A lighting device

Abstract

A lighting device (1, 100, 101) configured to, in operation provide lighting device light (50), and comprising a housing (2) comprising a front plate (3) forming a light exit surface of the lighting device, and at least one inner cavity (4) comprising a cavity surface (5), the cavity surface (5) comprising a bottom section (6) and a side section (7), the side section (7) extending between the front plate (3) and the bottom section (6), and at least one light emitting diode, LED, filament (81, 82) configured to, in operation, provide LED filament light (83, 84). The at least one LED filament (81, 82) is arranged in the at least one inner cavity (4) of the housing (2) in a distance (D) from the bottom section (6), the distance (D) being measured in a height direction (H) of the housing (2), the cavity surface (5) is a reflective surface, the front plate (3) is a translucent front plate, and the cavity surface (5) is rounded when seen in a cross-section extending in a plane spanned by the height direction (H) and a width direction (W) of the housing (2).

Description

[0001] A LIGHTING DEVICE

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a lighting device configured to, in operation provide lighting device light, the lighting device comprising a housing.

[0004] As used herein, the term “warm white light” is intended to refer to light with color temperature falling within the color temperature interval of 2500 K to 3500 K.

[0005] As used herein, the term “cool white light” is intended to refer to light with color temperature falling within the color temperature interval of 3500 K to 4500 K.

[0006] As used herein the term “rounded” is intended to mean having a smooth, curved surface, or in case of a surface being a smooth, curved surface.

[0007] BACKGROUND OF THE INVENTION

[0008] There is a continuous drive to improve the performance of light emitting diode, LED, based systems. A relatively new LED type is the LED filament which is frequently and exclusively used in LED lamps (“bulbs”). A LED filament is a long rodshaped emitter (typical length 30-50 mm, diameter: 1-3 mm) which emits light over the whole surface area (comparable to a fluorescent tube). A filament is composed of a linear array of blue LED dies on a lead frame (supported by a ceramic bar), covered with a layer of blue light converting material (“phosphor”). This specific “packageless” construction results in LEDs with a high efficacy of typically 230 Im / W. Up to now, LED filaments are exclusively applied in light bulbs. However, LED filaments can be applied in other lighting applications such as office lighting, creating several advantages compared to the more conventional small SMD LEDs based systems.

[0009] Many types of office lighting use so-called MLO (Micro Lens Optic) plates. MLO plates are plates formed of an array of micro-lenses. These plates use light recycling to obtain a well-defined beam in combination with a highly reflective light box and an array of SMD LEDs placed into the light box. The luminance value of such a light box depends on the distance between the LEDs and the MLO plate. The luminance of the bare LEDs is 8.0* 106cd / m2. At the given distance between the LEDs and the MLO plate, the luminance is reduced by a factor 17. Another aspect is the ring patterns produced by the LED point sources. These patterns become oval shaped at non-perpendicular (to the MLO plate) viewing angles. The oval light patterns may overlap at even higher viewing angles into rather complex patterns. The visual appearance of such patterns is often not appreciated. Another observation is the high luminance of the ring-shaped light patterns compared to the low background luminance (Fig. 2). Both effects could be solved by adding a diffuser between the LED sources and the MLO plate. However, this adds cost, lowers the optical efficiency of the lighting panel, and creates a rather dull appearance.

[0010] US 2022 / 0221113 Al discloses a light-emitting module comprising one or more flexible, elongated light-emitting diode, LED, strips and a mixing chamber. Each LED strip comprises a first side on which a plurality of LEDs is mounted, a second side opposite to said first side, and two lengthwise edges. The mixing chamber is arranged to mix light emitted by the LEDs and comprises a base. One of the lengthwise edges of each LED strip is arranged to face the base of the mixing chamber. At least a portion of each LED strip is bent (or folded) to extend radially from a center portion of the mixing chamber towards one or more outer points, so that the one or more light-emitting diode strips together form a number N of elongated arms. Each elongated arm comprises two segments of the LED strip, where the segments form opposite sides of the elongated arm.

[0011] It is desired to provide a lighting device with which one or more of the following may be improved: efficiency, glare, and visual appearance of luminaires for office lighting applications.

[0012] US 11739887 a lighting device comprising at least two LED filaments. The lighting device further comprises at least two optical modules, each arranged in relation to a corresponding one of the LED filaments to receive light emitted by the corresponding one of the LED filaments. Each optical module is configured to collimate the received light and produce a collimated light beam so as to increase the degree of collimation of the light produced by the optical module as compared to the light received by the optical module. The light produced by each optical module is emitted from the lighting device. Further, the optical modules are arranged in relation to each other such that collimated light beams of the respective ones of the optical modules are oriented in different directions.

[0013] SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to overcome this problem, and to provide a lighting device configured to, in operation provide lighting device light and comprising a housing, the lighting device being capable of providing lighting device light being improved in terms of one or more of efficiency, glare, and visual appearance.

[0015] According to a first aspect of the invention, this and other objects are achieved by means of a lighting device configured to, in operation, provide lighting device light, the lighting device comprising a housing comprising a height direction, H, a length direction, L and a width direction, W, a front plate forming a light exit surface of the lighting device, and at least one inner cavity comprising a cavity surface, the cavity surface comprising a bottom section and a side section, the side section extending between the front plate and the bottom section, and at least one light emitting diode, LED, filament configured to, in operation, provide LED filament light, wherein the at least one LED filament is arranged in the at least one inner cavity of the housing in a distance, D, from the bottom section, the distance, D, being measured in the height direction, H, wherein the cavity surface is a reflective surface, and the front plate is a translucent front plate, and wherein the cavity surface is rounded when seen in a cross-section extending in a plane spanned by the height direction, H, and the width direction, W.

