In embodiments, the second luminescent material may comprise one or more luminescent materials selected from Table 1, though the inclusion of other (whitish-appearing and/or blue emitting) luminescent materials not provided in Table 1 is herein not excluded. Further, in embodiments, the whitish appearance of the LED filament in an off-state may be facilitated by a (second encapsulant comprising a) second luminescent material comprising a combination of luminescent materials (especially from Table 1). For example, a luminescent material of the type (Lui-x-y-aY_xGdy)3A150i2:Ce_a³⁺ may (when present in the second encapsulant) not provide a LED filament having a whitish appearance in an off-state on its own, but may provide such whitish appearance when combined (in the second luminescent material) with another type of luminescent material from Table 1.

In embodiments, the whitish appearance of the second luminescent material may be facilitated by the reflectance of said second luminescent material. Especially, as indicated above, the second luminescent material may be configured to reflect at least part of incident blue light. Hence, the second luminescent material may have reflectance for blue light, wherein the reflectance of the second luminescent material may be characterized by a reflection coefficient. The reflection coefficient may be a measure for the fraction of an intensity of an incident wave that is reflected by the second luminescent material. For example, a reflection coefficient of 0.5 indicates half the energy of the incident wave is reflected by the second luminescent material (and the other half is absorbed). In embodiments, both specular and diffuse reflections are considered when determining the reflection coefficient. In embodiments, the second luminescent material may have a first reflection coefficient R450. In embodiments, the first reflection coefficient R450 may especially indicate the fraction of light having a wavelength of 450 nm that is reflected by the second luminescent material. Further, the first reflection coefficient R450 may especially indicate the reflectance towards light (having a wavelength of 450 nm) that irradiates the second encapsulant along a direction parallel to a surface normal of the second encapsulant. That is, the first reflection coefficient R450 may especially indicate the reflectance towards light (having a wavelength of 450 nm) incident perpendicular to the second encapsulant. In embodiments, the first reflection coefficient R450 may be selected from the range of > 0.3, such as from the range of > 0.4, especially from the range of > 0.5. Further, in embodiments, the first reflection coefficient R450 may be selected from the range of < 0.99, such as from the range of < 0.9, especially from the range of < 0.8. In specific embodiments, the first reflection coefficient R450 may be selected from the range of < 1.00. In embodiments, the second luminescent material may (further) have a second reflection coefficient R420. The second reflection coefficient R420 may in embodiments especially indicate the fraction of light having a wavelength of 420 nm that is reflected by the second luminescent material. Further, the second reflection coefficient R420 may especially indicate the reflectance towards light (having a wavelength of 420 nm) incident perpendicular to the second encapsulant. In embodiments, the second reflection coefficient R420 may be selected from the range of < 1.00, such as from the range of < 0.8, especially from the range of < 0.65. Further, in embodiments, the second reflection coefficient R420 may be selected from the range of < 0.5, such as from the range of < 0.4, especially from the range of < 0.3. Further yet, in embodiments, the second reflection coefficient R420 may be selected from the range of > 0.05, such as from the range of > 0.1, especially from the range of > 0.15. In embodiments, the second reflection coefficient R420 may be smaller than the first reflection coefficient R450, R420 < R450. That is, in embodiments, the second luminescent material may be configured to reflect more (of) light having a wavelength of 450 nm than (of) light having a wavelength of 420 nm. Especially, in embodiments, R450- R42o> 0.05, such as R450- R42o> 0.1, especially R450- R420 > 0.15. Hence, in specific embodiments, the second luminescent material may have a first reflection coefficient R450 for light incident perpendicular to the second encapsulant and having a wavelength of 450 nm, wherein R450 > 0.3, wherein the second luminescent material may further have a second reflection coefficient R420 for light incident perpendicular to the second encapsulant and having a wavelength of 420 nm, wherein R420 < 0.5, and wherein R420 < R450. A second luminescent material having a higher reflectance at 450 nm than at 420 nm may especially facilitate a whitish appearance of the second encapsulant. Especially, the human eye may be more sensitive towards blue light having a wavelength of 450 nm than towards blue light having a wavelength of 420 nm. Hence, by reflecting at least 30% of the light at 450 nm, the second encapsulant may appear as whitish under illumination with daylight.

Further, in embodiments, the LED filament, especially the LED filament comprising the second encapsulant, may have a first reflection coefficient R450. In embodiments, the first reflection coefficient R450 may especially be the reflection coefficient towards light (having a wavelength of 450 nm) that irradiates the LED filament along a direction parallel to a surface normal of the LED filament (i.e., a direction perpendicular to the LED filament). Further, the first reflection coefficient R450 may especially be determined for that part of the LED filament that is covered by a first (and second) encapsulant. That is, the LED filament may comprise sections not covered by an encapsulant (e.g. sections at the ends of the LED filament used to establish electrical contact with a power source), which may have a different reflection coefficient towards light of 450 nm. Hence, in embodiments, the LED filament may comprise an (elongated) encapsulant, wherein the elongated encapsulant is configured along at least part of the LED filament, wherein that part of the LED filament has a first reflection coefficient R450. In embodiments, the LED filament may have a first reflection coefficient R450 selected from the range of > 0.3, such as from the range of > 0.4, especially from the range of > 0.5. Further, in embodiments, the LED filament may have a first reflection coefficient R450 selected from the range of < 0.99, such as from the range of < 0.9, especially from the range of < 0.8. In specific embodiments, the LED filament may have a first reflection coefficient R450 selected from the range of < 1.00. In embodiments, the LED filament (especially the part covered by an encapsulant) may (further) have a second reflection coefficient R420 towards light (having a wavelength of 420 nm) incident perpendicular to the LED filament. In embodiments, the LED filament may have a second reflection coefficient R420 selected from the range of < 1.00, such as from the range of < 0.8, especially from the range of < 0.65. Further, in embodiments, the LED filament may have a second reflection coefficient R420 selected from the range of < 0.5, such as from the range of < 0.4, especially from the range of < 0.3. Further yet, in embodiments, the LED filament may have a second reflection coefficient R420 selected from the range of > 0.05, such as from the range of > 0.1, especially from the range of > 0.15. In embodiments, the second reflection coefficient R420 of the LED filament may be smaller than the first reflection coefficient R450 (of the LED filament), R420 < R450. That is, in embodiments, the LED filament may be configured to reflect more (of) light having a wavelength of 450 nm than (of) light having a wavelength of 420 nm. Especially, in embodiments, R450- R42o> 0.05, such as R450- R420 > 0.1, especially R450- R42o> 0.15. Hence, in specific embodiments, the LED filament may have a first reflection coefficient R450 for light incident perpendicular to the LED filament and having a wavelength of 450 nm, wherein R450 > 0.3, wherein the LED filament may further have a second reflection coefficient R420 for light incident perpendicular to the LED filament and having a wavelength of 420 nm, wherein R420 < 0.5, and wherein R420 < R450. A LED filament having a higher reflectance at 450 nm than at 420 nm may especially facilitate a whitish appearance of the LED filament, especially of the part of the LED filament covered by an (elongated) encapsulant. Especially, the human eye may be more sensitive towards blue light having a wavelength of 450 nm than towards blue light having a wavelength of 420 nm. Hence, by reflecting at least 30% of the light at 450 nm, the LED filament may appear as whitish under illumination with daylight.

