WO2012137126A1

WO2012137126A1 - Wavelength converting light-guide

Info

Publication number: WO2012137126A1
Application number: PCT/IB2012/051601
Authority: WO
Inventors: Ties Van Bommel; Rifat Ata Mustafa Hikmet; Roy Gerardus Franciscus Antonius Verbeek
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-04-07
Filing date: 2012-04-02
Publication date: 2012-10-11

Abstract

A light-guide (10, 12-24) configured to guide light through total internal reflection between a first face (107) and a second face (108) thereof; comprising a plurality of wavelength converting members (101) distributed across said light-guide and comprising at least one wavelength converting material configured to absorb light of a first wavelength and emit converted light of a second wavelength towards the second face; and a plurality of reflectors (100, 112, 113, 114, 115) each being arranged on a first side (104) of a respective one of said wavelength converting members (101), wherein said first side faces away from said second face (108) of said light-guide, thus shielding said wavelength converting members from a viewer (1) looking at said first face (107) of said light-guide.

Description

Wavelength converting light-guide

FIELD OF THE INVENTION

The present invention relates to a light-guide comprising a wavelength converting member and a reflector.

BACKGROUND OF THE INVENTION

Light-emitting diode (LED) based illumination devices are increasingly used for a wide variety of lighting 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.

Efficient high-power LEDs are often based on blue light emitting materials. A wavelength converting material, also known as a phosphor, may be employed to convert part of the blue light emitted by the LED into light of longer wavelengths and thereby affording a mixture of wavelengths corresponding to a desirable color output (e.g. white). In an illumination device, such phosphor material may be applied directly on the LED, or alternatively, in order to avoid heat conduction from the LED to the phosphor material, it may be arranged at a certain distance from the LED (so-called remote configuration).

WO 2010/052633 discloses a light guide wherein light is guided through total internal reflection at a front and rear surface of the light guide, and wherein the light guide comprises a plurality of outcoupling elements comprising a phosphor and arranged on the rear surface such that light is outcoupled from the front surface.

Light guides, such as the one disclosed in WO 2010/052633, comprising a phosphor material which is visible to a viewer, have a colored appearance, even when the LEDs are not operated. In some cases this may not be desirable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved wavelength converting light-guide, in particular having a reduced colored appearance.

According to a first aspect of the invention, this and other objects are achieved by a light-guide configured to guide light through total internal reflection between a first face and a second face thereof, comprising a plurality of wavelength converting members distributed across the light-guide and comprising at least one wavelength converting material configured to absorb light of a first wavelength and emit converted light of a second wavelength towards the second face; and a plurality of reflectors, each being arranged on a first side of a respective one of the wavelength converting members, wherein the first side faces away from the second face of the light-guide, thus shielding the wavelength converting members from a viewer looking at the first face of the light-guide.

The first wavelength is typically different from the second wavelength.

By the term "light-guide" as used herein, should be understood an optical element which is at least partly transmissive to light of at least one wavelength within the wavelength range including visible, infrared and ultra-violet light, and the light-guide may thus typically be made of any suitable material known to the skilled person in the art, for example a polymer based material.

The light-guide may be arranged in a light-emitting device comprising a reflective member which may be arranged at an outer side of the second face of the light- guide, for example along the extent of the second face of the light-guide, such that light that is emitted from the wavelength converting member and/or reflected at the reflectors and subsequently outcoupled from the second face, is reflected at the reflective member back (through the second face) towards the first face, and thus ensuring that light exits from a desired first face of the light-guide, i.e. in the direction of a viewer. The above described arrangement of a reflective member is also advantageous as it allows for further interactions between the reflected light and the wavelength converting members, which in turn may increase the amount of light of the first wavelength converted by the wavelength converting members, and consequently improving the efficacy of such device.

By arranging a reflector on the first side of each wavelength converting member, the wavelength converting members are not visible to a viewer looking at the first face of the light-guide and so the color appearance of the light-guide due to any interaction between ambient light and the wavelength converting members is reduced, whereas at the same time, by means of a reflective member as described above, light may be outcoupled from this first face towards the viewer.