[0016] Thereby a lighting device being capable of providing lighting device light being improved in terms of one or more of efficiency, glare, and visual appearance is provided for. Especially by providing a light emitting device with an inner cavity and a cavity surface as described above, a well-defined background luminance for the LED filaments are provided for.

[0017] The cavity surface may, when seen in the cross-section extending in a plane spanned by the height direction, H, and the width direction, W, be any one of (i) semicircular, (ii) semi-elliptic, (iii) semi-oval, (iv) semi-polygonal with at least two, three, four or five sides and / or with rounded comers, and (v) combinations thereof, or may comprise a freeform shape.

[0018] The cavity surface may, when seen in a cross-section extending in a plane spanned by the length direction, L, and the width direction, W, be any one of oval, oblong with rounded ends or corners, circular, elliptic, polygonal with or without rounded ends or corners, and combinations thereof.

[0019] Thereby, different shapes of the inner cavity may be chosen depending on the desired background luminance profile and / or the desired color mixing properties. For instance, the inner cavity may be shaped in such a way that only indirect light (via the cavity surface) can be seen by a viewer. This gives a highly uniform and low brightness appearance of the lighting device. The housing comprises a housing width, WH, extending in the width direction, W, and a housing length, LH, extending in the length direction, L, and the cavity comprises a cavity width, WC, extending in the width direction, W, and a cavity length, LC, extending in the length direction, L, and the cavity width, WC, may be smaller than the housing width, WH. Alternatively, or additionally, the cavity length, LC, may be smaller than or equal to the housing length, LH.

[0020] Thereby, further different shapes and configurations of the inner cavity may be chosen depending on the desired background luminance profile and / or the desired color mixing properties.

[0021] The cavity surface may comprise a reflectivity, RCS, being higher than 95 %, or higher than 98 %, or higher than 99 %, or 100 %.

[0022] Thereby, losses of light at the cavity surface is lowered or even eliminated, which in turn provides for a lighting device being more efficient.

[0023] The cavity surface may be coated with a reflective coating. Alternatively, or additionally, the cavity surface may comprise a reflective layer.

[0024] Thereby, a cavity surface with a high reflectivity may be obtained in a simple and durable manner.

[0025] The lighting device may comprise a plurality of LED filaments, wherein the plurality of LED filaments comprises a first LED filament configured to, in operation, emit cool white (CW) LED filament light, and a second LED filament configured to, in operation, emit warm white (WW) LED filament light.

[0026] Thereby, a lighting device providing lighting device light with a further improved color appearance and visual appearance is provided for.

[0027] The front plate may further be a diffusive front plate.

[0028] Thereby, a lighting device exhibiting a particularly low amount of glare is provided for.

[0029] The front plate may be a micro-lens optic, MLO, plate.

[0030] Thereby, a front plate being both translucent and diffusive, and thus a lighting device exhibiting a particularly low amount of glare, is provided in a particularly simple manner.

[0031] The housing further comprises a back surface, and the cavity surface may extend from the front plate towards the back surface such that the bottom section is arranged in a distance, Db, from the back surface, the distance, Db, being measured in the height direction, H. Thereby, the inner cavity is shaped in such a way that space for connectors and electrical wiring is provided between the back surface of the housing and the bottom section of the inner cavity. This ensures that connectors and electrical wiring can be placed outside the optical cavity.

[0032] Alternatively, the housing further comprises a back surface, the side section of the cavity surface extends between the front plate and the back surface, at least a part of the back surface forms the bottom section of the cavity surface, and the part of the back surface forming the bottom section is a reflective surface.

[0033] Thereby a deeper inner cavity with room for more LED filaments is provided for. This in turn provides for a lighting device providing lighting device light of at least one of a higher intensity and a higher brightness.

[0034] The lighting device may comprise a first LED filament and a second LED filament, wherein the first LED filament is arranged in a first distance, DI, from the bottom section of the cavity surface, and the second LED filament is arranged in a second distance, D2, from the bottom section of the cavity surface, and wherein the second distance, D2, is larger than the first distance, DI.

[0035] One factor which decreases the perceived brightness of the LED filament light is the low contrast between the filament luminance and the luminance of the background (contrast ratio between filament and background). This ratio can be influenced by the depth of the cavity and the height position of the filaments in the cavity. Thereby, a lighting device providing lighting device light with an improved homogeneity and brightness and thus an improved visual appearance is provided for.

[0036] The at least one LED filament comprises a longitudinal axis, LA, and the at least one LED filament may be arranged with the longitudinal axis, LA, extending in the width direction, W, of the housing. Alternatively, the at least one LED filament may be arranged with the longitudinal axis, LA, extending in the length direction, L, of the housing.

[0037] Thereby the LED filaments are arranged in a more symmetric way, which improves the color uniformity of the lighting device light even more.

[0038] The lighting device may comprise a plurality of LED filaments, wherein the LED filaments of the plurality of LED filaments each comprise a longitudinal axis, LA, and wherein the LED filaments may each be arranged with the longitudinal axis, LA, extending in the width direction, W, of the housing and with a pitch, PL, measured in the length direction, L, of the housing. Alternatively, the LED filaments may each be arranged with the longitudinal axis, LA, extending in the length direction, L, of the housing and with a pitch, PW, measured in the width direction, W, of the housing.

[0039] Thereby the LED filaments are arranged in an even more symmetric way, which improves the color uniformity of the lighting device light even more. An even further improvement of the color uniformity of the lighting device light may be obtained if the LED filaments are, additionally or alternatively, arranged symmetrically around a center axis of the inner cavity.