In embodiments, a second encapsulant comprising a second luminescent material as described herein may be applied in any LED filament. That is, the second encapsulant as described herein may not be limited to the embodiments of the (other components of the) LED filament as described herein. Hence, in specific embodiments, the invention may provide an encapsulant for a LED filament, wherein the encapsulant comprises a second luminescent material, wherein: (a) the second luminescent material may have a first reflection coefficient R450 for light incident perpendicular to the second encapsulant and having a wavelength of 450 nm, wherein R450 > 0.3; (b) the second luminescent material may have a second reflection coefficient R420 for light incident perpendicular to the second encapsulant and having a wavelength of 420 nm, wherein R420 < 0.5; and (c) R420 < R450. Such a second encapsulant may provide a whitish appearance to a LED filament. Further, depending on the second luminescent material used, such a second encapsulant may provide additional benefits for the LED filament light generated by said LED filament (e.g. improved CRI, reduced short-wavelength blue light, etc.).

In embodiments, the reflectance of the second luminescent material may be correlated to the absorbance of said second luminescent material. In specific embodiments, any light not reflected by the second luminescent material may be absorbed (by said second luminescent material). Hence, in embodiments, the second luminescent material may be configured to absorb at most 70%, such as at most 60%, especially at most 50%, of light having a wavelength of 450 nm and incident perpendicular to the second encapsulant. Further, the second luminescent material may be configured to absorb at least 1%, such as at least 10%, especially at least 20%, of light having a wavelength of 450 nm and incident perpendicular to the second encapsulant. Additionally or alternatively, in embodiments, the second luminescent material may be configured to absorb at least 50%, such as at least 60%, especially at least 70%, of light having a wavelength of 420 nm and incident perpendicular to the second encapsulant. Further, in embodiments, the second luminescent material may be configured to absorb at most 95%, such as at most 90%, especially at most 85%, of light having a wavelength of 420 nm and incident perpendicular to the second encapsulant. In embodiments, the second luminescent material may be configured to have a higher absorbance at 420 nm than at 450 nm. Hence, in specific embodiments, the second luminescent material may be configured to absorb at most 70% of light having a wavelength of 450 nm and incident perpendicular to the second encapsulant, wherein the second luminescent material may further be configured to absorb at least 50% of light having a wavelength of 420 nm and incident perpendicular to the second encapsulant, and wherein the second luminescent material may be configured to have a higher absorbance at 420 nm than at 450 nm.

In embodiments, the second luminescent material may need to be present in a high enough concentration in the second encapsulant to facilitate providing a whitish appearance to the LED filament. Hence, in embodiments, the second encapsulant may comprise the second luminescent material in a concentration selected from the range of > 2 wt.%, such as from the range of > 5 wt.%, especially from the range of > 10 wt.%. Further, the second encapsulant may comprise the second luminescent material in a concentration selected from the range of > 15 wt.%, such as from the range of > 20 wt.%, especially from the range of > 25 wt.%. Further, in embodiments, the second luminescent material may be present (in the second encapsulant) in a low enough concentration to facilitate transmitting at least part of one or more of the first luminescent material light and the light source light. Hence, in embodiments, the second encapsulant may comprise the second luminescent material in a concentration selected from the range of < 80%, such as from the range of < 70%, especially from the range of < 60%. Thus, in embodiments, the second encapsulant may comprise the second luminescent material in a concentration selected from the range of 2-80 wt.%, such as from the range of 5-70 wt.%, especially from the range of 10-60 wt.%. Further, in embodiments, the second encapsulant may be configured to transmit at least 70%, such as at least 80%, especially at least 85%, of the first luminescent material light received by the second encapsulant. Additionally or alternatively, in embodiments, the second encapsulant may be configured to transmit at least 50%, such as at least 60%, especially at least 70%, of the light source light received by the second encapsulant. Hence, in specific embodiments, the second encapsulant may comprise the second luminescent material in a concentration selected from the range of 5-70 wt.%, wherein the second encapsulant may further be configured to transmit (i) at least 70% of the first luminescent material light, and (ii) at least 50% of the light source light received by the second encapsulant. Such a concentration of second luminescent material may, as indicated, be high enough to facilitate providing a whitish appearance to the second encapsulant, yet low enough to allow transmission of (at least part of) one or more of the first luminescent material light and the light source light through the second encapsulant. Further, a second encapsulant configured to transmit at least 70% of the first luminescent material light may facilitate providing a desired whitish appearance at limited cost to the efficiency of the light generating system, especially of the LED filament.

