LED filament

Abstract

The present invention provides an LED filament arrangement (16) including a plurality of LEDs (22) adapted to emit LED light (24) disposed on a first major surface (20a) of an elongated carrier (18), and a first encapsulant (26a) at least partially surrounding the LEDs and at least partially covering the first major surface (20a), the first encapsulant comprising at least a light-scattering material adapted to scatter at least a portion of the LED light into scattered light and a light-conversion material adapted to convert at least a portion of the LED light into converted light (28) to provide an LED filament arrangement light (30). and a semi-reflective specular reflecting mirror (32) surrounding the LED filament configuration, the mirror having a reflectivity (R) configured to partially reflect the LED filament configuration light into reflected LED filament configuration light (34), and a transmittance, T, configured to partially transmit the LED filament configuration light into transmitted LED filament configuration light (36).

Description

[Technical Field]

[0001] The present invention relates to a light emitting diode (LED) filament. The present invention also relates to an LED filament lamp including at least one such LED filament. [Background technology]

[0002] A trend in lighting is the LED filament lamp, an LED lamp designed to resemble a traditional incandescent light bulb with a visible filament for aesthetic and light distribution purposes, but with the high efficiency of a light-emitting diode.

[0003] US2022186889A1 discloses an LED filament comprising an elongated substrate and a plurality of LEDs mechanically coupled to the substrate. The LED filament in US2022186889A1 further comprises an at least partially optically transparent encapsulation encapsulating the plurality of LEDs and at least partially encapsulating the substrate, and a plurality of at least partially optically reflective particles disposed on the outer surface of the encapsulation. According to US2022186889A1, the at least partially optically reflective particles on the outer surface of the encapsulation can impart a sparkling appearance to the LED filament in an off state (i.e., when the LEDs of the filament are not turned on) by reflecting ambient light (external light, ambient light, i.e., light from other light sources) in various directions. This sparkling appearance can enhance the decorative features of the LED filament. Furthermore, the at least partially light-reflective particles on the encapsulant surface can redirect the light emitted by the LED to other angles in the on state (i.e., when the LEDs of the filament are turned on). This redirection may result in a more omnidirectional diffusion of the emitted light, which can give the light a softer appearance and reduce the sharp contrast often caused by conventional LED filaments. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to improve the performance, functionality and / or appearance of LED filaments. [Means for solving the problem]

[0005] According to a first aspect of the present invention, this and other objects are provided by a light emitting diode (LED) filament arrangement providing LED filament light, the LED filament comprising: a plurality of LEDs adapted to emit LED light arranged on a first main surface of an elongated carrier; and a first encapsulant at least partially surrounding the plurality of LEDs and at least partially covering the first main surface of the elongated carrier, the first encapsulant comprising at least one of a light-scattering material adapted to scatter at least a portion of the LED light into scattered light and a light-converting material adapted to convert at least a portion of the LED light into converted light, for providing LED filament arrangement light, the LED filament arrangement light comprising the scattered light and / or the converted light, and optionally the LED light; and a semi-reflective specular-reflecting mirror (completely) surrounding the LED filament arrangement. This is achieved by an LED filament including a semi-reflective specular reflecting mirror having a reflectivity (R) configured to partially reflect the LED filament configuration light provided by the LED filament configuration into reflected LED filament configuration light, and a transmittance (T) configured to partially transmit the LED filament configuration light provided by the LED filament configuration into transmitted LED filament configuration light.

[0006] Herein, an LED filament configuration is understood to be a subset of an LED filament. Furthermore, "specular-reflecting" should be understood to provide a mirror-like reflection of light, as opposed to, for example, diffuse reflection. Furthermore, the transmitted LED filament configuration light may form (at least a portion of) the LED filament light.

[0007] The present invention is based, at least in part, on the realization that a nice LED filament providing a decorative light effect can be provided by surrounding an LED filament configuration, which may correspond to a conventional LED filament, with a semi-reflective specular mirror. Furthermore, the semi-reflective specular mirror can beneficially hide the usually yellow / orange color of the underlying LED filament configuration. In other words, an LED filament configuration, which may correspond to a conventional LED filament as described above, can be hidden by the semi-reflective specular mirror.