[0040] The at least one LED filament, or each LED filament of the plurality of LED filaments, may be supported by electrical connectors configured to supply the LED filament with electrical energy, wherein the electrical connectors comprise a reflectivity, REC, being higher than 95 %, or higher than 98 %, or higher than 99 %, or 100 %.

[0041] Thereby, losses of light at the electrical connectors is lowered or even eliminated, which in turn provides for a lighting device being more efficient.

[0042] The electrical connectors may be coated with a reflective coating. Alternatively, or additionally, the electrical connectors may comprise or may consist of a reflective polymer.

[0043] Thereby, electrical connectors with a high reflectivity may be obtained in a simple and durable manner.

[0044] The at least one LED filament, or each LED filament of the plurality of LED filaments, may be supported by electrical connectors configured to supply the LED filament with electrical energy, wherein the electrical connectors are connected to electrical circuitry, and wherein the electrical circuitry is arranged in the housing outside of the at least one inner cavity.

[0045] By arranging the electrical circuitry in the housing outside of the at least one inner cavity any influence of the electrical circuitry on the light propagating through the inner cavity is avoided. This in turn provides for a lighting device being more efficient.

[0046] The inner cavity may be made by one of deep drawing a microcellular polyethylene terephthalate (MCPET) sheet, 3D-printing and injection molding of a pigment filled polycarbonate material.

[0047] Thereby, the inner cavity may be manufactured in a simple and cost-efficient manner, whether in one piece with the remaining housing or not. Furthermore, the cavity surface of the inner cavity may be provided with the desired high reflectivity in a particularly simple manner using one of these manufacturing methods.

[0048] The front plate may be made by one of 3D-printing and injection molding. Thereby, the front plate may be manufactured in a simple and cost-efficient manner.

[0049] The housing may further comprise at least one further inner cavity comprising at least one further cavity surface, the at least one further cavity surface comprising a bottom section and a side section, and the lighting device may further comprise at least one further LED filament configured to, in operation, provide further LED filament light, wherein the at least one further LED filament is arranged in the at least one further inner cavity in a distance, E, from the bottom section of the at least one further cavity surface, the distance, E, being measured in the height direction, H, wherein the at least one further cavity surface is a reflective surface, and wherein the at least one further cavity surface is rounded when seen in a cross-section extending in a plane spanned by the height direction, H, and the width direction, W.

[0050] Thereby, a lighting device comprising two inner cavities is provided for. Thereby, the LED filaments may be arranged in a more symmetric way using the two inner cavities. This in turn improves the color uniformity of the resulting lighting device light even more.

[0051] The lighting device may comprise a further housing and at least one further LED filament configured to, in operation, provide LED filament light, the further housing comprising a further front plate forming a light exit surface of the lighting device, and at least one further inner cavity comprising at least one further cavity surface, the at least one further cavity surface comprising a bottom section and a side section, wherein the at least one further LED filament is arranged in the at least one further inner cavity in a distance, F, from the bottom section of the further cavity surface, the distance, F, being measured in a height direction, H, wherein the at least one further cavity surface is a reflective surface, and the further front plate is a translucent front plate, and wherein the at least one further cavity surface is rounded when seen in a cross-section extending in a plane spanned by the height direction, H, and a width direction, W. The height direction, H, may be a height direction of the housing or of the further housing. Likewise, the width direction, W, may be a width direction of the housing or of the further housing.

[0052] Thereby, a lighting device not only comprising at least two inner cavities, but also comprising at least two housings, is provided for. Thereby, the LED filaments may be arranged in a more symmetric way using the at least two inner cavities. This in turn improves the color uniformity of the resulting lighting device light even more. Furthermore, by adding more housings, a more versatile lighting device is provided for, for instance by making it possible to operate the LED filaments of each housing separately, or by enabling arranging the housings in several different ways with respect to one another, or by enabling illuminating a larger area, or the same area with light of a higher intensity, using only one lighting device.

[0053] The invention further relates to a luminaire comprising a lighting device according to any of the above claims.

[0054] It is noted that the invention relates to all possible combinations of features recited in the claims.

[0055] BRIEF DESCRIPTION OF THE DRAWINGS

[0056] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0057] Fig. 1 shows a perspective view of a lighting device according to the invention.

[0058] Fig. 2 shows a cross-sectional view of the lighting device according to Fig. 1

[0059] Fig. 3 shows luminance images of a lighting device according to Fig. 1 and comprising two LED filaments configured to, in operation, emit cold white (CW) and warm white (WW) LED filament light, respectively, when both LED filaments are in operation, and when observed from an on-angle view of 0 degrees with respect to a normal to a light exit surface of the lighting device.

[0060] Fig. 4 shows luminance images of a lighting device according to Fig. 1 and comprising two LED filaments configured to, in operation, emit CW and WW white LED filament light, respectively, when only the LED filament emitting CW LED filament light is in operation, and when observed from the on-angle view.

[0061] Fig. 5 shows luminance images of a lighting device according to Fig. 1 and comprising two LED filaments configured to, in operation, emit CW and WW white LED filament light, respectively, when only the LED filament emitting WW LED filament light is in operation, and when observed from the on-angle view.

[0062] Fig. 6 shows luminance images of a lighting device according to Fig. 1 and comprising two LED filaments configured to, in operation, emit cold white (CW) and warm white (WW) LED filament light, respectively, when both LED filaments are in operation, and when observed from an off-angle view of 30 degrees with respect to the normal to the light exit surface of the lighting device. Fig. 7 shows a cross-sectional view of another lighting device according to the invention.

[0063] Fig. 8 shows luminance images of a lighting device according to Fig. 7 and comprising two pairs of two LED filaments, each pair of two LED filaments configured to, in operation, emit cold white (CW) and warm white (WW) LED filament light, respectively, when all LED filaments are in operation, and when observed from an on-angle view of 0 degrees with respect to a normal to a light exit surface of the lighting device.