In embodiments, the amount of first luminescent material light transmitted by the second encapsulant may be determined by one or more of the second luminescent material concentration and the thickness of the second encapsulant. Further, in embodiments, the amount of light source light transmitted by the second encapsulant may be determined by one or more of the second luminescent material concentration and the thickness of the second encapsulant. Hence, in embodiments, the second encapsulant may have a (second encapsulant) thickness T2. In embodiments, the second encapsulant thickness T2 may be selected from the range of 0.1-5 mm, such as from the range of 0.15-4 mm, especially from the range of 0.2-3 mm. Further, the transmittance of the second encapsulant towards one or more of the first luminescent material light and the light source light may be determined by additional components present in the second encapsulant. For instance, in embodiments, the second encapsulant may comprise a light scattering material. In embodiments, the light scattering material may be configured to scatter (or “diffuse”) light received by the light scattering material, especially in a direction non-parallel to the direction of the incident wave. In specific embodiments, the light scattering material may comprise light scattering particles, such as e.g. at least one of BaSCU, AI2O3 and TiCE particles. In embodiments, the light scattering material may be configured to (diffusely) scatter first luminescent material light received by the light scattering material. Further, the light scattering material may be configured to (diffusely) scatter light source light received by the light scattering material. Especially, in embodiments, the light scattering material may be configured to convert light received by the light scattering material into diffuse light. Hence, during operation of the light generating system, the second encapsulant may be configured to provide diffuse (white) light, wherein the system light may comprise the diffuse (white) light. In specific embodiments, the second encapsulant may thus comprise a light scattering material, and the system light may comprise diffuse light. System light comprising diffuse light may provide illumination over a wider angle around a light escape surface (see below) of the light sources. Additionally, a second encapsulant comprising a light scattering material may have a higher reflectance towards visible light (compared to a second encapsulant without a light scattering material). Hence, a LED filament comprising such a second encapsulant comprising a light scattering material may appear whiter.

The first encapsulant comprises the first luminescent material. This first luminescent material may comprise one or more different phosphors. Hence, effectively the first encapsulant may comprise one or more different first luminescent materials. The second encapsulant comprises the second luminescent material. The term “second luminescent material” may (also) refer to two or more different second luminescent materials. In embodiments, the first luminescent material is not available in the second encapsulant, and the second luminescent material is not available in the first encapsulant. In embodiments, a secondary first weight percentage of a first luminescent material in the second encapsulant may be at least 10 times smaller than a primary first weight percentage of the same first luminescent material in the first encapsulant. Likewise, in embodiments, a primary second weight percentage of a second luminescent material in the first encapsulant may be at least 10 times smaller than a secondary second weight percentage of the same second luminescent material in the second encapsulant.

As indicated, the LED filament may comprise a plurality of solid state light sources. Each solid state light source may, in embodiments, comprise a light emitting diode (LED) or laser diode (or “diode laser”)). In embodiments, the plurality of solid state light sources may comprise different light sources. Alternatively, the plurality of solid state light sources may comprise identical light sources. The phrase “different light sources”, and similar phrases, may in embodiments refer to a plurality of solid-state light sources selected from at least two different bins. Likewise, the phrases “identical light sources”, and similar phrases, may in embodiments refer to a plurality of solid-state light sources selected from the same bin. In embodiments, a solid state light source may comprise a LED. In embodiments, the LED may comprise one or more solid state die(s). The die dimensions may be equal to or smaller than 2 mm, such as in the range of e.g. 0.2-2 mm. Herein, the term “light source” may also especially refer to a small solid state light source, such as having a mini size or micro size. For instance, the light sources may comprise one or more of mini LEDs and micro LEDs, such as especially micro LEDs or “microLEDs” or “pLEDs”. Herein, the term mini size or mini LED especially refers to solid state light sources having dimensions, such as die dimension, especially length and width, selected from the range of 100 pm - 1 mm. Herein, the term p size or micro LED especially refers to solid state light sources having dimensions, such as die dimension, especially length and width, selected from the range of 100 pm and smaller.

The light source may have a light escape surface. For LEDs the light escape surface may for instance be the LED die, or when a resin is applied to the LED die, the outer surface of the resin. The term escape surface especially relates to that part of the light source, where the light actually leaves or escapes from the light source. The light source is configured to provide a beam of light. This beam of light (thus) escapes from the light exit surface of the light source. Likewise, a light generating system may comprise a light escape surface, such as an end window.

The term “light source” may refer to a semiconductor light-emitting device, such as a light emitting diode (LEDs), a resonant cavity light emitting diode (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc.. The term “light source” may also refer to an organic light-emitting diode (OLED), such as a passive-matrix (PMOLED) or an active-matrix (AMOLED). The terms “light source” or “solid state light source” may also refer to a superluminescent diode (SLED). Especially, the term “solid state light source”, and similar terms, may refer to semiconductor light sources, such as a light emitting diode (LED), a laser diode, or a superluminescent diode.

In embodiments, 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, or a green light source, such as a green LED, and a red light source, such as a red LED. Such LEDs, which may not comprise a luminescent material (“phosphor”) may be indicated as direct color LEDs. In embodiments, the light generating system may comprise a direct LED (i.e. no phosphor). Especially, in embodiments, the light source may comprise a blue light source, such as a blue LED. Further, in embodiments, the light generating system may comprise a laser device, like a laser diode. In embodiments, the light generating system may comprise a superluminescent diode. The light source may especially be configured to generate light source light having an optical axis (O), (a beam shape,) and a spectral power distribution. The light source light may in embodiments comprise one or more bands, having band widths as known for lasers. The term “light source” may (thus) refer to a light generating element as such, like e.g. a solid state light source. Further, the term “light generating system” may be used to address a light source and further (optical components), like an optical filter and/or a beam shaping element, etc. For instance, a solid state light source as such, like a blue LED, is a light source. A combination of a solid state light source (as light generating element) and a light converter element, such as a blue LED and a light converter element, optically coupled to the solid state light source, may be indicated as light generating system.

The terms “laser device”, “laser”, or “laser light source” may especially refer to a laser diode (or diode laser). Such laser may especially be configured to generate laser light source light having one or more wavelengths selected from the spectral wavelength range of 200-2000 nm, such as from the spectral wavelength range of 300-1500 nm. The term “laser” especially refers to a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

In embodiments, the light source may be a light source that during operation at least emits (light source) light at a wavelength selected from the range of 200-490 nm, such as selected from the range of 400-490 nm, especially selected from the range of 440-490 (i.e., the light source may be configured to generate blue light). Further, in embodiments, the light source light may have a light source peak wavelength kpi.. In embodiments, the light source peak wavelength kpi. may be selected from the range of 440-490 nm, such as from the range of 440-480 nm, especially from the range of 440-470 nm. Hence, in specific embodiments, the light source light may have a light source peak wavelength kpi., wherein the light source peak wavelength kpi. may be selected from the range of 440-470 nm. A light source having a light source peak wavelength kpi. selected from the range of 440-470 nm may provide light source light having a spectral power distribution at least partially overlapping with the excitation spectrum of the first luminescent material, such as at least partially overlapping with the excitation spectrum of the first phosphor, second phosphor, and the optional third phosphor. For example, such a peak wavelength may be within 70 nm, such as within 60 nm, especially within 50 nm, of an excitation maximum of the first luminescent material. Further, such a peak wavelength may be within 25 nm, such as within 20 nm, especially within 15 nm, of an excitation maximum of the first luminescent material. Especially, such a peak wavelength may be within 25 nm, such as within 20 nm, especially within 15 nm, of an excitation maximum of one or more of the first phosphor, the second phosphor, and (optionally) the third phosphor. Further, in embodiments, light source light having a light source peak wavelength kpi. selected from the range of 440-470 nm may be capable of exciting the second luminescent material, thereby facilitating the generation of second luminescent material light.