[0008] The LED filament light may be white light. To this end, the LEDs may be, for example, blue LEDs, and the light conversion material may include a phosphor, such as a green-yellow phosphor (which converts part of the blue LED light into green-yellow converted light) and a red phosphor (which converts part of the blue LED light into red converted light). This white light may have a first correlated color temperature (CCT1) in the range of 1500K to 6500K (preferably in the range of 1600K to 3000K, more preferably in the range of 1700K to 2700K, and most preferably in the range of 1800K to 2500K) and a first color rendering index (CRI1) of at least 80. The resulting effect is improved transmitted LED filament light. This is because, starting from high-quality light, the transmitted light is likely to also have high quality, even though part of the spectrum is reflected. The provided LED filament light may have a second color rendering index (CRI2), which may be higher than CRI1.

[0009] The reflectance of the semi-reflective specular mirror may be ≥30%, and / or the transmittance of the semi-reflective specular mirror may be ≥30%. The reflectance and transmittance may be average reflectance and average transmittance across the visible wavelength range of 400 nm to 800 nm. For a pleasing appearance and / or decorative light, a reflectance of ≥30%, particularly ≥40%, is required. For good efficiency, a transmittance of ≥30%, particularly ≥40%, is required. Excessive reflection will result in excessive light loss. Furthermore, the absorption of the semi-reflective specular mirror may be less than 10%, preferably less than 5%, more preferably less than 3%, and most preferably less than 2%, e.g., 1% or 0%.

[0010] The semi-reflective specular mirror may have a consistent reflectivity across the wavelength range of 400 nm to 800 nm. That is, the semi-reflective specular mirror reflects the LED filament light in the same way regardless of the color / wavelength of the LED filament light. In this way, a relatively simple / inexpensive semi-reflective specular mirror can be used while still hiding the underlying LED filament, which is typically yellow / orange. If the semi-reflective specular mirror has this consistent reflectivity, the LED filament may have a silvery appearance (when turned off).

[0011] Alternatively, the semi-reflective specular mirror has a non-constant optical reflectance and non-constant optical transmittance (T) versus wavelength across the wavelength range of 400 nm to 800 nm. In this way, various optical effects can be achieved. Preferably, for one or more sub-wavelength ranges within the wavelength range of 400 nm to 800 nm, the semi-reflective specular mirror has a reflectance of at least 70% (and preferably ≦95%, i.e., 70≦R≦95), and for one or more further sub-wavelength ranges within the wavelength range of 400 nm to 800 nm, the semi-reflective specular mirror has a transmittance of at least 70%.

[0012] The semi-reflective specular mirror may be configured to (i) primarily reflect blue light by having a reflectance R of at least 70% in the blue wavelength range and primarily transmit green and red light by having a transmittance T of at least 70% in the green and red wavelength ranges, or (ii) primarily reflect green light by having a reflectance R of at least 70% in the green wavelength range and primarily transmit blue and red light by having a transmittance T of at least 70% in the blue and red wavelength ranges, or (iii) primarily reflect red light by having a reflectance R of at least 70% in the red wavelength range and primarily transmit blue and green light by having a transmittance T of at least 70% in the blue and green wavelength ranges.

[0013] In an embodiment in which the LED filament light is white light having a first correlated color temperature (CCT1) and the first encapsulant includes a light conversion material adapted to convert at least a portion of the LED light to converted light, a semi-reflective specular mirror may be configured to primarily reflect light within a blue wavelength range such that LED light not initially converted by the light conversion material is reflected back to the first encapsulant including the light conversion material, whereby at least a portion of the LED light not initially converted by the light conversion material is converted by the light conversion material after reflection by the semi-reflective specular mirror so that the LED filament light is white light having a second correlated color temperature (CCT2) lower than the first correlated color temperature (CCT1) of the white LED filament light. A lower CCT2 may be achieved, for example, by the reflected blue LED light being absorbed by a green phosphor light conversion material in the first encapsulant to produce more green light and / or by a red phosphor light conversion material in the first encapsulant to produce more red light. For example, CCT2 = CCT1 - 500K.

[0014] Also, if the semi-reflective specular mirror is configured to primarily reflect blue light, the LED filament may alternatively have a thinner (first) encapsulant containing a light conversion material to (substantially) maintain the “original” correlated color temperature CCT1.

[0015] Also, if the semi-reflective specular mirror is configured to reflect primarily blue light, the LED filament will appear blue when off.

[0016] Also, if the semi-reflective specular mirror is configured to primarily reflect blue light, more red light may be generated by the light conversion material, which in turn may increase the CRI of the LED filament light (CRI2>CRI1).

