Virtual LED filaments via multiple reflections

Abstract

The invention provides a light generating system (1000) comprising a LED filament (400), a first optical element (500), and a second optical element (600); wherein: (A) the first optical element (500) and the second optical element (600) are configured parallel; wherein the first optical element (500) and the second optical element (600) have a shortest mutual distance (d1); (B) the LED filament (400) comprises (i) an array of a plurality of solid state light sources (10) arranged on an elongated carrier (450), and (ii) an elongated encapsulant (410) at least partly enclosing the plurality of solid state light sources (10) and covering at least part of the elongated carrier (450); wherein the LED filament (400) is configured to generate filament light (401); wherein the LED filament (400) comprises a light emitting surface (420), wherein during operation of the LED filament (400) the filament light (401) escapes from the LED filament (400) via the light emitting surface (420); wherein the light emitting surface (420) is configured in between the first and second optical elements (500,600) and extending from the first optical element (500) to the second optical element (600); (C) each of the first optical element (500) and the second optical element (600) is configured to specularly reflect at least 25% of the filament light (401) received by the first and second optical element (500,600), respectively; and (D) the first optical element (500) is further configured to transmit 25-75% of the filament light (401) received by the first optical element (500).

Description

[0001] VIRTUAL LED FILAMENTS VIA MULTIPLE REFLECTIONS

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a light generating system. The invention further relates to a lighting device comprising the light generating system.

[0004] BACKGROUND OF THE INVENTION

[0005] Virtual light sources are known in the art. For instance, WO2015130327A1 describes lighting systems and devices including a light-transmissive tube and a light source assembly. The light-transmissive tube defines a cavity that extends along a longitudinal axis, at least a portion of the tube having an inner structured surface facing the cavity, and an outer structured surface facing away from the cavity. The light source assembly is disposed to inject light into the cavity, and includes one or more discrete light sources such as LED sources. The inner and outer structured surfaces of the tube are configured to direct a first portion of the injected light out of the tube through the outer structured surface and to direct a second portion of the injected light back into the cavity, such that a virtual filament, or pattern of virtual filaments, appears in the tube.

[0006] SUMMARY OF THE INVENTION

[0007] Conventional light generating systems (e.g. incandescent or fluorescent lamps) are rapidly being replaced by light emitting diode (LED) based lighting solutions. Especially LED filaments may be used, as LED filaments may have a relatively high efficiency. Due to their omnidirectional light emittance and options for decorative shaping, LED filaments may be especially suited to replace conventional filaments in filament (light) bulbs. However, in certain types of lamps and luminaires, limited space is available for the light source. In such lighting systems, either a spot light source (e.g. a LED package) or a short LED filament may be used. Spot light sources and short LED filaments may have as a disadvantage that there may be a relatively large contrast between the small and relatively bright beam of light source light and the relatively dark background, resulting in a higher degree of glare. Further, spot light sources and short LED filaments may be less energy-efficient and decorative than longer filaments. As such, there is a need and desire for a compact light generating system providing decorative lighting effects with reduced glare. Hence, it is an aspect of the invention to provide an alternative light generating system, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0008] According to a first aspect, the invention provides a light generating system comprising a LED filament, a first optical element, and a second optical element. The first optical element and the second optical element are configured parallel. Further, the first optical element and the second optical element have a shortest mutual distance di.

[0009] The LED filament comprises (i) an array of a plurality of solid state light sources arranged on (at least a first major surface of) an elongated carrier, and (ii) an elongated encapsulant at least partly enclosing the plurality of solid state light sources and covering at least part of the elongated carrier.

[0010] Further, the LED filament is configured to generate filament light.

[0011] The first optical element is configured to specularly reflect at least 25% of the filament light (perpendicularly) received by the first optical element. Additionally, the second optical element is configured to specularly reflect at least 25% of the filament light (perpendicularly) received by the second optical element.

[0012] The first optical element is further configured to transmit 25-75% of the filament light (perpendicularly) received by the first optical element.

[0013] The LED filament comprises a light emitting surface that is configured in between the first optical element and the second optical element. The light emitting surface extends from the first optical element to the second optical element over a distance of at least 0.8*di.

[0014] The LED filament has a projected shape in a projection on the second optical element, selected from the group of a circle, an ellipse, a spiral, and a polygonal shape.

[0015] Hence, the invention provides a light generating system comprising a LED filament, a first optical element, and a second optical element; wherein: (A) the first optical element and the second optical element are configured parallel; wherein the first optical element and the second optical element have a shortest mutual distance di; (B) the LED filament comprises (i) an array of a plurality of solid state light sources arranged on an elongated carrier, and (ii) an elongated encapsulant at least partly enclosing the plurality of solid state light sources and covering at least part of the elongated carrier; wherein the LED filament is configured to generate filament light; wherein the LED filament comprises a light emitting surface, wherein during operation of the LED filament the filament light escapes from the LED filament via the light emitting surface; wherein the light emitting surface is configured in between the first and second optical elements and extending from the first optical element to the second optical element; (C) the first optical element is configured to specularly reflect at least 25% of the filament light received by the first optical element, and the second optical element is configured to specularly reflect at least 25% of the filament light received by the second optical element; and (D) the first optical element is further configured to transmit 25-75% of the filament light received by the first optical element.

[0016] Such a light generating system may facilitate providing one or more virtual LED filaments. The one or more virtual LED filaments may provide a decorative effect or may form a decorative shape in the light generating system. Further, the one or more virtual LED filaments may facilitate that a radiant flux of the filament light may appear to be provided by either multiple or an enlarged LED filament, wherein the radiant flux may decrease with increasing distance from the (real) LED filament (in one or more directions). Hence, with such a configuration, a more gradual transition may be provided from the relatively bright (real) LED filament to the relatively dark background, such that a contrast between the relatively bright (real) LED filament and the relatively dark background may be reduced, thereby decreasing glare from the light generating system.

[0017] The light generating system may comprise the first optical element, the second optical element, and the LED filament, wherein the LED filament may be at least partially configured in between the first and second optical element. The combination of the first optical element, LED filament, and second optical element may especially be referred to as an optical assembly stack. Hence, the light generating system may comprise an optical assembly stack, wherein the optical assembly stack may comprise the first optical element, the LED filament, and the second optical element. The first optical element and second optical element may be semi-transparent mirror elements. Especially, the first (and / or second) optical element may be configured to specularly reflect (at least) part of the filament light received by the first (and / or second) optical element. Herein, the term “specularly reflect” may indicate that a beam of light may be reflected at the first (and / or second) optical element, wherein the angle of the reflected beam relative to a surface normal of the first (and / or second) optical element may be equal to the angle of the incoming beam relative to the surface normal of said first (and / or second) optical element. In embodiments, the first (and / or second) optical element may be configured to reflect at least 15%, such as at least 25%, especially at least 35%, of (the spectral power of) the filament light received by the first (and / or second) optical element (assuming perpendicular irradiation). Additionally or alternatively, the first (and / or second) optical element may be configured to reflect at most 90%, such as at most 80%, especially at most 75%, of (the spectral power of) the filament light received by the first (and / or second) optical element (assuming perpendicular irradiation). Yet, in embodiments, the second optical element may be a (reflective) mirror element. That is, the second optical element may be configured to (specularly) reflect > 75%, such as > 80%, especially > 90%, including (essentially) 100%, of (the spectral power of) the filament light received by the second optical element (assuming perpendicular irradiation). Hence, in specific embodiments, the second optical element may be configured to specularly reflect > 80% of the filament light received by the second optical element. Such a second optical element may facilitate providing virtual (extensions of the) LED filament(s) on only one side of the LED filament. Further, such a second optical element may facilitate emitting most of the filament light on one side of the light generating system.

[0018] The first (and / or second) optical element may further be configured to transmit (at least) part of the filament light received by the first (and / or second) optical element. Especially, the first (and / or second) optical element may be configured to specularly transmit the filament light, i.e., the first (and / or second) optical element may (essentially) not diffuse (or “scatter”) the filament light. In embodiments, the first (and / or second) optical element may be configured to transmit at least 15%, such as at least 25%, especially at least 35%, of (the spectral power of) the filament light received by the first (and / or second) optical element (assuming perpendicular irradiation). Additionally or alternatively, the first (and / or second) optical element may be configured to transmit at most 85%, such as at most 75%, especially at most 65%, of (the spectral power of) the filament light received by the first (and / or second) optical element (assuming perpendicular irradiation). That is, the first (and / or second) optical element may be configured to transmit (selected from the range of) 15-85%, such as 25-75%, especially 35-65%, of the filament light received by the first (and / or second) optical element. Hence, in specific embodiments, the second optical element may be configured to transmit 25-75% of the filament light received by the second optical element. Such a second optical element may facilitate providing virtual (extensions of the) LED filament(s) on at least two sides of the LED filament. Further, such a second optical element may facilitate that filament light may be emitted from at least two sides of the light generating system. Hence, the second optical element may in embodiments be: (i) a (reflective) mirror element, wherein the second optical element may be configured to reflect > 80% (and transmit < 20%) of the filament light; or (ii) a semi-transparent mirror element, wherein the second optical element may be configured to transmit (selected from the range of) 25-75% (and reflect selected from the range of 25-75%) of the filament light.

[0019] The first optical element may have a first length Li, a first width Wi, and a first height Hi, wherein the first width Wi and the first height Hi may be configured perpendicular to the first length Li and each other. In embodiments, the first optical element may have relatively high aspect ratios (Li / Hi and / or Wi / Hi). Especially, one or more may apply of (i) Li / Hi > 5, such as Li / Hi > 10, and (ii) Wi / Hi > 5, such as Wi / Hi > 10. The first optical element may be planar. Alternatively, the first optical element may be curved, such as especially along the first length Li and / or the first width Wi. In such embodiments, one may apply of (i) the first height Hi may be the same over the first length Li and first width Wi (i.e., both a first and second major surface of the first optical element may be curved with (essentially) the same curvature); and (ii) the first height Hi may change over the first length Li and / or first width Wi, wherein one of the following may apply: (a) one of a first and second major surface of the first optical element may be curved, while the other of the first and second major surface may be planar; and (b) both the first and second major surface of the first optical element may be curved, wherein the first major surface may curve in an opposite direction from (and / or with a different curvature than) the second major surface. Further, the first optical element may be curved, wherein at least one of the first and second major surface may be configured concave or convex with respect to the LED filament.

