LED filament comprising a colored non-luminescent elongated outer encapsulant

Abstract

The present invention relates to a light-emitting diode, LED, filament (100) configured to, in an on-state of the LED filament, emit LED filament light, the LED filament comprises an elongated carrier (101) comprising a first major surface (101´) and a second major surface (101´´) opposite to the first major surface, and an array of a plurality of LEDs (102) arranged on the first major surface (101´) of the elongated carrier (101´´), wherein each LED (102) of the plurality of LEDs is configured to, in an on-state, emit LED light; and a coloured non-luminescent elongated outer encapsulant (103), wherein the coloured non- luminescent elongated outer encapsulant (103) has, in an off-state of the LED filament, a yellow or an orange appearance.

Description

[0001] LED FILAMENT COMPRISING A COLORED NON-LUMINESCENT ELONGATED

[0002] OUTER ENCAPSULANT

[0003] FIELD OF THE INVENTION

[0004] The present invention generally relates to a LED filament comprising a coloured non-luminescent elongated outer encapsulant.

[0005] BACKGROUND OF THE INVENTION

[0006] The use of LED filaments is continuing to attract attention. In particular, such LED filaments may be incorporated in lighting devices due to its high energy and cost efficiency, and because they have shown to be useful in many applications. The LED filament comprises an array of light emitting diodes arranged on a carrier. The LED filament is often encapsulated by a phosphor-based luminescent encapsulant which at least partly converts the light emitted by the LEDs into converted light to obtain a certain desired light (spectrum). In such an embodiment, the desired light directed to the user is chosen after parameters such as color temperature and brightness.

[0007] However, a problem often perceived in relation to LED filaments used in lighting devices is that some undesired wavelengths may be present. In particular, it has been discovered that blue light has negative impact on human well-being.

[0008] Blue light is part of the visible light spectrum, and has the shortest wavelength in the range from 400 to 490 nm and highest energy.

[0009] Sunlight is the biggest source of blue light. Artificial sources of blue light include fluorescent light, LED TVs, computer monitors, smartphones, and tablet screens.

[0010] Blue light boosts alertness, helps memory and brain function, and elevates mood. It regulates the body's natural wake and sleep cycle (circadian rhythm). Sunlight is also important for the growth and development of eyes and vision in children. However, there is concern about long-term effects of blue light exposure.

[0011] Since our eyes are not good at blocking blue light, nearly all visible blue light passes through the front of the eye (cornea and lens) and reaches the retina, the cells that convert light for the brain to process into images. Constant exposure to blue light over time could damage retinal cells and cause vision problems such as age-related macular degeneration. It can also contribute to cataracts, eye cancer and growths on the clear covering over the white part of the eye. According to a vision study by the National Eye Institute, children are more at risk than adults because their eyes absorb more blue light from digital devices.

[0012] Exposure to blue light before bedtime also can disrupt sleep patterns as it affects when our bodies create melatonin. Interruption of the circadian system plays a role in the development of type 2 diabetes, cardiovascular disease, cancer, sleep disorders, and cognitive dysfunctions.

[0013] Considering the above, there is a need to provide a LED filament providing a soft light with improved spectral distribution of the light emitted by the LED filament, while being energy and cost efficient. Further, it is desirable to provide a LED filament having the ability to remove electromagnetic irradiation within a certain wavelength range. Further, it is desired to improve the appearance of a LED filament.

[0014] The application WO 2024 / 067778 relates to the field of illumination, and discloses an LED filament. The LED filament comprises an LED chip unit, a light conversion layer, and an electrode, and is characterized in that: the light conversion layer covers the LED chip unit and part of the electrode; the outer surface of the light conversion layer is provided with a layered body, the layered body covering the light conversion layer and at least part of the electrode; and the layered body has provided therein a chromogenic material or a light- induced conversion material. The invention has uniform light emission, good heat dissipation, and high reliability.

[0015] SUMMARY OF THE INVENTION

[0016] The object of the present invention is thus to solve at least one of the aboveidentified problems. To this end, the present invention provides a light-emitting diode (LED) filament configured to, in an on-state of the LED filament, emit LED filament light. The LED filament comprises an elongated carrier. The term “elongated” is in the context of the present invention intended to mean having an extension in one direction being significantly greater than an extension in any other direction. The elongated carrier comprises a first major surface and a second major surface opposite to the first major surface. The surfaces of the elongated carrier may be flat or may have other geometrical shapes such as a round surface, or an ellipsoid surface, or a diamond shaped surface. The first major surface and the second major surface face opposite directions such that there may be an angle 180° between each of the directions of the first major surface and the second major surface.

