WO2013057660A2

WO2013057660A2 - Light emitting arrangement

Info

Publication number: WO2013057660A2
Application number: PCT/IB2012/055629
Authority: WO
Inventors: Rifat Ata Mustafa Hikmet; Ties Van Bommel
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-10-21
Filing date: 2012-10-16
Publication date: 2013-04-25
Also published as: WO2013057660A3

Abstract

A light-emitting arrangement is provided, comprising - an elongated, at least partially transparent housing; - an array of light emitting diodes (LEDs) arranged in a longitudinal direction within said housing; and - an anisotropic scattering member arranged within said housing, in the path of light from said light emitting diodes to said housing. The light emitting arrangement of the invention is particularly suitable for use in a fluorescent tube replacement lamp, since the anisotropic scattering member may reduce the spotty appearance associated with known LED-based TL replacement lamps, and it may also prevent or reduce problems with glare.

Description

Light emitting arrangement

FIELD OF THE INVENTION

The present invention relates to the use of light emitting diodes (LEDs) with adapted light scattering characteristics, for use in an elongated lamp for replacement of fluorescent tubes.

BACKGROUND OF THE INVENTION

Fluorescent lamps, also referred to as TL lamps, are today widely used for general lighting, in particular for professional environments. Fluorescent lamps are gas discharge lamps in which mercury vapor is electrically excited to produce emission of UV light, which is subsequently converted to visible light by a fluorescent material. However, drawbacks of fluorescent lamps include health and environmental safety aspects, in particular due to the mercury content. Also, the efficiency of traditional fluorescent lamps is

undesirably low.

Replacement lamps using light-emitting diodes (LEDs) have been proposed in order to solve the above problems. In addition, the lifetime of LEDs is about five times the lifetime of a conventional fluorescent lamp. Using LEDs also avoids the flickering light and humming noises associated with fluorescent lamps. In LED based TL replacement lamps, an array of high power LEDs is arranged within a tubular housing, the LEDs being arranged at certain distances with respect to each other. However, this arrangement typically produces bright spots on the light-emitting surface, resulting in an undesirable spotty appearance, which may be unpleasant to a viewer.

WO 2011/005562 describes a fluorescent tube replacement lamp, for use in a conventional fluorescent tube fixture, comprising a tubular housing, a circuit board disposed within the housing, an array of LEDs arranged longitudinally on the circuit board, and a wavelength converting material arranged in contact with at least a portion of the tubular housing. The wavelength converting material is excited by light from the LEDs to produce visible light. A diffracting structure may also be provided on the interior of the tube;

however, a spotty appearance is still visible and the LEDs must be placed close to each other. SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this problem, and to provide a solution suitable for a fluorescent tube replacement lamp which has a more uniform, in particular less spotty, appearance.

According to a first aspect of the invention, this and other objects are achieved by a light emitting arrangement, typically for use as a fluorescent tube replacement lamp, comprising

- an elongated, typically tubular, at least partially transparent housing;

- an array of light emitting diodes (LEDs) arranged in a longitudinal direction within said housing typically on a support member; and

- an elongated anisotropic scattering member arranged within said housing, in the path of light from said light emitting diodes to said housing.

The light emitting arrangement of the invention is particularly suitable for use in an elongated luminaire, such as a TL replacement lamp, since the anisotropic scattering member may reduce or avoid the spotty appearance associated with known LED-based TL replacement lamps, and it may also prevent or reduce problems with glare. The anisotropic scattering member typically comprises an elongated member arranged lengthwise in said housing and aligned with said array of LEDs. The array of LEDs is typically mounted, via said support member, on or near an inner wall of said tubular housing.

The anisotropic scattering member typically comprises uniaxially aligned anisometric domains distributed in a transparent carrier material, which domains may be aligned in the longitudinal direction of the elongated scattering member or perpendicular (in plane) to the longitudinal direction of the scattering member. Light incident on the anisometric domains is scattered mainly along an imaginary axis perpendicular to the long axis of the anisometric domains. Hence, by adapting the orientation of the anisometric domains in relation to the longitudinal extension of the scattering member and the LED array, the direction of light scattering from the anisotropic scattering member can be controlled.

The anisometric domains have a refractive index nai and said transparent carrier material has a refractive index ¾ι . Typically, n_ci is different from nai . Each of said refractive indices may be anywhere between 1 and 2.