[0020] Similarly, the second optical element may have a second length L2, a second width W2, and a second height H2. The second length L2 may be equal to the first length Li. Alternatively, the first length Li and second length L2 may differ. Similarly, the second width W2 may be equal to or differ from the first width Wi. Additionally, the second height H2 may be equal to or differ from the first height Hi. In embodiments, the second optical element may have relatively high aspect ratios (L2 / H2 and / or W2 / H2). Especially, one or more may apply of (i) L2 / H2 > 5, such as L2 / H2 > 10, and (ii) W2 / H2 > 5, such as W2 / H2 > 10. The second optical element may be planar. Alternatively, the second optical element may be curved, such as especially along the second length L2 and / or the second width W2. In such embodiments, one may apply of (i) the second height H2 may be the same over the second length L2 and second width W2 (i.e., both a first and second major surface of the second optical element may be curved with (essentially) the same curvature); and (ii) the second height H2 may change over the second length L2 and / or second width W2, wherein one of the following may apply: (a) one of a first and second major surface of the second optical element may be curved, while the other of the first and second major surface may be planar; and (b) both the first and second major surface of the second optical element may be curved, wherein the first major surface may curve in an opposite direction from (and with a different curvature than) the second major surface. Further, the second optical element may be curved, wherein at least one of the first and second major surface may be configured concave or convex with respect to the LED filament.

[0021] The first optical element may have a first cross-sectional shape in a plane parallel to the first length Li and the first width Wi. Similarly, the second optical element may have a second cross-sectional shape in a plane parallel to the second length L2 and the second width W2. In embodiments, the first cross-sectional shape and second cross-sectional shape may be individually selected from the group of a circle, an ellipse, a polygonal shape, such as a regular (simple) polygonal shape (having straight and / or curved sides), and a freeform shape.

[0022] In embodiments, the first optical element may be configured aligned with the second optical element in the optical assembly stack. That is, the optical assembly stack may have an assembly center axis Aaconfigured (i) intersecting the first optical element and the second optical element, and (ii) parallel to a surface normal of at least one of the first optical element and the second optical element, wherein a geometrical center of the first optical element may be aligned with a geometrical center of the second optical element along the assembly center axis Aa. Especially, the assembly center axis Aamay be configured intersecting the geometrical centers of (both) the first and second optical element, wherein optionally the assembly center axis Aamay further be configured parallel to the surface normals of both the first and second optical element. Hence, in embodiments, the second optical element may be configured parallel to the first optical element. That is, a second plane parallel to the second length L2 and the second width W2 may be configured at an angle of < 10°, such as an angle of < 5°, especially an angle of < 2°, with a first plane parallel to the first length Li and the first width Wi. Further, the second optical element may be configured at a shortest mutual distance di from the first optical element. That is, a closest face (with respect to the second optical element) of the first optical element may be configured at a distance di from a closest face (with respect to the first optical element) of the second optical element. In embodiments, the shortest mutual distance di may be selected from the range of < 10 cm, such as from the range of < 5 cm, especially from the range of < 2 cm. Additionally or alternatively, the shortest mutual distance di may be selected from the range of > 0.1 cm, such as from the range of > 0.3 cm, especially from the range of > 0.5 cm. That is, the shortest mutual distance di may be selected from the range of 0.1-10 cm, such as from the range of 0.3-5 cm, especially from the range of 0.5-2 cm. Hence, in specific embodiments, the shortest mutual distance di may be selected from the range of 0.3-5 cm. Such a shortest mutual distance di may facilitate that the light generating system may be applied in relatively small lamps and / or luminaires. Yet, such a shortest mutual distance di may facilitate that a relatively larger LED filament may be placed in between the optical elements.

[0023] The first (and / or second) optical element may comprise a light transmissive, such as especially light transparent, material. Herein, the terms “light transmissive” and “light transparent” material indicate the material may be (specular) transmissive for one or more wavelengths selected from the range of 190-1500 nm, such as from the range of 200- 1000 nm, especially from the range of 380-780 nm (i.e. visible light). In embodiments, the light transmissive material may be individually selected for the first optical element and the second optical element, and may comprise one or more materials selected from the group comprising glass, polycarbonate (PC), polyethylene (PE), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), (clear) polyvinyl chloride (PVC), cyclic olefin copolymers (COC), fluorinated ethylene propylene (FEP), styrene methyl methacrylate (SMMA), polysiloxanes, and poly(methyl methacrylate) (PMMA). Especially, the light transmissive material (of the first and / or second optical element) may comprise, such as consist of, one or more of PMMA and PC.

[0024] Further, in embodiments, the first (and / or second) optical element may comprise a light reflective material. The light reflective material (of the first optical element and the second optical element) may be individually selected from the group comprising a dielectric material, a reflective metal (e.g. configured as a metal layer coating), and a reflective polymer (e.g. a (cholesteric) liquid crystal polymer). The dielectric material may be reflective (for filament light), yet may also be transmissive (for filament light). The dielectric material may especially comprise (such as consist of) one or more of titanium dioxide, silver, and aluminum. In embodiments, the dielectric material may be configured as a layer, such as between two layers of light transmissive material. Alternatively, the dielectric material may be configured as a (light transmissive) coating on the light transmissive material. Especially, in embodiments, the first optical element may comprise one or more first layers. Similarly, the second optical element may comprise one or more second layers. Each of the one or more first (and / or second) layers may comprise a light transmissive material and an (at least partially) light transmissive coating. The light transmissive coating may especially comprise a (light transmissive) dielectric material. In such embodiments, the light transmissive material may have a first refractive index m, and the light transmissive coating may have a second refractive m. In embodiments, a difference between the first refractive index m and the second refractive index n2 may be selected from the range of > 0.2, such as from the range of > 0.5, especially from the range of > 0.7, like from the range of > 1.0. That is, in embodiments, n2- > 0.2, such as n2- > 0.5, especially n2- > 0.7, like n2- > 1.0. Hence, in specific embodiments, the first optical element may comprise one or more first layers, wherein each of the one or more first layers may comprise a light transmissive material and a light transmissive coating; wherein the light transmissive material may have a first refractive index m, wherein the light transmissive coating may have a second refractive index n2, and wherein n2- > 0.5. Such a difference between the first and second refractive index m and n2 may facilitate that the filament light may be partially reflected at the interface between the light transmissive material and the light transmissive coating (due to Fresnel reflections). Hence, such a first optical element may be configured to reflect at least part of the filament light, while (essentially only) consisting of light transmissive material.

[0025] Hence, the first optical element may comprise one or more first layers. Especially, the first optical element may comprise > 1, such as > 2, especially > 3 first layers. Additionally or alternatively, the first optical element may comprise < 10, such as < 8, especially < 6 first layers. Further, the second optical element may comprise > 1, such as > 2, especially > 3 second layers. Additionally or alternatively, the second optical element may comprise < 10, such as < 8, especially < 6 second layers. As indicated above, the one or more first (and / or second) layers may comprise an (at least partially) light transmissive coating. The (at least partially) light transmissive coating may comprise a birefringent dielectric material. In such embodiments, adjacent first (and / or second) layers may have a different orientation (of the birefringent material), such that the filament light may be refracted to a different extent and / or in a different direction at each layer, thereby providing a partially reflective first (and / or second) optical element. Additionally or alternatively, the (at least partially) light transmissive coating may comprise a metal layer coating. In such embodiments, the metal layer coating may especially have a smaller thickness than is needed to reflect at least 98% of the filament light. That is, the metal layer coating may have a thickness selected such, that the metal layer coating may transmit at least part of the filament light. Alternatively, in embodiments, the metal layer coating may have a thickness selected such, that (essentially) all of the filament light may be reflected by the metal layer coating, wherein the metal layer coating may further comprise a plurality of holes (or openings) to facilitate (partial) transmission of the filament light. Said holes may especially have dimensions (length, width, and / or diameter) selected from the range of < 1 mm, such as from the range of < 0.5 mm, especially from the range of < 0.1 mm. Alternatively, the second optical element may be configured to reflect > 80% of the filament light. In such embodiments, the metal layer coating may especially be (essentially) free from holes, and may have a thickness selected such, that (essentially) all of the filament light may be reflected by the metal layer coating.

[0026] The first (and / or second) optical element may further comprise an electrically conductive material. In embodiments, the electrically conductive material may be selected from the group comprising an (electrically conductive) metal and an electrically conductive polymer. In embodiments, the electrically conductive material may be configured as electrically conductive tracks (configured on top of one or more of the first (and / or second) layers). Alternatively, the first (and / or second) optical element may comprise the light transmissive coating, wherein the light transmissive coating may comprise (such as be) the electrically conductive material. Hence, the electrically conductive material may be light transmissive or opaque. The electrically conductive material may be configured to electrically couple the LED filament to a power source (e.g. a LED driver). Hence, in specific embodiments, one or more of the first optical element and second optical element may comprise an electrically conductive material. Optical elements comprising an electrically conductive material may facilitate powering the LED filament from the optical elements. Hence, the space in between the optical elements may be free from electrical wiring, providing a more decorative and “clean” look to the light generating system, such as especially to the optical assembly stack.

[0027] The light generating system, especially the optical assembly stack, may further comprise the LED filament. LED filaments as such are known, and are e.g. described in US 8,400,051 B2, W02020016058, WO2019197394, etc., which are hereby herein incorporated by reference. In general, a LED filament may comprise (i) a plurality of light emitting diodes (LEDs), arranged on (at least a first major surface of) an elongated carrier, and (ii) an elongated encapsulant at least partially enclosing the plurality of LEDs and covering at least part of the elongated carrier. In embodiments, the LED filament may be straight. Alternatively, the LED filament may be curved. For instance, the filament may have a (2D or 3D) spiraling shape, (like) a helical shape (see also below). The LED filament may be defined by a filament length LF, a filament width WF, and a filament thickness TF. The LED filament may have relatively high aspect ratios (LF / WF or LF / TF), such as > 10, especially > 15, such as > 20. Yet, in embodiments, the aspect ratio (LF / WF and / or LF / TF) may be < 900, such as < 650, especially < 500. Hence, in specific embodiments, 10*WF < LF < 900*WF, and 10*TF< LF< 900*TF.

[0028] The LED filament may thus comprise an elongated carrier (“carrier”), solid state light sources, and an encapsulant. Especially, the elongated carrier may support the solid state light sources. The elongated carrier may e.g. comprise glass, quartz, metal, or sapphire. Alternatively, the elongated carrier may comprise a polymeric material or (flexible) metal, e.g., a film or foil. The elongated carrier may be rigid (self-supporting), but may (in polymeric embodiments) also be flexible. In embodiments, the elongated carrier may be light transmissive, translucent, or transparent for light, especially visible light. The term “visible light”, and similar terms, refers to light having one or more wavelengths in the range of about 380-780 nm. Alternatively, in embodiments, the carrier may be light reflective, especially reflective for one or more of the light source light (see below) and the filament light, such as reflective for at least the light source light and the filament light. In specific embodiments, the carrier may be diffuse reflective. The carrier may especially be configured to reflect at least 80%, such as at least 90%, especially at least 95%, including (essentially) 100% of the (visible) light received by the carrier. The (elongated) carrier may comprise a first major surface at a first side of the carrier and a second major surface at a second side of the carrier, opposite to the first side. The solid state light sources may be arranged on at least one of these surfaces. Hence, at least part of, such as all of, the solid state light sources may be mounted onto the first major surface. Additionally or alternatively, at least part of the solid state light sources may be mounted onto the second major surface. Especially, in embodiments, the plurality of solid state light sources may be configured on (only) the first major surface of the carrier, wherein the carrier may be light transparent. Alternatively, the plurality of solid state light sources may be configured on (both) the first major surface and the second major surface of the carrier, wherein the carrier may be light transmissive or light reflective. Hence, the solid state light sources may be arranged, mounted and / or mechanically coupled on / to the carrier, wherein the carrier may be configured to mechanically and / or electrically support the solid state light sources.