In embodiments of the light-guide according to the invention, the light-guide may comprise at least one reflective member arranged on a second side of the wavelength converting members, wherein the second side of the wavelength converting members is opposite the first side thereof. In embodiments of the light-guide according to the invention, the light-guide may comprise a plurality of reflective members each being arranged on the second side of a respective one of the wavelength converting members. Thus, each wavelength converting member may be sandwiched between a reflector and a reflective member and thereby a partly transparent light-guide having reduced color appearance from the both a first and a second face thereof may be achieved.

In embodiments of the present invention, the wavelength converting member may comprise a second wavelength converting material typically configured to absorb light of a first wavelength and emit converted light of a third wavelength. Alternatively, the second wavelength converting material may be configured to absorb light of a wavelength different from the first wavelength and emit converted light of the second wavelength.

The third wavelength is typically different from the first wavelength and the second wavelength.

In embodiments of the invention, the first wavelength may be in the range of from 380 to 520 nm, such as, for example, from 440 to 480 nm.

In embodiments of the invention the first and/or second wavelength converting material may comprise an organic luminescent molecule such as a perylene derivative.

In embodiments of the invention the first and/or second wavelength converting material may comprise an inorganic luminescent material such as cerium doped yttrium aluminum garnet (YAG) or lutetium aluminum garnet (LuAG).

In embodiments of the invention the first and/or second wavelength converting material may comprise quantum dots.

Furthermore, the light-guide according to the invention may be comprised in a light-emitting device further comprising at least one light-source arranged at an incoupling face of the light-guide, wherein the incoupling face is arranged to receive light from the light- source such that total internal reflection at the first and second face of the light-guide is enabled.

The light-guide according to the invention may be comprised in a light- emitting device, further comprising a plurality of light-sources, each being arranged between the first side of a respective one of the wavelength converting members and a respective one of the reflectors.

In embodiments of the invention, the light-emitting device may comprise a reflective member arranged on an outer side of the second face of the light-guide such that light outcoupled from the first face of the light-guide may be reflected back into the light- guide and subsequently outcoupled from the first face of the light-guide. Such reflective member may be arranged directly on the outer side of the second face, or alternatively, arranged at a distance therefrom. In the latter case, the reflective member may be separated from the outer side of the second face by any medium or material, however, preferably a transparent medium or material such as, for example, air or a polymeric material, whose refraction index is lower than that of the core material of the light-guide such that light can be guided in the light-guide by means of total internal reflection at the second face.

In embodiments of the invention the reflectivity of the reflective member may, for example, be at least 60%, preferably at least 80%, and more preferably at least 90%.

According to embodiments of the invention, the light-source(s) may preferably comprise at least one solid state light-source such as a LED or a laser.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing exemplary embodiment(s) of the invention, wherein:

Figs la-n show a cross-sectional side view of embodiments of the light-guide according to the invention; and

Figs 2a-d show a cross-sectional side view of embodiments of the light- emitting device according to the invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

In the following description the present invention is described with reference to a light-guide comprising wavelength converting members which are at least partly shielded from a viewer thereof by reflectors.

Figs, la-n show exemplary embodiments of the light-guide according to the invention. Fig la shows a light-guide 10 configured to guide light emitted from a light-source (not shown) through total internal reflection between a first face 107 and a second face 108 thereof. The core body 102 of the light- guide may preferably be made of any translucent or transparent material such as, for example, any suitable polymeric material such as polymethylmethacrylate (PMMA) or glass or a fluid. In Fig. la, the light-guide 10 comprises a plurality of wavelength converting members 101 arranged on an outer side 106 of the first face 107 of the light guide, wherein each wavelength converting member 101 comprises at least one wavelength converting material configured to absorb light of a first wavelength and to emit converted light of a second wavelength. The light-guide in Fig. la further comprises a plurality of reflectors 100, each being arranged on a first side 104 of a respective one of the wavelength converting members 101, wherein the first side 104 faces away from the second face 108 of the light-guide 10, thus shielding the wavelength converting members 101 from a viewer 1 looking at the first face 107 of the light-guide 10. In embodiments of the invention the reflectors 100 may be provided directly on the first side 104 of each wavelength converting member, for example by providing a reflective coating thereon. Alternatively, in embodiments of the invention, the reflectors 100 may be arranged at a distance from the wavelength converting members 101, on the first side 104 thereof, such that at least a portion of the wavelength converting members is shielded by the reflectors 100.