In embodiments of the invention, the scattering member (either the anisometric domains or the carrier material) may comprise an optically anisotropic material, for example a liquid crystal material. For example, the transparent carrier may be an optically isotropic polymeric material. In such embodiments, the optically isotropic carrier material may have a refractive index ¾ι , which is different from a refractive index nai of the anisometric domains.

Alternatively the transparent carrier material may comprise a uniaxially oriented optically anisotropic polymeric material. In such embodiments, the optically anisotropic material may have at least one refractive index n_ci which is different from nai .

In embodiments of the invention, said anisometric domains may comprise fibers or elongated particles. Alternatively, the anisometric domains may be elongated cavities e.g. filled with air or another inert gas.

In embodiments of the invention, said anisotropic scattering member may be arranged in on or near said LEDs, for example in direct contact with said LEDs. In alternative embodiments, said LEDs and said anisotropic scattering member may be arranged mutually spaced apart. For example, the anisotropic scattering member may be arranged centrally within said tubular housing or at a location between the center of the housing and said array of LEDs. The anisotropic scattering member may alternatively be arranged in direct contact with an inner wall of the housing. It is also contemplated that a combination of at least two anisotropic scattering members may be used, wherein one scattering member is arranged on or near the LEDs and one is arranged remotely from the LEDs.

In embodiments of the invention, the light emitting arrangement further comprises a wavelength converting material capable of converting light of a wavelength range emitted by the light emitting diodes into light of a different wavelength range, arranged in the path of light from said LEDs to said transparent housing. The wavelength converting material may be arranged at a distance from the array of light emitting diodes. Arranging the wavelength converting material remotely from the LEDs may prevent overheating of the wavelength converting material during operation of the LEDs, which may be particularly desirable where an organic wavelength converting material is used.

In embodiments of the invention, the anisotropic scattering member may comprise said wavelength converting material. Thus, a combined anisotropic scattering and wavelength converting member may be provided. The anisotropic scattering member may optionally comprise an anisotropic scattering layer and a wavelength converting layer.

In another aspect, the invention relates to the use of the light emitting arrangement as a fluorescent tube replacement lamp, i.e. use of the light emitting

arrangement in a luminaire of fitting adapted for a conventional fluorescent tube. The invention also relates to a luminaire which typically is a fluorescent tube replacement lamp, comprising a light emitting arrangement as described herein.

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. la shows a perspective view of tubular light emitting arrangement for use as a TL replacement lamp.

Fig. lb shows an exemplary structure of a scattering member according to embodiments of the invention.

Fig 2a is a cross-sectional side view of a light emitting arrangement according to embodiments of the invention, and Fig. 2b is a top view showing the resulting light beams.

Fig 3 is a cross-sectional side view of a light emitting arrangement according to other embodiments of the invention.

Fig 4 is a cross-sectional side view of a light emitting arrangement according to other embodiments of the invention.

Fig 5 is a cross-sectional side view of a light emitting arrangement according to other embodiments of the invention.

Fig 6a is a cross-sectional side view of a light emitting arrangement according to embodiments of the invention, and Fig. 6b is a top view showing the resulting light beams.

Fig 7a is a cross-sectional side view of a light emitting arrangement according to other embodiments of the invention, and

Fig 7b is a top view showing the resulting light beams.

Fig 8 a is a cross-sectional side view of a light emitting arrangement according to other embodiments of the invention, combining at least two scattering members, and

Fig 8b is a top view showing the resulting light beams.

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.

"Isotropy" refers to uniform physical properties in all directions; "anisotropy" means that at least one property, for example an optical property (then referred to as optical anisotropy) such as refractive index is not uniform (not the same) in all directions, i.e. it is dependent on the direction.

Furthermore, as used herein, "isometric" means uniform, direction- independent shape, meaning that an isometric object is symmetrical in all directions, whereas "anisometric" means that the physical shape of an object is not uniform (not symmetrical) in all directions. Hence, for an anisometric object, the dimensions along the x, y and z directions are not identical. As used herein, "uniaxially aligned domains" means that an axis, typically a longitudinal axis, of each domain points substantially in the same direction, i.e., the axes of all the domains are substantially parallel.