[0064] Fig. 9 shows a cross-sectional view of another lighting device according to the invention.

[0065] As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

[0066] DETAILED DESCRIPTION

[0067] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0068] Fig. 1 shows a perspective view of a lighting device 1 according to the invention, and Fig. 2 shows a cross-sectional view of the lighting device 1. Generally, and irrespective of the embodiment the lighting device 1 is configured to, in operation, emit lighting device light 50 (cf. Fig. 2) and comprises a housing 2 and at least one light emitting diode, LED, filament 81, 82.

[0069] The housing 2 comprises a height direction H, a length direction L and a width direction W. The housing 2 further comprises a housing width WH extending in the width direction W and a housing length LH extending in the length direction L (cf. Fig. 1). The housing 2 comprises a front plate 3 and at least one inner cavity 4. The housing 2 further comprises a back surface 9.

[0070] The front plate 3 forms a light exit surface of the lighting device 1 through which the lighting device light 50 is emitted. The front plate 3 is a translucent front plate. Additionally, the front plate 3 may be a diffusive front plate. The front plate 3 may be a micro-lens optic, MLO, plate. Alternatively, the front plate 3 may be a clear poly(methyl methacrylate) (PMMA) plate with a textured surface or a PMMA plate containing scattering particles. In another alternative, the front plate 3 may be a PMMA plate containing small pyramid features on top in order to reduce glare. The front plate 3 may be made by 3D- printing. Alternatively, the front plate 3 may be made by injection molding.

[0071] In the embodiment shown in Fig. 1 one inner cavity 4 is provided. The inner cavity 4 comprises a cavity surface 5. Alternatively, more than one inner cavity 4, such as two or three inner cavities, may be provided. The cavity 4 comprises a cavity width WC extending in the width direction W and a cavity length LC extending in the length direction L (cf. Fig. 1). The cavity width WC may be smaller than the housing width WH. Alternatively, the cavity width WC may be equal to the housing width WH. Alternatively, or additionally, the cavity length LC may be smaller than or equal to the housing length LH. The inner cavity

[0072] 4 may be made by deep drawing a microcellular polyethylene terephthalate (MCPET) sheet. Alternatively, the inner cavity 4 may be made by 3D-printing. In yet another alternative, the inner cavity 4 may be made by injection molding of a pigment filled polycarbonate material. In each case it is feasible that the inner cavity 4 and the housing 2 are made at the same time.

[0073] The cavity surface 5 comprises a bottom section 6 and a side section 7. The side section 7 extends between the front plate 3 and the bottom section 6. The cavity surface

[0074] 5 is a reflective surface. The cavity surface 5 comprises a reflectivity RCS. The reflectivity RCS may be chosen to be higher than 95 %, or higher than 98 %, or higher than 99 %, or even 100 %. The cavity surface 5 may be coated with a reflective coating. Alternatively, or additionally, the cavity surface 5 may comprise a reflective layer.

[0075] When seen in a cross-section extending in a plane spanned by the height direction H and the width direction W (cf. Fig. 2), the cavity surface 5 is a rounded surface. In the embodiment shown in Figs. 1 and 2, when seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the cavity surface 5 is semi-circular. The cavity surface 5 comprises a radius of curvature r (cf. Fig. 2). The radius of curvature r may for instance be 25 mm, although many other radii of curvature likewise are feasible, for instance depending on the size of the lighting device 1 and the number of LED filaments 81, 82 to be accommodated in the inner cavity 4. More generally, when seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the cavity surface 5 may be any one of semi-circular, semi-elliptic, semi-oval, semi-polygonal with at least two, three, four or five sides and / or with rounded corners, and combinations thereof, whether symmetric or asymmetric. When seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the cavity surface 5 may also comprise a freeform shape (that is, a shape not conforming to a regular or formal structure or shape), such as a wavy shape or an asymmetric shape. Furthermore, when seen in a cross-section extending in a plane spanned by the length direction L and the width direction W (cf. Fig. 1) the cavity surface 5 may be any one of oval, oblong with rounded ends or corners as illustrated in Fig. 1, circular, elliptic, polygonal with or without rounded ends or corners, and combinations thereof.

[0076] In the embodiment shown in Figs. 1 and 2, the cavity surface 5 extends from the front plate 3 towards the back surface 9 in such a way that at least a part of the bottom section 6 is arranged in a distance Db from the back surface 9 (cf. Fig. 2). The distance Db is measured in the height direction H as the shortest distance between the back surface 9 and a point of the bottom section 6 in which a tangent to the cavity surface 5 extends in a plane spanned by the length direction L and the width direction W. The distance Db may be at least 2 mm, at least 4 mm or at least 5 mm. Alternatively, the cavity surface 5 may extend from the front plate 3 to the back surface 9 in such a way that at least a part of the back surface 9 forms the bottom section 6. In other words, the side section 7 may extend between the front plate 3 and the back surface 9, and at least a part of the back surface 9 forms the bottom section 6. In this case, the part of the back surface 9 forming the bottom section 6 is a reflective surface.

[0077] In the embodiment shown in Figs. 1 and 2 two LED filaments 81, 82 are provided. Alternatively, only one LED filament or more than two LED filaments, such as three or four LED filaments may be provided. The LED filaments 81, 82 are configured to, in operation, provide LED filament light 83, 84, respectively (cf. Fig. 2). A first LED filament 81 may be configured to, in operation, emit cool white (CW) LED filament light, and a second LED filament 82 may be configured to, in operation, emit warm white (WW) LED filament light.