In embodiments, the second luminescent material may thus be configured to convert the light source light (having a light source peak wavelength kpi.) into second luminescent material light, wherein the second luminescent material light may have a spectral power distribution at longer (blue) wavelengths than the light source light. Hence, in embodiments, the second luminescent material light may have a centroid wavelength Zc2 larger than the light source peak wavelength kpi.. Further, in embodiments, the second luminescent material light may especially have a centroid wavelength Zc2 larger than a (second) peak wavelength Xpr .2 comprised by the light source light received by the second luminescent material. In embodiments, Xc2 - Apr.2 > 5 nm, such as Xc2 - Apr.2 > 10 nm, especially Xc2 - Apr.2 > 20 nm. Further, in embodiments, Xc2 - Apr.2 < 60 nm, such as Xc2 - kpL,2 < 50 nm, especially Xc2 - Apr.2 < 40 nm, like Xc2 - Apr.2 < 30 nm. Hence, in specific embodiments, the light source light may have a peak wavelength Xpr .2, the second luminescent material light may have a second centroid wavelength Zc2, and Xc2 - Apr.2 > 10 nm. Such a difference between the second centroid wavelength Zc2 and the (second) peak wavelength Xpr .2 may facilitate converting at least part of the short- wavelength blue light into longer- wavelength blue light. Such a difference between Zc2 and Xpr .2 may further facilitate increasing the intensity of the system light at longer (blue) wavelengths, thereby increasing the CRI of the system light (see above).

Returning to general embodiments of the light generating system, in embodiments, the light generating system may comprise a (single) LED filament. Further, in embodiments, the light generating system may comprise a plurality of LED filaments, such as 2-12 LED filaments, especially 2-6 LED filaments. The plurality of LED filaments may differ in one or more of the solid state light sources used, the composition of the first luminescent material, the composition of the second luminescent material, and the thickness T2. Hence, in embodiments, the LED filament light provided by each of the plurality of LED filaments may differ (such as e.g. in CRI, correlated color temperature, and/or color). Further, in embodiments, the intensity of the LED filament light (of the one or of the plurality of LED filaments) may be dependent on the amount of current flowing through the LED filament(s). In embodiments, the light generating system may (therefore) comprise a control system. The control system may in embodiments be configured to control the current flowing to (each of the plurality of) the LED filament(s). Hence, the control system may be configured to control one or more of the color point, correlated color temperature, intensity, and color rendering index of the system light (comprising the LED filament light of the one or of the plurality of LED filaments). Hence, in specific embodiments, the light generating system may comprise a control system, wherein the control system may be configured to control one or more of the color point, correlated color temperature, intensity, and color rendering index of the system light. A light generating system comprising a control system may provide a consumer more control over the spectral properties of the system light. As such, a light generating system comprising a control system may facilitate personalization of the system light, e.g. to suit particular lighting needs.

The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may e.g. refer to imposing behavior on the element, such as e.g. measuring, displaying, actuating, etc.. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior on an element and 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. In embodiments, the control system and element may not be physically coupled. Control can be done via wired and/or wireless control. The term “control system” may also refer to a plurality of different control systems, which especially are functionally coupled, and of which e.g. one control system may be a master control system and one or more others may be slave control systems. A control system may comprise or may be functionally coupled to a user interface.

The system, or apparatus, or device may execute an action in a “mode” or “operational mode”. The term “operational mode” may also be indicated as “controlling mode”. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and/or after executing the mode one or more other modes may be executed. However, in embodiments a control system may be available, that is adapted to provide at least the controlling mode. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence of a sensor signal or a (time) scheme, may also be possible. The operational mode may in embodiments also refer to a system, or apparatus, or device, that can only operate in a single operational mode (i.e. “on”, without further tunability). Hence, in embodiments, 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.

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, 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, or digital projection. The light generating system (or luminaire) may be part of or may be applied in e.g. optical communication systems or disinfection systems.

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 further 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 system 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 of 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. The lighting device may comprise a housing or a carrier, configured to house or support, one or more elements of the light generating system.

Further, in specific embodiments, the lighting device may comprise a LED filament lamp. A LED filament lamp comprising the light generating system, especially the LED filament, as described herein may be more decorative than a conventional LED filament lamp. Especially, the whitish appearance of the LED filament as described herein may be more desired (by consumers) than the usually colored appearance of conventional LED filaments. Further, in such embodiments, the LED filament lamp may comprise a housing, such as a light transmissive envelope, surrounding the LED filament(s), and a base configured to support the LED filament(s). In embodiments, the base may (further) be configured to electrically couple the LED filament(s) to an energy source.

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. The terms “blue light” or “blue emission”, and similar terms, may especially relate to light having a wavelength in the range of about 440-490 nm. In specific embodiments, the blue light may have a centroid wavelength in the 440-490 nm range. The terms “green light” or “green emission”, and similar terms, may especially relate to light having a wavelength in the range of about 490-560 nm. In specific embodiments, the green light may have a centroid wavelength in the 490-560 nm range. The terms “yellow light” or “yellow emission”, and similar terms, may especially relate to light having a wavelength in the range of about 560-590 nm. In specific embodiments, the yellow light may have a centroid wavelength in the 560-590 nm range. The terms “orange light” or “orange emission”, and similar terms, may especially relate to light having a wavelength in the range of about 590-620 nm. In specific embodiments, the orange light may have a centroid wavelength in the 590-620 nm range. The terms “red light” or “red emission”, and similar terms, may especially relate to light having a wavelength in the range of about 620-750 nm. In specific embodiments, the red light may have a centroid wavelength in the 620-750 nm range. The phrase “light having a wavelength in a wavelength range” and similar phrases may especially indicate that the indicated light (or radiation) has a spectral power distribution with at least an intensity or intensities at the wavelength in the indicated wavelength range. For instance, a blue emitting solid state light source will have a spectral power distribution with intensities at at least a wavelength in the 440-490 nm wavelength range.