[0017] In another embodiment in which the first encapsulant includes a light conversion material adapted to convert at least a portion of the LED light to converted light, a semi-reflective specular mirror is configured to primarily reflect light in the green wavelength range (but transmit blue and red light) such that, when the LED filament is on, at least a portion of the converted light is reflected back to the first encapsulant including the first light conversion material, whereby, after reflection by the semi-reflective specular mirror, at least a portion of the converted light may be reconverted by the light conversion material into reconverted light having a peak wavelength higher than the peak wavelength of the converted light, which in turn can result in white LED filament light having a correlated color temperature CCT3 different from CCT1. This embodiment can also provide an environmentally friendly color for the LED filament when it is off (i.e., when the LEDs are not emitting LED light).

[0018] Alternatively, the semi-reflective specular mirror may be configured to primarily reflect red light to provide a flame glowing effect of the LED filament when it is off. Additionally, when the LED filament is on, the semi-reflective specular mirror reflects red phosphor (light conversion material) light, which is typically not (re)absorbed and therefore does not affect the correlated color temperature of the white LED filament light.

[0019] Notwithstanding the above, the semi-reflective specular mirror is preferably (at least) partially transmissive to blue, green and red to enable providing white LED filament light.

[0020] In one embodiment, the semi-reflective specular mirror (with non-constant light reflectivity) is a dichroic mirror, which can selectively reflect a (small / limited) range of colors / wavelengths of light while transmitting other colors / wavelengths.

[0021] In another embodiment, the semi-reflective specular mirror (having a non-constant light reflectivity) is a cholesteric mirror. For details about cholesteric mirrors themselves, see Gao, Y.; Luo, Y.; Lu, J. High-Reflective Templated Cholesteric Liquid Crystal Filters. Molecules 2021, 26, 6889. https: / / doi.org / 10.3390 / molecules26226889 (the contents of which are incorporated herein by reference).

[0022] A semi-reflective specular mirror (which has a non-constant reflectivity of light depending on the wavelength of the light) may have color-variable reflection along its length. In this way, an LED filament may exhibit different colors along its length when off, and there may be different light colors (CCTs) along the length of the LED filament when on. A semi-reflective specular mirror may, for example, have different regions with different color reflections along its length. The different regions may be discrete (stepped), or there can be a gradual transition between the different color reflectances (i.e., a gradual change in color variable reflectance over the length of the filament). The different regions may also have the same or different lengths. The different regions may, for example, include at least a first region having a first color reflectance (e.g., primarily reflecting blue light), a second region having a different color reflectance (e.g., primarily reflecting red light), and optionally a third region having a different color reflectance (e.g., primarily reflecting green light). If the semi-reflective specular mirror having color variable reflectance over its length is a cholesteric mirror, the color variable reflectance of the cholesteric mirror can be tuned by the pitch of the molecular structure of the cholesteric mirror.

[0023] The semi-reflective specular mirror may be flexible and / or may be arranged in a curved configuration around the LED filament arrangement as viewed in a cross section of the LED filament perpendicular to the longitudinal axis of the LED filament. Alternatively, the semi-reflective specular mirror may be arranged in a polygonal (e.g., rectangular) configuration around the LED filament arrangement, for example.

[0024] The LED filament configuration may have a spiral or helix shape and the semi-reflective specular reflector has a corresponding spiral or helix shape, resulting in the LED filament (as a whole) having a spiral or helix shape or configuration. Alternatively, the LED filament configuration may have a linear (straight) shape and the semi-reflective specular reflector has a cylindrical shape, e.g., a right circular or elliptical cylinder, resulting in the LED filament (as a whole) having a linear / straight shape or configuration.

[0025] The semi-reflective specular mirror may be continuous and / or extend along (substantially) the entire length of the LED filament arrangement, such that the complete LED filament arrangement may be hidden by the semi-reflective specular mirror and the light effect provided by the semi-reflective specular mirror may be provided across the entire LED filament.

[0026] The semi-reflective specular mirror may be in (physical / mechanical) contact with the encapsulant. This provides at least a slim LED filament. Alternatively, the semi-reflective specular mirror may be positioned at a distance (e.g., ≦7 mm or ≦3 mm) from the encapsulant using, for example, an air gap or a transparent further encapsulant such as silicone. The transparent further encapsulant may be, for example, a silicone adhesive that fixes the semi-reflective specular mirror to (the outside of) the encapsulant of the LED filament configuration.

[0027] The semi-reflective specular mirror may be disposed on a foil, for example a sheet with a blue (or red or green) dichroic layer.