[0029] In embodiments, the solid state light sources may comprise LEDs. Alternatively or additionally, the solid state light sources may comprise laser diodes. Further, the LED filament may comprise one or more of LEDs, laser diodes, superluminescent diodes, and multi -junction light emitting diodes. Especially, the LED filament may comprise a plurality of LEDs. The (plurality of) solid state light sources may be arranged in an array (on the elongated carrier), especially over (at least part of) the filament length LF. The number of solid state light sources in the array may be > 4, such as > 8, even more especially > 12. Especially, the number of solid state light sources in the array may be selected from the range of 10-2000, such as from the range of 10-1500, especially from the range of 10-1000. In embodiments, the solid state light sources may be configured in a ID (linear) array over at least part of the filament length LF. Further, in embodiments, the solid state light sources may be configured in two ID arrays, one on the first major surface of the carrier and one on the second major surface. A 2D array of solid state light sources of n*m LEDs may also be possible. In embodiments, n may be selected from the range of 1-4, such as 1-3, like 1-2, such as 1, or such as 2, and m may be selected from the range of > n, such as especially selected from the range of > 4 (when n<4), like > 6, such as > 8. Hence, a 2D array of solid state light sources may have a smaller number of rows (n) than the number of solid state light sources in those respective rows (m), such as n / m < 0.2, like n / m < 0.1, especially n / m < 0.05.

[0030] The LED filament may comprise an encapsulant. The encapsulant may especially (at least partly) enclose the plurality of solid state light sources. Further, the encapsulant may cover at least part of the elongated carrier, such as at least (part of) one of the first major and second major surfaces. In general, the encapsulant may be in contact with the elongated carrier and may enclose all of the solid state light sources. The encapsulant may be a continuous coating along the filament length LF, at one or both of the first major and the second major surface. Further, the encapsulant may at least partly cover (and / or enclose) the solid state light sources, such as > 50%, like > 75%, especially > 95%, up to 100%, of the total number of solid state light sources in the array. The encapsulant may comprise one or more of a luminescent material and a light scattering material. The one or more of the luminescent material and the light scattering material may be configured embedded in an encapsulant material, e.g. a (flexible) polymer material (such as a silicone). The luminescent material may be configured to convert at least part, such as all, of the light source light (generated by the solid state light sources) into luminescent material light. In embodiments, the luminescent material may comprise a phosphor (such as an inorganic phosphor) and / or quantum dots or rods. Further, the light scattering material may be configured to scatter (or “diffuse”) the light source light, especially in a direction transverse to a normal of the (first and / or second) major surface. In embodiments, the light scattering material may comprise light scattering particles, such as e.g. at least one of BaSCU, A12O3 and TiCL particles. Further, in embodiments, the LED filament may comprise multiple sub-filaments.

[0031] The LED filament may be configured to generate filament light. Further, the solid state light sources may be configured to generate light source light. In embodiments, at least two, such as all, of the solid state light sources may be configured to emit light source light having different spectral power distributions. In other embodiments, at least two, such as all, of the solid state light sources may be configured to provide light source light having essentially the same spectral power distribution. In embodiments, the filament light may comprise the light source light, or may essentially consist of (scattered) light source light. However, in embodiments wherein the encapsulant may comprise a luminescent material, the filament light may comprise luminescent material light, or may essentially consist of luminescent material light. Further, the filament light may comprise luminescent material light and at least part of the (non-converted and / or scattered) light source light. In embodiments, the LED filament may provide filament light with a desired spectral light distribution, e.g., white light having a correlated color temperature (CCT) selected from the range of 1500-7000 K. In such embodiments, the filament light may comprise luminescent material light and optionally transmitted light source light. Further, the filament light may at least comprise light at a wavelength selected from the range of 380-780 nm, i.e., visible light. In embodiments, the filament light may comprise white light. The term “white light”, and similar terms, is known to the person skilled in the art. It may especially relate to light having a CCT between 1800 K and 20000 K, such as between 2000 K and 20000 K, especially between 2700 K and 20000 K, for general lighting especially in the range of about 2000-7000 K, such as in the range of 2700-6500 K. The CCT may especially be within 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within 10 SDCM from the BBL, such as within 5 SDCM from the BBL. Especially, the filament light may be white light having a CCT selected from the range of 1500-7000 K, such as from the range of 1700-6500 K, especially from the range of 2000-5000 K.

[0032] Alternatively, the filament light may be colored light, such as one or more of violet light, blue light, green light, yellow light, orange light, and red light. Further, the filament light may be colored light having a color point selected from the CIE 1931 color space. The term “violet light”, and similar terms, may especially relate to light having a wavelength in the range of about 380-440 nm. The term “blue light”, and similar terms, may especially relate to light having a wavelength in the range of about 440-490 nm. The term “green light”, and similar terms, may especially relate to light having a wavelength in the range of about 490-560 nm. The term “yellow light”, and similar terms, may especially relate to light having a wavelength in the range of about 560-590 nm. The term “orange light”, and similar terms, may especially relate to light having a wavelength in the range of about 590- 620 nm. The term “red light”, and similar terms, may especially relate to light having a wavelength in the range of about 620-780 nm.

[0033] The LED filament may be configured to emit the filament light via a light emitting surface. That is, the LED filament may comprise a light emitting surface. During operation of the LED filament, the filament light may especially escape from the LED filament via the light emitting surface. In embodiments, the encapsulant may comprise the light emitting surface. Especially, the light emitting surface may be (at least part of) the outer (outside) edge of the encapsulant. The light emitting surface may be configured on one or more of a side of the first major surface of the carrier and a side of the second major surface of the carrier. In specific embodiments, the light emitting surface may be configured over (at least part of) a circumference of the LED filament in a cross-section of the LED filament perpendicular to the filament length LF. Hence, in embodiments, the light emitting surface may at least partly define the filament width WF and filament thickness TF of the LED filament. The light emitting surface may further be configured over at least part of the filament length LF, such as over > 0.6*LF, especially over > 0.8*LF, like over > 0.9*LF. Yet, in embodiments, the light emitting surface may be configured over < LF. Especially, the LED filament may comprise one or more electrical contact elements at one or both ends of the LED filament, wherein the light emitting surface may be configured adjacent to the one or more electrical contact elements. In specific embodiments, the LED filament may comprise a first electrical contact element at a first end of the LED filament (along the filament length LF), and a second electrical contact element at a second opposite end of the LED filament (along the filament length LF), wherein the light emitting surface may be configured (centered) between the first and second electrical contact element. In embodiments, one or more of the first electrical contact element and the second electrical contact element may be configured electrically coupled to the electrically conductive material in one or more of the first and second optical element. Hence, in embodiments, one or more of the first electrical contact element and the second electrical contact element may be configured at least partially extending through the first and / or second optical element (see also below).

[0034] The LED filament may be configured in between the first optical element and the second optical element. Especially, the first optical element may be configured in a light receiving relationship with the LED filament at a first side (and / or end) of the LED filament, and the second optical element may be configured in a light receiving relationship with the LED filament at a second opposite side (and / or end) of the LED filament. Hence, filament light emitted from the LED filament during operation of the LED filament may be incident on the first and second optical element. Especially, the optical assembly stack (comprising the first and second optical element and the LED filament) may have an optical axis Ao, wherein the optical axis Ao may be configured intersecting the first optical element, the second optical element, and a geometrical center of the LED filament. The optical axis Ao may further be (configured) parallel to a surface normal of one or more of the first and second optical element. In embodiments, the optical axis Ao may be (equal to) the assembly center axis Aa. The optical axis Ao may indicate the average optical path along which the filament light may travel during operation of the LED filament. Hence, the second optical element may be configured to reflect > 80% of the filament light, wherein the optical axis Ao may extend from a reflective surface of the second optical element, through (a geometrical center of) the LED filament, and past the first optical element. Alternatively, the second optical element may be configured to transmit (selected from the range of) 25-75% of the filament light, wherein the optical axis Ao may extend from (a geometrical center of) the LED filament past the first optical element, and past the second optical element.

[0035] In embodiments, the filament light may be (at least partially) reflected back- and-forth between the first and second optical element. Especially, in embodiments, each time a beam of filament light is incident on the first (and / or second) optical element, a percentage of the luminous flux density of the (beam of) filament light may be transmitted through the first (and / or second) optical element, and a (second) percentage of the luminous flux density of the (beam of) light source light may be reflected by the first (and / or second) optical element. In embodiments, the percentage of filament light transmitted by the first (and / or second) optical element (i.e., the transmission percentage (T)) and the percentage of filament light reflected by the first (and / or second) optical element (i.e., the reflection percentage (R)) may determine the percentage of the luminous flux density of the (beam of) filament light that is transmitted and reflected, respectively. That is, the beam of filament light incident on the first (and / or second) optical element may have a luminous flux density Ls, and the beam of light transmitted through the first (and / or second) optical element may have a luminous flux density L of Ti*Ls, wherein Ti is the transmission percentage (T) at the first location of incidence. Further, the beam of light reflected by the first (and / or second) optical element may have a luminous flux density L of Ri*Ls, wherein Ri is the reflection percentage (R) at the first location of incidence. In embodiments, for a first beam of filament light propagating towards the first optical element, the reflected beam of light from the first optical element may be incident on the second optical element. In embodiments, at the second optical element, the (reflected) beam may be (essentially fully) reflected. Alternatively, the second optical element may be configured to transmit part of the filament light, such that again a part of the luminous flux L density of the (reflected) beam of light may be transmitted. Especially, the luminous flux density of the beam of light reflected by the first semitransparent mirror and transmitted by the second semitransparent mirror may be provided by L = RI*T2*LS, wherein T2 is the transmission percentage (T) at the second location of incidence (on the second optical element) for the reflected beam. In embodiments, part of a beam of filament light may be reflected a plurality of x times before being transmitted. In such embodiments, the luminous flux density of the beam of light transmitted after x (prior) reflections may be provided by L = RI*R2* . . . *Rx*Tx+i*Ls. In embodiments, each time a (part of a) (reflected) beam of light is transmitted through one of the first and second optical element, a virtual (image of the) LED filament may be provided on a side of the light generating system (such as especially a side of the optical assembly stack) opposite to the side at which the optical element (through which the beam of light is transmitted) is configured. For instance, would the (part of a) (reflected) beam of light be transmitted through the first optical element, the virtual (image of the) LED filament may be provided on the side of (the optical assembly stack closer to) the second optical element. Hence, in embodiments, a (partially) virtual (array of) LED filament(s) may be provided. In embodiments, the size of the virtual (array of) LED filament(s) may depend on the maximum number of reflections (on either optical element) possible from a viewing angle of an observer observing the light generating system (wherein the viewing angle may determine an angle of incidence of the filament light on the optical elements). For example, the second optical element may be configured to transmit part of the filament light, such that for a single LED filament not configured in contact with the first and second optical element, and emitting filament light which is (observed to have) reflected up to 5 times between the optical elements (e.g. 3 times on the second optical element, and 2 times on the first optical element), a virtual array of 6 LED filaments may be provided.

