and wherein the LED filament light (65) comprises the first converted light (61) and / or the first scattered light (62).

2. The LED filament (10) according to claim 1, wherein the LED filament light (65) is white light having a correlated color temperature in a range from 1700 K to 6500 K and a color rendering index of at least 70.

3. The LED filament (10) according to claim 1 or 2, wherein the matrix driving circuit (40) is an active matrix driving circuit (41), wherein each LED switch (47) of the plurality of Z LED switches (46) comprises a transistor (48) and a capacitor (49).

4. The LED filament (10) according to any one of the preceding claims, wherein M > 20N.

5. The LED filament (10) according to any one of the preceding claims, wherein the elongated carrier (20) is a light transmissive carrier (23), and wherein the LED filament (10) further comprises a second elongated encapsulant (50’) covering at least part of a second major surface (22), opposite to the first major surface (21), of the elongated carrier (20), the second elongated encapsulant (50’) comprising at least one of a second luminescent material (51’) configured to at least partly convert LED light (60) and / or first converted light (61) into second converted light (61’) and a second light scattering material (52’) configured to scatter at least part of the LED light (60) and / or the first scattered light (62) into second scattered light (62’), wherein the LED filament light (65) comprises the second converted light (61’) and / or the second scattered light (62’).

6. The LED filament (10) according to claim 5, wherein at least one of the following applies: the first luminescent material (51) has a first concentration, Cl, in the first elongated encapsulant (50), the second luminescent material (51’) has a second concentration, C2, in the second elongated encapsulant (50’), wherein C1^C2; the first luminescent material (51) is a first phosphor type, Pl , the second luminescent material (51’) is a second phosphor type, P2, wherein P1^P2; and the first elongated encapsulant (50) has a first thickness (T 1 ), the second elongated encapsulant (51’) has a second thickness (T2), wherein T1 / T2.

7. The LED filament (10) according to any one of the preceding claims, wherein one of the following applies: the first elongated encapsulant (50) comprises the first luminescent material (51), and wherein the plurality of LEDs (32) comprises blue LEDs configured to emit blue light having a peak emission wavelength in a wavelength range of 430-470 nm; and the first elongated encapsulant (50) comprises the first light scattering material (52), and wherein the plurality of LEDs (32) comprises red LEDs configured to, in operation, emit red light having a peak emission wavelength (X3) in a wavelength range of 600-690 nm, green LEDs configured to, in operation, emit green light having a peak emissionwavelength (X2) in a wavelength range of 500-590 nm and blue LEDs configured to in operation, emit blue light having a peak emission wavelength (XI) in a wavelength range of 430-490 nm.

8. The LED filament (10) according to any one of the claims 1 to 6, wherein the first elongated encapsulant (50) comprises the first luminescent material (51), and wherein the plurality of LEDs (32) comprises red LEDs configured to emit, in operation, red light having a peak emission wavelength (X3) in a wavelength range of 600-690 nm and blue LEDs configured to emit, in operation, blue light having a peak emission wavelength (XI) in a wavelength range of 430-490 nm, and wherein the LED filament is free from green LEDs configured to emit, in operation, green light having a peak emission wavelength (X2) in wavelength range of 500- 590 nm9. The LED filament (10) according to any one of the preceding claims, wherein each LED (31) of the plurality of LEDs (32) comprises a die having a surface area (SA), wherein the surface area has a largest spatial extent (SE) that is less than or equal to 100 micrometers.

10. The LED filament (10) according to any one of the preceding claims, wherein the first major surface (21) of the elongated carrier has a carrier surface area (SI), the carrier surface area (SI) comprises a covered surface area (S2) being covered by the plurality of LEDs (32) and the plurality of Z LED switches (46) and an uncovered surface area (S3), wherein the uncovered surface area (S3) is in a range of 55% to 85% of the carrier surface area (SI).

11. The LED filament (10) according to any one of the preceding claims, wherein the elongated carrier (20) has a 3D spiral-shape (29) having at least 2 loops.

12. A LED filament arrangement (9), comprising: the LED filament (10) according to any one of claims 1-11; and a driver (4) comprising a source driver (5) and a gate driver (6), the driver (4) is configured for switching the plurality of Z LED switches (46) and powering the plurality of LEDs (32).

13. The LED filament arrangement (9) according to claim 12, wherein the driver (4) and LED filament (10) are configured to generate pixelated LED filament light (66), wherein the pixelated LED filament light (66) is at least one of the following, it has: i) a gradient in intensity over the elongation direction (25) of the elongated carrier (20), ii) a gradient in correlated color temperature over the elongation direction (25) of the elongated carrier (20), iii) a text, logo or picture over the elongation direction (25) of the elongated carrier (20); and wherein the pixelated LED filament light is changed from first pixelated LED filament light into second pixelated LED filament different from the first pixelated LED filament light.

14. The LED filament arrangement (9) according to claim 12 or 13, wherein the LED filament arrangement (9) further comprises a multichannel connector (7) and wherein the driver (4) is connected to the LED filament (10) using the multichannel connector (7), the LED filament (100) further comprises electrically conductive pads (8) wherein the multichannel connector (7) is connecting the LED filament (10) at the electrically conductive pads (8), preferably the electrically conductive pads (8) are arranged at an elongated side (28) of the LED filament (10).

15. The LED filament arrangement (9) according to claim 12 or 13, wherein the driver (4) is arranged on the elongated carrier (20), at an outer end (27) of the elongated carrier (20).

16. A LED filament lamp (1), comprising: the LED filament (10) according to any one of claims 1-11 or the LED filament arrangement (9) according to any one of claims 12-15; a light-transmissive tube or a light-transmissive envelope (2) at least partly enclosing the LED filament (10); and a connector (3) for electrically and mechanically connecting said LED filament lamp (1) to a socket (99) of a luminaire (100).

Images