[0028] According to a second aspect of the present invention, there is provided an LED filament lamp including at least one light-emitting diode (LED) filament according to the first aspect. The LED filament lamp may include, for example, a single LED filament or dual LED filaments, typically, but not necessarily, in a spiral or helical configuration. Alternatively, the LED filament lamp may include multiple LED filaments (e.g., 2 to 8 LED filaments), typically in a linear or straight configuration. The LED filament lamp may further include an envelope inside which at least one light-emitting diode filament is disposed, and a cap (including a base) for electrically and mechanically connecting the LED filament lamp to an external socket, particularly a socket of a lighting fixture. The envelope is preferably a light-transmitting envelope. The light-transmitting envelope may be made of, for example, glass. The light-transmitting envelope may have various shapes, such as a bulb, a candle, a globe, etc. The cap or base may be, for example, E14, E27, B22, etc. The LED filament lamp may also be, for example, a (retrofit) light bulb.

[0029] It is to be noted that the invention relates to all possible combinations of the features recited in the claims. [Brief explanation of the drawings]

[0030] This and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings, which illustrate one or more embodiments of the present invention. As shown in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and are thus provided to illustrate the general structure of embodiments of the present invention. Like reference numerals refer to like elements throughout. [Figure 1] FIG. 1 is a schematic cross-sectional view of an LED filament according to one or more embodiments of the present invention. [Figure 2]FIG. 2 is a schematic side view of the LED filament of FIG. [Figure 3] FIG. 3 is a schematic side view of the LED filament configuration of the LED filament of FIGS. [Figure 4] FIG. 4 is a diagram of constant light reflectance. [Figure 5] 5a-c are diagrams of non-constant light reflectance. [Figure 6] Figure 6 shows the (CIE 1931) color space with various correlated color temperatures. [Figure 7] 7a-b are schematic cross-sectional views of LED filaments according to different embodiments. [Figure 8] 8a-b are side views of an embodiment of the present LED filament in which the semi-reflective specular mirror has a color-variable reflection along its length. [Figure 9] 9a-d are diagrams of various LED filament lamps according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention is described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. However, the present invention may 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, so that the scope of the disclosure will be fully conveyed to those skilled in the art.

[0032] 1-2 illustrate an LED filament 10 adapted to provide an LED filament light 12 according to one or more embodiments of the present invention. In particular, FIG. 1 illustrates a cross-section of the LED filament 10 in a plane perpendicular to the longitudinal axis 14 of the LED filament 10, e.g., cross-section AA in FIG. 2.

[0033] Preferably, the LED filament 10 has a length L and a width W, where L>5W. The width W may be, for example, in the range of 0.5-5 mm. The LED filament 10 may be arranged in a linear configuration (see Figures 2 and 9a) or in a non-linear configuration, for example, a curved configuration, a 2D / 3D spiral or helix (see Figures 9b-c).

[0034] The LED filament 10 includes an LED filament configuration 16, shown separately in Figure 3. Here, an LED filament configuration should be interpreted as a subset of the LED filament 10. Consistent with the overall configuration of the LED filament 10, the LED filament configuration 16 may have a linear (straight) shape, as in Figure 3, or a spiral or helical shape.

[0035] The LED filament configuration 16 includes an elongated carrier 18. The elongated carrier 18 may have substantially the same length and width as the LED filament 10. The elongated carrier 18 may be a substrate, such as a printed circuit board (PCB). The elongated carrier 18 may be rigid (e.g., made from a polymer, glass, quartz, metal, or sapphire) or flexible (e.g., made from a polymer or metal, such as a film or foil). The elongated carrier 18 has a first major surface 20a and an opposite second major surface 20b. The carrier 18 may be reflective or light-transmitting, such as translucent and preferably transparent.

[0036] The LED filament configuration 16 further includes a plurality of light-emitting diodes (LEDs) 22 disposed on the elongated carrier 18. Specifically, the plurality of LEDs 22 may be disposed on at least the first major surface 20a of the elongated carrier 18. The plurality of LEDs 22 are typically arranged in a linear array. The plurality of LEDs 22 are adapted to emit LED light 24. That is, when the plurality of LEDs 22 are turned on, they emit LED light 24. The plurality of LEDs 22 may be, for example, blue LEDs adapted to emit blue LED light 24. Alternatively, the plurality of LEDs 22 may be or include red, green, and blue LEDs adapted to emit red, green, and blue LED light, respectively, which may combine to form white light. The number of LEDs 22 may be, for example, at least 10, preferably at least 15, more preferably at least 20, and most preferably at least 25, e.g., 30 or 40 LEDs.