BRIEF DESCRIPTION OF THE DRAWINGS

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, and in which:

Figs. 1-7 schematically depict embodiments of the light generating system;

Fig. 8 schematically depicts a further embodiments of the light generating system;

Figs. 9-10 schematically depict embodiments of the system light; Fig. 11 schematically depicts an embodiment of the lighting device; and

Fig. 12 schematically depicts a further embodiment of the lighting device. The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figs. 1-7 schematically depict (a cross-sectional view of) embodiments of the light generating system 1000. In embodiments, the light generating system 1000 may comprise a LED filament 100. The LED filament 100 may comprise a plurality of solid state light sources 10. In embodiments, the plurality of solid state light sources 10 may be arranged on (at least a first major surface of) an elongated carrier 5. Additionally, in embodiments, the solid state light sources 10 may be selected from the group of light emitting diodes, laser diodes, and superluminescent diodes. Further, the LED filament 100 may comprise a first encapsulant 2100. Additionally, the LED filament 100 may comprise a second encapsulant 2200. In embodiments, as depicted in Fig. 2, the plurality of solid state light sources 10 may be configured to generate light source light 11. The light source light 11 may in embodiments comprise blue light. Further, the first encapsulant 2100 may be configured (at least partly) covering the plurality of solid state light sources 10 (and at least part of the elongated carrier 5). Hence, the first encapsulant 2100 may be configured in a light-receiving relationship with the plurality of solid state light sources 10. Further, the first encapsulant 2100 may comprise a first luminescent material 2110. The first luminescent material 2110 may especially be configured to convert at least part of the light source light 11 received by the first luminescent material 2110 into first luminescent material light 2111. In embodiments, the first encapsulant 2100 may have a (non-white) colored appearance.

In embodiments, the second encapsulant 2200 may be configured at least partly covering the first encapsulant 2100. Further, the second encapsulant 2200 may comprise a second luminescent material 2210. The second luminescent material 2210 may especially be different from the first luminescent material 2110. Further, the second luminescent material 2210 may be configured to at least partly convert daylight received by the second luminescent material 2210 into second luminescent material light 2211. In embodiments, the second luminescent material light 2211 may comprise blue light. Further, in embodiments, the LED filament 100 may be configured to generate LED filament light 101. The LED filament light 101 may comprise light source light 11 and first luminescent material light 2111. Further, in embodiments, the light generating system 1000 may be configured to generate in a first operational mode of the light generating system 1000 system light 1001 comprising light source light 11 and first luminescent material light 2111. Especially, the system light 1001 may comprise the LED filament light 101, such as (essentially) consist of the LED filament light 101. Further, in embodiments, the system light 1001, especially the LED filament light 101, may comprise the second luminescent material light 2211 (see below).

The light generating system 1000, especially the LED filament 100, may have an on-state and an off-state. An “off-state” of the light generating system 1000 and/or of the LED filament 100 may refer to a state in which no electricity is provided to the light generating system 1000 and/or to the LED filament 100, and thus a state wherein the solid state light sources 10 may not generate light source light 11. The off-state is schematically depicted in Fig. 1. Conversely, an “on-state” of the light generating system 1000 and/or of the LED filament 100 may refer to a state in which electricity is provided to the light generating system 1000 and/or to the LED filament 100, and thus wherein the solid state light sources 10 may generate light source light 11. The on-state may also be referred to as an “operational mode”, and is schematically depicted in Fig. 2. As indicated, the first encapsulant 2100 may have a non-white colored appearance. Especially, the first encapsulant 2100 may have a nonwhite colored appearance in an off-state of the LED filament 100. The (non-white) colored appearance of the first encapsulant 2100 may be facilitated by the absorption of blue light by the first encapsulant 2100, especially by the first luminescent material 2110. Further, as indicated, the second encapsulant 2200, especially the second luminescent material 2210, may be configured to at least partly convert daylight (here indicated by reference 6) received by the second encapsulant 2200 into second luminescent material light 2211. Especially, the second encapsulant 2200 (especially the second luminescent material 2210) may be configured to at least partly convert (N)UV and/or blue light having intensity at one or more wavelengths selected from the range of 240-430 nm into second luminescent material light 2211. Such conversion may occur in the off-state of the light generating system 1000, as is schematically depicted in Fig. 1. Further, in embodiments, the second encapsulant 2200, especially the second luminescent material 2210, may be configured to (at least partly) transmit and/or reflect one or more of blue light, green light, yellow light, orange light, and red light, such as at least blue light, green light, yellow light, orange light, and red light. Hence, in embodiments, in an off-state of the LED filament 100, the LED filament 100 (especially the second encapsulant 2200) may have a whitish appearance under illumination with daylight 6. The whitish appearance of the LED filament 100 may be defined by chromaticity coordinates corresponding to a specific color point in the CIE 1931 color space. Especially, the LED filament 100, in an off-state, may have chromaticity coordinates [x, y] in the CIE 1931 color space. In such embodiments, x and y may be individually selected from the range of 0.3-0.45.