[0036] The LED filament, such as especially the light emitting surface, may be configured extending from the first optical element to the second optical element. Especially, the first optical element may be configured at a shortest mutual distance di from the second optical element, and the light emitting surface may be configured extending over at least part of this distance di. In embodiments, the light emitting surface may be configured at least partially extending through the first and / or second optical element, wherein the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of > di, such as over a distance of > 1.05*di, especially over a distance of > 1.1 *di. Yet, in embodiments, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of < 1.5*di, such as over a distance of < 1.2*di, especially over a distance of < 1.1 *di. Further, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of < di, such as over a distance of < 0.8*di, especially over a distance of < 0.6*di. Additionally or alternatively, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of at least 0.1 *di, such as over a distance of at least 0.2*di, especially over a distance of at least 0.3*di. In specific embodiments, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of WF or TF. That is, in embodiments, the LED filament may be configured either (flat) on top of the first or second optical element or (suspended) between the first and second optical elements, wherein the filament length LF may be configured parallel to one or more of (i) the first plane parallel to the first length Li and the first width Wi, and (ii) the second plane parallel to the second length L2 and the second width W2. Additionally or alternatively, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of at least 0.6*di, such as over a distance of at least 0.8*di, especially over a distance of at least 0.9*di, including over a distance of (essentially) di. Hence, in specific embodiments, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of at least 0.8*di. Extending the light emitting surface over a distance of at least 0.8*di may provide a relatively efficient use of the space between the optical elements, by reducing the “empty space” in the light generating system. Further, extending the light emitting surface over a distance of at least 0.8*di may provide a decorative lighting effect of a single (virtually) elongated LED filament or a (partially virtual) array of LED filaments with relatively narrow spaces in between the LED filaments.

[0037] As indicated above, the light emitting surface may be configured extending from the first optical element to the second optical element over a distance of di. Hence, in embodiments, the light emitting surface may be configured in physical contact with (a face of) the first optical element and (a face of) the second optical element. Especially, the light emitting surface may comprise a light emitting surface first end and a light emitting surface second end. The light emitting surface second end may be configured (along the filament length LF) opposite the light emitting surface first end. Further, the light emitting surface may have a surface length Lsalong the filament length LF, wherein the light emitting surface first end may comprise at most the first 10%, such as at most the first 5%, like at most the first 2%, of the surface length Ls, and the light emitting surface second end may comprise at most the last 10%, such as at most the last 5%, like at most the last 2%, of the surface length Ls. That is, the light emitting surface first end may have a length of < 0.1 *LS, such as a length of < 0.05*Ls, especially a length of < 0.02*Ls. Additionally, the light emitting surface second end may have a length of < 0.1 *LS, such as a length of < 0.05*Ls, especially a length of < 0.02*Ls. The light emitting surface may be configured in (direct) physical contact with the first optical element at the light emitting surface first end. Additionally, the light emitting surface may be configured in (direct) physical contact with the second optical element at the light emitting surface second end. Hence, in specific embodiments, the light emitting surface may comprise a light emitting surface first end and a light emitting surface second end, wherein the light emitting surface may be configured in physical contact with (i) the first optical element at the light emitting surface first end, and (ii) the second optical element at the light emitting surface second end. Physical contact between the light emitting surface and the first and second optical elements may facilitate that during operation of the LED filament, a (single) continuous and virtually extended LED filament may be provided.

[0038] In embodiments, the LED filament may be configured perpendicular to the first optical element and the second optical element. That is, the LED filament may be configured such that the filament length LF may be parallel to a surface normal of the first plane (and / or a surface normal of the second plane). Alternatively, the LED filament may be configured at an angle with respect to the first and second optical elements, or the LED filament may have an (at least partially) curved shape (see also below). In such embodiments, the light emitting surface first end and / or the light emitting surface second end may be configured at an angle with the first plane and / or the second plane, respectively. Yet, in embodiments, (at least) the light emitting surface first end may be configured perpendicular to the first optical element. Further, in embodiments, (at least) the light emitting surface second end may be configured perpendicular to the second optical element. That is, in embodiments, the light emitting surface first end and / or the light emitting surface second end may be configured at an angle with (at least part of) the remainder of the light emitting surface. Hence, in specific embodiments, the light emitting surface first end may be configured perpendicular to the first optical element, and the light emitting surface second end may be configured perpendicular to the second optical element. Configuring the light emitting surface first and second end perpendicular to the first and second optical element may facilitate that the first and / or second electrical contact element may be extended perpendicularly through the first and / or second optical element, thereby minimizing the effect on the transmissive and / or reflective properties of the first and / or second optical element.

[0039] The LED filament may have a projected shape in a projection on (a face of) the second optical element (or on (a face of) the first optical element). That is, looking from the first optical element towards the LED filament and the second optical element along a direction parallel to a surface normal of the (second plane of the) second optical element, the LED filament may (virtually) project the projected shape on (a face of) the second optical element. In embodiments, the projected shape may be selected from the group of a point, a line, a curve, a circle, an ellipse, a (2D) spiral, and a polygonal shape, such as especially from the group of a circle, an ellipse, a (2D) spiral, and a regular (simple) polygonal shape. In embodiments, the projected shape may especially be an outline shape. That is, e.g. for a circular projected shape, the projected shape may especially be an outline of a circle (i.e., an annulus). In embodiments, the projected shape may further comprise one or more shapes selected from the group of a circle, an ellipse, a (2D) spiral, and a polygonal shape, such as a regular (simple) polygonal shape. For instance, the projected shape may be a double circle or double ellipse (e.g. a lemniscate shape), or a flower shape (e.g., a circular shape surrounded by circular and / or elliptical shapes). Hence, in specific embodiments, the LED filament may have a projected shape in a projection on the second optical element, selected from the group of a circle, an ellipse, a spiral, and a polygonal shape, such as a regular polygonal shape. Such a (projected) shape may be more decorative than e.g. a linear shape. Further, during operation of the LED filament, such a projected shape may facilitate creating a virtual helical shape for the (partially virtual) LED filament.

[0040] In embodiments, the LED filament may be configured in a two-dimensional (2D) shape between the optical elements. In such embodiments, the height of the 2D shape may especially be defined by the filament width WF or filament thickness TF, i.e., the LED filament may form the (outline of the) 2D shape along the filament length LF. The LED filament configured in a 2D shape may be configured in physical contact with one of the first optical element and the second optical element. Especially, the LED filament configured in a 2D shape may be configured on top of (and in physical contact with) the second optical element. Alternatively, the LED filament configured in a 2D shape may be configured suspended between (and physically separated from) the first optical element and the second optical element. The LED filament configured in a 2D shape may be configured parallel to the first and / or second optical element, such that the filament length LF may be configured parallel to the first and / or second plane, and the light emitting surface may extend from the first to the second optical element over a distance of WF or TF. Alternatively, the LED filament configured in a 2D shape may be configured at a smallest angle ai with the first and / or second optical element. In embodiments, the LED filament may be configured in a (2D) shape (comprising one or more shapes) selected from the group of a line, a curve, a circle, an ellipse, a (2D) spiral, and a polygonal shape, such as a regular (simple) polygonal shape. The 2D shape may especially be an outline shape. That is, for example for a circular 2D shape, the LED filament may especially be configured to form an outline of a circle (i.e., an annulus). In embodiments, the LED filament may especially be configured in a circular shape. As indicated above, in embodiments, the (circularly-shaped) LED filament may be configured parallel to the first and / or second optical element. That is, a plane parallel to and intersecting the (circularly-shaped) LED filament (along the (full) filament length LF) may be configured parallel to (the first and / or second plane of) the (respectively) first and / or second optical element. Alternatively, the plane parallel to and intersecting the (circularly-shaped) LED filament may be configured at a smallest angle ai with respect to the first optical element and the second optical element. In embodiments, the smallest angle ai may be selected from the range of > 2°, such as from the range of > 5°, especially from the range of > 10°. Additionally or alternatively, the smallest angle ai may be selected from the range of < 70°, such as from the range of < 60°, especially from the range of < 50°. That is, ai may be selected from the range of 2-70°, such as from the range of 5-60°, especially from the range of 10-50°. In embodiments, the (angled) LED filament configured in a (circular) 2D shape may be configured in physical contact with one or more of the first optical element and the second optical element. Alternatively, the (angled) LED filament configured in a (circular) 2D shape may be configured suspended between (and physically separated from) the first and second optical element. Hence, in specific embodiments, the LED filament may be configured in a circular shape, wherein a plane parallel to and intersecting the LED filament may be configured at a smallest angle ai with respect to the first optical element and the second optical element, and wherein ai may be selected from the range of 5-60°. During operation of the LED filament, such an angled LED filament configured in a circular shape may provide an illusion of a (dis)connected chain of circular LED filaments.

[0041] The LED filament may further be configured in a three-dimensional (3D) shape. Especially, the LED filament may be configured in a 3D shape selected from the group comprising a helical shape and a spiral shape. The spiral shape may further be selected from the group comprising a conical spiral shape, a spherical spiral shape, a toroidal spiral shape, and a conchospiral shape. Hence, in specific embodiments, the LED filament may be configured in a helical or spiral shape. Such a shape may especially be decorative. In embodiments, the LED filament configured in a 3D shape (especially a helical or spiral shape) may be configured in physical contact with the first optical element and the second optical element. Especially, the light emitting surface of the LED filament (configured in a 3D shape) may be configured in physical contact with the first optical element and the second optical element, wherein optionally the light emitting surface first and / or second end may be configured perpendicular to the first and / or second optical element, respectively. In such embodiment, the first and second electrical contact elements may be configured parallel to and on top of the first and second optical elements, respectively, wherein the first and second electrical contact elements may be configured electrically coupled with e.g. conductive tracks configured on the surface of the first and second optical elements. Alternatively, the first electrical contact element and / or the second electrical contact element may be configured electrically coupled to the electrically conductive material comprised by the first and / or second optical element, respectively, wherein the first and / or second electrical contact element may be configured at least partially extending through respectively the first and / or second optical element. Further yet, the first electrical contact element may be configured electrically coupled to an electrical connection element configured on an opposite side of the first optical element from the LED filament, wherein the LED filament, especially the first electrical contact element, may be configured at least partially extending through the first optical element. Additionally or alternatively, the second electrical contact element may be configured electrically coupled to an electrical connection element configured on an opposite side of the second optical element from the LED filament, wherein the LED filament, especially the second electrical contact element, may be configured at least partially extending through the second optical element. Hence, in specific embodiments, the LED filament may be configured in a helical or spiral shape, wherein the LED filament may be configured at least partially extending through the first optical element and / or the second optical element. At least partially extending the LED filament through the first and / or second optical element may facilitate providing a virtually elongated LED filament extending seamlessly in a direction of the first and / or second optical element. Further, at least partially extending the LED filament through the first and / or second optical element may facilitate hiding the electrical contact elements of the LED filament from view behind the optical elements, thereby providing a more decorative appearance of the light generating system.