[0037] The LED filament configuration 16 further includes an encapsulant 26a that (at least partially) surrounds the plurality of LEDs 22 and (at least partially) covers the first major surface 22a of the elongated carrier 18. The encapsulant 26a may be elongated, similar to the elongated carrier 18. The encapsulant 26a includes at least one of a light-scattering material adapted to scatter at least a portion of the LED light 24 into scattered light and a light-converting material adapted to convert at least a portion of the LED light 24 into converted light 28 to provide an LED filament configuration light 30, the LED filament configuration light 30 including the scattered light and / or the converted light 28, and optionally the LED light 24. The light-scattering material may be light-scattering particles, such as BaSO, TiO, and / or AlO. The light-converting material may be a luminescent material, such as an inorganic phosphor and / or a phosphor such as quantum dots or quantum rods. In particular, the light conversion material may include one or more of a green phosphor, a green-yellow phosphor, and a red phosphor. Apart from the light scattering material and / or the light conversion material, the encapsulant 26a may be made of a polymer material, which may be flexible, such as silicone.

[0038] The LED filament light 30 is typically white light and may be realized using, for example, a blue LED adapted to emit blue LED light 24 and a light conversion material such as a phosphor. The white LED filament light 30 may have a first correlated color temperature CCT1 in the range of 1500K to 6500K and a first color rendering index of at least 80.

[0039] The LED filament configuration 16 may further include a second encapsulant 26b at least partially covering the second major surface 20b of the elongated carrier 18; in this case, the aforementioned encapsulant 26a may be referred to as a first encapsulant 26a. The second encapsulant 26b may also include at least one of a light-scattering material and a light-converting material. As seen in FIG. 1 , the cross-section of the LED filament configuration 16 including the first encapsulant 26a and the (optional) second encapsulant 26b may have, for example, a circular or elliptical outer profile.

[0040] According to the present invention, the LED filament 10 further includes a semi-reflective specular mirror 32 surrounding the LED filament arrangement 16. The semi-reflective specular mirror 32 is configured to partially reflect the LED filament arrangement light 30 into reflected LED filament arrangement light 34 and to partially transmit the LED filament arrangement light 30 into transmitted LED filament arrangement light 36. The transmitted LED filament arrangement light 36 may form (at least a portion of) the aforementioned LED filament light 12, and the reflected LED filament arrangement light 34 may be (re)absorbed by a light conversion material.

[0041] The semi-reflective specular mirror 32 surrounding the LED filament arrangement 16 may result in the LED filament 10 providing decorative light effects, as exemplified below. Furthermore, the semi-reflective specular mirror 32 may beneficially hide (when the LEDs 22 are off) the typical yellow / orange color of the underlying LED filament arrangement 16. In other words, the LED filament arrangement 16, which may correspond to a conventional LED filament, may be hidden by the semi-reflective specular mirror 32.

[0042] The semi-reflective specular mirror 32 should completely surround the LED filament configuration 16 both circumferentially (see FIG. 1) and longitudinally (see FIG. 2). To this end, the semi-reflective specular mirror 32 may be continuous and disposed around the complete outer profile (e.g., in a curved configuration) of the LED filament configuration 16 (see FIG. 1) and extend along the entire length L′ of the LED filament configuration 16 (see FIG. 2).

[0043] Furthermore, if the LED filament configuration 16 has a linear (straight) shape, the semi-reflective specular reflecting mirror 32 may have a corresponding cylindrical shape, such as a right circular or elliptical cylindrical shape (see FIGS. 1-2). Alternatively, if the LED filament configuration 16 has a spiral or helical shape, the semi-reflective specular reflecting mirror 32 may have a corresponding spiral or helical shape, such that the LED filament 10 (as a whole) has a spiral or helical shape or configuration (see FIGS. 9b-c).

[0044] Furthermore, the semi-reflective specular mirror 32 may be in direct contact with the encapsulant 26a and the optional second encapsulant 26b, for example, using an adhesive. Alternatively, the semi-reflective specular mirror 32 may be positioned a distance D from the encapsulant 26a and the optional second encapsulant 26b using a transparent additional encapsulant 38, such as an air gap or silicone. The air gap may be achieved using a holder (not shown). The holder may be attached, for example, to a portion of the electrode at the end of the LED filament 10. The transparent additional encapsulant 38 may be, for example, a silicone adhesive that secures the semi-reflective specular mirror 32 to the encapsulant 26a and the optional second encapsulant 26b. The distance D is preferably ≦3 mm. The thickness of the semi-reflective specular mirror 32 may be in the range of 0.05 to 2 mm, typically 0.2 mm, allowing the LED filament 10 to maintain its typical, slim appearance.