[0078] The LED filaments 81, 82 are arranged in the inner cavity 4 of the housing 2. The LED filaments 81, 82 are arranged in a distance D from the bottom section 6. The distance D is measured in the height direction H. The distance D may be at least 2 mm, at least 3 mm or at least 5 mm. More particularly, and as illustrated in Fig. 2, the first LED filament 81 is arranged in a first distance DI from the bottom section 6, and the second LED filament 82 is arranged in a second distance D2 from the bottom section 6. In the embodiment shown in Fig. 1, the second distance D2 is larger than the first distance DI. In alternatives, the second distance D2 may be smaller than the first distance DI, or the second distance D2 may be equal to the first distance DI. When the second distance D2 is different from the first distance DI, the first and second LED filament 81, 82 are arranged with a spacing or pitch PV in the height direction H. The spacing or pitch PV may be 6 mm, 8 m or 10 mm. It is furthermore also feasible to arrange the first and second LED filament 81, 82 with a spacing or pitch PW in the width direction W and / or with a spacing or pitch PL in the length direction L (i.e., perpendicular to both the width direction W and the height direction H), especially when the first distance DI is equal to the second distance D2.

[0079] Furthermore, the first LED filament 81 is arranged in a third distance D3 from the front plate 3, and the second LED filament 82 is arranged in a fourth distance D4 from the front plate 3. In the embodiment shown in Figs. 1 and 2, the third distance D3 is larger than the fourth distance D4. In alternatives, the third distance D3 may be smaller than the fourth distance D4, or the third distance D3 may be equal to the fourth distance D4.

[0080] Furthermore, each LED filament 81, 82 comprises a longitudinal axis LA (cf. Fig. 1). In the embodiment shown in Figs. 1 and 2, the LED filaments 81, 82 are arranged with the longitudinal axis LA extending in the length direction L of the housing. Alternatively, the LED filaments 81, 82 may be arranged with the longitudinal axis LA extending in the width direction W of the housing. In yet another alternative, the LED filaments 81, 82 may be arranged with the longitudinal axis LA extending in a plane spanned by the length direction L and the width direction W, and with the longitudinal axis LA extending in an angle different from zero to one or both of the length direction L and the width direction W.

[0081] The LED filaments 81, 82 are supported by respective electrical connectors 10, 11 (cf. Fig. 2). The electrical connectors 10, 11 are configured to supply the LED filaments 81, 82 with electrical energy. The electrical connectors 10, 11 are reflective elements. The electrical connectors 10, 11 comprise a reflectivity REC. The reflectivity REC is chosen to be higher than 95 %, or higher than 98 %, or higher than 99 %, or 100 %. The electrical connectors 10, 11 may be coated with a reflective coating. Alternatively, or additionally, the electrical connectors 10, 11 may comprise or consist of a reflective polymer. The electrical connectors 10, 11 may be connected to electrical circuitry 12, 13 (cf. Fig. 2). The electrical circuitry 12, 13 may be arranged in the housing 2 outside of the at least one inner cavity 4.

[0082] Figs. 3-6 shows simulations of the luminance of the lighting device light emitted by a lighting device 1 of the general type described above with reference to Figs. 1 and 2. Generally, the lighting device 1 used for the simulations shown in Figs. 3-6 comprises two LED filaments 81, 82. One LED filament 82 is configured to, in operation, emit cold white (CW) LED filament light with a correlated color temperature, CCT, of 6500 K, and is arranged in a distance D4 of 10 mm below the front plate 3. The other LED filament 81 is configured to, in operation, emit warm white (WW) LED filament light with a CCT of 2300 K, and is arranged in a distance D3 of 20 mm below the front plate 3. Both LED filaments 81 and 82 comprise a diameter of 3 mm and a length of 50 mm. Both LED filaments 81 and 82 are configured to, when in operation, emit LED filament light with a flux of 100 Im. The front plate 3 is an MLO plate. The radius of curvature r of the cavity surface 5 of the inner cavity 4 is 25 mm, and the cavity surface 5 is a white, diffuse surface with a reflectivity, RCS, of 100%.

[0083] Fig. 3 illustrates the luminance (cd / m2= nit) of the lighting device light when both LED filaments are in operation, and when observed from an on-angle view 40 (cf. Fig. 2), that is a view from a direction forming an angle of 0 degrees with respect to a normal to a light exit surface of the lighting device.

[0084] Fig. 4 illustrates the luminance (cd / m2= nit) of the lighting device light when only the LED filament emitting CW LED filament light is in operation, and when observed from the on-angle view 40.

[0085] Fig. 5 illustrates the luminance (cd / m2= nit) of the lighting device light when only the LED filament emitting WW LED filament light is in operation, and when observed from the on-angle view 40.

[0086] Fig. 6 illustrates the luminance (cd / m2= nit) of the lighting device light when both LED filaments are in operation, and when observed from an off-angle view, being a view from a direction forming an angle of 30 degrees with respect to the normal to the light exit surface of the lighting device, cf. view 41 in Fig. 2.

[0087] As may be seen a lighting device 1 according to the present invention provides lighting device light with a highly uniform and high brightness appearance as perceived by a viewer.

[0088] Fig. 7 shows a cross-sectional view of another lighting device 100 according to the invention. The lighting device 100 differs from the lighting device 1 described above with reference to Figs. 1 and 2 in virtue of the following features.

[0089] The housing 2 of the lighting device 100 comprises a further inner cavity 14. The further inner cavity 14 comprises a further cavity surface 15. The further cavity surface 15 comprises a bottom section 16 and a side section 17. As shown in Fig. 7, the inner cavity 4 and the further inner cavity 14 are identical. Alternatively, the inner cavity 4 and the further inner cavity 14 may be mutually different in terms of shape and / or size.