[0017] An array of a plurality of LEDs is arranged on the first major surface of the elongated carrier such that the plurality of LEDs is carried by the elongated carrier. Alternatively, or additionally, the LEDs may be arranged in the carrier. Each LED of the plurality of LEDs is configured to, in an on-state, emit LED light. The elongated carrier may further be a light transmissive carrier. The term transmissive shall not be construed to be limiting, rather it shall be interpreted broadly to include synonyms as e.g. translucent or transparent. In such an embodiment as described, the LED filament light may be emitted in all directions, such that the light emission profile is preferably omnidirectional.

[0018] The LED filament according to the present invention further comprises a coloured non-luminescent elongated outer encapsulant. The coloured non-luminescent elongated outer encapsulant has, in an off-state of the LED filament, a yellow or an orange appearance. The term “outer” implies that the coloured non-luminescent elongated outer encapsulant may be observed by the end user.

[0019] Moreover, the end user will perceive the coloured non-luminescent elongated outer encapsulant, in the off-state, as having a yellow or an orange appearance. It shall be noted that the yellow or orange appearance of the coloured non-luminescent elongated outer encapsulant may also be a “yellowish” or an “orangish”, or a yellow-orange appearance. The terms “yellowish” and “orangish” are in the context of the present invention intended to mean a color significantly close to the definition of yellow or significantly close to the definition of orange, but not limited to being exactly yellow or exactly orange. Furthermore, the term yellow-orange are intended to mean a mixed color appearance of yellow and orange.

[0020] It should be stressed that the yellow or orange appearance of the coloured non- luminescent elongated outer encapsulant in the off-state means the yellow or orange color is not due to yellow or orange light e.g. of the LEDs or a further luminescent encapsulant.

[0021] The term “non-luminescent” is in this context of the present invention intended to mean being (substantially) free from luminescent material. In the context of the present invention, the wording “substantially free from luminescent material” may mean a luminescent material concentration in elongated outer encapsulant of equal to or less than 0.5 v / v%, or less than 0.1 v / v%.

[0022] The coloured non-luminescent elongated outer encapsulant of the LED filament may at least partly cover or enclose the plurality of LEDs and at least partly cover the first major surface. In other words, the first major surface may be fully encapsulated by the coloured non-luminescent elongated outer encapsulant. Alternatively, a part of the first major surface may be encapsulated by the coloured non-luminescent elongated outer encapsulant and another part of the first major surface may be free from the coloured non- luminescent elongated outer encapsulant. If the first major surface is fully encapsulated by the coloured non-luminescent elongated outer encapsulant, it implies that all of the LEDs of the plurality of LEDs are encapsulated by the coloured non-luminescent elongated outer encapsulant. If the first major surface is not fully encapsulated by the coloured non- luminescent elongated outer encapsulant, it may imply that a part of the LEDs of the plurality of LEDs is free from the coloured non-luminescent elongated outer encapsulant.

[0023] In embodiments, the coloured non-luminescent elongated outer encapsulant may cover the second major surface of the elongated carrier. Thus, at the side of the second major surface (of the LED filament) the LED filament may comprise the coloured non- luminescent elongated outer encapsulant. Thus, the LED filament portion below the (bottom of the) LEDs may comprise the coloured non-luminescent elongated outer encapsulant.

[0024] In embodiments, the elongated carrier may be free from luminescent material and / or at the side of the second major surface (of the LED filament) the LED filament may be free from luminescent material. In embodiments, the LED filament portion below the (bottom of the) LEDs may be free from luminescent material.

[0025] In embodiments, at the side of the first major surface (of the LED filament) the LED filament may be free from luminescent material. The LED filament portion above the (bottom of the) LEDs may be free from luminescent material.

[0026] In embodiments, the coloured non-luminescent elongated outer encapsulant may cover the first major surface of the elongated carrier. Thus, at the side of the first major surface (of the LED filament) the LED filament may comprise the coloured non-luminescent elongated outer encapsulant. Thus, the LED filament portion above the (bottom of the) LEDs may comprise the coloured non-luminescent elongated outer encapsulant.

[0027] In embodiments, at the side of the first major surface (of the LED filament) the LED filament may be free from the coloured non-luminescent elongated outer encapsulant. The LED filament portion above the (bottom of the) LEDs may be free from the coloured non-luminescent elongated outer encapsulant.

[0028] In embodiments, in the off-state of the LED filament, the LED filament may have a yellow or an orange appearance on both sides of the elongated carrier. The LED filament may have a yellow appearance on both sides of the elongated carrier or the LED filament may have an orange appearance on both sides of the elongated carrier. The frontside of the LED filament (i.e. the side of the LED filament at which the plurality of LEDs are arranged) may have a yellow or an orange appearance due to the color of the coloured non- luminescent elongated outer encapsulant or due to the color of the luminescent elongated encapsulant. The backside of the LED filament (opposite to the frontside of the LED filament) may have a yellow or an orange appearance due to the color of the coloured non- luminescent elongated outer encapsulant. Thus the coloured non-luminescent elongated outer encapsulant may mimic a or the luminescent elongated encapsulant.