Fig. la illustrates a light emitting arrangement for use as a TL replacement lamp, which may be adapted to be attached to a conventional TL fixture. The light emitting arrangement 100 comprises a tubular housing 101 at least a part of which is transparent to allow emission of light in a light output direction. The housing contains an array of LEDs 102a, 102b etc on a printed circuit board (PCB) 103 (see Fig. 2a) mounted on the housing interior wall via a support member 104, in a longitudinal direction of the tubular housing. A scattering member 105 is provided over the LEDs, either directly on top of the LEDs (direct contact) as illustrated in Fig 2a, or at a certain distance from the LEDs in the light output direction (vicinity or remote configuration), as illustrated in Figs. 3-5 and described below. The scattering member is provided as a longitudinal strip aligned with the array of LEDs. The support member may optionally comprise a reflective surface, or the light emitting arrangement may additionally comprise reflective members arranged to increase the light output in the direction of the scattering member and prevent or avoid light absorption by the support member.

Fig. 2a shows a tubular light emitting arrangement 100 in cross-section. In this embodiment, the anisotropic scattering member 105 is arranged directly on the LED array 102. Fig. 2b is a top view of the LED array of Fig. 2a during operation of the LEDs, and shows the resulting light beam in a polar diagram. A possible structure of the anisotropic scattering member is schematically depicted in Fig. lb. The anisotropic scattering

member 105 comprises anisometric domains 107 distributed in a transparent carrier material 108. The anisometric domains are typically elongated, having a long axis and a short axis. The anisometric domains 107 and the carrier material 108 may differ with respect to refractive index. Due to the anisometry of the domains 107, the scattering of light is anisotropic, such that the scattered light 106 is to a large extent confined around one axis, as shown with opposing arrows in Fig. 2b. The axis of light scattering is perpendicular to the long axis of the anisometric domains of the scattering member. In the embodiments of Fig. 2- 5, the anisometric domains of the scattering member are oriented with their long axes aligned (pointing in the same in-plane direction) in the longitudinal direction of the scattering member 105 and the LED array 102, such that the axis of scattered light 106 is perpendicular to the LED array. This light distribution typically prevents or reduces glare.

Fig. 3 illustrates an embodiment where the scattering member 105 is arranged at a small distance from the LED array 102, notably at a location between the LED array and the centre of the tubular housing 101, and is wide enough to essentially bridge the tubular housing in cross-section at its location. The light distribution is similar to that illustrated in Fig. 2b. An advantage of the embodiment of Fig. 3 is that since the scattering member is arranged at a certain distance from the LEDs and thus is less exposed to heat generated by the LEDs during operation, this embodiments allows the use of less temperature resistant materials, for example a plastic film comprising the anisometric material. At the same time, a light exit window of up to 270° can be obtained.

Fig. 4 illustrates an embodiment of the light emitting arrangement where the scattering member 105 is arranged at a distance from the LED array, centrally within the tubular housing. In this embodiment the scattering member extends across the housing in the transversal direction. The light distribution as shown in a polar diagram is similar to that illustrated in Fig. 2b. By placing the scattering member farther away from the LEDs, less temperature resistant materials may be used, while still obtaining a light exit window of 180°. However, this embodiment may require a higher concentration of anisometric domains compared to the embodiments of Fig. 1 and Fig. 2.

Fig. 5 shows another embodiment where the scattering member 105 is applied on an inner surface of the tubular housing 101. The light distribution as shown in a polar diagram is similar to that illustrated in Fig. 2b. Figs. 6a-b and 7a-b show different embodiments of the light emitting arrangement in which an anisotropic scattering member 605, 705 is used mainly for preventing a spotty appearance. In these embodiments, the anisometric domains of the scattering member are rotated 90° in the plane compared to the embodiments of Figs. 2-5. Hence, in the embodiments of Fig. 6a-b and 7a-b, the anisometric domains of the scattering member are oriented with their long axes aligned (pointing in the same in-plane direction) perpendicular to the lengthwise extension of the scattering member and the array of LEDs 602a, 602b, 702a, 702b, such that the axis of scattered light 606 is in the direction of the LED array, as shown in Fig. 6b.

