WO2013132381A1

WO2013132381A1 - Light emitting arrangement

Info

Publication number: WO2013132381A1
Application number: PCT/IB2013/051458
Authority: WO
Inventors: Ties Van Bommel; Rifat Ata Mustafa Hikmet
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2012-03-06
Filing date: 2013-02-22
Publication date: 2013-09-12
Anticipated expiration: 2014-09-06

Description

Light emitting arrang

FIELD OF THE INVENTION

The present invention relates to a light emitting arrangement adapted to produce a desirable light distribution.

BACKGROUND OF THE INVENTION

Solid state light sources, such as light-emitting diodes (LEDs), are increasingly used for a wide variety of lighting and signaling applications. LEDs offer advantages over traditional light sources, such as incandescent and fluorescent lamps, including long lifetime, high lumen efficacy, low operating voltage and fast modulation of lumen output. LEDs generally emit light with a Lambertian distribution.

Light emitting arrangements and luminaires comprising LEDs are known to cause glare problems. Glare is caused by excessive contrast between bright and dark areas in the field of the observer. Particularly, in the design of light emitting arrangements and luminaires intended for application in the area of the in-house lighting and office lighting, the issue of glare reduction receives much attention. Light sources are placed in luminaires with glare reducing measures, such as a lamella. However, even in such luminaires, there is still too much overhead glare which is visible when users look into the luminaire. Further improvements regarding glare reduction and flexibility in beam shaping are desirable.

WO 2011/151762 Al relates to a luminaire comprising a housing, a light source positioned in the housing, and a curved optically transmissive sheet having a plurality of linear prism structures with right top angles on its concave surface, facing away from the light source, which shows reduced glare.

However, it would be desirable to find a light emitting arrangement that shows a further reduced glare, but also an improved flexibility in beam shaping.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partly overcome these limitations, and to provide a light emitting arrangement that shows further reduced glare and an improved flexibility in beam shaping. In one aspect, this and other objects are achieved by a light emitting arrangement for producing a batwing beam shape. Batwing beam shapes are desirable in several lighting applications, such as for retail in shop rack lighting, streetlights and different kinds of luminaires and task lights. The light emitting arrangement shows reduced or no glare when viewed from the front. Furthermore, the light emitting arrangement according to the invention offers a white or whitish appearance in off-state.

According to a first aspect of the invention, the light emitting arrangement comprises a solid state light source adapted to emit light of a first wavelength range; and a wavelength converting member arranged to receive light of the first wavelength range emitted by the solid state light source and capable of converting light of the first wavelength range into light of a second wavelength range. The wavelength converting member and the solid state light source are mutually spaced apart. Further, an optically transmissive sheet is arranged to receive light from the solid state light source and the wavelength converting member. The optically transmissive sheet comprises a first surface facing towards the solid state light source and the wavelength converting member, and a second surface, parallel to the first surface, facing away from the solid state light source and the wavelength converting member. The first surface comprises a prismatic surface structure.

The present invention offers advantages such as a flexible light distribution and reduced glare. The invention further offers the advantage that a wavelength converting member is not clearly visible in the off-state, thus having a white off-state appearance. The invention also allows for efficient recycling of light.

The light emitting arrangement according to the present invention is adapted to a produce a batwing light distribution. A batwing light distribution has not, in contrast to a Lambertian light distribution, a light intensity maximum in the direction of the optical axis of the light emitting arrangement. The shift of the light intensity maximum contributes to a reduced glare when the arrangement is viewed from the front.

A solid state light source may be a light emitting diode (LED), e.g. a blue LED, which can emit broad-spectrum white light when used together with a wavelength converting member.

A wavelength converting member as used in the present invention has, in itself, a colored appearance. The colored appearance is due to an inherently colored photoluminescent material. In light emitting arrangements in which the wavelength converting member is visible to an observer, the colored appearance may be undesirable for aesthetic and other reasons. However, advantageously, by using an optically transmissive sheet with a prismatic surface structure according to the present invention, the color of the wavelength converting member is no longer clearly visible, resulting in a white or whiter off- state appearance of the light emitting arrangement.

The optically transmissive sheet is typically formed of a transparent polymeric material, such as a thermoplastic polymer, for example poly(methylmethacrylate) (PMMA), polyethylene terephthalate (PET) and polycarbonate (PC). The prismatic structure on the first surface of the optically transmissive sheet may have a dimension smaller than 1 mm, preferably in the range between 10-500 μιη.

In embodiments, a prismatic surface structure on the first surface of an optically transmissive sheet may be arranged so as to form linear grooves in order to have the ability to recycle light that is emitted in undesired directions back to a solid state light source instead of directly transmitting it. Such an arrangement enhances the batwing light distribution.