Further, the reflectance of the LED filament 100 may be defined by one or more reflection coefficients, wherein the reflection coefficient is a measure of the fraction of an incoming wave that is reflected by the LED filament 100, especially by a part of the LED filament 100 covered by a first encapsulant 2100 and second encapsulant 2200. In embodiments, the LED filament 100 may have a first reflection coefficient R450 for light incident perpendicular to the LED filament 100 and having a wavelength of 450 nm. In embodiments, R450 > 0.3. Further, the LED filament 100 (especially the part covered by a first encapsulant 2100 and second encapsulant 2200) may have a second reflection coefficient R420 for light incident perpendicular to the LED filament 100 and having a wavelength of 420 nm. In embodiments, R420 < 0.5. Further, in embodiments, the LED filament 100 may be more reflective towards light at 450 nm than towards light at 420 nm. Hence, in embodiments, R420 < R450. The first and second reflection coefficients R450 and R420 of the LED filament 100 may be at least partially determined by the reflectance of the second luminescent material 2210 present in the second encapsulant 2200. The reflectance of the second luminescent material 2210 may be related to the absorbance of the second luminescent material 2210. That is, theoretically, the light that is not reflected by the second luminescent material 2210 may be absorbed by the second luminescent material 2210. Hence, the second luminescent material 2210 may be configured to absorb at most 70% of light having a wavelength of 450 nm and incident perpendicular to the second encapsulant 2200. Further, the second luminescent material 2210 may be configured to absorb at least 50% of light having a wavelength of 420 nm and incident perpendicular to the second encapsulant 2200. Additionally, the second luminescent material 2210 may be configured to have a higher absorbance at 420 nm than at 450 nm.

Returning to the first luminescent material 2110, the first luminescent material 2110 may comprise a first phosphor 210 of the type As-xBsOnCex, wherein A comprises one or more of Y, La, Gd, Tb and Lu, wherein B comprises one or more of Al, Ga, In and Sc, and wherein 0.001 < x < 0.1. The first phosphor 210 may be configured to convert light source light 11 received by the first phosphor 210 into first phosphor light 211. Further, the first phosphor 210 may comprise a primary first phosphor of the type (YxiiLuxnA’xisCexw^BsOn and a secondary first phosphor of the type (Y_X2iLux22A’_X23Ce_X24)3B5Oi2, wherein A’ comprises one or more of La, Gd, and Tb, wherein B comprises one or more of Al, Ga, In and Sc. In embodiments, xn + X12 + XB + XI4 = 1, xn + xn > 0, 0 < xi3 < 1, and 0.001 < xu< 0.1. Further, in embodiments, X21 + X22 + X23 + X24= 1, X21 + X22 > 0, 0 < X23 < 1, and 0.001 < X24 < 0.1. In specific embodiments, the primary first phosphor may comprise on a molar basis more Y than the secondary first phosphor. Additionally, in embodiments, the secondary first phosphor may comprise on a molar basis more Lu than the primary first phosphor. Hence, in embodiments, xn > X21 and X22 > X12.

The first luminescent material 2110 may further comprise a second phosphor 220. The second phosphor 220 may especially provide second phosphor light 221 having a different spectral power distribution that the first phosphor light 211 provided by the first phosphor 210. Further, the second phosphor 220 may be configured to convert light source light 11 received by the second phosphor 220 into second phosphor light 221. In embodiments, the second phosphor light 221 may especially comprise one or more of orange and red light. Optionally, the first luminescent material 2110 may further comprises a third phosphor 230. In embodiments, the third phosphor 230 may comprise a luminescent material of the type M’_xM2-2_XAXe doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, wherein M comprises an alkaline cation, wherein A comprises a tetravalent cation, and wherein X comprises a monovalent anion, at least comprising fluorine (F). Further, the third phosphor 230 may be configured to convert light source light 11 received by the third phosphor 230 into third phosphor light 231. In embodiments, the third phosphor light 231 may especially comprise red light.

Turning to the second luminescent material 2210, in embodiments, the second luminescent material 2210 may comprise a luminescent material configured to generate blue luminescent material light. Further, in embodiments, the second luminescent material 2210 may comprise a luminescent material having a whitish appearance under illumination with daylight 6. In embodiments, the second luminescent material 2210 may comprise a luminescent material of the type M5-_qEu_q(PO4)3Cl, wherein M may comprise one or more of Sr, Ba, Ca, Mg, and Mn, and wherein q may be selected from the range of 0.005-0.3. In embodiments, the second encapsulant 2200 may comprise the second luminescent material 2210 in a specific concentration. The concentration of second luminescent material 2210 within the second encapsulant 2200, as well as the (second) thickness T2 of the second encapsulant 2200, may determine the fraction of light transmitted by the second encapsulant 2200. Especially, the concentration of second luminescent material 2210 within the second encapsulant 2200 may be high enough to facilitate providing a whitish appearance to the second encapsulant 2200, yet low enough to allow sufficient transmission of one or more of first luminescent material light 2111 and light source light 11. Hence, the second encapsulant 2200 may comprise the second luminescent material 2210 in a concentration selected from the range of 5-70 wt.%. Further, the second encapsulant 2200 may be configured to transmit at least 70% of the first luminescent material light 2111. Additionally or alternatively, the second encapsulant 2200 may be configured to transmit at least 50% of the light source light 11 received by the second encapsulant 2200. In embodiments, as depicted in Fig. 1, the second encapsulant 2200 may (further) comprise a light scattering material 2220. In embodiments wherein the second encapsulant 2200 comprises a light scattering material 2220, the system light 1001 may especially comprise diffuse (white) light.

Figs. 1-7 schematically depict different embodiments of the light generating system 1000, especially of the LED filament 100, of the present invention. In Fig. 1, an embodiment is depicted wherein both the first encapsulant 2100 and the second encapsulant 2200 are applied as continuous encapsulants across the light sources 10. Further, in Fig. 1, the second encapsulant 2200 comprises both the second luminescent material 2210 and a light scattering material 2220.

Fig. 2 schematically depicts the same configuration of first encapsulant 2100 and second encapsulant 2200, yet here the second encapsulant 2200 does not comprise the light scattering material 2220.

Fig. 3 schematically depicts an embodiment wherein the first encapsulant 2100 is configured (at least partly) covering only one major surface of the elongated carrier 5, while the second encapsulant 2200 is configured (at least partly) covering both a first and a second major surface of the elongated carrier 5.

Fig. 4 schematically depicts an embodiment wherein on the first major surface of the elongated carrier 5 (here the surface onto which the light sources 10 are mounted), the first encapsulant 2100 is configured as a coating around the light sources 10, wherein in an opening between two light sources 10 no first encapsulant 2100 is configured. Further, on the second major surface of the elongated carrier 5, the first encapsulant 2100 is configured as a continuous coating. Additionally, the second encapsulant 2200 is configured filling the spaces between the light sources 10 (where no first encapsulant 2100 is configured), and configured providing a continuous coating on both the first and second major surface of the elongated carrier 5. Fig. 5 depicts a similar embodiment to Fig. 4, yet here the first encapsulant is configured not (at least partly) covering the second major surface of the elongated carrier 5, i.e., the first encapsulant is configured (only) covering (part of) the first major surface of the elongated carrier 5, wherein the second major surface of the elongated carrier 5 is configured (at least partly) covered by (only) the second encapsulant 2200.