[0029] In embodiments, the plurality of LEDs may comprise or consists of blue LEDs. In embodiments, the plurality of LEDs may comprise or consists of red, blue and green LEDs. In embodiments, the plurality of LEDs may comprise or consists of white phosphor converted LEDs.

[0030] In embodiments, a translucent elongated encapsulant may at least partly cover the first major surface and at least partly encloses the plurality of LEDs. The translucent elongated encapsulant may be transparent. The translucent elongated encapsulant may be arranged between the coloured non-luminescent elongated outer encapsulant and the first major surface.

[0031] The LED filament of the present invention may further comprise a luminescent elongated encapsulant at least partly enclosing the plurality of LEDs and at least partly covering the first major surface. For example, the luminescent elongated encapsulant may be applied onto the first major surface and / or the plurality of LEDs. The luminescent elongated encapsulant comprises a luminescent material. The luminescent elongated encapsulant may comprise a luminescent material comprising luminescent particles configured to, in the on-state, convert at least part of the LED light into a converted light. Put differently, all of the LED light diffusing through the luminescent elongated encapsulant may be converted by the luminescent material into a converted light. Alternatively, a part of the LED light diffusing through the luminescent elongated encapsulant will be converted by the luminescent material into converted light, while a second part of the LED light diffusing through the luminescent elongated encapsulant may not be converted into converted light. In other words, the LED filament light may comprise one of

[0032] (i) part of the LED light and at least part of the converted light.

[0033] (ii) at least part of the converted light.

[0034] The luminescent material may be any of an inorganic luminescent particles, quantum dots, quantum rods, an organic luminescent material or a combination of two or more of these luminescent particles. The first luminescent material may also comprise other types of luminescent particles.

[0035] The luminescent material may comprise a green-yellow and / or red phosphor.

[0036] The luminescent material may comprise a luminescent material of the type AsBsOn Ce. A may comprise one or more of Lu, Y, La, Gd, Tb. B may comprise one or more of Al, Ga, In and Sc.

[0037] The luminescent material may comprises a luminescent material of the type AsBsOn Ce, wherein A in embodiments comprises one or more of Y, La, Gd, Tb and Lu, especially (at least) one or more of Y, Gd, Tb and Lu, and wherein B in embodiments comprises one or more of Al, Ga, In and Sc. Especially, A may comprise one or more of Y, Gd and Lu, such as especially one or more of Y and Lu. Especially, B may comprise one or more of Al and Ga, more especially at least Al, such as essentially entirely Al. Hence, especially suitable luminescent materials are cerium comprising garnet materials. Embodiments of garnets especially include A3B5O12 garnets, wherein A comprises at least yttrium or lutetium and wherein B comprises at least aluminium. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium; especially however with Ce. Especially, B may comprise aluminium (Al); however, in addition to aluminium, B may also partly comprise gallium (Ga) and / or scandium (Sc) and / or indium (In), especially up to about 20% of B, more especially up to about 10 % of B (i.e. the B ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and / or Tb are especially only present up to an amount of about 20% of A. In a specific embodiment, the garnet luminescent material comprises (Yi-xLux)3B50i2:Ce, wherein x is equal to or larger than 0 and equal to or smaller than 1. The term “:Ce”, indicates that part of the metal ions (i.e. in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Yi-xLux)3A150i2:Ce, part of Y and / or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10%; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2% (relative to A). Assuming 1% Ce and 10% Y, the full correct formula could be (Yo.iLuo.89Ceo.oi)3A150i2. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art. The coloured non-luminescent elongated outer encapsulant of the LED filament according to the present invention may be arranged to diffuse at least part of the LED light and / or at least part of the converted light. In such an embodiment the LED light and / or the converted light may be perceived as more homogenous by the end user. Further, in such an embodiment the LEDs of the plurality of LEDs are prevented from being perceived as dots or multiple light sources by the end user. Rather the plurality of LEDs may be perceived as a single light source.

[0038] In embodiments, the coloured non-luminescent elongated outer encapsulant may have a thickness in a range from 0.3 mm to 3 mm, a width in a range from 0.3 mm to 3 mm and / or a length in a range from 3 cm to 60 cm.

[0039] In embodiments, the LED filament may have a thickness in a range from 0.3 mm to 3 mm, a width in a range from 0.3 mm to 3 mm and / or a length in a range from 3 cm to 60 cm.

[0040] In embodiments, the LED filament light may be white light. The LED filament light may have a correlated color temperature in a range from 1800K to 6500K (or in a range from 1800K to 2700K) and / or a color rendering index of at least 80 or at least 85.