[0090] The lighting device 100 further comprises one or more, as shown in Fig. 7 two, further LED filaments 181, 182. The further LED filaments 181, 182 are configured to, in operation, provide further LED filament light (not shown for the sake of simplicity). The further LED filaments 181, 182 are arranged in the at least one further inner cavity 14. The further LED filaments 181, 182 are arranged in a distance E from the bottom section 16, the distance E being measured in the height direction H. The distance E may be at least 2 mm, at least 3 mm or at least 5 mm. More particularly, and as illustrated in Fig. 7, the first LED filament 181 is arranged in a first distance El from the bottom section 16, and the second LED filament 182 is arranged in a second distance E2 from the bottom section 16. In the embodiment shown in Fig. 7, the second distance E2 is larger than the first distance EL In alternatives, the second distance E2 may be smaller than the first distance El, or the second distance E2 may be equal to the first distance EL

[0091] The further cavity surface 15 is a reflective surface. The further cavity surface 15 comprises a reflectivity RCS. The reflectivity RCS may be chosen to be higher than 95 %, or higher than 98 %, or higher than 99 %, or even 100 %. The further cavity surface 15 may be coated with a reflective coating. Alternatively, or additionally, the further cavity surface 15 may comprise a reflective layer.

[0092] When seen in a cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 is a rounded surface. In the embodiment shown in Fig. 7, when seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 is semicircular. The cavity surface 5 comprises a radius of curvature s. The radius of curvature s may for instance be 25 mm, although many other radii of curvature likewise are feasible, for instance depending on the size of the lighting device 100 and the number of LED filaments 181, 182 to be accommodated in the further inner cavity 14. The radius of curvature s may be equal to or different from the radius of curvature r of the cavity surface 5 of the inner cavity 4. More generally, when seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 may be any one of semicircular, semi-elliptic, semi-oval, semi-polygonal with more than three, four or five sides and combinations thereof. Furthermore, when seen in a cross-section extending in a plane spanned by the length direction L and the width direction W the further cavity surface 15 may be any one of oval, oblong with rounded ends, circular, elliptic, polygonal, and combinations thereof.

[0093] In the embodiment shown in Fig. 7, the further cavity surface 15 extends from the front plate 3 towards the back surface 9 in such a way that the bottom section 16 is arranged in a distance Eb from the back surface 9. The distance Eb is measured in the height direction H as the shortest distance between the back surface 9 and a point of the bottom section 6 in which a tangent to the further cavity surface 15 extends in a plane spanned by the length direction L and the width direction W. The distance Eb may be at least 2 mm, at least 4 mm or at least 5 mm. The distance Eb may be equal to or different from the distance Dd. Alternatively, the further cavity surface 15 may extend from the front plate 3 to the back surface 9 in such a way that at least a part of the back surface 9 forms the bottom section 16. In other words, the side section 17 may extend between the front plate 3 and the back surface 9, and at least a part of the back surface 9 forms the bottom section 16. In this case, the part of the back surface 9 forming the bottom section 16 is a reflective surface.

[0094] Fig. 8 shows simulations of the luminance (cd / m2= nit) of the lighting device light emitted by a lighting device 100 as described above with reference to Fig. 7.

[0095] The lighting device 100 used for the simulations comprises an inner cavity 4 and a further inner cavity 14. Generally, the inner cavity 4 and the further inner cavity 14 are identical. Generally, each of the inner cavity 4 and the further inner cavity 14 comprise two LED filaments 81, 82, respectively 181, 182. One LED filament 82, respectively 182, is configured to, in operation, emit cold white (CW) LED filament light with a correlated color temperature, CCT, of 6500 K, and is arranged in a distance of 10 mm below the front plate 3. The other LED filament 81, respectively 181, is configured to, in operation, emit warm white (WW) LED filament light with a CCT of 2300 K, and is arranged in a distance D3 of 20 mm below the front plate 3. All LED filaments 81, 82, respectively 181, 182, comprise a diameter of 3 mm and a length of 50 mm. All LED filaments 81, 82, respectively 181, 182, are configured to, when in operation, emit LED filament light with a flux of 100 Im. The front plate 3 is an MLO plate. The radius of curvature r of the cavity surface 5 of the inner cavity 4 and the radius of curvature s of the further cavity surface 15 of the further inner cavity 14 is 25 mm, and both the cavity surface 5 and the further cavity surface 15 is a white, diffuse surface with a reflectivity, RCS, of 100%. The lighting device 100 used for the simulations is thus symmetric around a plane of symmetry SP indicated in Figs. 7 and 8.

[0096] Fig. 8 illustrates the luminance of the lighting device light when all LED filaments are in operation, and when observed from an on-angle view 400 (cf. Fig. 7), that is a view form a direction forming an angle of 0 degrees with respect to a normal to a light exit surface of the lighting device 100.

[0097] As may be seen a lighting device 100 according to the present invention provides lighting device light with an even higher color uniformity as perceived by a viewer due to the symmetry of the lighting device 100.

[0098] Fig. 9 shows a cross-sectional view of another lighting device 101 according to the invention. The lighting device 101 differs from the lighting devices 1 and 100 described above with reference to Figs. 1, 2 and 7 in virtue of the following features.

[0099] The lighting device 101 generally comprises a further housing 21 and at least one further LED filament 181, 182, 183. In the embodiment shown in Fig. 3, three further LED filaments 181, 182, 183 are provided. The further LED filament(s) 181, 182, 183 is / are configured to, in operation, provide LED filament light (not shown for the sake of simplicity).