In some embodiments, the light emitting arrangement has no intermediate optically functional layer between the wavelength converting member and the optically transmissive sheet. It may be preferable to use such an arrangement with regard to production process, environmental aspects and material costs.

In some embodiments, the optically transmissive sheet and the wavelength converting member are not in direct optical contact. Hence, for example, there may be an air gap in between the optically transmissive sheet and the wavelength converting member.

In an embodiment, the prismatic surface structure may be a pattern of linear prism grooves. In another embodiment, the prismatic surface structure is a pattern of pyramids.

The prismatic surface structure of the first surface of the optically transmissive sheet may be irregular or regular. Examples of regular prismatic structures include pyramids, such as square pyramids, cones and/or elongated linear prism structures. A preferred structure is a linear prismatic structure, both with respect to the production process and light distribution. Such a prismatic structure has the ability to recycle light in undesired emitting directions back to the solid state light source instead of transmitting it. Further, a prismatic structure may give the arrangement a white off- state appearance at a viewing angle perpendicular to the arrangement.

According to an embodiment, the second surface of the optically transmissive sheet may be a smooth surface. A smooth second surface has the advantage of not contributing to a further adjusted light output after that the light has passed through the first surface of the optically transmissive sheet.

In some embodiments, the optically transmissive sheet may be planar. A planar optically transmissive sheet may result in a simple, compact design and relatively easy production.

According to an embodiment, the optically transmissive sheet may comprise a scattering element. A scattering material, such as A1₂0₃ particles, Ti0₂ particles, or scattering pores, may be included in the optically transmissive sheet in order to increase light redirection.

In some embodiments the light emitting arrangement comprises at least two optically transmissive sheets, each comprising a first surface 'facing towards said solid state light source and said wavelength converting member, and a second surface, parallel to said first surface, facing away from said solid state light source and said wavelength converting member, wherein the first surface of each optically transparent sheet comprises a prismatic surface structure. Typically the two optically transmissive sheets may be stacked, so that light exiting from the wavelength converting member is first received by a first optically transmissive sheet via its prismatic surface, and after exiting the first optically transmissive sheet the light, now having a batwing distribution is immediately received by a second optically transmissive sheet via its prismatic surface structure. The second optically transparent sheet may thus further influence the light distribution.

For example, the light emitting arrangement may comprise a first optically transmissive sheet and a second optically transmissive sheet, arranged in a stack and oriented so that the linear prismatic grooves of the first optically transmissive sheet are perpendicular to the linear prismatic grooves of the second optically transmissive sheet. Optically transmissive sheets stacked with their linear prismatic grooves perpendicular to each other may be referred to as "crossed" optically transmissive sheets. Such an arrangement may result in an enhanced or modified batwing distribution.

In other embodiments, the light emitting arrangement may comprise a first optically transmissive sheet and a second optically transmissive sheet, arranged in a stack and oriented so that the linear prismatic grooves of the first optically transmissive sheet are perpendicular to the linear prismatic grooves of the second optically transmissive sheet. Optically transmissive sheets stacked with their linear prismatic grooves parallel to each other may be referred to as "parallel" optically transmissive sheets. Such an arrangement may result in a enhanced or modified batwing distribution. According to an embodiment, the light emitting arrangement further comprises a reflective member having a tapering wall arranged to redirect light exiting from said optically transmissive sheet. The reflective member may thus be arranged to modify the light output from having a batwing distribution into a light output having a modified batwing distribution. In an example, the reflective member is funnel shaped or at least partly funnel- shaped.

According to another embodiment, the optically transmissive sheet is rotatable in an in-plane direction of said optically transmissive sheet. The optically transmissive sheet may be rotatable around an imaginary axis extending in parallel with the optical axis of the solid state light source of the light emitting arrangement. Such an arrangement has the advantage of making it possible to obtain a light spot with an adjustable beam shape. An adjustable beam shape may be useful for a user using a light emitting arrangement for various purposes.

In embodiment, the wavelength converting member comprises at least one inorganic wavelength converting material, organic wavelength converting material and/or quantum dots.

In an embodiment the wavelength converting member comprises a stack of wavelength converting layers. A stack of wavelength converting layers is advantageous due to improved system efficacy by decreasing absorption, and/or flexibility in obtaining different color points.

In another embodiment the wavelength converting member comprises a plurality of in-plane regions having different wavelength converting characteristics. Potential benefits of this arrangement include increased efficiency and potential decorative effects.

According to embodiments of the invention , the wavelength converting member may comprise scattering elements. For example, a scattering material, such as A1₂0₃ particles, Ti0₂ particles, or scattering pores, may be included in the wavelength converting member in order to enhance the light extraction.