Fig. 6 depicts an embodiment wherein the first encapsulant 2100 and the second encapsulant 2200 are configured on the first major surface of the elongated carrier 5, wherein the second major surface of the elongated carrier 5 is configured not covered by the first encapsulant 2100 and the second encapsulant 2200.

Fig. 7 depicts a similar embodiment to Fig. 6, yet here the first encapsulant 2100 is configured as a coating around the light sources 10, wherein in an opening between two light sources 10 (and on the second major surface of the elongated carrier 5) no first encapsulant 2100 is configured. Further, the second encapsulant 2200 is configured filling the spaces between the light sources 10 (where no first encapsulant 2100 is configured), and configured providing a continuous coating on the first (but not the second) major surface of the elongated carrier 5.

Fig. 8 schematically depicts a further embodiment of the light generating system 1000. As depicted here, the LED filament 100 may comprise a plurality of solid state light sources 10 configured on both a first major surface and a second major surface of the elongated carrier 5. In embodiments, the second luminescent material 2210 may be selected such that the second luminescent material 2210 is configured to convert at most 50% of the light source light 11 into (blue) second luminescent material light 2211. In such embodiments, the light generating system 1000 may be configured such, that in the first operational mode, the light generating system 1000 may be configured to generate system light 1001 comprising light source light 11, first luminescent material light 2111, and (optionally) second luminescent material light 2211. Especially, in embodiments, at most 20% of a spectral power of the system light 1001 in the range of 380-490 nm may be provided by the second luminescent material light 2211. In embodiments, the light generating system 1000 may comprise a plurality of LED filaments 100. In embodiments, the LED filament light 101 provided by each of the plurality of LED filaments 100 may differ (such as e.g. in CRI, correlated color temperature, and/or color). Further, in embodiments, the intensity of the LED filament light 101 may be dependent on the amount the current flowing through the LED filament(s) 100. In embodiments, the light generating system 1000 may (therefore) comprise a control system 300. The control system 300 may be configured to control the current flowing to each of the plurality of LED filaments 100. Hence, the control system 300 may be configured to control one or more of the color point, correlated color temperature, intensity, and color rendering index of the system light 1001.

Fig. 9 schematically depicts an embodiment of the system light 1001, such as especially the system light 1001 generated by the light generating system 1000 in the first operational mode. In embodiments, the system light 1001 may (essentially) consist of the LED filament light 101. Hence, Fig. 9 may further schematically depict an embodiment of the LED filament light 101. In embodiments, in the first operational mode, the light generating system 1000 may be configured to generate white system light 1001 having a correlated color temperature selected from the range of 1500-6500 K. In such embodiments, the system light 1001 may especially comprise at least part of the (blue) light source light 11 and the first luminescent material light 2111. In embodiments, the first luminescent material light 2111 may have a first centroid wavelength ci selected from the range of 490-590 nm. Further, in embodiments, the system light 1001 may comprise the second luminescent material light 2211. The second luminescent material light 2211 may especially have a second centroid wavelength Xc2. In embodiments, the second centroid wavelength Xc2 may be selected from the range of (440-520 nm, such as especially selected from the range of) 440- 490 nm. Further, the light source light 11 may have a light source peak wavelength kpi.. In embodiments, the light source peak wavelength kpi. may be selected from the range of (440- 490 nm, more especially selected from the range of) 440-470 nm. The light source light 11 may in embodiments have a spectral power distribution at shorter (blue) wavelengths than the second luminescent material light 2211. In embodiments, the first luminescent material 2110 may absorb blue light at longer (blue) wavelengths (e.g. in the range of 440-490 nm). Hence, the light source light 11 received by the second luminescent material 2210 may have a different spectral power distribution than the light source light 11 emitted by the solid state light sources 10. Especially, the light source light 11 (received by the second luminescent material 2210) may have a (second) peak wavelength Xpr .2. The (second) peak wavelength kpL,2 may especially be lower than the second centroid wavelength Zc2. In embodiments, Xc2 - kpL,2 > 10 nm.

Fig. 10 schematically depicts a (further) embodiment of the system light 1001 and/or of the LED filament light 101 comprising the first phosphor light 211, the second phosphor light 221, and (optionally) the third phosphor light 231. In embodiments, the first phosphor light 211 may comprise one or more of green light and yellow light, and may especially have a first phosphor centroid wavelength ci,i selected from the range of 490- 590. Further, in embodiments, the second phosphor light 221 may comprise one or more of orange and red light, and may especially have a second phosphor centroid wavelength ci,2 selected from the range of 590-750 nm. Additionally, in embodiments, the third phosphor light 231 may comprise red light, and may especially have a third phosphor centroid wavelength ci,3 selected from the range of 620-750 nm.

Fig. 11 schematically depicts an embodiment of a lighting device 1200 comprising (one or more of) the light generating system 1000 as described herein. In embodiments, the lighting device 1200 may comprise a LED filament lamp 2000. The LED filament lamp 2000 may comprise 1-8 light generating systems 1000, such as especially 1-8 LED filaments 100. Further, the LED filament lamp 2000 may comprise a housing, such as a light transmissive envelope 2010, surrounding the LED filament(s) 100. Additionally, the LED filament lamp 2000 may comprise a base 2020 configured to support the LED filament(s) 100. In embodiments, the base 2020 may (further) be configured to electrically couple the LED filament(s) 100 to an energy source.

Fig. 12 schematically depicts an embodiment of a luminaire 2 comprising the light generating system 1000 as described above. Reference 301 indicates a user interface which may be functionally coupled with the control system 300 comprised by or functionally coupled to the light generating system 1000. Fig. 12 also schematically depicts an embodiment of lamp 1 comprising the light generating system 1000. Reference 3 indicates a projector device or projector system, which may be used to project images, such as at a wall 1307, which may also comprise the light generating system 1000. Hence, Fig. 12 schematically depicts embodiments of a lighting device 1200 selected from the group of a lamp 1, a luminaire 2, a projector device 3, a disinfection device, a photochemical reactor, and an optical wireless communication device, comprising the light generating system 1000 as described herein. Lighting device light escaping from the lighting device 1200 is indicated with reference 1201. Lighting device light 1201 may essentially consist of system light 1001, and may in specific embodiments thus be system light 1001. Reference 1300 refers to a space, such as a room. Reference 1305 refers to a floor and reference 1310 to a ceiling.