[0041] The luminescent elongated encapsulant of the LED filament may be arranged between the first major surface and the coloured non-luminescent elongated outer encapsulant. In such an embodiment, the luminescent elongated encapsulant may be applied onto the first major surface and / or the plurality of LEDs. Furthermore, the luminescent elongated encapsulant may also be applied onto the second major surface, such that the luminescent elongated encapsulant at least partly covers the second major surface. Thus, the luminescent elongated encapsulant may cover both the first major surface and the second major surface.

[0042] The coloured non-luminescent elongated outer encapsulant of the LED filament may cover the second major surface of the elongated carrier. In such an embodiment the elongated carrier is preferably a light transmissive / translucent or transparent elongated carrier and a portion of the luminescent elongated encapsulant may at least partly cover the second major surface. Moreover, the portion of the luminescent elongated encapsulant may preferably be arranged between the coloured non-luminescent elongated outer encapsulant and the second major surface.

[0043] The LED filament of the present invention may further comprise a second luminescent elongated encapsulant. In such embodiment, the second luminescent elongated encapsulant may at least partly cover the second major surface. Moreover, the second luminescent elongated encapsulant may preferably be arranged between the coloured non- luminescent elongated outer encapsulant and the second major surface. Furthermore, the second luminescent material comprised in the second luminescent elongated encapsulant may either be the same as or different from the luminescent material comprised in the luminescent elongated encapsulant.

[0044] The coloured non-luminescent elongated outer encapsulant of the LED filament may fully hide or fully enclose the luminescent elongated encapsulant. In such an embodiment the end user may not be able to perceive the luminescent elongated encapsulant since it is fully hidden or fully enclosed by the coloured non-luminescent elongated outer encapsulant. Further, in embodiments wherein a second luminescent elongated encapsulant at least partly cover the second major surface, the coloured non-luminescent elongated outer encapsulant may fully hide or fully enclose the second luminescent elongated encapsulant.

[0045] The coloured non-luminescent elongated outer encapsulant of the LED filament may be configured to absorb at least part of the LED light and / or to absorb part of the converted light. In such an embodiment LED light and / or converted light of certain undesired wavelengths, may be absorbed by the coloured non-luminescent elongated outer encapsulant. Thus LED light and / or converted light of such undesired wavelength may not pass through the coloured non-luminescent elongated outer encapsulant and is thus not perceived by the end user.

[0046] Further, at most 2% of the emitted LED filament light, defined in terms of luminous flux in the visible wavelength range, may be in a wavelength range below 490 nm. The obtained effect is improved sleep and circadian health, and / or reduced eye strain and fatigue. By the term “emitted LED filament light” is intended to mean the LED filament light emitted by the LED filament after passing through the coloured non-luminescent elongated outer encapsulant. In other words, LED light and / or converted light may be absorbed by the coloured non-luminescent elongated outer encapsulant with such efficiency that at most 2% or at most 1% of the total luminous flux of the emitted LED filament light may be visible light with a wavelength range below 490 nm, i.e. blue light.

[0047] The LED filament of the present invention may further comprise at least one electrical contact and / or a frame. In such an embodiment, the coloured non-luminescent elongated outer encapsulant may preferably at least partly cover (e.g. fully cover) or at least partly enclose (e.g. fully enclose) the at least one electrical contact and / or the frame. The electrical contact or frame may be configured to, in operation, provide electrical power to the plurality of LEDs. The LED filament may further comprise connection means for mechanically connecting the LED filament to a connector. In embodiments, the coloured non-luminescent elongated outer encapsulant may be dispensed on or moulded over the at least one electrical contact and / or the frame.

[0048] In the LED filament of the present invention, the elongated carrier may be a printed circuit board, PCB. The PCB carrier may in such an embodiment provide electrical means and mechanical connecting means to each LED comprised in the lightning device of the present invention.

[0049] The coloured non-luminescent elongated outer encapsulant of the LED filament may be a coating and / or it may have a tubular shape. In embodiments, the coloured non-luminescent elongated outer encapsulant may be a tube. In embodiments, the coating may be directly applied on the first and / or second major surface.

[0050] The LED filament of the present invention may comprise a light guide. In such an embodiment the yellow non-luminescent elongated outer encapsulant may be applied on the light guide.

[0051] The coloured non-luminescent elongated outer encapsulant of the LED filament may comprise a polymer matrix. The polymer matrix may comprise a cross-linked silicone polymer e.g. crosslinked PDMS, PMPS and / or PDPS. These materials have a high light transmission, a low light absorption and are very stable e.g. less browning during lifetime of the LED filament.