In another aspect, the invention provides a luminaire comprising a light emitting arrangement as defined herein. The luminaire typically also comprises an optical chamber in which the light source is arranged, and optionally also a reflective member as described herein. The optical chamber typically has a base portion and at least one sidewall which defines a light exit window. An optical chamber may increase recycling and mixing of light and ensure a homogeneous distribution of light incident on the wavelength converting member. The solid state light source may be positioned at the base portion of the optical chamber. A plurality of solid state light sources may be positioned at the base portion of the optical chamber.

In embodiments of the invention, the optically transmissive sheet may cover the entire wavelength converting member, typically by being attached to a sidewall of the optical chamber, thereby also covering a light exit window of the light emitting arrangement.

The light emitting arrangement may be in the form of, for example, a lamp, a luminaire, a tasklight, a streetlight or a backlight.

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

BRIEF DESCRIPTION OF THE DRAWINGS

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.

Fig. 1 is a perspective view of a light emitting arrangement according to an embodiment of the invention.

Fig. 2a is a perspective view of a light emitting arrangement according to an embodiment comprising a stack of wavelength converting layers.

Fig. 2b is a perspective view of a light emitting arrangement according to an embodiment comprising a plurality of in-plane regions.

Fig. 3a is a perspective view of a light emitting arrangement according to an embodiment wherein the optically transmissive sheet comprises scattering elements.

Fig. 3b is a perspective view of a light emitting arrangement according to an embodiment wherein the wavelength converting member comprises scattering elements.

Fig. 4a is a perspective view of a light emitting arrangement according to an embodiment comprising two stacked, crossed optically transmissive sheets.

Fig. 4b is a perspective view of a light emitting arrangement according to an embodiment comprising two stacked, parallel optically transmissive sheets.

Fig. 5a is a perspective, partially cross-sectional view of a light emitting arrangement according to an embodiment comprising an optical chamber.

Fig. 5b is a perspective, partially cross-sectional view of a light emitting arrangement according to another embodiment comprising an optical chamber.

Fig. 6 is a perspective, partially cross-sectional view of a light emitting arrangement according to an embodiment comprising a optical chamber, wherein the optically transmissive sheet is mechanically rotatable. Fig. 7a is a graph showing an intensity profile of a symmetric batwing light distribution.

Fig. 7b is a graph showing an intensity profile of an asymmetric batwing light distribution.

Fig. 8 is a cross-sectional view of a light emitting arrangement further comprising a symmetric reflective member.

Fig. 9a is a perspective view of a light emitting arrangement comprising an asymmetric reflective member with the optically transmissive sheet in a first position.

Fig. 9b is a perspective view of a light emitting arrangement further comprising an asymmetric reflective member with the optically transmissive sheet in a second position.

As illustrated in the figures, the sizes of layers and regions may be 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.

DETAILED DESCRIPTION

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.

The present invention offers advantages such as a flexible light distribution and reduced glare. The adjustable components of the light emitting arrangement allow a flexible light distribution. The light emitting arrangement allows a reduced glare, for example by being adapted to produce a batwing light distribution which lowers the light intensity in the normal direction of the light exit window.

The invention further offers the advantage that the phosphor is not clearly visible in the off-state, thus having a white off-state appearance. By arranging an optically transmissive sheet with a prismatic structure on its first surface facing the wavelength converting member, the light emitting arrangement according to the invention is having a white off-state appearance. The invention also allows for efficient recycling of light. As used herein "batwing beam shape", "batwing distribution", "batwing light distribution" or "batwing-shaped distribution", when referring to light, is defined as a light beam having a light intensity as a function of an angle relative to the optical axis of a light emitting arrangement, for which the intensity goes through a maximum when the angle changes from 0° (corresponding to light in the optical axis), to -90° or 90°, respectively

(corresponding to the plane perpendicular to the optical axis). The maximum may be within the range of from 10° to 80°, for example from 30° to 60°, and from -10° to -80°, for example from -30° to -60°, respectively. If the batwing intensity profile is symmetric, as shown in Fig. 7a, the intensity profile has a first maximum between 0° and 90° and a second maximum between 0° and -90°, both on equal angles from the normal, such as at 45° and -45°, respectively. If the batwing intensity profile is asymmetric, as shown in Fig. 7b, the intensity profile may have only one maximum between -90° and 90°, anywhere in this range except at 0°, -90° and 90°. Batwing light distributions reduce overhead glare in the front direction and can easily be further adapted using reflective members, et cetera, as will be appreciated by a person skilled in the art.

A wavelength converting member may comprise a single wavelength converting material or a plurality of wavelength converting materials, such as an inorganic wavelength converting material, an organic wavelength converting material or quantum dots. A wavelength converting material has a certain wavelength converting characteristics. The wavelength converting characteristics of a wavelength converting member depends on the composition - amounts, concentrations, proportions - of wavelength converting materials contained within the wavelength converting member.