[0100] The further housing 21 comprises a further front plate 31 forming a part of the light exit surface of the lighting device 101. The further housing 21 comprises a further inner cavity 14. The further inner cavity 14 comprises a further cavity surface 15. The further cavity surface 15 comprises a bottom section 16 and a side section 17. The further housing 21, the further inner cavity 14 and the inner surface 15 may be identical to or different from the housing 2, the inner cavity 4 and the inner surface 5 described further above with reference to Fig. 1 in terms of size and / or shape. In any event, however, the further housing 21, the further inner cavity 14 and the inner surface 15 is of the same general type as the housing 2, the inner cavity 4 and the inner surface 5 described further above with reference to Fig. 1.

[0101] The three further LED filaments 181, 182, 183 are arranged in the further inner cavity 14 in respective distances Fl, F2, F3 from the bottom section 16. The distances Fl, F2, F3 are measured in the height direction H. The distances Fl, F2, F3 may as shown be mutually different. Alternatively, two or all of the distances Fl, F2, F3 may be identical. The height direction, H, may be a height direction of the housing 2 or of the further housing 21. Likewise, the width direction, W, may be a width direction of the housing or of the further housing.

[0102] The further cavity surface 15 is a reflective surface. The further cavity surface 15 comprises a reflectivity RCS. The reflectivity RCS may be chosen to be higher than 95 %, or higher than 98 %, or higher than 99 %, or even 100 %. The further cavity surface 15 may be coated with a reflective coating. Alternatively, or additionally, the further cavity surface 15 may comprise a reflective layer.

[0103] When seen in a cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 is a rounded surface. The height direction, H, may be a height direction of the housing 2 or of the further housing 21. Likewise, the width direction, W, and the length direction, L, may be a width direction and a length direction, respectively, of the housing 2 or of the further housing 21. In the embodiment shown in Fig. 9, when seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 is semicircular. The further cavity surface 15 comprises a radius of curvature t. The radius of curvature t may for instance be 25 mm, although many other radii of curvature likewise are feasible, for instance depending on the size of the lighting device 100 and the number of LED filaments 181, 182, 183 to be accommodated in the further inner cavity 14. The radius of curvature t may be equal to or different from the radius of curvature r of the cavity surface 5 of the inner cavity 4. More generally, when seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 may be any one of semi-circular, semi-elliptic, semi-oval, semi-polygonal with at least two, three, four or five sides and / or with rounded comers, and combinations thereof, whether symmetric or asymmetric. When seen in the cross-section extending in a plane spanned by the height direction H and the width direction W, the further cavity surface 15 may also comprise a freeform shape (that is, a shape not conforming to a regular or formal structure or shape), such as a wavy shape or an asymmetric shape.. Furthermore, when seen in a crosssection extending in a plane spanned by the length direction L and the width direction W the further cavity surface 15 may be any one of oval, oblong with rounded ends or comers, circular, elliptic, polygonal with or without rounded ends or comers, and combinations thereof.

[0104] In the embodiment shown in Fig. 9, the further cavity surface 15 extends from the further front plate 31 to a further back surface 19 of the further housing 21 in such a way that at least a part of the further back surface 19 forms the bottom section 16. In other words, the side section 17 extends between the further front plate 31 and the further back surface 19, and at least a part of the further back surface 19 forms the bottom section 16. In this case, the part of the further back surface 19 forming the bottom section 16 is a reflective surface. Alternatively, the further cavity surface 15 may extend from the further front plate 31 towards the further back surface 19 in such a way that the bottom section 16 is arranged in a distance from the further back surface 19.

[0105] The further front plate 31 is a translucent front plate. Additionally, the front plate 3 may be a diffusive front plate. The further front plate 31 may be a micro-lens optic, MLO, plate. Alternatively, the further front plate 31 may be a clear poly(methyl methacrylate) (PMMA) plate with a textured surface or a PMMA plate containing scattering particles. In another alternative, the further front plate 31 may be a PMMA plate containing small pyramid features on top in order to reduce glare. The further front plate 31 may be made by 3D-printing. Alternatively, the further front plate 31 may be made by injection molding.

[0106] Furthermore, the LED filaments 181, 182, 183 arranged in the further inner cavity 14 are each arranged with the longitudinal axis LA extending in the length direction L of the housing 2 or 21 and with a pitch PW measured in the width direction W of the housing 2 or 21. Alternatively, the LED filaments 181, 182, 183 may be arranged in the further inner cavity 14 with the longitudinal axis LA extending in the width direction W of the housing 2 or 21 and with a pitch PL measured in the length direction L of the housing 2 or 21.

[0107] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0108] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

CLAIMS:

1. A lighting device (1, 100, 101) configured to, in operation, provide lighting device light (50), the lighting device comprising: a housing (2) comprising: a height direction (H), a length direction (L) and a width direction (W), a front plate (3) forming a light exit surface of the lighting device, and at least one inner cavity (4) comprising a cavity surface (5), the cavity surface comprising a bottom section (6) and a side section (7), the side section extending between the front plate and the bottom section, and a first LED filament (81) and a second LED filament (82) configured to, in operation, provide LED filament light (83, 84), wherein the first LED filament (81) and the second LED filament (82) are arranged in the at least one inner cavity (4) of the housing (2) in a distance from the bottom section, the distance being measured in the height direction (H), wherein the cavity surface (5) is a reflective surface, and the front plate (3) is a translucent front plate, and wherein the cavity surface (5) is rounded when seen in a cross-section extending in a plane spanned by the height direction (H) and the width direction (W), wherein the first LED filament (81) is arranged in a first distance (DI) from the bottom section (6) of the cavity surface, and the second LED filament (82) is arranged in a second distance (D2) from the bottom section (6) of the cavity surface, and wherein the second distance (D2) is larger than the first distance (DI).