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”. Furthermore, the terms first, second, third, etc. 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.

The devices, apparatus, 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, apparatus, 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.

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.

The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or 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 computer program product, which, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system. The invention further applies to a device, apparatus, 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 or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. 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 (100), wherein the LED filament (100) comprises (i) a plurality of solid state light sources (10), (ii) a first encapsulant (2100), and (iii) a second encapsulant (2200), wherein: the plurality of solid state light sources (10) are configured to generate light source light (11); the first encapsulant (2100) is configured covering the plurality of solid state light sources (10), wherein the first encapsulant (2100) is configured in a light-receiving relationship with the plurality of solid state light sources (10), wherein the first encapsulant (2100) comprises a first luminescent material (2110), wherein the first luminescent material (2110) is configured to convert at least part of the light source light (11) received by the first luminescent material (2110) into first luminescent material light (2111); wherein the first encapsulant (2100) has a colored appearance; the second encapsulant (2200) is configured at least partly covering the first encapsulant (2100), wherein the second encapsulant (2200) comprises a second luminescent material (2210), different from the first luminescent material (2110), wherein the second luminescent material (2210) is configured to at least partly convert daylight received by the second luminescent material (2210) into second luminescent material light (2211), wherein the second luminescent material light (2211) comprises blue light; and the light generating system (1000) is configured to generate in a first operational mode of the light generating system (1000) system light (1001) comprising light source light (11) and first luminescent material light (2111).

2. The light generating system (1000) according to claim 1, wherein: the second luminescent material (2210) is selected such that the second luminescent material (2210) is configured to convert at most 50% of the light source light (11) into second luminescent material light (2211); the light generating system (1000) is configured such, that in the first operational mode the light generating system (1000) is configured to generate system light (1001) comprising light source light (11), first luminescent material light (2111), and second luminescent material light (2211), wherein at most 20% of a spectral power of the system light (1001) in the range of 380-490 nm is provided by the second luminescent material light (2211).

3. The light generating system (1000) according to any one of the preceding claims, wherein in an off-state of the LED filament (100) the first encapsulant (2100) has a non-white colored appearance, and wherein in an off-state of the LED filament (100) the LED filament (100) has a whitish appearance under illumination with daylight.

4. The light generating system (1000) according to any one of the preceding claims, wherein the LED filament (100), in an off-state, has chromaticity coordinates [x, y] in the CIE 1931 color space, wherein x and y are individually selected from the range of 0.3- 0.45.

5. The light generating system (1000) according to any one of the preceding claims, wherein: the LED filament (100) has a first reflection coefficient R450 for light incident perpendicular to the LED filament (100) and having a wavelength of 450 nm, wherein R450 > 0.3; the LED filament (100) has a second reflection coefficient R420 for light incident perpendicular to the LED filament (100) and having a wavelength of 420 nm, wherein R420 < 0.5; and

R420 < R450.

6. The light generating system (1000) according to any one of the preceding claims, wherein the second luminescent material (2210) comprises a luminescent material of the type M5-_qEu_q(PO4)3Cl, wherein M comprises one or more of Sr, Ba, Ca, Mg, and Mn, and wherein q is selected from the range of 0.005-0.3.

7. The light generating system (1000) according to any one of the preceding claims, wherein the second luminescent material light (2211) has a second centroid wavelength Xc2, wherein the second centroid wavelength Xc2 is selected from the range of 440-490 nm.

8. The light generating system (1000) according to any one of the preceding claims, wherein the second encapsulant (2200) comprises the second luminescent material (2210) in a concentration selected from the range of 5-70 wt.%, and wherein the second encapsulant (2200) is configured to transmit (i) at least 70% of the first luminescent material light (2111), and (ii) at least 50% of the light source light (11) received by the second encapsulant (2200).

9. The light generating system (1000) according to any one of the preceding claims, wherein the first luminescent material (2110) comprises a first phosphor (210) of the type As-xBsOnCex, wherein A comprises one or more of Y, La, Gd, Tb and Lu, wherein B comprises one or more of Al, Ga, In and Sc, and wherein 0.001 < x < 0.1.

10. The light generating system (1000) according to claim 9, wherein the first phosphor (210) comprises a primary first phosphor of the type (YxiiLuxnA’xisCexi^sBsOn and a secondary first phosphor of the type (Yx2iLux22A’x23Ce_X24)3B5Oi2, wherein A’ comprises one or more of La, Gd, and Tb, wherein B comprises one or more of Al, Ga, In and Sc; wherein:

Xu + xn + X13 + xu= 1; Xu + xn> 0; 0 < xi3 < 1; and 0.001 < xu< 0.1;

X21 + X22 + X23 + X24= 1; X21 + X22> 0; 0 < X23 < 1; and 0.001 < X24< 0.1; and Xu > X21 and X22> X12.

11. The light generating system (1000) according to any one of the preceding claims 9-10, wherein the first luminescent material (2110) comprises a second phosphor (220), wherein the second phosphor (220) is configured to convert light source light (11) received by the second phosphor (220) into second phosphor light (221), wherein the second phosphor light (221) comprises one or more of orange and red light.

12. The light generating system (1000) according to any one of the preceding claims, wherein the second encapsulant (2200) comprises a light scattering material (2220), wherein the system light (1001) comprises diffuse light.

13. The light generating system (1000) according to any one of the preceding claims, wherein in the first operational mode, the light generating system (1000) is configured to generate white system light (1001) having a correlated color temperature selected from the range of 1500-6500 K.

14. A lighting device (1200) selected from the group of a lamp (1), a luminaire (2), a projector device (3), a disinfection device, a photochemical reactor, and an optical wireless communication device, comprising the light generating system (1000) according to any one of the preceding claims.

15. The lighting device (1200) according to claim 14, wherein the lamp (1) comprises a LED filament lamp (2000).