[0045] The reflectance R of the semi-reflective specular mirror 32 may be R≧30%, particularly R≧40%. The transmittance T of the semi-reflective specular mirror 32 may be T≧30%, particularly T≧40%. The reflectance R and transmittance T may be average reflectance and average transmittance over the visible wavelength range of 400 nm to 800 nm. The absorbance of the semi-reflective specular mirror 32 may be less than 10%, preferably less than 5%, more preferably less than 3%, and most preferably less than 2%, for example, 1% or 0%.

[0046] The semi-reflective specular mirror 32 may have a constant light reflectivity (relative to wavelengths, here those of the LED filament light 30 and / or ambient light) over a wavelength range of 400 nm to 800 nm, as shown illustratively in Figure 4, where reflectivity R is on the vertical axis and wavelength is on the horizontal axis.

[0047] Alternatively, the semi-reflective specular mirror 32 may have a non-constant optical reflectance (and non-constant optical transmittance (T)) for wavelengths of light across the wavelength range of 400 nm to 800 nm, as exemplarily shown in FIGS. 5a-c. For example, as in FIG. 5a, for the blue sub-wavelength range, the semi-reflective specular mirror 32 may have a reflectance of at least 70%, while for further / other sub-wavelength ranges (green and red), the semi-reflective specular mirror may have a transmittance of at least 70%. Thus, in FIG. 5a, the semi-reflective specular mirror 32 is configured to primarily reflect blue light, i.e., to primarily reflect light within the blue wavelength range. The semi-reflective specular mirror 32 with a non-constant optical reflectance may be, for example, a dichroic mirror.

[0048] In one embodiment, the LED light 24 is blue, the LED filament light 30 is white light having a first correlated color temperature CCT1, and the semi-reflective specular / dichroic mirror 32 is configured to primarily reflect the blue light (and transmit other colors / wavelengths, see FIG. 5a) so that the LED filament light 12 is white light having a second correlated color temperature CCT2 that is lower than CCT1. For example, CCT2=CCT1−500K (see FIG. 6). A lower CCT2 can be achieved by having blue LED light 24′ that is not initially converted by the light-conversion material reflected back by mirror 32 as reflected blue LED light 42, which is absorbed by the green phosphor light-conversion material in first encapsulant 26a and optional encapsulant 26b to produce more green light 28 and by the red phosphor light-conversion material in first encapsulant 26a and optional encapsulant 26b to produce more red light 28 (see FIG. 7a). Also, if semi-reflective specular mirror 32 is configured to primarily reflect blue light, LED filament 10 will appear blue in the off state.

[0049] In another embodiment, the semi-reflective specular / dichroic mirror 32 is configured to primarily reflect green light so that the LED filament 10 exhibits an environmentally friendly color (more green) when the LED filament 10 is off (see FIG. 5b). Furthermore, when the LED filament 10 is on, the semi-reflective specular / dichroic mirror 32 reflects green phosphor (light conversion material) light 44 (see FIG. 7b) back to the first encapsulant 26a and / or optional encapsulant 26b, so that at least a portion of this light 44 may be reconverted into reconverted light 28′ by the light conversion material (e.g., green phosphor) in the first encapsulant 26a and / or optional encapsulant 26b. The reconverted light 28′ may have a peak wavelength higher than the peak wavelength of the converted light 28, which in turn can result in a white LED filament light 12 having a correlated color temperature CCT3 different from CCT1 (see FIG. 6).

[0050] In yet another embodiment, the semi-reflective specular / dichroic mirror 32 is configured to primarily reflect red light so that the LED filament 10 exhibits a flame-like effect (more red) when the LED filament 10 is off (see FIG. 5c). Furthermore, when the LED filament 10 is on, the semi-reflective specular / dichroic mirror 32 reflects red phosphor (light conversion material) light, which is typically not (re)absorbed and therefore does not affect the correlated color temperature of the white LED filament light 12.

[0051] 8a-b, a semi-reflective specular mirror 32 with non-constant reflectivity may have a color-variable reflectance over its length L''. This mirror 32 may be, for example, a dichroic or cholesteric mirror.