As is exemplified in Figs. lb-i, many different configurations of the wavelength converting members and each respective reflector comprised in the light-guide are possible. In figs, lb-c the wavelength converting member 101 is arranged on the outer side 106 of the first face 107 of the light guide 12, 13 and the reflector 112, 113 is arranged to cover the first side 104 of the wavelength converting member 101 as well as at least one of a vertical side 118 thereof, whereas in the light-guides 14, 15 shown in Figs, ld-e, the first side 104 and both vertical sides 118 are coated with the reflector 114, 115. Furthermore, as shown in Fig. le, two wavelength converting members 101 can be enclosed by a reflector 115. Figs, lf-i show further exemplary embodiments of various possible arrangements of the wavelength converting members 101 and reflectors 100 in the light-guides 16-19. In Fig. If the reflector 100 is arranged on the outer side 106 of the first face 107 of the light-guide 16, whereas a respective wavelength converting member 101 is arranged on a corresponding inner side 109 of the first face 107 of the light-guide 16. In Figs, lg-i the reflector 100 is arranged on a first side 104 of the wavelength converting member 101, both of which are arranged in between the first 107 and second 108 face of the light-guide 17, 18, 19. In Fig. lg the reflector 100 is arranged on an inner side 109 of the first face 107, and in Fig li the wavelength converting member is arranged on an inner side 110 of the second face 108 of the light-guide 19. Also, as shown in Fig lh, the reflector 100 and the wavelength converting member 101 arranged thereon may be disposed in the core body 102 of the light-guide.

Furthermore, the light-guide may comprise a plurality of reflective members 117 as shown Figs, lj-n, having a similar size as that of the reflectors 100 and wherein each reflective member 117 is arranged on a second side 103 of a respective wavelength converting member 101 such that each respective wavelength converting member 101 is at least partly arranged in between the reflector 100 and reflective member 117. The reflective member 117 may be arranged in between the first face 107 and second face 108 of the light guide 20-24, for example, arranged on the inner side 110 thereof (Figs, lj-1), or arranged on the outer side 111 thereof (Fig. lm), or arranged such that each respective wavelength converting member 101 is sandwiched in between and in direct contact with the reflector 101 and reflective member 117, respectively, which arrangement is embedded within the core body 102 of the light-guide 24 (Fig In). (As is also shown in Figs, lj-n, the arrangement of the reflector 100 and wavelength converting member 101 may vary as exemplified in the Figs. f-i). The reflector may be arranged on the first side 104 of the wavelength converting member 101 such that a second side 105 thereof, opposite the first side 104, faces the reflective member 117 (Fig. lj), or the wavelength converting

member 101 may be arranged on the second reflector 117 to face the reflector 100 (Fig. Ik), or alternatively, a first wavelength converting member 101 may be arranged on the reflector 101 and a second wavelength converting member 101 may be arranged on the second reflectorl l7, such that the two wavelength converting members 101 face each other (Fig. 11).

It should be further noted that in embodiments of the light-guide, each wavelength converting member may comprise a plurality of different wavelength converting materials of which each one may be configured to absorb and emit light, respectively, of any desirable wavelengths.

Fig. 2a shows a light-emitting device 200 according to one embodiment of the invention. The light-emitting device 200 comprises the light-guide according to the invention and a light-source 201 arranged at an incoupling face 204 of the light-guide such that the received light may be guided in the light-guide by means of total internal reflection at the first 107 and second 108 face thereof.

The light-emitting device may advantageously comprise a reflective member 205 arranged along the longitudinal extend of the light-guide to reflect light that is outcoupled from the second face 108 of the light-guide.