[0052] The coloured non-luminescent elongated outer encapsulant may comprise any one or both of

[0053] (i) a yellow non-luminescent dye and / or yellow non-luminescent particles.

[0054] (ii) an orange non-luminescent dye and / or orange non-luminescent particles.

[0055] In embodiments, the (yellow and / or orange) particles may have a concentration of at least 5 v / v%.

[0056] The present invention relates to a LED filament arrangement comprising a controller and a LED filament as described above. The controller may be configured to control the LED filament light emitted by the LED filament. In embodiments, the controller may be configured to control (subsets) of the plurality of LEDs.

[0057] Finally, the present invention relates to a lamp or a luminaire comprising a LED filament described above. The lamp may comprise at least one of an envelope at least partly enclosing the LED filament, a connector for mechanically and electrically connecting the lamp to a socket or a socket of a luminaire. Further, the luminaire may comprise a light exit window for exiting the LED filament light. It is noted that the invention relates to all possible combinations of features recited in the claims. 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. 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.

[0058] BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Fig. 1 schematically shows a cross-sectional view of a LED filament according to an exemplifying embodiment of the present invention;

[0060] Fig. 2 schematically shows a cross-sectional view of a LED filament according to a second exemplifying embodiment of the present invention;

[0061] Fig. 3 schematically shows a cross-sectional view of a LED filament according to a third exemplifying embodiment of the present invention;

[0062] Fig 4 schematically shows a cross-sectional view of a LED filament according to a fourth exemplifying embodiment of the present invention;

[0063] Fig. 5 schematically shows a LED filament in a horizontal direction according to the present invention.

[0064] Fig 6 schematically shows a lamp comprising the LED filament of the present invention;

[0065] Fig 7 schematically shows a LED filament in a vertical direction of the present invention;

[0066] DETAILED DESCRIPTION

[0067] 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.

[0068] Fig. 1 shows an embodiment of the light-emitting diode (LED) filament 100 comprising an elongated carrier 101. The elongated carrier 101 comprises a first major surface 10L and a second major surface 101" opposite to the first major surface 10L. The elongated carrier 101 has a flat surface. The first major surface 101 ' and the second major surface 101" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 101 ' and the second major surface 101". An array of a plurality of LEDs 102 is arranged on the first major surface 101 ' of the elongated carrier 101 such that the plurality of LEDs is carried by the elongated carrier 101. Alternatively, or additionally, the LEDs may be arranged in the carrier. Each LED 102 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 101 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 102 is emitted in all directions, such that the light emission profile of each LED 102 of the plurality of LEDs is spherical.

[0069] The LED filament 100 in Fig. 1 comprises a luminescent elongated encapsulant 104 enclosing the plurality of LEDs 102 and partly covering the first major surface 101 '. In other words, a part the first major surface 101 ' is encapsulated by the luminescent elongated encapsulant 104, while a second part of the first major surface 101 ' is free from the luminescent elongated encapsulant 104. Since the plurality of LEDs 102 is fully encapsulated by the luminescent elongated encapsulant 104, it implies that all of the LEDs 102 of the plurality of LEDs are encapsulated by the luminescent elongated encapsulant 104.

[0070] The LED filament 100 in Fig. 1 comprises a second luminescent elongated encapsulant 105 partly covering the second major surface 101". In other words, a part of the second major surface 101" is encapsulated by the second luminescent elongated encapsulant 105, while a second part of the second major surface 101" is free from the second luminescent elongated encapsulant 105.

[0071] The luminescent elongated encapsulant 104 in Fig. 1 comprises a luminescent material 110 comprising luminescent particles and configured to, in the on-state, convert at least part of the LED light into a converted light. Put differently, all of the LED light diffusing through the luminescent elongated encapsulant 104 may be converted by the luminescent material 110 into converted light. Alternatively, a part of the LED light diffusing through the luminescent elongated encapsulant 104 will be converted by the luminescent material 110 into converted light, while a second part of the LED light diffusing through the luminescent elongated encapsulant 104 may not be converted into converted light. The second luminescent elongated encapsulant 105 in the LED filament 100 in Fig. 1 comprises a luminescent material 111. The second luminescent material 111 comprises luminescent particles. The second luminescent material I l l is configured to, in the on-state, at least partly convert the LED light into converted light . Thus, a part of the LED light diffusing through the second luminescent elongated encapsulant 105 will be converted into converted light, while a second part of the LED light diffusing through the second luminescent elongated encapsulant 105 may not be converted into converted light.