In analogy to Fig. 5, the spot-reducing orientation of the scattering member may be applied in an embodiment as shown in Fig. 7a-b, where the scattering member 705 is arranged as a layer or coating on an inner surface of the tubular housing 701. The

embodiment of Fig. 7a-b further comprises a wavelength converting material 707 provided as a layer on a surface of the scattering member 705 facing the LEDs. It is however possible to arrange a wavelength converting material directly on or close to the LED array 702, or in another remote configuration, e.g. centrally within the housing (as seen in cross-section, corresponding to the position of the scattering member in Fig. 4). The wavelength converting member may be arranged in the path of light between the LEDs and the scattering member, such that a portion of the light emitted by the LEDs is color converted before being reaching the anisotropic scattering member 705.

Furthermore, a glare-reducing scattering member providing light scattering essentially according to Fig. 2b may be used in combination with a spot-reducing scattering member providing light scattering essentially according to Fig. 6b. As illustrated in Fig. 8a-b, a glare-reducing scattering member 805a may be arranged in an inner surface of the tubular housing, and a spot-reducing scattering member 805b may be arranged directly on or in the vicinity of the LED array 802. As a result, light 806a is scattered in a direction perpendicular to the LED array, and light 806b is scattered in a direction along the LED array.

The anisotropic scattering member of the present invention may be formed as a sheet comprising anisometric domains contained in a transparent matrix. Typically, the refractive index of the anisometric domains is different from the refractive index of the transparent matrix. For instance, the scattering member may be a film produced by dispersing domains of a first isotropic polymeric material in a carrier phase of a second, different isotropic polymeric material, wherein the polymeric material are non-miscible and have different refractive indices. Subsequently the film is stretched in the longitudinal direction whereby the shape of the domains of the first polymeric material become elongated and thus anisometric.

The isotropic polymer material may act as a carrier for the anisometric material. The isotropic polymeric material may comprise for example PMMA,

polycarbonate, polystyrene, and/or fluorinated polymer.

The material of the anisometric domains may be a polymeric material which shows optical anisotropy such as poly(ethylene naphthalate) (PEN), poly(ethylene terephthalate) (PET), and typically has an optical axis oriented along the long axis of the anisometric domains.

Alternatively, an anisotropic scattering film may be produced by dispersing anisometric elements, such as elongated nanoparticles, nanorods or nanofibers of organic or inorganic material or cavities such as air gaps, in an isotropic polymer matrix. The anisometric elements typically have a refractive index that is different from the refractive index of the isotropic carrier. The anisometric elements may be oriented by various means. For example, the anisometric elements may be oriented by stretching the film. Alternatively, the anisometric elements may be oriented by applying the anisometric elements to a sheet having a groove structure (thus inducing orientation along the groove direction) and subsequently applying a filler material to cover the anisometric elements, wherein preferably the filler material is fluid and may optionally be solidified after application.

Anisotropic scattering can also be obtained by using a uniaxially oriented optically anisotropic polymer matrix such as poly(ethylene naphthalate) (PEN), poly(ethylene terephthalate) (PET), containing anisometric domains of another material or anisometric cavities, e.g. filled with air or a gas. The refractive index of the anisotropic matrix is different from that of the isometric domains.

In other embodiments, an anisotropic scattering film may comprise an anisotropic liquid crystal gel. For example, an anisotropic liquid crystal may be contained as a liquid in a polymer matrix. Optionally, the polymer matrix may be completely polymerized to form a solid, self-supporting film.

The scattering member may be polarization independent, and may scatter both polarization directions. However, in embodiments of the invention where the anisotropic scattering member comprises an optically anisotropic material, polarization dependent scattering can be observed. In such embodiments, only one of the refractive indices of the optically anisotropic material is different from the refractive index of the transparent isotropic matrix. The light emitting arrangement of the present invention may further comprise a wavelength converting material capable of converting light emitted by the LEDs into light of a second wavelength range. The wavelength converting material may be an inorganic phosphor. Examples of inorganic phosphors suitable for the wavelength converting material include, but are not limited to, cerium doped yttrium aluminum garnet (Y₃Al₅0i₂:Ce³⁺, also referred to as YAG:Ce or Ce doped YAG) or lutetium aluminum garnet (LuAG, Lu₃Al₅0i₂), a-SiA10N:Eu²⁺, and M₂Si₅N₈:Eu²⁺ wherein M is at least one element selected from calcium Ca, Sr and Ba. A preferred example of an inorganic phosphor that may be used in