Accordingly, light of a first wavelength, which is emitted from the light- source 201 and guided in the light-guide, may be absorbed by the wavelength converting members 101 and emitted therefrom in such directions that at least a portion of the converted light is refracted through the second face 108 of the light-guide, that is, at least a portion of the light emitted directly from the wavelength converting member 101, or via a first reflection at the reflector 100, corresponds to an angle of incident at the second face 108 of the light-guide at which total internal reflection is not allowed (and so light is refracted through). The refracted light is then reflected at the reflective member 205 back into the core body 102 of the light-guide such that light finally exits through the first face 107 thereof, i.e. in the direction of a viewer 1. Thereby, a viewer 1, looking at the first face 107 of the light- guide, which light-guide is comprised in the light-emitting device 200, can, on the one hand, observe the outcoupled light from the first face 107, but cannot, on the other hand, discern the light converting members 101 of the light-guide, and so from the viewer's point of view, i.e. from the first face 107, the light-guide will appear to have less color in ambient light, i.e. when light-source 201 is not operated.

Fig. 2b shows a light-emitting device 202 comprising the light-guide according to the invention and a plurality of light-sources 201 each being arranged between the first side 104 of a respective one of the wavelength converting members 101 and a respective one of the reflectors 100. Thus, according to this embodiment of the light-emitting device 202, light of a first wavelength may be emitted by a plurality of light- sources 201 embedded in the core body 102 of the light- guide and configured such that a least a portion of the emitted light therefrom is either directly, or via a first reflection at the reflector 100, absorbed by the respective one of the wavelength converting members 101, which in turn emits light such that at least a portion is directly, or via a reflection at the reflective member 205, outcoupled from the first face 107 of the light-guide. Given that the plurality of light-sources 201 are arranged across the longitudinal extent of the light-guide, an even outcoupling of light from first face thereof may be achieved (without the need of guiding light therein through total internal reflection).

Typically, the light-source emits light of a first wavelength in the range of from 380 to 520 nm.

The light- sources of the light-emitting device may typically comprise at least one solid light source such as a LED or a laser, emitting light in the ultraviolet, violet and/or blue part of the spectrum.

As is exemplified in Figs. 2b-c many arrangements of the plurality of light- sources with the respective reflectors and wavelength converting members are possible. For example, the reflector 100 and the respective light-source 201 may either be arranged on the outer side 106 (Fig. 2b) or the inner side 109 (Fig. 2c) of the first face 107 of the light-guide.

Further, as is illustrated in Fig 2d, the reflector 100 may be shaped as a dome 208, which may be arranged on the first side 104 of a respective one of the wavelength converting members 101 such that all light emitted from a respective one of the light- sources 201 enclosed therein must pass through the wavelength converting member 101 before being outcoupled from the light-guide. Thereby, increasing the amount of light of a first wavelength which is converted to a second wavelength by the wavelength converting members.

The reflective member 205 may be arranged directly on the outer surface 111 of the second face 108 of the light-guide as shown in Fig 2d, or as depicted in Figs. 2a-c, arranged at a distance therefrom. For example, there may be provided a material 206, such as a polymeric material, on the outer side 111 of the second face 108 on which material the second reflector 206 may be arranged, or the space between the second face 108 and the second reflector 205 may comprise of a gaseous atmosphere, for example, filled with air. In any case, in order to enable total internal reflection at the interface of second face 108 of the light-guide such material or medium 206 should have a lower refraction index compared to the core material 102 of the light-guide. Furthermore, in the embodiments of Figs. 2a-d, reflective member 205 may exhibit specular reflection or diffuse reflection, such as exhibiting Lambertian reflectance.

In embodiments of the invention, the first and the second wavelength converting material comprised in the wavelength converting members may be of any suitable luminescent materials comprising, for example, organic luminescent molecules such as perylene derivates including commercially available "Red F305", "Yellow F083" or "Yellow F170", "Orange F240", "Blue F650" and "Violet F570", and/or inorganic luminescent materials such as YAG, LuAG, ECAS, BSSN, and/or quantum dots such as InP, CdSe, or any combinations thereof.

Furthermore, in embodiments of the invention the reflective member(s)/ reflector(s) may be of any suitable reflective material(s) including, for example, scattering materials comprising Ti0₂ and A1₂0₃ particles, aluminum and silver reflective layers, and/or white polyethylene terephtalate (PET) in form of so-called microcellular reflective sheet (MCPET).