[0072] The LED filament 100 shown in Fig. 1 further comprises a coloured non- luminescent elongated outer encapsulant 103 partly covering the first and second major surface 10L, 100", and fully encapsulating the luminescent elongated encapsulant 104 and the second luminescent elongated encapsulant 105. The coloured non-luminescent elongated outer encapsulant 103 is free from luminescent material. The color non-luminescent elongated outer encapsulant 103 comprises either yellow non-luminescent dyes / particles or orange non-luminescent dyes / particles or a combination thereof. The non-luminescent elongated outer encapsulant 103 is configured to, in the off-state of the LED filament, have a yellow or an orange appearance.

[0073] Fig. 2 illustrates yet another embodiment of the light-emitting diode (LED) filament 200 comprising an elongated carrier 201. The elongated carrier 201 comprises a first major surface 20 L and a second major surface 201" opposite to the first major surface 20 L. The elongated carrier 201 has a flat surface. The first major surface 20 L and the second major surface 201" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 20 L and the second major surface 201 ". An array of a plurality of LEDs 202 is arranged on the first major surface 20 L of the elongated carrier 201 such that the plurality of LEDs is carried by the elongated carrier 201. Each LED 202 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 201 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 202 is emitted in all directions, such that the light emission profile of each LED 202 of the plurality of LEDs is spherical.

[0074] The LED filament 200 in Fig. 2 comprises a luminescent elongated encapsulant 204 enclosing the plurality of LEDs 202 and fully covering the first major surface 20 L. In other words, the plurality of LEDs 202 and the first major surface 20 L is fully encapsulated by the luminescent elongated encapsulant 204. Since the first major surface 20 L is fully encapsulated by the luminescent elongated encapsulant 204, it implies that all of the LEDs 202 of the plurality of LEDs are encapsulated by the luminescent elongated encapsulant 204.

[0075] The LED filament 200 in Fig. 2 comprises a second luminescent elongated encapsulant 205 fully covering the second major surface 201 ". In other words, the second major surface 201" is fully encapsulated by the second luminescent elongated encapsulant 205 such that no part of the second major surface 201" is free from the second luminescent elongated encapsulant 205.

[0076] The luminescent elongated encapsulant 204 in Fig. 2 comprises a luminescent material 210 comprising luminescent particles and configured to, in the on-state, convert at least part of the LED light into a converted light. Put differently, all of the LED light diffusing through the luminescent elongated encapsulant 204 may be converted by the luminescent material into converted light. Alternatively, a part of the LED light diffusing through the luminescent elongated encapsulant 204 will be converted by the luminescent material 210 into converted light, while a second part of the LED light diffusing through the luminescent elongated encapsulant 204 may not be converted into converted light.

[0077] The second luminescent elongated encapsulant 205 in the LED filament 200 in Fig. 2 comprises a luminescent material 211. The second luminescent material 211 comprises luminescent particles. The second luminescent material 211 is configured to, in the on-state, at least partly convert the LED light into converted light . Thus, a part of the LED light diffusing through the second luminescent elongated encapsulant 205 will be converted into converted light, while a second part of the LED light diffusing through the second luminescent elongated encapsulant 205 may not be converted into converted light.

[0078] The LED filament 200 shown in Fig. 2 further comprises a coloured non- luminescent elongated outer encapsulant 203 fully covering the luminescent elongated encapsulant 204 and fully covering the second luminescent elongated encapsulant 205. The coloured non-luminescent elongated outer encapsulant 203 is free from luminescent material. The coloured non-luminescent elongated outer encapsulant 203 comprises either yellow non- luminescent dyes / particles or orange non-luminescent dyes / particles or a combination thereof.

[0079] The non-luminescent elongated outer encapsulant is configured to, in the off- state of the LED filament, have a yellow or an orange appearance.

[0080] Fig. 3 shows a third embodiment of the light-emitting diode (LED) filament 300 comprising an elongated carrier 301. The elongated carrier 301 comprises a first major surface 30 L and a second major surface 301" opposite to the first major surface 30 L. The elongated carrier 301 has a flat surface. The first major surface 30 L and the second major surface 301" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 30 L and the second major surface 301". An array of a plurality of LEDs 302 is arranged on the first major surface 30L of the elongated carrier 301 such that the plurality of LEDs is carried by the elongated carrier 301. Each LED 302 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 301 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 302 is emitted in all directions, such that the light emission profile of each LED 302 of the plurality of LEDs is spherical.

[0081] The embodiment of the LED filament 300 in Fig. 3 does not comprise a luminescent elongated encapsulant 104 nor a second luminescent elongated encapsulant 105. Thus the plurality of LEDs 302 is not encapsulated by a luminescent elongated encapsulant 104.

[0082] The LED filament 300 shown in Fig. 3 further comprises a coloured non- luminescent elongated outer encapsulant 303 partly covering the first and second major surface 30L, 300". The coloured non-luminescent elongated outer encapsulant 303 is free from luminescent material. The coloured non-luminescent elongated outer encapsulant 303 comprises either yellow non-luminescent dyes / particles or orange non-luminescent dyes / particles or a combination thereof. Moreover, the coloured non-luminescent elongated outer encapsulant 303 of the LED filament 300 is arranged to diffuse at least part of the LED light and / or at least part of the converted light.