[0042] The light generating system, such as especially the optical assembly stack, may further comprise one or more side walls. The one or more side walls may be configured bridging the first optical element and the second optical element. In embodiments, the one or more side walls may comprise an electrically conductive material. Further, the one or more side walls may each have a first side face (bridging the first and second optical elements and) configured facing (towards) the LED filament, and a second side face opposite the first side face, wherein the second side face may be configured facing away from the LED filament. In embodiments, especially the second side face may comprise the electrically conductive material. In such embodiments, the LED filament (optionally configured in a helical or spiral shape) may be configured at least partially extending through a side wall (of the one or more side walls). Especially, the LED filament may be configured extending through the side wall with the first and / or second electrical contact elements. Further, the LED filament may be configured at least partially extending through the side wall at a location touching or close to the first optical element and / or the second optical element, e.g. at a location within 0.2*di of the first and / or second optical element, especially a location within 0.1 *di of the first and / or second optical element. Hence, in specific embodiments, the LED filament may be configured in a helical or spiral shape, and the light generating system may comprise one or more side walls configured bridging the first optical element and the second optical element, wherein the LED filament may be configured at least partially extending through a side wall at a location touching or close to the first optical element and / or the second optical element. At least partially extending the LED filament through a side wall may facilitate suspending the LED filament between the first and second optical elements, wherein LED filament may be physically separated from the first and second optical elements.

[0043] The one or more side walls may be configured to reflect light. Especially, the one or more side walls may comprise, such as be, one or more side mirrors. Hence, in specific embodiments, the light generating system, especially the optical assembly stack, may comprise one or more side mirrors. The one or more side mirrors may be configured bridging the first optical element and the second optical element. Hence, the one or more side mirrors may have a side mirror height Hmof (at least) di. Further, the one or more side mirrors may be configured surrounding the LED filament. In embodiments, in a cross-section of the one or more side mirrors parallel to the first (and / or second) plane, the one or more side mirrors may be configured in a circle. Alternatively, the one or more side mirrors may be configured in one or more of ellipse and a regular (simple) polygonal shape (in a cross-section parallel to the first (and / or second) plane). In embodiments, the one or more side mirrors may be curved in one or two directions. Alternatively, the one or more side mirrors may be planar. Especially, the one or more side mirrors may be configured in a square (and surrounding the LED filament). Further, the one or more side mirrors may be curved or planar along the side mirror height Hm. The one or more side mirrors may be configured to specularly reflect > 40%, such as > 50%, especially > 60%, of the filament light received by the one or more side mirrors. Further, the one or more side mirrors may be configured to specularly reflect > 80%, such as > 90%, especially > 95%, like > 98%, including (essentially) 100%, of the filament light received by the one or more side mirrors. Alternatively, the one or more side mirrors may be configured to specularly reflect at least part of the filament light received by the one or more side mirrors, wherein the one or more side mirrors may further be configured to transmit > 15%, such as > 25%, especially > 35%, of the filament light received by the one or more side mirrors. Additionally or alternatively, the one or more side mirrors may be configured to transmit < 85%, such as < 75%, especially < 65%, of the filament light received by the one or more side mirrors. The one or more side mirrors may thus be configured to reflect at least part of the filament light received by the one or more side mirrors, wherein the one or more side mirrors may optionally further be configured to transmit part of the filament light received by the one or more side mirrors. Hence, in specific embodiments, the light generating system may comprise one or more side mirrors, wherein the one or more side mirrors may be configured bridging the first optical element and second optical element, and wherein the one or more side mirrors may be configured to specularly reflect > 50% of the filament light received by the one or more side mirrors. A light generating system comprising one or more side mirrors may facilitate providing virtual LED filaments in multiple directions around the LED filament. Hence, such a configuration may facilitate providing a three-dimensional array of LED filaments from a single LED filament.

[0044] The light generating system, such as especially the optical assembly stack, may further comprise a second LED filament. Embodiments described above relating to the LED filament may mutatis mutandis apply to the second LED filament. Especially, in embodiments, the second LED filament may be identical to the (first) LED filament. Alternatively, the second LED filament may differ from the (first) LED filament in one or more of (i) the dimensions (LF, WF, TF) of the filament, (ii) the number (and / or type) of solid state light sources, (iii) the composition of the elongated encapsulant, (iv) the shape in which the filament may be configured, and (v) the optical properties of the filament light (see also below). The second LED filament may especially comprise (i) an array of a plurality of second solid state light sources arranged on (at least a first major surface of) a second elongated carrier, and (ii) a second elongated encapsulant at least partly enclosing the plurality of second solid state light sources and covering at least part of the elongated carrier. In embodiments, the plurality of second solid state light sources may be arranged on (only) the first major surface of the second elongated carrier, wherein the second elongated carrier may be light transmissive (for at least the second filament light). Alternatively, the plurality of second solid state light sources may be arranged on (both) the first major surface and an (opposite) second major surface of the second elongated carrier, wherein the second elongated carrier may be one of opaque and light transmissive (for at least the second filament light). The second LED filament may be configured in between the first and second optical elements. Further, the second LED filament may be configured to generate second filament light. Hence, in specific embodiments, the light generating system may comprise a second LED filament configured in between the optical elements, wherein the second LED filament may comprise (i) an array of a plurality of second solid state light sources arranged on a second elongated carrier, and (ii) a second elongated encapsulant at least partly enclosing the plurality of second solid state light sources and covering at least part of the elongated carrier; wherein the second LED filament may be configured to generate second filament light. A light generating system comprising a second LED filament may facilitate increasing the intensity of the light provided by the light generating system. Further, a light generating system comprising two LED filaments may provide more (options for) decorative lighting effects.

[0045] The second LED filament may be configured in a 2D or 3D shape (selected from the options provided above). Hence, the second LED filament may be configured in a 2D shape (individually) selected from the group of a line, a curve, a circle, an ellipse, a (2D) spiral, and a polygonal shape, such as a regular (simple) polygonal shape. Alternatively, the second LED filament may be configured in a 3D shape (individually) selected from the group of a helical shape, a conical spiral shape, a spherical spiral shape, a toroidal spiral shape, and a conchospiral shape. The second LED filament may be configured in a different shape than the (first) LED filament. For instance, the (first) LED filament may be configured in a helical shape, and the second LED filament may be configured in a circular shape (configured parallel to the first and / or second plane) and suspended between the optical elements, wherein the (circular) second LED filament may further be configured surrounding (the helical shape of) the (first) LED filament. Alternatively, the second LED filament may be configured in the same shape as the (first) LED filament. Especially, the second LED filament may be configured in a shape forming a mirror image of the shape of the (first) LED filament. For instance, the (first) LED filament may be configured in a right-handed helical shape, and the second LED filament may be configured in a left-handed helical shape. Hence, in specific embodiments, the second LED filament may be configured in a shape mirroring the shape of the LED filament. Embodiments wherein the LED filaments are configured as mirror images from each other may provide a more symmetrical appearance to the light generating system. Hence, such embodiments may be more decorative.

[0046] The second LED filament may be configured physically separated from the (first) LED filament. Especially, a projected shape of the second LED filament (in a projection on the second optical element) may be configured at a second shortest mutual distance d? from the projected shape of the (first) LED filament. The second shortest mutual distance d? may be selected from one or more of (i) the range of > 0.02*L2, such as the range of > 0.05*L2, especially the range of > O. L2; and (ii) the range of > 0.02*W2, such as the range of > 0.05*W2, especially the range of > O.PW2. Additionally or alternatively, the second shortest mutual distance d2 may be selected from one or more of (i) the range of < 0.7*L2, such as the range of < 0.6*L2, especially the range of < 0.5*L2; and (ii) the range of < 0.7*W2, such as the range of < 0.6*W2, especially the range of < 0.5*W2. Alternatively, the Second LED filament may be configured in physical contact with the (first) LED filament at at least one point along a filament length LF of the second LED filament. Further, a geometrical center of the second LED filament may overlap with a geometrical center of the (first) LED filament. It should be noted that a geometrical center of a LED filament need not lie along the filament length LF, and may be configured outside the physical boundaries of the LED filament. For instance, the LED filament may be configured in a circular or (3D) spiral shape, wherein the geometrical center may be configured at the center of the circle or (3D) spiral, respectively. Hence, a geometrical center of the second LED filament may overlap with a geometrical center of the (first) LED filament, wherein the second LED filament may not intersect (and / or be in physical contact with) the (first) LED filament. Additionally, as indicated above, the second LED filament may be configured in a shape mirroring the shape of the LED filament. In such embodiments, the light generating system may especially comprise a filament mirror plane configured (a) perpendicular to the first and second optical elements, (b) intersecting a geometrical center of the (first) LED filament, and (c) intersecting a geometrical center of the second LED filament. In embodiments, the (first) LED filament and the second LED filament may mirror each other through the filament mirror plane. For instance, the (first) LED filament may be configured in a right-handed helical shape having a geometrical center on the filament mirror plane (such that one half of the helix is located on one side of the filament mirror plane, and the other half of the helix is located on the opposite side of the filament mirror plane), and the second LED filament may be configured in a left-handed helical shape having a geometrical center on the filament mirror plane, wherein the geometrical center of the second LED filament may overlap with the geometrical center of the (first) LED filament, and wherein the (helix of the) (first) LED filament may be a mirror image of and be entwined with the (helix of the) second LED filament. Hence, in specific embodiments, a geometrical center of the LED filament and the second LED filament may overlap. Embodiments wherein the geometrical centers of the filaments overlap may provide a more symmetrical appearance of the LED filaments and virtual LED filaments. For instance, the (first) LED filament may be configured in a right- handed helical shape and in physical contact with the first and second optical elements, such that during operation of the LED filament a virtually extended LED filament may be provided comprising (essentially) no gaps at the optical elements. In such embodiments, at the point of physical contact with the optical elements, the right-handed helix may be reflected (and transmitted) to appear as a virtual LED filament configured in a left-handed helical shape, such that a sharp transition from a right-handed to a left-handed helix may appear at the interface between the LED filament and the optical element. Upon the addition of a second LED filament configured in a mirror-symmetric left-handed helical shape (wherein the geometrical centers of the first and second LED filaments may overlap), said left-handed helix may be reflected (and transmitted) to appear as a virtual second LED filament configured in a right-handed helical shape, such that the (right-handed helical) reflection of the second LED filament may appear as a continuation of the (right-handed helical) (first) LED filament, and the (left-handed helical) reflection of the (first) LED filament may appear as a continuation of the (left-handed helical) second LED filament, thereby providing a continuous shape of the (partially virtual) LED filament(s).