A wavelength converting member may comprise a single wavelength converting layer or a plurality of wavelength converting layers. Each wavelength converting layer may comprise a single wavelength converting material or a plurality of wavelength converting materials. The layer may be homogeneous with regard to wavelength converting characteristics or heterogeneous by comprising various regions with different wavelength converting characteristics. A wavelength converting member may be a remote element, wherein the wavelength converting member may be bound to a substrate instead of being incorporated to a solid state light source.

The wavelength converting material may be an inorganic material, an organic material and/or quantum dots.

Examples of inorganic wavelength converting materials may include, but are not limited to, cerium (Ce) doped YAG (Y₃Al₅0i₂) or LuAG (Lu₃Al₅0i₂). Ce doped YAG emits yellowish light, whereas Ce doped LuAG emits yellow-greenish light. Examples of other inorganic phosphors materials which emit red light may include, but are not limited to ECAS (ECAS, which is Cai__xAlSiN₃:Eu_x wherein 0<x<l; preferably 0<x<0.2) and BSSN (BSSNE, which is Ba₂-_x-_zM_xSi₅-_yAl_yN₈-yO_y:Eu_z wherein M represents Sr or Ca, 0<x<l and preferably 0<x<0.2, 0<y<4, and 0.0005<z<0.05).

Examples of suitable organic wavelength converting materials are organic luminescent materials based on perylene derivatives, for example compounds sold under the name Lumogen^® by BASF. Examples of suitable compounds include, but are not limited to, Lumogen^® Red F305, Lumogen^® Orange F240, Lumogen^® Yellow F083, and Lumogen^® F170. Advantageously, a layer comprising organic luminescent material may be transparent and non-scattering.

Quantum dots are small crystals of semiconducting material generally having a width or diameter of only a few nanometers, which exhibit size-dependent electronic and optical properties which are different from those of bulk solids. When excited by incident light, a quantum dot emits light of a color determined by the size and material of the crystal. Light of a particular color can therefore be produced by adapting the size of the dots. Most known quantum dots with emission in the visible range are based on cadmium selenide (CdSe) with shell such as cadmium sulfide (CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indium phosphode (InP), and copper indium sulfide (CuInS₂) and/or silver indium sulfide (AgInS₂) can also be used. Quantum dots show very narrow emission band and thus they show saturated colors. Furthermore, the emission color can be tuned by adapting the size of the quantum dots. Any type of quantum dot known in the art may be used in the present invention, provided that it has the appropriate wavelength conversion characteristics. However, it may be preferred for reasons of environmental safety and concern to use cadmium- free quantum dots or at least quantum dots having very low cadmium content.

In the context of the present invention, an "optically transmissive sheet" is a sheet through which visible light may pass to some degree. The sheet may be completely transparent, or it may transmit only a portion of the incident light. An example of an optically transmissive sheet with linear prism grooves, optionally with right angles, is a so-called brightness enhancement film (e..g.Vikuiti™ marketed by 3M). In embodiments of the present invention, such a brightness enhancement film may be used "upside-down", i.e. with the prismatic structure facing the wavelength converting member, contrary to the normal intended use. The term "white appearance" is used to denote the visual appearance of an arrangement allowing white incident light be reflected as white light. Such a white appearance is preferable also in the off-state of the light emitting arrangement. When, for instance, an inorganic phosphor is used as wavelength converting material, it may have an inherent yellowish appearance in off-state, which is considered aesthetically unpleasant. Then a light emitting arrangement allowing a white off-state appearance, such as the light emitting arrangement according to the present invention, is advantageous.

The term "mutually spaced apart" means that the two components in question are not attached or laminated to each other but are provided at a certain distance from each other, e.g. separated by air or another medium or another component.

In the context of the present invention, the expression "no intermediate optically functional layer" means that there is no optical component arranged in between the wavelength converting member and the optically transmissive sheet, which in itself transforms or modifies (e.g. diffuses, scatters, reflects, diffracts, or polarizes) the light passing from the solid state light source via the wavelength converting member and the optically transmissive sheet out through the light exit window. For example, in some embodiments, there is no polarizer or reflective member in between the wavelength converting member and the optically transmissive sheet.

Fig. 1 illustrates a light emitting arrangement 100 according to an embodiment of the invention, which may for instance be used in a luminaire. The light emitting arrangement comprises a solid state light source 101 and a wavelength converting member 102, mutually spaced apart, and an optically transmissive sheet 103 having a first surface 104 with a prismatic surface structure forming prism grooves 106, facing the solid state light source 101 and the wavelength converting member 102, and a second surface 105, facing away from the wavelength converting member 102 in the light output direction.

A wavelength converting member 102 is arranged in the light output direction from the solid state light source 101. The wavelength converting member 102 and the solid state light source 101 are mutually spaced apart. Typically, the distance between the wavelength converting member 102 and the solid state light source 101 is 1-10 cm.