Typically, the reflectivity of the reflective member(s)/ reflector(s) may be at least 60%, more preferably at least 80%, and most preferably at least 90%. However, it should be noted that a small amount of light may be transmitted through the reflective member(s)/ reflector(s).

Typically the reflective member(s)/ reflector(s) may have a size in the range of from 1 μιη to 1 mm.

The person skilled in the art realizes that the present invention by no means is limited to the exemplary embodiments described above as 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. For example, different lighting applications may need complex configurations of wavelength converting members and/or the reflective member(s)/ reflector(s). Further, in order to achieve an homogeneous light extraction from the light guide the configurations of wavelength converting members and/or the reflective member(s)/ reflector(s) may differ in terms of, for example, size, pattern and pitch.

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. A single processor or other unit may fulfill the functions of several items recited in the claims. 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-guide (10, 12-24) configured to guide light through total internal reflection between a first face (107) and a second face (108) thereof, comprising:

a plurality of wavelength converting members (101) distributed across said light-guide and comprising at least one wavelength converting material configured to absorb light of a first wavelength and emit converted light of a second wavelength towards said second face; and

a plurality of reflectors (100, 112, 113, 114, 115) each being arranged on a first side (104) of a respective one of said wavelength converting members (101), wherein said first side faces away from said second face (108) of said light-guide, thus shielding said wavelength converting members from a viewer (1) looking at said first face (107) of said light- guide.

2. The light-guide (20-24) according to claim 1, comprising at least one reflective member (117) arranged on a second side (103) of said wavelength converting members (101), wherein said second side of said wavelength converting members is opposite said first side (104) thereof.

3. The light-guide (20-24) according to claim 2, comprising a plurality of reflective members (117) each being arranged on said second side (103) of a respective one of said wavelength converting members (101).

4. The light-guide (10, 12-24) according to any one of the preceding claims, wherein at least one of said wavelength converting members (101) comprises a second wavelength converting material configured to absorb light of the first wavelength and emit converted light of a third wavelength towards said second face.

5. The light-guide (10, 12-24) according to any one of the preceding claims, wherein said first wavelength converting material comprises an organic luminescent molecule.

6. The light-guide (10, 12-24) according to any one of the preceding claims, wherein said first wavelength converting material comprises an inorganic luminescent material.

7. The light-guide (10, 12-24) according to any one of the preceding claims, wherein said first wavelength converting material comprises quantum dots.

8. The light-guide according (10, 12-24) to any one of the preceding claims, wherein said first wavelength is in the range of from 380 to 520 nm.

9. A light-emitting device (200), comprising the light-guide (10) according to any one of preceding claims and at least one light-source (201) arranged at an incoupling face (205) of the light-guide, wherein said incoupling face is configured to receive light from said light-source such that total internal reflection at said first (107) and second (108) face of said light-guide is enabled.

10. A light-emitting device comprising the light-guide according to any one of claims 1 to 8, and a plurality of light-sources (201), each being arranged between said first side (104) of a respective one of said wavelength converting members and a respective one of said reflectors (100).

11. The light-emitting device (200, 202, 206, 207) according to claim 9 or 10, comprising a reflective member (205) arranged on an outer side (111) of said second face (108) of said light-guide, to reflect light that is outcoupled from said second face such that said outcoupled light is redirected back into the light-guide.

12. The light-emitting device (200, 202, 206, 207) according to claim 11, wherein the reflectivity of said reflectors (100, 112, 113, 114, 115, 117) and said reflective

member (205) is at least 60%.

13. The light-emitting device (200, 202, 206, 207) according to claim 12, wherein the reflectivity of said reflectors (100, 112, 113, 114, 115, 117) and said reflective

member (205) is at least 80%.

14. The light-emitting device (200, 202, 206, 207) according to claim 13, wherein the reflectivity of said reflectors (100, 112, 113, 114, 115, 117) and said reflective member (205) is at least 90%.

15. The light-emitting device (200, 202, 206, 207) according to any one of claims 9 to 14, wherein said light-source comprises at least one solid state light-source (201) such as a LED or a laser.