[0047] As indicated above, the second LED filament may be configured to generate second filament light. The second filament light may be colored light, such as one or more of violet light, blue light, green light, yellow light, orange light, and red light. Especially, the second filament light may be colored light having a color point selected from the CIE 1931 color space. Alternatively, the second filament light may be white light, such as white light having a CCT selected from the range of 1500-7000 K, such as from the range of 1700-6500 K, especially from the range of 2000-5000 K. In embodiments, the (first) filament light may be white light, and the second filament light may be white light, wherein the combined (filament) light may be white light. Alternatively, one of the (first) filament light and the second filament light may be white light, and the other of the (first) filament light and the second filament light may be colored light, wherein the combined (filament) light may be white light or colored light. Alternatively, the (first) filament light may be colored light, and the second filament light may be colored light, wherein the combined (filament) light may be white light or colored light. Yet, in specific embodiments, the filament light and / or the second filament light may be white light having a correlated color temperature selected from the range of 1700-6500 K. White light having a CCT selected from the range of 1700-6500 K may be especially suitable for general lighting applications (in e.g. housing of office spaces).

[0048] Hence, in embodiment the (first) filament light and the second filament light may (both) be white light. Especially, the (first) filament light may be white light having a first correlated color temperature Tci selected from the range of 1500-7000 K, such as from the range of 1700-6500 K, especially from the range of 2000-5000 K. Further, the (white) (first) filament light may have a first color rendering index CRIi selected from the range of > 70, such as from the range of > 80, especially from the range of > 90. The second filament light may be white light having a second correlated color temperature Tc? selected from the range of 1500-7000 K, such as from the range of 1700-6500 K, especially from the range of 2000-5000 K. Further, the (white) second filament light may have a second color rendering index CRI2 selected from the range of > 70, such as from the range of > 80, especially from the range of > 90. In embodiments, the second filament light may have the same CRI as the (first) filament light, i.e., |CRIi - CRI2I < 5, such as |CRIi - CRI2I < 2, especially |CRIi - CRI2I < 1, including |CRIi - CRI2I = 0. Alternatively, the second filament light may have a different CRI as the (first) filament light, such as |CRIi - CRI2I > 5, like |CRIi - CRI2I > 7, especially |CRIi - CRI2I > 10. Yet, in embodiments, |CRIi - CRI2I < 15, such as |CRIi - CRI2I < 12, especially |CRIi - CRI2I < 10. Further, the first CCT Tci of the (first) filament light may be the same as the second CCT TC2 of the second filament light, such as |Tci - TC2I < 200 K, especially |Tci - TC2I < 100 K, like |Tci - TC2I < 50 K, including (essentially) Tci = TC2. Alternatively, the first CCT Tci may be different from the second CCT TC2, such as |Tci - TC2I > 200 K, especially |Tci - TC2I > 300 K, like |Tci - TC2I > 500 K. Additionally or alternatively, in embodiments, |Tci - TC2I < 2000 K, such as |Tci - TC2I < 1500 K, especially |Tci - TC2I < 1000 K. Hence, in embodiments, the (first) filament light and the second filament light may have the same optical properties, i.e., the same CCT and CRI. Alternatively, the (first) filament light and the second filament light may have the same CCT, and a different CRI. Alternatively, the (first) filament light and the second filament light may have a different CCT, and the same CRI. Alternatively, the (first) filament light and the second filament light may have a different CCT and a different CRI. Especially, the first CCT Tci may be different from the second CCT TC2. Hence, in specific embodiments, the filament light may be white light having a first correlated color temperature Tci selected from the range of 1700-6500 K, and the second filament light may be white light having a second correlated color temperature Tc? selected from the range of 1700-6500 K, wherein |Tci - Tc2| > 300 K. A light generating system wherein the LED filaments may provide white light having different CCTs may provide decorative multi -toned lighting effects.

[0049] In embodiments, the light generating system may comprise a control system. The control system may especially be configured to individually control the (first) LED filament and the second LED filament. In embodiments, the (first and / or second) LED filament may comprise a plurality of subsets of (first and / or second) solid state light sources, wherein each of the plurality of subsets of (first and / or second) solid state light sources may be configured to provide light source light having different optical properties, and wherein the control system may be configured to individually control the plurality of subsets of (first and / or second) solid state light sources. In such embodiments, the control system may be configured to control one or more of (i) an intensity, color point, CCT, and / or CRI of the (first) filament light, and (ii) an intensity, color point, CCT, and / or CRI of the second filament light. Hence, in specific embodiments, the light generating system may further comprise a control system, wherein the control system may be configured to individually control the LED filament and the second LED filament. Individual control over the (first) LED filament and the second LED filament may facilitate adjusting the optical properties (e.g. intensity and / or color point) of the light generated by the light generating system.

[0050] The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein the term “controlling” and similar terms may include imposing behavior on an element and / or monitoring the element. The controlling of the element can be done with a control system. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. The control system and element may not be physically coupled. Control can be done via wired and / or wireless control. A control system may comprise or may be functionally coupled to a user interface. The control system may also be configured to receive and execute instructions from a remote control. The control system may be controlled via an App on a device, such as a portable device. In such embodiments the control system of the lighting system may be a slave control system. The lighting system may also comprise means for communicating with other systems or devices, such as on the basis of Bluetooth, Thread, WIFI, LiFi, ZigBee, BLE or WiMAX, or another wireless technology. The control system may control in dependence of one or more of an input signal of a user interface, a sensor signal (of a sensor), and a timer. The term “timer” may refer to a clock and / or a predetermined time scheme.

[0051] The light generating system may comprise a reflector arrangement. The reflector arrangement may be configured at least partially enclosing the optical assembly stack, such as at least partially enclosing one or more of the first optical element, the (first and / or second) LED filament, and the second optical element. Especially, the reflector arrangement may be configured at least partially enclosing the first optical element. In specific embodiments, the reflector arrangement may (essentially) fully enclose the (edges of the) first optical element. Further, the reflector arrangement may (essentially) fully enclose the (edges of the) optical assembly stack. The reflector arrangement may be configured extending from the (optical assembly stack, such as especially from the) first optical element (in at least a direction parallel to a surface normal of the first plane). Further, with respect to the first optical element, the reflector arrangement may be at least partially (such as fully) configured on an opposite side as the second optical element. That is, the second optical element may be configured on a first side of the first optical element, and (at least part of) the reflector arrangement may be configured on an opposite second side of the first optical element. In embodiments, the reflector arrangement may be configured to reflect (at least part of) the (first) filament light received by the reflector arrangement. Further, the reflector arrangement may be configured to reflect (at least part of) the second filament light received by the reflector arrangement. Especially, the reflector arrangement may be configured to reflect > 50%, such as > 70%, especially > 90%, including (essentially) 100%, of the filament light and / or the second filament light received by the reflector arrangement. Hence, in specific embodiments, the light generating system may comprise a reflector arrangement, wherein the reflector arrangement may be configured at least partially enclosing the first optical element; wherein with respect to the first optical element the reflector arrangement may be at least partially configured on an opposite side as the second optical element; and wherein the reflector arrangement may be configured to reflect the filament light and the optional second filament light received by the reflector arrangement. Such a reflector arrangement may facilitate guiding the filament light and (optionally) the second filament light. Further, such a reflector arrangement may facilitate providing further virtual LED filaments (on the reflector arrangement).

[0052] The reflector arrangement may be configured extending from the first optical element (in a direction away from the second optical element) and at least partially enclosing at least the first optical element. Especially, the reflector arrangement may have a reflector height Hrin a plane perpendicular to the first plane (and along the optical axis Ao of the optical assembly stack). The reflector height Hrmay be selected from the range of > 1 cm, such as from the range of > 2 cm, especially from the range of > 5 cm. Additionally or alternatively, the reflector height Hrmay be selected from the range of < 15 cm, such as from the range of < 10 cm, especially from the range of < 8 cm. Further, the reflector height Hrmay be selected from the range of > di, such as from the range of > 1.5*di cm, especially from the range of > 2*di cm. Additionally or alternatively, the reflector height Hrmay be selected from the range of < 100*di, such as from the range of < 50*di, especially from the range of < 25*di. Further, the reflector arrangement may have a shape. Especially, the reflector arrangement may have a tapering shape. The tapering shape may be selected from the group comprising a cone shape, a paraboloid shape, an (semi-)elliptical (tapering) shape, and an irregular (or free) tapering shape. The reflector arrangement may taper towards the first optical element (i.e., a width of the reflector arrangement may decrease towards the first optical element). Especially, the reflector arrangement may have a reflector central axis Ar. The reflector central axis Armay intersect a geometrical center of the reflector arrangement, wherein the reflector arrangement may taper along the reflector central axis Ar. The reflector central axis Armay be configured parallel to the optical axis Ao of the optical assembly stack (and / or perpendicular to one or more of the first plane and the second plane). In embodiments, the reflector arrangement may have an open (or “hollow”) shape. That is, the reflector arrangement may (essentially) not (cover and / or) be configured over a major face of the first optical element. Hence, in specific embodiments, the reflector arrangement may have a tapering shape, wherein the reflector arrangement may taper towards the first optical element. Such a tapering shape may facilitate guiding the filament light and / or the second filament light out of the reflector arrangement and away from the first optical element. Further, such a tapering shape may facilitate providing a diverging beam of (combined) filament light.

[0053] As indicated above, a LED filament may comprise a luminescent material. The term “luminescent material” may herein refer to a material that can convert first radiation, especially one or more of UV radiation and blue radiation, into second radiation, especially visible light. Herein, UV (ultraviolet) may especially refer to a wavelength selected from the range of 190-380 nm, such as 200-380 nm, though other wavelengths may also be possible. In general, the first radiation and second radiation have different spectral power distributions, with the second radiation especially having a spectral power distribution at larger wavelengths than the first radiation (i.e. “down-conversion”). Hence, upon excitation with radiation, the luminescent material may emit radiation. Further, the term “luminescent material” may refer to phosphorescence and / or fluorescence. The term “luminescent material” may also refer to a plurality of different luminescent materials. Hence, the term “luminescent material” may in specific embodiments also refer to a luminescent material composition. Examples of possible luminescent materials are indicated below. Instead of the term “luminescent material” also the term “phosphor” may be applied, as is known to the person skilled in the art.

[0054] In embodiments, luminescent materials may be selected from garnets and nitrides, especially doped with trivalent cerium or divalent europium, respectively. The term “nitride” may also refer to oxynitride or nitridosilicate, etc. Alternatively or additionally, the luminescent material(s) may be selected from silicates, especially doped with divalent europium. The luminescent material may comprise a divalent europium comprising oxynitride luminescent material. Further, in embodiments, the luminescent material may comprise a divalent europium comprising nitride luminescent material.