Nevertheless, the arrangement may also be used in vicinity mode, where the distance is typically 0.5-1 cm. In this embodiment, the wavelength converting member 102 substantially covers the whole distribution of light output from the solid state light source, such that it may receive all of the light emitted by the solid state light source. In embodiments of the invention, the solid state light source 101 is a light emitting diode (LED) that emits blue light. However, it may also be possible to use light sources emitting green or red light. In alternative embodiments, the light source may emit violet light, or UV light. For example, in embodiments where the solid state light source is an LED, it may be a blue emitting LED such as GaN or InGaN based LED. However also LEDs emitting light of other colors may be used, and are known to the skilled person. Laser diodes emitting light of any suitable wavelength range may also be used.

In embodiments of the invention, the first wavelength range, emitted by the solid state light source 101, may be from 380 to 490 nm, for example from 440 to 460 nm. The second wavelength range, emitted by the wavelength converting member 102, may be from 500 nm to 850 nm, typically visible light. In one embodiment, the second wavelength range is from 500 to 650 nm. The second wavelength range depends on the characteristics of the wavelength converting member, which may comprise an inorganic wavelength converting material, an organic wavelength converting material or quantum dots.

On top of the wavelength converting member 102, an optically transmissive sheet 103 is arranged. Typically, the wavelength converting member 102 is not in direct optical contact with the optically transmissive sheet 103. As used herein, two components being in "direct optical contact" means that light is coupled directly from one component directly into the other, without having to pass through an intermediate optical component or medium. Since the present invention does not require the wavelength converting member to be in direct optical contact with the optically transmissive sheet, in some embodiments the wavelength converting member 102 and the optically transmissive sheet 103 may be separated by an air gap. Preferably however there is no intermediate layer or component positioned between the wavelength converting member 102 and the optically transmissive sheet 103, in order to keep the arrangement simple and efficient.

In some embodiments, the optically transmissive sheet may be arranged to cover the substantially whole surface of the wavelength converting member facing the optically transmissive sheet.

The optically transmissive sheet 103 comprises a first surface 104 facing towards the solid state light source 101 and the wavelength converting member 102, and a second surface 105 facing away from the solid state light source 101 and the wavelength converting member 102. The first surface 104 comprises a prismatic surface structure. The prismatic structure may be a pattern of linear elongated prism grooves 106, preferably with right angles. In other embodiments, the prismatic surface structure on the first surface 104 of the optically transmissive sheet 103 may be formed irregularly or regularly. Examples of regular prisms, in addition to linear prism grooves, are pyramids, such as square pyramids, spheres and cones. The second surface 105 of the optically transmissive sheet is typically a smooth surface.

In Fig. 1, the optically transmissive sheet 103 is substantially planar. In other embodiments, however, it may have a curvature. In yet other embodiments, the second surface 105 of the optically transmissive sheet may have a curvature, while the first surface 104 is substantially planar, and vice versa.

The respective surface areas of the wavelength converting member 102 and the optically transmissive sheet 103, respectively, may be substantially equal and may be larger than the light emitting area of the solid state light source 101. A single wavelength converting member 102 and optically transmissive sheet 103 may cover a plurality of solid state light sources. A plurality of optically transmissive sheets 103 may cover a single wavelength converting member 102 and a single solid state light source 101 or a plurality of solid state light sources 101.

Fig. 2a-b illustrate light emitting arrangements 100. In Fig. 2a, the wavelength converting member 102 comprises a stack of two wavelength converting layers 102a, 102b, arranged in between a solid state light source 101 and an optically transmissive sheet 103 as shown in Fig.l . The wavelength converting layers 102a, 102b may have different wavelength conversion characteristics. For example the first wavelength converting layer may comprise a first wavelength converting material, and the second wavelength converting layer 102b may comprise a second wavelength converting material, different from the first wavelength converting material. It is also contemplated that any one of the first or second wavelength converting layers may comprise more than one type of wavelength converting material. Alternatively, in some embodiments, the first and second wavelength converting layers may comprise the same wavelength converting material but in different amounts or

concentrations, and/or in different combinations with other wavelength converting material, scattering elements, or carrier materials.

In Fig. 2b, a wavelength converting member 102, arranged in between a solid state light source 101 and an optically transmissive sheet 103, as shown in Fig. 1, comprises a pattern of well-defined regions of two kinds of wavelength converting materials. Fig. 2b illustrates schematically how the well-defined regions of a wavelength converting materials extend in three dimensions. The pattern may be either regular or irregular. Examples of different kinds of wavelength converting material are an inorganic wavelength converting material, an organic wavelength converting material and quantum dots. By combining different kinds of wavelength converting members in varying amounts and/or proportions, the second wavelength range can be adjusted as desired.