2. A lighting device according to claim 1, wherein the cavity surface (5), when seen in the cross-section extending in a plane spanned by the height direction (H) and the width direction (W), is any one of: (i) semi-circular, (ii) semi-elliptic, (iii) semi-oval, (iv) semi-polygonal with at least two, three, four or five sides and with rounded comers, and (v) combinations thereof, or comprises a freeform shape.

3. A lighting device according to claim 1 or 2, wherein the cavity surface (5), when seen in a cross-section extending in a plane spanned by the length direction (L) and the width direction (W), is any one of oval, oblong with rounded ends or comers, circular, elliptic, polygonal with or without rounded ends or corners, and combinations thereof.

4. A lighting device according to any of the above claims, wherein the housing (2) comprises a housing width (WH) extending in the width direction (W) and a housing length (LH) extending in the length direction (L), wherein the cavity (4) comprises a cavity width (WC) extending in the width direction (W) and a cavity length (LC) extending in the length direction (L), and wherein one or more of the following applies:- the cavity width (WC) is smaller than the housing width (WH), and- the cavity length (LC) is smaller than or equal to the housing length (LH).

5. A lighting device according to any of the above claims, wherein the cavity surface (5) comprises a reflectivity (RCS) being higher than 95 %, or higher than 98 %, or higher than 99 %, or 100 %.

6. A lighting device according to any of the above claims, wherein the housing (2) further comprises a back surface (9), and wherein one of the following applies: the cavity surface (5) extends from the front plate (3) towards the back surface (9) such that at least a part of the bottom section (6) is arranged in a distance (Db) from the back surface (9), the distance (Db) being measured in the height direction (H) as the shortest distance between the back surface (9) and a point of the bottom section (6) in which a tangent to the cavity surface (5) extends in a plane spanned by the length direction (L) and the width direction (W), and the side section (7) of the cavity surface (5) extends between the front plate (3) and the back surface (9), at least a part of the back surface (9) forms the bottom section (6) of the cavity surface, and the part of the back surface forming the bottom section is a reflective surface.

7. A lighting device according to any of the above claims, wherein the at least one LED filament (81, 82) comprises a longitudinal axis (LA), and wherein one or more of the following applies:the at least one LED filament is arranged with the longitudinal axis (LA) extending in the width direction (W) of the housing, and the at least one LED filament is arranged with the longitudinal axis (LA) extending in the length direction (L) of the housing.

8. A lighting device according to any of the above claims, and comprising a plurality of LED filaments, wherein the LED filaments (81, 82) of the plurality of LED filaments each comprise a longitudinal axis (LA), and wherein: the LED filaments (81, 82) each are arranged with the longitudinal axis (LA) extending in the width direction (W) of the housing (2) and with a pitch (PL) measured in the length direction (L) of the housing, or the LED filaments (81, 82) each are arranged with the longitudinal axis (LA) extending in the length direction (L) of the housing (2) and with a pitch (PW) measured in the width direction (W) of the housing.

9. A lighting device according to any of the above claims, wherein the at least one LED filament (81, 82), or each LED filament (81, 82) of the plurality of LED filaments, is supported by electrical connectors (10, 11) configured to supply the LED filament with electrical energy, and wherein the electrical connectors (10, 11) comprise a reflectivity (REC) being higher than 95 %, or higher than 98 %, or higher than 99 %, or 100 %.

10. A lighting device according to any of the above claims, wherein the at least one LED filament (81, 82), or each LED filament (81, 82) of the plurality of LED filaments, is supported by electrical connectors (10, 11) configured to supply the LED filament with electrical energy, wherein the electrical connectors (10, 11) are connected to electrical circuitry (12, 13), and wherein the electrical circuitry (12, 13) is arranged in the housing outside of the at least one inner cavity (4).

11. A lighting device according to any of the above claims, wherein one or more of the following applies: the inner cavity (4) is made by one of deep drawing a microcellular polyethylene terephthalate (MCPET) sheet, 3D-printing and injection molding of a pigment filled polycarbonate material, the front plate (3) is further a diffusive front plate, andthe front plate (3) is made by one of 3D-printing and injection molding.

12. A lighting device (100) according to any of the above claims, wherein the housing (2) further comprises at least one further inner cavity (14) comprising at least one further cavity surface (15), the at least one further cavity surface (15) comprising a bottom section (16) and a side section (17), and wherein the lighting device further comprises: at least one further LED filament (181, 182) configured to, in operation, provide further LED filament light, wherein the at least one further LED filament (181, 182) is arranged in the at least one further inner cavity (14) in a distance (E) from the bottom section (16) of the at least one further cavity surface (15), the distance (E) being measured in the height direction (H), wherein the at least one further cavity surface (15) is a reflective surface, and wherein the at least one further cavity surface (15) is rounded when seen in a crosssection extending in a plane spanned by the height direction (H) and the width direction (W).

13. A lighting device according to any of the above claims, the lighting device (101) comprising a further housing (21) and at least one further LED filament (181, 182, 183) configured to, in operation, provide LED filament light, the further housing (21) comprising: a further front plate (31) forming a light exit surface of the lighting device, and at least one further inner cavity (14) comprising at least one further cavity surface (15), the at least one further cavity surface (15) comprising a bottom section (16) and a side section (17), wherein the at least one further LED filament (181, 182, 183) is arranged in the at least one further inner cavity (14) in a distance (F) from the bottom section (16) of the further cavity surface, the distance (F) being measured in the height direction (H), wherein the at least one further cavity surface (15) is a reflective surface, and the further front plate (31) is a translucent front plate, and wherein the at least one further cavity surface (15) is rounded when seen in a crosssection extending in a plane spanned by the height direction (H) and the width direction (W).

14. A luminaire comprising a lighting device (1, 100, 101) according to any of the above claims.

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