[0052] In FIG. 8a, the semi-reflective specular mirror 32 has a first region 40a facing one end of the LED filament 10, a second region 40c facing the opposite end of the LED filament, and a third, intermediate region 40b between the first region 40a and the second region 40c. For example, the first region 40a may be configured to primarily reflect blue light, the second region 40c may be configured to primarily reflect green light, and the third region 40b may be configured to primarily reflect red light. Furthermore, the regions 40a-c in FIG. 8a are discrete and have equal lengths. This allows a viewer to see different color effects on the LED filament 10 in the off state. A viewer may also see differences in the color (temperature) of the light in the on state, at least in the near field.

[0053] In FIG. 8b, the semi-reflective specular mirror 32 is configured to primarily reflect light of a first color at one end 46a of the LED filament 10, and further configured to primarily reflect light of a second color (different from the first color) at the opposite end 46b of the LED filament 10, with a gradual transition therebetween.

[0054] Figures 9a-d are diagrams of various LED filament lamps 100a-d, each including at least one LED filament 10. Figure 9a is a perspective view, and Figures 9b-d are side views.

[0055] In FIG. 9a, the LED filament lamp 100a includes multiple LED filaments 10, i.e., four LED filaments 10. Here, each LED filament 10 has a linear or straight configuration. The LED filaments 10 may be arranged substantially vertically, as seen in the diagram of FIG. 9a. The LED filaments 10 may also be substantially parallel to one another. The LED filaments 10 may have semi-reflective specular mirrors 32 with the same or different reflective properties. For example, the semi-reflective specular mirrors 32 of all the LED filaments 10 may be configured to primarily reflect green light so that they appear green when they are off.

[0056] 9b-c, each LED filament lamp 100b-c includes only one LED filament 10. Here, the LED filament 10 has a spiral or helical configuration. The LED filament 10 may be arranged substantially vertically, as can be seen in the views of FIGS.

[0057] The semi-reflective specular mirror 32 of the LED filament 10 of Figure 9b may be, for example, a dichroic mirror configured to primarily reflect blue light. In this way, the LED filament 10 of Figure 9b may appear bluer (more) when off due to the blue color of the ambient light reflected by the dichroic mirror 32, and may provide a white LED filament light 12 that is warmer / less cool (e.g., CCT2) when on, as previously described.

[0058] The semi-reflective specular mirror 32 of the LED filament 10 of Figure 9c has a color-variable reflectivity over its length L''. For example, the mirror 32 may have a blue lower region 40a (near / proximal to the cap 104) that gradually transitions to an upper yellow region 40d (far / distal from the cap 104).

[0059] In Fig. 9d, the LED filament lamp 100d includes only one LED filament 10 having a linear / rectangular configuration. The semi-reflective specular mirror 32 of the LED filament 10 of Fig. 9d has a color-variable reflectivity over its length L'', where blue, red, and green regions 40a-c are arranged in succession as triplets.

[0060] Each of the LED filament lamps 100a-d may further include a light-transmitting envelope 102 in which at least one LED filament 10 is disposed, and a cap 104 (including a base) for electrically and mechanically connecting the LED filament lamp 100a-d to a socket (not shown) of a lighting fixture. The light-transmitting envelope 102 may be made of glass, for example. The light-transmitting envelope 102 may have various shapes, such as a bulb, a candle, a globe, etc. The cap or base 104 may be, for example, E14, E27, B22, etc. The LED filament lamps 100a-d may also be, for example, a (retrofit) light bulb.

[0061] Those skilled in the art will recognize that the present invention is by no means limited to the preferred embodiments described above: on the contrary, many modifications and variations are possible within the scope of the appended claims.

[0062] For example, the semi-reflective specular mirror 32 may be disposed on a foil, e.g., a sheet having a blue (or red or green) dichroic layer. The dichroic layer may be on the outside, facing away from the first encapsulant 26a and the optional second encapsulant 26b. An advantage of having the dichroic layer on the outside is reduced mechanical stress in the dichroic layer. Alternatively, the dichroic layer may be on the inside, facing the first encapsulant 26a and the optional second encapsulant 26b. An advantage of having the dichroic layer on the inside is that the dichroic layer is better protected, for example, from scratches.