Fig. 3a depicts a light emitting arrangement 100. The light emitting

arrangement comprises a solid state light source 101, a wavelength converting member 102 and an optically transmissive sheet 103 arranged, in said order, in the light emitting direction of the solid state light source 101. In this embodiment, the optically transmissive sheet 103 comprises scattering elements 107. Examples of scattering elements include particles, such as A1₂0₃ particles or Ti0₂ particles, and pores. The scattering elements 107 may be included in the optically transmissive sheet 103 in order to enhance the light redirection by

homogenizing the light beam.

Fig. 3b depicts a light emitting arrangement 100 comprising a solid state light source 101, and a wavelength converting member 102 and an optically transmissive sheet 103, arranged, in said order, in the light emitting direction of the solid state light source 101. In this embodiment, the wavelength converting member 102 comprises scattering elements 107. The scattering elements may be as described above. A scattering element 107 is included in the wavelength converting member 102 in order to enhance the light extraction.

As illustrated in Fig. 4a-b, a light emitting arrangement 100 may comprise a stack of optically transmissive sheets arranged on top of, in order, a solid state light source 101 and a wavelength converting member 102. Each of the optically transmissive sheets 103 has a first surface 104 and a second surface 105 as defined above. The first surface 104 of the first optically transmissive sheet 103 a, arranged closest to the wavelength converting member 102, has its prismatic surface structure facing the wavelength converting member 102. The second optically transmissive sheet 103b, arranged on top of the first optically sheet 103a, has its prismatic surface structure facing the second surface 105 of the first optically transmissive sheet 103a. In Fig. 4a-b, a stack of only two optically transmissive sheets is illustrated, but this illustration should be regarded as general, and consequently the stack may comprise any suitable number of optically transmissive sheets.

In Fig. 4a, the first optically transmissive sheet 103a has linear prismatic grooves 106a extending in one direction. The second optically transmissive sheet 103b, arranged on top of the first sheet 103 a, has linear prism grooves 106b arranged in a direction perpendicular to the direction of the linear prism grooves 106a of the first optically transmissive sheet 103 a. Two optically transmissive sheets arranged with their linear prismatic grooves perpendicular to each other may be referred to as "crossed" optically transmissive sheets. This configuration is not limited to a stack of two optically transmissive sheets; the stack may comprise any number of optically transmissive sheets.

In Fig. 4b, the first optically transmissive sheet 103a has linear prismatic grooves 106a. The second optically transmissive sheet 103b, arranged on top of the first sheet 103 a, has linear prismatic grooves 106b arranged in a direction parallel to the direction of the linear prismatic grooves 106a of the first optically transmissive sheet 103 a. Two optically transmissive sheets with their linear prismatic grooves parallel to each other may be referred to as "parallel" optically transmissive sheets. This configuration is not limited to a stack of two optically transmissive sheets; the stack may comprise any number of optically transmissive sheets.

In an embodiment, at least two optically transmissive sheets are arranged one on top of the other, with their prism grooves orientated with a relative angle to each other in between the parallel and crossed configurations. In such a configuration, two adjacent optically transmissive sheets form a smallest angle between their respective linear prismatic groove directions that is larger than 0° (0° corresponding to the parallel configuration), and smaller than 90° (90° corresponding to the crossed configuration). In other embodiments, the configurations may be adjustable during production or by the user, for example by allowing at least the optically transmissive sheet arranged the most far away from the wavelength converting member in the light direction be mechanically rotatable in its in-plane direction, as illustrated in Fig. 6a-b.

Each of Fig. 5a-b shows a light emitting arrangement 100 in partial cross- section. The arrangements illustrate each a solid state light source 101, a wavelength converting member 102, an optically transmissive sheet 103 with a first surface 104 having a prismatic surface structure, facing towards the wavelength converting layer 102 and the solid state light source 101, and a smooth second surface 105, facing away from the wavelength converting layer 102 in the light output direction. These arrangements further comprise an optical chamber 108 in which the solid state light source 101 and the wavelength converting member 102 are arranged. The optical chamber 108 comprises a base portion 109, a side wall 110 and a light exit window 111. The solid state light source 101 is arranged at the base portion 109 of the optical chamber. The number of solid state light sources that can contained the optical chamber is not limited to one; optionally the optical chamber may contain a plurality of solid state light sources, for example three solid state light sources as in Fig. 5a. If the optical chamber is circular, there may be only one sidewalk If the optical chamber, instead, is square or rectangular, there may be four sidewalls. Other geometries, such as triangular, hexagonal and octagonal, are also possible. The base portion 109 and interior walls 110 of the optical chamber 108 may be reflective.