[0055] The luminescent material may comprise a cerium comprising garnet luminescent material of the type AsEEOn Ce, wherein A comprises one or more of yttrium (Y), lanthanum (La), gadolinium (Gd), terbium (Tb) and lutetium (Lu), and wherein B comprises one or more of aluminum (Al), gallium (Ga), indium (In), and scandium (Sc); and wherein the light source light may comprise blue light. Embodiments of garnets especially include A3B5O12 garnets, wherein A comprises at least Y or Lu, and wherein B comprises at least Al. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of Ce and Pr. Further, B and O may at least partly be replaced by Si and N. 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. This is known to the person skilled in the art.

[0056] The luminescent material may comprise a luminescent material of the type AsSieNiuCe3, wherein A comprises one or more of Y, La, Gd, Tb and Lu, such as in embodiments one or more of La and Y. The luminescent material may alternatively or additionally comprise one or more of MS:Eu2+and / or LSisN^Eu2and / or MAlSiHvEu2and / or Ca2AlSi3O2Ns:Eu2+, etc., wherein M comprises one or more of Ba, Sr and Ca, especially in embodiments at least Sr.

[0057] The term “luminescent material” herein especially relates to inorganic luminescent materials. Alternatively or additionally, also other luminescent materials may be applied. For instance quantum dots and / or organic dyes may be applied and may optionally be embedded in transmissive matrices like e.g. polymers, like PMMA, or polysiloxanes, etc.. The luminescent material may comprise a tetravalent manganese-comprising luminescent material, i.e., a luminescent material doped with tetravalent manganese. Especially, in embodiments, the luminescent material may comprise a luminescent material of the type M M2-2xAXe:Mn4+, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x may be selected from the range of 0-1, wherein A comprises a tetravalent cation, for instance comprising one or more of silicon and titanium, and wherein X comprises a monovalent anion, at least comprising fluorine. The alkaline earth cation M’ may comprise one or more of magnesium (Mg), strontium (Sr), calcium (Ca), and barium (Ba), especially one or more of Sr and Ba. Further, the alkaline cation M may comprise one or more of sodium (Na), potassium (K), rubidium (Rb), ammonium (NH ), lithium (Li), and cesium (Cs), such as at least K, or such as at least Rb. In embodiments, A may comprise a tetravalent cation, and preferably at least comprises silicon. A may (further) comprise one or more of titanium (Ti), germanium (Ge), stannum (Sn) and zinc (Zn). The monovalent anion X may comprise fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), such as at least F. The luminescent material may be coated, as described in WO2013121355A1.

[0058] The term “light source” may in principle relate to any light source known in the art. In a specific embodiment, the light source may comprise a solid state light source (such as a LED or laser diode). The term “light source” may also refer to a chip scale package (CSP) and / or a chip scale packaged (CSP) LED. A CSP may comprise a single solid state die (such as a LED) with provided thereon a luminescent material comprising layer. The term “light source” may also refer to a midpower package. A midpower package may comprise one or more solid state die(s), optionally covered by a luminescent material comprising layer. The die dimensions may be < 2 mm, such as in the range of e.g. 0.2-2 mm. Herein, the term “light source” may also refer to mini LEDs or micro LEDs, such as especially micro LEDs or “microLEDs”. Herein, the term mini LED refers to solid state light sources having (die) dimensions, especially length and width, selected from the range of 0.1- 1 mm. Further, the term micro LED refers to solid state light sources having (die) dimensions, especially length and width, selected from the range of < 100 pm.

[0059] The term “light source” may refer to a semiconductor light-emitting device, such as an LED, a resonant cavity LED (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc... The term “light source” may also refer to an organic LED (OLED), such as a passive-matrix (PMOLED) or an active-matrix (AMOLED). In an embodiment, the light source a LED, a laser diode, a superluminescent diode, or a multi -junction LED. The light source may be configured to provide primary radiation, which is used as such, such as e.g. a blue light source, like a blue LED. Such LEDs may be indicated as direct color LEDs. In other embodiments, the light source may be configured to provide primary radiation and part of the primary radiation may converted into secondary radiation (e.g. by a luminescent material). The luminescent material may be comprised by the light source, such as an LED with a luminescent material layer or dome. Such LEDs may be indicated as phosphor converted LEDs or PC LEDs. In other embodiments, the light source may be configured to provide primary radiation and part of the primary radiation is converted into secondary radiation. Secondary radiation may be based on conversion by a luminescent material. The luminescent material may in embodiments be comprised by the light source, such as an LED with a luminescent material layer or dome comprising luminescent material. Such LEDs may be indicated as phosphor converted LEDs or PC LEDs.

[0060] The light generating system may be part of or may be applied in e.g. office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, automotive applications, (outdoor) (road) lighting systems, urban lighting systems, green house lighting systems, horticulture lighting, digital projection, or LCD backlighting. The light generating system (or luminaire) may be part of or may be applied in e.g. optical communication systems or disinfection systems.

[0061] In yet a further aspect, the invention also provides a lamp or a luminaire comprising the light generating system as defined herein. The luminaire may further comprise a housing, optical elements, louvres, etc.. The lamp or luminaire may comprise a housing enclosing the light generating system. The lamp or luminaire may comprise a light window in the housing or a housing opening, through which the filament light and / or second filament light may escape from the housing. In yet a further aspect, the invention also provides a projection device comprising the light generating system as defined herein. Especially, a projection device or “projector” or “image projector” may be an optical device that projects an image (or moving images) onto a surface, such as e.g. a projection screen. The projection device may include one or more light generating systems such as described herein. Hence, in an aspect the invention also provides a lighting device selected from the group comprising a lamp, a luminaire, a projector device, a disinfection device, a photochemical reactor, and an optical wireless communication device, comprising the light generating system as defined herein. Especially, in a second aspect, the invention provides a lighting device comprising the light generating system as defined herein. The lighting device may comprise a housing or a carrier, configured to house or support, one or more elements of the light generating system.

[0062] The terms “light” and “radiation” are herein interchangeably used, unless clear from the context that the term “light” only refers to visible light. The terms “light” and “radiation” may thus refer to UV radiation, visible light, and IR radiation. In specific embodiments, especially for lighting applications, the terms “light” and “radiation” refer to (at least) visible light.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts.

[0065] Figures 1 A and IB schematically depict a light generating system.

[0066] Figure 2 schematically depicts a light generating system.

[0067] Figures 3A, 3B, and 3C schematically depict a light generating system.

[0068] Figure 4 schematically depicts a LED filament.

[0069] Figure 5 schematically depicts a light generating system.

[0070] Figure 6 schematically depicts a lighting device.

[0071] The schematic drawings are not necessarily to scale.

[0072] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0073] Fig. 1 A schematically depicts an embodiment of the light generating system 1000. The light generating system 1000 may comprise (an optical assembly stack 2000 comprising) a LED filament 400, a first optical element 500, and a second optical element 600. The first optical element 500 and the second optical element 600 may be configured parallel. Further, the first optical element 500 and the second optical element 600 may have a shortest mutual distance di. The LED filament 400 may comprise (i) an array of a plurality of solid state light sources 10 arranged on (at least a first major surface 451 of) an elongated carrier 450, and (ii) an elongated encapsulant 410 at least partly enclosing the plurality of solid state light sources 10 and covering at least part of the elongated carrier 450 (see Fig. 4). The LED filament 400 may be configured to generate filament light 401. Further, the LED filament 400 may comprise a light emitting surface 420. Especially, during operation of the LED filament 400 the filament light 401 may escape from the LED filament 400 via the light emitting surface 420. The light emitting surface 420 may be configured in between the first and second optical elements 500,600 and extending from the first optical element 500 to the second optical element 600 (over a distance of at least 0.8*di). In embodiments, the first optical element 500 is configured to specularly reflect at least 25% of the filament light 401 (perpendicularly) received by the first optical element 500, and the second optical element 600 is configured to specularly reflect at least 25% of the filament light 401 (perpendicularly) received by the second optical element 600.

[0074] Further, the first optical element 500 may further be configured to transmit 25- 75% of the filament light 401 (perpendicularly) received by the first optical element 500. The optical assembly stack 2000 may comprise an optical axis Ao, along which on average the filament light 401 may be emitted during operation of the LED filament 400.

[0075] The second optical element 600 may be configured to specularly reflect > 80% of the filament light 401 (perpendicularly) received by the second optical element 600. Such an embodiment is depicted in Fig. 1 A. In embodiments wherein the second optical element 600 reflects > 80% of the filament light 401, and during operation of the LED filament 400, virtual LED filaments 400’, 400” may appear (only) on the side of the second optical element 600. Virtual LED filament are indicated by references 400’ and 400”, wherein virtual LED filament 400’ may be the result of a beam of filament light 401 reflected at the second optical element 600 and subsequently transmitted by the first optical element 500, and virtual LED filament 400” may be the result of a beam of filament light 401 reflected at the second optical element 600, reflected at the first optical element 500, again reflected at the second optical element 600, and subsequently transmitted by the first optical element 500. Yet, in embodiments, the second optical element 600 may be configured to transmit 25-75% of the filament light 401 (perpendicularly) received by the second optical element 600.

[0076] The light emitting surface 420 may be configured extending from the first optical element 500 to the second optical element 600 over a distance of at least 0.8*di. The shortest mutual distance di may be selected from the range of 0.3-5 cm. Further, the LED filament 400 may be configured in a helical or spiral shape. Additionally, the LED filament 400 may have a projected shape in a projection on (a surface of) the second optical element 600 selected from the group of a circle, an ellipse, a spiral, and a polygonal shape, such as a regular (simple) polygonal shape. In Fig. 1 A, the LED filament 400 has a helical shape, wherein the projected shape of the LED filament 400 may especially be a circle. The LED filament 400 may be configured at least partially extending through the first optical element 500 and / or the second optical element 600. Especially, an electrical contact element of the LED filament 400 may be configured at least partially extending through the first optical element 500 and / or the second optical element 600. In Fig. 1 A, the electrical contact element extending through the second optical element 600 is indicated by a dashed line.

[0077] The light emitting surface 420 may comprise a light emitting surface first end 421 and a light emitting surface second end 422 (opposite the light emitting surface first end 421 along the filament length LF). The light emitting surface 420 may configured in physical contact with the first optical element 500 at the light emitting surface first end 421. Further, the light emitting surface 420 may configured in physical contact with the second optical element 600 at the light emitting surface second end 422.

[0078] Fig. IB schematically depicts a further embodiment of the light generating system 1000. The light generating system 1000 (especially the optical assembly stack 2000) may comprise a second LED filament 800 configured in between the first and second optical elements 500,600. The second LED filament 800 may especially comprise (i) an array of a plurality of second solid state light sources 20 arranged on (at least a first major surface 851 of) a second elongated carrier 850, and (ii) a second elongated encapsulant 810 at least partly enclosing the plurality of second solid state light sources 20 and covering at least part of the elongated carrier 850. Further, the second LED filament 800 may be configured to generate second filament light 801. Hence, the second LED filament 800 may comprise a second light emitting surface 820. Further, the second LED filament 800 may be configured (i) in physical contact with the first optical element 500 at a second light emitting surface first end 821, and (ii) in physical contact with the second optical element 600 at a second light emitting surface second end 822. The second LED filament 800 may be configured in a shape mirroring the shape of the LED filament 400. Further, a geometrical center of the LED filament 400 and the second LED filament 800 may overlap. In Fig. IB, the filament mirror plane (through which the LED filament 400 and second LED filament 800 may mirror each other) is schematically depicted by the dashed line with reference Pf.