[0063] Furthermore, variations to the disclosed embodiments can be understood by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims, and can be implemented in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. LED Filament A light emitting diode (LED) filament that provides light, the LED filament comprising: an LED filament configuration comprising: a plurality of LEDs adapted to emit LED light arranged on a first main surface of an elongated carrier; and a first encapsulant at least partially surrounding the plurality of LEDs and at least partially covering the first main surface of the elongated carrier, wherein the first encapsulant comprises at least one of a light-scattering material adapted to scatter at least a portion of the LED light into scattered light and a light-conversion material adapted to convert at least a portion of the LED light into converted light to provide an LED filament configuration light, the LED filament configuration light comprising the scattered light and / or the converted light, and optionally the LED light; a semi-reflective specular reflecting mirror surrounding the LED filament configuration, the semi-reflective specular reflecting mirror having a reflectivity configured to partially reflect the LED filament configuration light provided by the LED filament configuration into reflected LED filament configuration light, and a transmittance configured to partially transmit the LED filament configuration light provided by the LED filament configuration into transmitted LED filament configuration light; Including, a first encapsulant including a light conversion material adapted to convert at least a portion of the LED light into converted light, and a semi-reflective specular mirror configured to primarily reflect light within a green wavelength range such that at least a portion of the converted light is reflected back into the first encapsulant including the first light conversion material, whereby at least a portion of the converted light is reconverted by the light conversion material after reflection by the semi-reflective specular mirror into reconverted light having a peak wavelength higher than the peak wavelength of the converted light.

2. 10. The light emitting diode filament of claim 1, wherein the LED filament comprises a white light having a first correlated color temperature in the range of 1500K to 6500K and a first color rendering index of at least 80.

3. 3. The light-emitting diode filament according to claim 1, wherein the reflectance of the semi-reflective specular mirror is ≥ 30% and the transmittance of the semi-reflective specular mirror is ≥ 30%.

4. 4. A light-emitting diode filament according to claim 1, wherein the semi-reflective specular mirror has a non-constant light reflectance and a non-constant light transmittance with respect to wavelength over a wavelength range of 400 nm to 800 nm, and for one or more sub-wavelength ranges within the wavelength range of 400 nm to 800 nm, the semi-reflective specular mirror has a reflectance of at least 70%, and for one or more further sub-wavelength ranges within the wavelength range of 400 nm to 800 nm, the semi-reflective specular mirror has a transmittance of at least 70%.

5. 5. The light-emitting diode filament of claim 4, wherein the semi-reflective specular mirror is configured to (i) primarily reflect blue light by having at least 70% reflectivity in the blue wavelength range and primarily transmit green and red light by having at least 70% transmittance in the green and red wavelength ranges, or (ii) primarily reflect green light by having at least 70% reflectivity in the green wavelength range and primarily transmit blue and red light by having at least 70% transmittance in the blue and red wavelength ranges, or (iii) primarily reflect red light by having at least 70% reflectivity in the red wavelength range and primarily transmit blue and green light by having at least 70% transmittance in the blue and green wavelength ranges.

6. 6. The light-emitting diode of claim 2, wherein the first encapsulant includes a light conversion material adapted to convert at least a portion of the LED light into converted light, and the semi-reflective specular reflecting mirror is configured to primarily reflect light within a blue wavelength range such that LED light that is not initially converted by the light conversion material is reflected back into the first encapsulant including the light conversion material, whereby at least a portion of the LED light that is not initially converted by the light conversion material is converted by the light conversion material after reflection by the semi-reflective specular reflecting mirror so that the LED filament light is white light having a second correlated color temperature that is lower than the first correlated color temperature.

7. 7. A light-emitting diode filament according to claim 1, wherein the semi-reflective specular mirror is a dichroic mirror.

8. 8. A light emitting diode filament according to any one of claims 1 to 7, wherein the semi-reflective specular mirror has a color-variable reflectance over its length.

9. 9. A light emitting diode filament according to any one of claims 1 to 8, wherein the semi-reflective specular mirror is flexible and is arranged in a curved configuration around the LED filament arrangement.

10. 10. A light emitting diode filament according to any one of claims 1 to 9, wherein the LED filament configuration has a spiral or helical shape and the semi-reflective specular reflecting mirror has a corresponding spiral or helical shape.

11. 9. A light emitting diode filament according to any one of claims 1 to 8, wherein the LED filament arrangement has a linear shape and the semi-reflective specular reflector has a cylindrical shape.

12. 12. A light emitting diode filament according to any one of claims 1 to 11, wherein the semi-reflective specular mirror is continuous and extends along the entire length of the LED filament arrangement.

13. 13. A light emitting diode filament according to any one of claims 1 to 12, wherein the semi-reflective specular mirror is in contact with the encapsulant or is located at a distance of ≦3 mm from the encapsulant.

14. An LED filament lamp, At least one light-emitting diode filament according to any one of claims 1 to 13; an envelope within which the at least one light emitting diode filament is disposed; a base for electrically and mechanically connecting the LED filament lamp to a socket of a lighting fixture; An LED filament lamp comprising:

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