[0083] The non-luminescent elongated outer encapsulant 303 is configured to, in the off-state of the LED filament, have a yellow or an orange appearance.

[0084] Fig. 4 shows a fourth embodiment of the light-emitting diode (LED) filament 400 comprising an elongated carrier 401. The elongated carrier 401 comprises a first major surface 40 L and a second major surface 401" opposite to the first major surface 40 L. The elongated carrier 401 has a flat surface. The first major surface 40 L and the second major surface 401" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 40 L and the second major surface 401 ". An array of a plurality of LEDs 402 is arranged on the first major surface 40 L of the elongated carrier 401 such that the plurality of LEDs is carried by the elongated carrier 401. Each LED 402 of the plurality of LEDs is configured to, in the on-state, emit LED light. The elongated carrier 401 is a transparent carrier. Thus, the LED light emitted by the plurality of LEDs 402 is emitted in all directions, such that the light emission profile of each LED 402 of the plurality of LEDs is spherical.

[0085] The LED filament 400 in Fig. 4 comprises a luminescent elongated encapsulant 404 enclosing the plurality of LEDs 402 and fully covering the first major surface 40 L. Since the plurality of LEDs 402 is fully encapsulated by the luminescent elongated encapsulant 404, it implies that all of the LEDs 402 of the plurality of LEDs are encapsulated by the luminescent elongated encapsulant 404.

[0086] The LED filament 400 in Fig. 4 comprises a second luminescent elongated encapsulant 405 fully covering the second major surface 401". In other words, the second major surface 401" is fully encapsulated by the second luminescent elongated encapsulant 405 such that no part of the second major surface 401" is free from the second luminescent elongated encapsulant 205.

[0087] The luminescent elongated encapsulant 404 in Fig. 4 comprises a luminescent material 410 comprising luminescent particles and configured to, in the on-state, convert at least part of the LED light into a converted light. Put differently, all of the LED light diffusing through the luminescent elongated encapsulant 404 may be converted by the luminescent material into converted light. Alternatively, a part of the LED light diffusing through the luminescent elongated encapsulant 404 will be converted by the luminescent material 410 into converted light, while a second part of the LED light diffusing through the luminescent elongated encapsulant 404 may not be converted into converted light.

[0088] The second luminescent elongated encapsulant 405 in the LED filament 400 in Fig. 4 comprises a luminescent material 411. The second luminescent material 411 comprises luminescent particles. The second luminescent material 411 is configured to, in the on-state, at least partly convert the LED light into converted light. Thus, a part of the LED light diffusing through the second luminescent elongated encapsulant 405 will be converted into converted light, while a second part of the LED light diffusing through the second luminescent elongated encapsulant 405 may not be converted into converted light.

[0089] The LED filament 400 shown in Fig. 4 further comprises a coloured non- luminescent elongated outer encapsulant 403 fully covering the second major surface 401". The coloured non-luminescent elongated outer encapsulant 403 is free from luminescent material. The coloured non-luminescent elongated outer encapsulant 403 comprises either yellow non-luminescent dyes / particles or orange non-luminescent dyes / particles or a combination thereof. The non-luminescent elongated outer encapsulant 403 is configured to, in the off-state of the LED filament, a yellow or an orange appearance.

[0090] Fig.5 illustrates a side view of the light-emitting diode (LED) filament 500 of the present invention in a horizontal direction, comprising an elongated carrier 101. The elongated carrier 101 comprises a first major surface 10L and a second major surface 101" opposite to the first major surface 10L. The elongated carrier 101 has a flat surface. The first major surface 10L and the second major surface 101" face opposite directions such that there is an angle 180° between each of the directions of the first major surface 101 ' and the second major surface 101".

[0091] In embodiments, the colored non-luminescent elongated outer encapsulant may not cover or not (at least partly) enclose any LEDs. In embodiments, the colored non- luminescent elongated outer encapsulant may at least partly cover or at least partly enclose electrical components other then LEDs e.g. a sensor or transistor.

[0092] The LED filament 500 shown in Fig. 5 further comprises a coloured non- luminescent elongated outer encapsulant 503 partly covering the first and second major surface 50L, 501". The coloured non-luminescent elongated outer encapsulant 503 is free from luminescent material. The coloured non-luminescent elongated outer encapsulant 503 comprises either yellow non-luminescent dyes / particles or orange non-luminescent dyes / particles or a combination thereof. The non-luminescent elongated outer encapsulant 503 is configured to, in the off-state of the LED filament, a yellow or an orange appearance.