[0079] In embodiments, the filament light 401 and / or the second filament light 801 may be white light having a correlated color temperature selected from the range of 1700- 6500 K. Especially, the filament light 401 may be white light having a first correlated color temperature Tci selected from the range of 1700-6500 K. Further, the second filament light 801 may be white light having a second correlated color temperature Tc? selected from the range of 1700-6500 K. In embodiments, |Tci - Tc2| > 300 K. The light generating system 1000 may further comprise a control system 300. The control system 300 may be configured to individually control the LED filament 400 and the second LED filament 800.

[0080] Fig. 2 schematically depicts a further embodiment of the light generating system 1000. The first optical element 500 may comprise one or more first layers 510, 520, etc.. Each of the one or more first layers 510, 520, etc. may comprise a light transmissive material and a light transmissive coating (especially comprising titanium dioxide). The light transmissive material may have a first refractive index m, and the light transmissive coating may have a second refractive index n2. In embodiments, m- > 0.5.

[0081] The light generating system 1000 (especially the optical assembly stack 2000) may further comprise one or more (side walls comprising one or more) side mirrors 900. The one or more side mirrors 900 may be configured bridging the first optical element 500 and second optical element 600 (and surrounding the LED filament 400). Further, the one or more side mirrors 900 may be configured to specularly reflect > 50% of the filament light 401 (and / or the second filament light 801) received by the one or more side mirrors 900.

[0082] Fig. 3 schematically depicts a further embodiment of the light generating system 1000. Fig. 3 A schematically depicts an embodiment of the light generating system 1000 comprising (only) the LED filament 400, and Fig. 3B schematically depicts an embodiment of the light generating system 1000 comprising the LED filament 400 and the second LED filament 800. The LED filament 400 may be configured in a circular shape. Further, a plane parallel to and intersecting the (circular) LED filament 400 may be configured at a smallest angle ai with respect to the first optical element 500 and the second optical element 600. In embodiments, ai may be selected from the range of 5-60°.

[0083] Fig. 3C schematically depicts a perspective view of a further embodiment of aspects of the light generating system 1000, wherein the LED filament 400 and the second LED filament 800 may be configured in a spiral shape, and wherein the second LED filament 800 may further be configured in a shape mirroring the shape of the LED filament 400. Here, the light emitting surface first end 421 of the LED filament 400 may be configured in physical contact with the second light emitting surface first end 821 of the second LED filament 800, and the light emitting surface second end 422 of the LED filament 400 may be configured in physical contact with the second light emitting surface second end 822 of the second LED filament 800, though this need not be the case.

[0084] Fig. 4 schematically depicts an embodiment of the LED filament 400 and / or the second LED filament 800. The array of a plurality of solid state light sources 10 and / or the array of a plurality of second solid state light sources 20 may be configured on at least a first major surface 451,851 of the elongated carrier 450 and / or second elongated carrier 850, respectively. In embodiments, the array of a plurality of solid state light sources 10 and / or the array of a plurality of second solid state light sources 20 may further be configured on a second major surface 452,852 of the elongated carrier 450 and / or second elongated carrier 850, respectively. In such embodiments, the elongated carrier 450 and / or the second elongated carrier 850 may especially be light transmissive or opaque.

[0085] Fig. 5 schematically depicts an embodiment of the light generating system 1000. The light generating system 1000 may comprise a reflector arrangement 700. The reflector arrangement 700 may be configured at least partially enclosing the optical assembly stack 2000. Especially, the reflector arrangement 700 may be configured at least partially enclosing the first optical element 500 (and (essentially) not enclosing the LED filament 400 and the second optical element 600). For clarity, the first optical element 500 is not depicted in Fig. 5, though it is clear to the person skilled in the art that the first optical element 500 would be located at the top of the one or more side mirrors 900. The reflector arrangement 700 may be configured extending from the first optical element 500. Further, with respect to the first optical element 500 the reflector arrangement 700 may be at least partially configured on an opposite side as the second optical element 600. The reflector arrangement 700 may be configured to reflect (at least 50% of) the filament light 401 and / or the second filament light 801 received by the reflector arrangement 700. Further, the reflector arrangement 700 may have a tapering shape, wherein the reflector arrangement 700 may especially taper towards the first optical element 500. The reflector arrangement 700 may have a reflector central axis Arintersecting a geometrical center of the reflector arrangement 700, wherein the reflector arrangement 700 may taper along the reflector central axis Ar. The reflector central axis Armay be configured parallel to the optical axis Ao of the optical assembly stack 2000. Hence, the reflector arrangement 700 may be configured as a “collar” around the first optical element 500.

[0086] Fig. 6 schematically depicts an embodiment of a luminaire 2 comprising the light generating system 1000. Reference 301 indicates a user interface which may be functionally coupled with a control system 300 comprised by or functionally coupled to the light generating system 1000. Fig. 6 also schematically depicts an embodiment of a lamp 1 comprising the light generating system 1000. Hence, Fig. 6 schematically depicts embodiments of a lighting device 1200 comprising the light generating system 1000. Lighting device light escaping from the lighting device 1200 is indicated with reference 1201. Lighting device light 1201 may essentially consist of filament light 401 (and / or second filament light 801), and may in specific embodiments be filament light 401 (and / or second filament light 801). Reference 1300 refers to a space, such as a room. Reference 1305 refers to a floor, reference 1310 to a ceiling, and reference 1307 to a wall.

[0087] The term “plurality” refers to two or more. The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” also includes embodiments wherein the term “comprises” means “consists of’. The term “and / or” especially relates to one or more of the items mentioned before and after “and / or”. For instance, a phrase “item 1 and / or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of’ but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0088] The devices, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, or systems in operation. It should be noted that the above- mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. 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. The invention also provides a control system that may control the device or system, or that may execute a mode of operation of the system. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, or system, controls one or more controllable elements of such device, or system. The invention further applies to a device, or system comprising one or more of the characterizing features described in the description and / or shown in the attached drawings. The invention further pertains to a method comprising one or more of the characterizing features described in the description and / or shown in the attached drawings.

[0089] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

Claims

CLAIMS:

1. A light generating system (1000) comprising a LED filament (400), a first optical element (500), and a second optical element (600); wherein: the first optical element (500) and the second optical element (600) are configured parallel; wherein the first optical element (500) and the second optical element (600) have a shortest mutual distance (di); the LED filament (400) comprises (i) an array of a plurality of solid state light sources (10) arranged on an elongated carrier (450), and (ii) an elongated encapsulant (410) at least partly enclosing the plurality of solid state light sources (10) and covering at least part of the elongated carrier (450); wherein the LED filament (400) is configured to generate filament light (401); the first optical element (500) is configured to specularly reflect at least 25% of the filament light (401) received by the first optical element (500); the second optical element (600) is configured to specularly reflect at least 25% of the filament light (401) received by the second optical element (600); the first optical element (500) is further configured to transmit 25-75% of the filament light (401) received by the first optical element (500), the LED filament (400) comprises a light emitting surface (420) that is configured in between the first optical element (500) and the second optical element (600), the light emitting surface (420) extends from the first optical element (500) to the second optical element (600) over a distance of at least 0.8*di, and the LED filament (400) has a projected shape in a projection on the second optical element (600), selected from the group of a circle, an ellipse, a spiral, and a polygonal shape.

2. The light generating system (1000) according to claim 1, wherein one of the following applies: the LED filament (400) is configured in a helical or spiral shape; and the LED filament (400) is configured in a circular shape, wherein a plane parallel to and intersecting the LED filament (400) is configured at a smallest angle ai withrespect to the first optical element (500) and the second optical element (600), and wherein ai is selected from the range of 5-60°.

3. The light generating system (1000) according to claim 2, wherein the LED filament (400) is configured in a helical or spiral shape; and wherein the LED filament (400) is configured at least partially extending through the first optical element (500) and / or the second optical element (600).

4. The light generating system (1000) according to any one of the preceding claims, wherein the light emitting surface (420) comprises a light emitting surface first end (421) and a light emitting surface second end (422), wherein the light emitting surface (420) is configured in physical contact with (i) the first optical element (500) at the light emitting surface first end (421), and (ii) the second optical element (600) at the light emitting surface second end (422).

5. The light generating system (1000) according to any one of the preceding claims, wherein the light generating system (1000) comprises a second LED filament (800) configured in between the optical elements (500,600), wherein the second LED filament (800) comprises (i) an array of a plurality of second solid state light sources (20) arranged on a second elongated carrier (850), and (ii) a second elongated encapsulant (810) at least partly enclosing the plurality of second solid state light sources (20) and covering at least part of the elongated carrier (850); wherein the second LED filament (800) is configured to generate second filament light (801).

6. The light generating system (1000) according to claim 5, wherein the second LED filament (800) is configured in a shape mirroring the shape of the LED filament (400).

7. The light generating system (1000) according to any one of the preceding claims, wherein the second optical element (600) is configured to specularly reflect > 80% of the filament light (401) received by the second optical element (600).

8. The light generating system (1000) according to any one of the preceding claims 1-6, wherein the second optical element (600) is configured to transmit 25-75% of the filament light (401) received by the second optical element (600).

9. The light generating system (1000) according to any one of the preceding claims, wherein the shortest mutual distance (di) is selected from the range of 0.3-5 cm.

10. The light generating system (1000) according to any one of the preceding claims, wherein the filament light (401) and / or the second filament light (801) as defined in any one of claims 5-6, is white light having a correlated color temperature selected from the range of 1700-6500 K.

11. The light generating system (1000) according to any one of the claims 5, 6 and 10, wherein the filament light (401) is white light having a first correlated color temperature (Tci) selected from the range of 1700-6500 K, wherein the second filament light (801) is white light having a second correlated color temperature (Tc2) selected from the range of 1700-6500 K, and wherein |Tci - Tc2| > 300 K.

12. The light generating system (1000) according to any one of the preceding claims, wherein the light generating system (1000) comprises a reflector arrangement (700), wherein the reflector arrangement (700) is configured at least partially enclosing the first optical element (500); wherein with respect to the first optical element (500) the reflector arrangement (700) is at least partially configured on an opposite side as the second optical element (600); and wherein the reflector arrangement (700) is configured to reflect the filament light (401) and the optional second filament light (801) as defined in any one of claims 5, 6, 10, and 11 received by the reflector arrangement (700).

13. The light generating system (1000) according to any one of the preceding claims, wherein the light generating system (1000) comprises one or more side mirrors (900), wherein the one or more side mirrors (900) are configured bridging the first optical element (500) and second optical element (600), and wherein the one or more side mirrors (900) are configured to specularly reflect > 50% of the filament light (401) received by the one or more side mirrors (900).

14. A lighting device (1200) comprising the light generating system (1000) according to any one of the preceding claims.

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