In Fig. 5a, a wavelength converting member 102 is arranged on top of the optical chamber 108, attached to the distal portion of the sidewall 110 of the optical chamber with respect to the base portion 109, covering the light exit window 111. In Fig. 5b, the wavelength converting member 102 and the optically transmissive sheet 103 are arranged within the optical chamber 108, attached with their respective edges to the inside of the sidewall 109, still mutually spaced apart from the solid state light source 101.

Fig. 6 depicts a light emitting arrangement 100 comprising an optical chamber 108 with a base portion 109 and a sidewall 110, wherein a solid state light source 101 is arranged centrally at the base portion 109 on the inside of the optical chamber 108. Further, the light emitting arrangement 100 comprises a wavelength converting member 102 arranged in the light exit window 111. On top of the wavelength converting member 102, an optically transmissive sheet 103 is arranged with its first surface, having a prismatic surface structure, facing the wavelength converting member and covering the surface area of the wavelength converting member which it is facing. The wavelength converting member 102 and the optically transmissive sheet 103 are arranged in the direction of the light output from the solid state light source 101.

In Fig. 6, the optically transmissive sheet 103 is planar and may be mechanically rotatable in the plane defined by said sheet, around an imaginary axis extending centrally through the light emitting arrangement and the sheet. The imaginary axis typically extends in the direction of the surface normal of the optically transmissive sheet, and may be parallel to an optical axis of the solid state light source. The feature of being rotatable is advantageous , allowing adjusted beam shaping. A light emitting arrangement comprising a stack of at least two optically transmissive sheets, as illustrated in Fig. 4a-b, may have at least one rotatable optically transmissive sheet. In such an arrangement, at least the optically transmissive sheet position further away from the solid state light source may be rotatable. However, solutions in which all, or any one, of the optically transmissive sheets are rotatable are possible.

The rotation of the optically transmissive sheet(s) may be manually or electrically controlled. An alternative to manually rotatable sheets are optically transmissive sheets which are rotatable by an electrically controllable mini-motor.

Each of Fig. 7a-b is showing a diagram of how the light intensity I from a light emitting arrangement 100 according to the present invention may vary with the angle Θ relative the imaginary axis arranged centrally of the light emitting arrangement and parallel to the optical axis of the same. The imaginary axis is arranged at the angle 9=0° in the diagrams, and the angles 9=90° and θ=-90° correspond to the plane perpendicular with the imaginary axis. Preferably, the imaginary axis is in the normal direction of the optically transmissive sheet, while the perpendicular plane is in the in-plane direction of the optically transmissive sheet. In Fig. 7a, a symmetric light intensity profile of a light emitting arrangement adapted to produce a symmetric batwing distribution is shown. For example, such an arrangement may be an arrangement as shown in Fig. 1. A light emitting

arrangement according to the invention may produce a symmetric intensity profile, but may alternatively produce an asymmetric intensity profile depending on the arrangement of the components relative each other. In Fig. 7b, an asymmetric light intensity profile of a light emitting arrangement adapted to produce an asymmetric batwing distribution is shown.

In Fig. 8, a light emitting arrangement further comprising a reflective member 112 is shown. For example, it may be a light emitting arrangement as shown in Fig. 5a to which a reflective member 112 is further added. The reflective member 112 is arranged as a shield surrounding the wavelength converting member 102 and the optically transmissive sheet 103.

The optically transmissive sheet 103 is arranged to produce a light output having a batwing distribution. The reflective member 112 may be arranged to modify the light output having a batwing distribution into a light output having a modified batwing distribution. The batwing distribution is adjusted to a modified batwing distribution when parts of the light beams are hitting the reflective member 112 or a reflective wall of an optical chamber 108 working as a reflective member.

A reflective member is a component having, for example, a reflective interior wall. The reflective member may have a wall parallel to the optical axis of the light emitting arrangement. Preferably however, an interior wall of the reflective member is tapering, for example with an angle in the range from 0° to 80°, such as from 10° to 60°, for example from 15° to 45°, relative to an imaginary axis extending centrally though the light emitting arrangement in the general light output direction, typically parallel to the optical axis of the light emitting arrangement. Typically, the reflective member has a proximal portion and a distal portion, relative the solid state light source. The proximal portion typically may have a smaller cross-section area than the distal portion.

The reflective member may be symmetric or asymmetric. A symmetric reflective member has a wall tapering with the same angle in all directions relative the imaginary axis. For a symmetric reflective member, the cross-section of the distal portion and the cross-section of the distal portion have the same geometrical shape, e.g. shape of a circle or a square. An asymmetric reflective member has a wall tapering with different angles in different directions, relative the imaginary axis. In an asymmetric reflective member the cross-section of the distal portion and the cross-section of the proximal portion have different geometrical shapes, or at least geometrical shapes that are not proportional to each other, e.g. the cross-section of the proximal portion has the shape of a circle and the cross-section of the distal portion as the shape of an ellipse, alternatively, the cross-section of the proximal portion has the shape of a square and the cross-section of the distal portion as the shape of a rectangular.