[0093] In the embodiment shown in Fig.5 the plurality of LEDs 102, the luminescent elongated carrier 104 and the second luminescent elongated carrier 105 are fully encapsulated by the coloured non-luminescent elongated outer encapsulant and are thus hidden and not shown in Fig. 5.

[0094] Fig. 6 illustrates an exemplifying embodiment of the present invention of the LED filament 600, where the LED filament 600 is part of a lamp for illumination.

[0095] Fig. 7 illustrates an exemplifying embodiment of the present invention of the LED filament 700 comprising an elongated carrier 701 and a coloured non-luminescent elongated outer encapsulant 703 partly covering the elongated carrier 701.

[0096] The LED filament 701 in Fig. 700 further comprise at least one electrical contact (707). In such an embodiment the coloured non-luminescent elongated outer encapsulant partly enclose the at least one electrical contact and / or the frame. The electrical contact or frame is configured to, in operation, provide electrical power to the plurality of LEDs.

Claims

CLAIMS:

1. A light-emitting diode, LED, filament (100) configured to, in an on-state of the LED filament, emit LED filament light, the LED filament comprising: an elongated carrier (101) comprising a first major surface (10L) and a second major surface (101") opposite to the first major surface; an array of a plurality of LEDs arranged on the first major surface (10L) of the elongated carrier (101) or in the carrier, wherein each LED (102) of the plurality of LEDs is configured to, in an on-state, emit LED light; and a coloured non-luminescent elongated outer encapsulant (103); wherein the coloured non-luminescent elongated outer encapsulant (103) has, in an off-state of the LED filament, a yellow or an orange appearance; wherein the coloured non-luminescent elongated outer encapsulant (103) covers the second major surface (101") of the elongated carrier (101); and wherein the elongated carrier (101) is free from luminescent material and wherein at the side of the second major surface the LED filament is free from luminescent material.

2. The LED filament (100) according to claim 1, wherein in the off-state of the LED filament, the LED filament has a yellow appearance on both sides of the elongated carrier (101) or the LED filament has an orange appearance on both sides of the elongated carrier (101).

3. The LED filament (100) according to claim 1 or 2, wherein the coloured non- luminescent elongated outer encapsulant (103) at least partly encloses the plurality of LEDs (102) and at least partly covers the first major surface (10L).

4. The LED filament (100) according to any one of the preceding claims, further comprising a luminescent elongated encapsulant (104) at least partly enclosing the plurality of LEDs (102) and at least partly covering the first major surface (10L), the luminescentelongated encapsulant (104) comprising a luminescent material (110) configured to at least partly convert the LED light into converted light; wherein the LED filament light comprises one of (i) part of the LED light and at least part of the converted light, and (ii) at least part of the converted light.

5. The LED filament (100) according to claim 4, wherein the luminescent elongated encapsulant (104) is arranged between the first major surface (10L) and the coloured non-luminescent elongated outer encapsulant (103).

6. The LED filament (100) according to claim 4 or 5, wherein the coloured non- luminescent elongated outer encapsulant (103) fully hides or fully encloses the luminescent elongated encapsulant (104).

7. The LED filament (100) according to any one of claims 1 to 3, wherein at the side of the first major surface the LED filament is free from luminescent material.

8. The LED filament (100) according to any one of the preceding claims, wherein the coloured non-luminescent elongated outer encapsulant (103) is arranged to (i) diffuse at least part of the LED light and / or at least part of the converted light and / or (ii) absorb at least part of the LED light and / or to absorb part of the converted light.

9. The LED filament (100) according to any one of the preceding claims, wherein at most 2% of the emitted LED filament light in the visible wavelength range is in a wavelength range below 490 nm.

10. The LED filament (700) according to any one of the preceding claims, wherein the LED filament (700) further comprises at least one electrical contact and / or a frame (707), wherein the coloured non-luminescent elongated outer encapsulant (703) at least partly covers or at least partly encloses the at least one electrical contact and / or the frame (707).

11. The LED filament (100) according to any one of the preceding claims, wherein the coloured non-luminescent elongated outer encapsulant (103) is a coating and / or has a tubular shape.

12. The LED filament (100) according to any one of the preceding claims, wherein the coloured non-luminescent elongated outer encapsulant (103) comprises a polymer matrix.

13. The LED filament (100) according to any one of the preceding claims, wherein the coloured non-luminescent elongated outer encapsulant (103) comprises (i) a yellow non-luminescent dye and / or yellow non-luminescent particles, or (ii) an orange non- luminescent dye and / or orange non-luminescent particles.

14. A LED filament arrangement comprising a controller and a LED filament (100) according to any one of the claims 1 to 13, wherein the controller is configured to control the LED filament light emitted by the LED filament (100).

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

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