embodiments of the invention, typically in combination with a blue light emitting light source, is YAG:Ce. Furthermore, a part of the aluminum of YAG:Ce may be substituted with gadolinium (Gd) or gallium (Ga), wherein more Gd results in a red shift of the yellow emission. Other suitable materials may include (Sri__x_yBa_xCay)₂-_zSi₅-_aAl_aN8-_aO_a:Eu_z ²⁺ wherein 0 < a <5, 0 < x <1, 0 < y < 1 and 0 < z < 1, and (x+y) < 1, such as Sr₂Si₅N₈:Eu²⁺ which emits light in the red range.] Alternatively, the wavelength converting material may comprise an organic phosphor material, typically perylene derivatives such as Lumogen^® F 083,

Lumogen^® F 170, Lumogen^® F 240, and/or Lumogen^® F 305.

In embodiments of the invention the wavelength converting material may comprise quantum dots. Quantum dots are small crystals of semiconducting material generally having a width or diameter of only a few nanometers. 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 easily 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 a very low cadmium content.

The wavelength converting material may be provided in the path of light from the LEDs to the scattering member. In embodiments of the invention, a wavelength converting material may be contained in the anisotropic scattering member. In particular, where an organic phosphor is used as the wavelength converting material it may be incorporated into a scattering member described above, which is typically arranged at a remote location from the LEDs, for example as illustrated in Figures 4 and 5. Alternatively or additionally, a wavelength converting material may be provided as a separate layer. For example, a combined anisotropic scattering and wavelength converting sheet may comprise a first, wavelength converting layer, and a second, anisotropic scattering layer. The combined sheet may be arranged on the interior wall of the housing, the wavelength converting layer facing the LEDs and the anisotropic scattering layer facing the housing.

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, 600, 700, 800) comprising

- an elongated, at least partially transparent housing (101, 601, 701);

- an array (102, 602, 702, 802) of light emitting diodes (LEDs) (102a, 102b, 602a, 602b, 702a, 702b, 802a, 802b) arranged in a longitudinal direction within said housing; and

- an elongated anisotropic scattering member (105, 605, 705, 805a, 805b) arranged within said housing, in the path of light from said light emitting diodes to said housing.

2. A light-emitting arrangement according to claim 1, wherein said anisotropic scattering member comprises uniaxially aligned anisometric domains (107) distributed in a transparent carrier material (108), said anisometric domains being aligned in the longitudinal direction of the elongated scattering member, or perpendicular to the longitudinal direction of the scattering member.

3. A light-emitting arrangement according to claim 2, wherein said anisometric domains has a refractive index nai and said transparent carrier material has a refractive index n_ci different from ndi.

4. A light-emitting arrangement according to claim 2, wherein the anisometric domains or the carrier material comprises an optically anisotropic material.

5. A light-emitting arrangement according to claim 2, wherein said anisometric domains comprise fibers or elongated particles.

6. A light-emitting arrangement according to claim 2, wherein said anisometric domains are elongated cavities.

7. A light-emitting arrangement according to claim 4, wherein the anisotropic scattering member comprises a liquid crystal material.

8. A light-emitting arrangement according to claim 1, wherein said anisotropic scattering member is arranged on or near said LEDs.

9. A light-emitting arrangement according to claim 1, wherein said LEDs and said anisotropic scattering member are arranged mutually spaced apart.

10. A light-emitting arrangement according to claim 9, wherein said anisotropic scattering member is arranged centrally within said tubular housing or at a location between the center of the housing and said array of LEDs.

11. A light-emitting arrangement according to claim 9, wherein said anisotropic scattering member is arranged in direct contact with an inner wall of said housing.

12. A light-emitting arrangement according to claim 1, further comprising a wavelength converting material (707) capable of converting light of a wavelength range emitted by the light emitting diodes into light of a different wavelength range, arranged in the path of light from said LEDs to said transparent housing.

13. A light-emitting arrangement according to claim 12, wherein said anisotropic scattering member comprises said wavelength converting material.

14. A light-emitting arrangement according to claim 12, wherein said anisotropic scattering member comprises an anisotropic scattering layer and a wavelength converting layer.

15. A luminaire, in particular a fluorescent tube replacement lamp, comprising a light emitting arrangement according to any one of the claims 1 to 14.