Fig. 9a-b shows a further development of the light emitting arrangement 100 in Fig. 6, in which an asymmetric reflective member 112 is added. By allowing rotation of the optically transmissive sheet 103 inside the asymmetric reflective member 112, the batwing distribution and the beam shaping may be adjustable during production or by the user. Although not shown in Fig. 9a, this embodiment may also comprise a reflective chamber e.g. as described with reference to Figs. 5a-b, Fig. 6 or Fig. 8.

The batwing distribution of the light emitted from the optically transmissive sheet 103 of the light emitting arrangement 100 may be adjusted into a modified batwing distribution when hitting the reflective member 112. If using an asymmetric reflective member 112, the batwing distribution may hit the reflective member differently depending on the orientation of the prismatic structure of the optically transmissive sheet 103, such as the prism grooves 106, relative the asymmetric shape of the reflective member 112.

In Fig. 9a-b, it is shown that the modified batwing distribution is adjusted further when the optically transmissive sheet 103 is switched from a first position, shown in Fig. 9a, allowing a modified batwing distribution with an average beam shape of an angle i relative the angle 9=0°, into a second position, shown in Fig. 9b, allowing a modified batwing distribution with an average beam shape of an angle a₂ relative the angle 9=0°, wherein a₂ > a_{l s} as described in relation to Fig. 6.

A light emitting arrangement 100 according to any embodiment of the invention may be used in a lamp, a luminaire, a task light, a backlight, a streetlight or the like.

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. 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 light emitting arrangement (100) adapted to produce a batwing light distribution, comprising

- a solid state light source (101) adapted to emit light of a first wavelength range;

- a wavelength converting member (102) arranged to receive light of said first wavelength range emitted by the solid state light source and capable of converting light of said first wavelength range into light of a second wavelength range, said wavelength converting member and said solid state light source being mutually spaced apart; and

- an optically transmissive sheet (103), arranged to receive light from said solid state light source (101) and said wavelength converting member (102), said optically transmissive sheet comprising a first surface (104) facing towards said solid state light source and said wavelength converting member, and a second surface (105), parallel to said first surface (104), facing away from said solid state light source and said wavelength converting member,

wherein said first surface (104) comprises a prismatic surface structure.

2. A light emitting arrangement according to claim 1, wherein said prismatic surface structure is a pattern of linear prism grooves (106).

3. A light emitting arrangement according to claim 1, wherein said prismatic surface structure is a pattern of pyramids.

4. A light emitting arrangement according to claim 1, wherein said second surface (105) is a smooth surface.

5. A light emitting arrangement according to claim 1, wherein said optically transmissive sheet (103) is planar.

6. A light emitting arrangement according to claim 1, wherein there is no intermediate optically functional layer between said wavelength converting member (102) and said optically transmissive sheet (103).

7. A light emitting arrangement according to claim 1, wherein said optically transmissive sheet (103) comprises scattering elements (107).

8. A light emitting arrangement according to claim 1, comprising at least two stacked optically transmissive sheets, each comprising a first surface (104) facing towards said solid state light source and said wavelength converting member, and a second surface (105), parallel to said first surface (104), facing away from said solid state light source and said wavelength converting member, wherein the first surface (104) of each optically transparent sheet (103a, 103b) comprises a prismatic surface structure.

9. A light emitting arrangement according to claim 8, comprising a first optically transmissive sheet (103a) and a second optically transmissive sheet (103b), arranged in a stack and oriented so that the linear prismatic grooves (106a) of the first optically transmissive sheet (103 a) are perpendicular to the linear prismatic grooves (106b) of the second optically transmissive sheet (103b).

10. A light emitting arrangement according to claim 8, comprising a first optically transmissive sheet (103a) and a second optically transmissive sheet (103b), arranged in a stack and oriented so that the linear prismatic grooves (106a) of the first optically transmissive sheet (103 a) are parallel to the linear prismatic grooves (106b) of the second optically transmissive sheet (103b).

11. A light emitting arrangement according to claim 1 , further comprising a reflective member (112) having a tapering wall arranged to redirect light exiting from said optically transmissive sheet (103).

12. A light emitting arrangement according to claim 1, wherein said optically transmissive sheet (103) is rotatable in an in-plane direction of said optically transmissive sheet.

13. A light emitting arrangement according to claim 1, wherein said wavelength converting member (102) comprises a stack of wavelength converting layers (102a, 102b).

14. A light emitting arrangement according to claim 1, wherein said wavelength converting member (102) comprises a plurality of in-plane regions having different wavelength converting characteristics.

15. A luminaire comprising a light emitting arrangement according to claim 1.