Light conversion devices and lighting devices

Abstract

Lighting devices for providing a secondary light with high luminance are provided. The lighting devices include a light conversion element and a light emitting unit with a light source that emits a primary light. The light conversion element has a front side illuminated with the primary light and, in response to the primary light, to emit a secondary light from the front side. The secondary light has a larger wavelength than the primary light.

Claims

1. A lighting device that provides a secondary light with high luminance, comprising: a light emitting unit with a light source and with an exit opening, the light emitting unit being configured to provide primary light along a beam path; and a light conversion element with a front side arranged in the beam path, the light conversion element being configured to, in response to the primary light, to emit the secondary light, the secondary light having a wavelength and/or wavelength range that differs from the primary light, wherein the light conversion element comprises a material that emits the secondary light via one or more of scattering, absorption, and/or conversion, wherein the front side has a primary light receiving surface where the front side is illuminated with the primary light, a primary light emitting surface that is formed when the front side is illuminated with the primary light, and a secondary light emitting surface within which the front side emits the secondary light, and wherein the light emitting unit is arranged so that the primary light is irradiated onto the light conversion element along an optical axis that has an angle greater than 60 degrees with respect to either a normal-line axis of the light conversion element or an axis of the secondary light.

2. The lighting device of claim 1, wherein the secondary light emitting surface emits light of a longer wavelength than a wavelength of the primary light, and wherein the secondary light emitting surface is larger than the primary light emitting surface.

3. The lighting device of claim 1, wherein the light conversion element comprises a ratio of a diameter of the primary light receiving surface to a thickness of the light conversion element of 2:1 or less.

4. The lighting device of claim 1, wherein the light conversion element comprises a ratio of a diameter of the primary light receiving surface to a thickness of the light conversion element of 1:4 or less.

5. The lighting device of claim 1, comprising a luminance of the secondary light that is at least 1000 cd/mm.sup.2.

6. The lighting device of claim 1, wherein the light emitting unit is configured so that the primary light is blue primary light having a wavelength of 450±10 nm and the light conversion element is configured so that the secondary light is white secondary light.

7. The lighting device of claim 1, wherein the light source comprises a diode laser with a laser power in a range selected from a group consisting of between 0.1 to 100 watts, between 0.1 to 100 watts, and between 5 to 8 watts.

8. The lighting device of claim 1, wherein the light emitting unit further comprises an optical element or an optical component between the light source and the light conversion element.

9. The lighting device of claim 8, wherein the optical element or the optical component comprises a lens configured to bundle the primary light on the primary light receiving surface.

10. The lighting device of claim 1, wherein the light emitting unit further comprises a light guide configured to emit the primary light on the primary light receiving surface.

11. The lighting device of claim 10, wherein the light source comprises a plurality of light sources that are combined in the light guide to reduce a size of the primary light receiving surface.

12. The lighting device of claim 1, further comprising a base body having a cooling element on one side and the light conversion element at an opposite side.

13. The lighting device of claim 12, further comprising a reflector on the opposite side and the cooling element on the reflector.

14. The lighting device of claim 1, further comprising secondary optics downstream of the light conversion element that captures the secondary light.

15. The lighting device of claim 1, wherein the light emitting unit is arranged so that the primary light has a range of scatter around the optical axis of ±5 degrees.

16. The lighting device of claim 1, wherein the primary light emitting surface is larger by a factor of 1.1 or more than the primary light receiving surface.

17. The lighting device of claim 1, wherein the primary light emitting surface and/or the secondary light emitting surface comprises an entire area of the front side.

18. The lighting device of claim 1, wherein the secondary light, in a hot operating state of the lighting device, lies in an ECE range.

19. The lighting device of claim 1, wherein the primary light receiving surface comprises a size and wherein said size is 1 mm.sup.2 or less.

20. The lighting device of claim 1, wherein reflectances at the light conversion element are not emitted together with or at a similar angle or a same angle to the secondary light from the light conversion element.

21. A lighting device that provides a secondary light with high luminance, comprising: a light emitting unit with a light source and with an exit opening, the light emitting unit being configured to provide primary light along a beam path; and a light conversion element with a front side arranged in the beam path, the light conversion element being configured to, in response to the primary light, to emit the secondary light, the secondary light having a wavelength and/or wavelength range that differs from the primary light, wherein the light conversion element comprises a material that emits the secondary light via one or more of scattering, absorption, and/or conversion, wherein the front side has a primary light receiving surface where the front side is illuminated with the primary light, a primary light emitting surface that is formed when the front side is illuminated with the primary light, and a secondary light emitting surface within which the front side emits the secondary light, wherein the secondary light emitting surface is larger than the primary light receiving surface, and wherein the light conversion element comprises a ratio of a diameter of the primary light receiving surface to a thickness of the light conversion element of 2:1 or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in detail below on the basis of several figures.

(2) FIG. 1 a lighting device known from the prior art, in which a light conversion element (converter) is utilized in transmittance operation,

(3) FIG. 2 a lighting device in which a converter is utilized in remission operation,

(4) FIG. 3 a lighting device with cooling elements,

(5) FIG. 4 a view from the top onto a light conversion element,

(6) FIG. 5 a side sectional view of a lighting device with a plurality of light sources,

(7) FIG. 6 a side sectional view of a lighting device with a fiber element,

(8) FIG. 7 a side sectional view of a lighting device with an optical element,

(9) FIG. 8 a side sectional view of a lighting device with secondary light optics (for example, a headlight), and

(10) FIG. 9 luminances obtained using a device according to the invention.

DETAILED DESCRIPTION

(11) FIG. 1 shows a known lighting device 10, which is designed for transmittance operation. The lighting device 10 comprises a light emitting unit 20, with which primary light 25 is beamed onto the back side 32 of a light conversion element 30. Accordingly, the light conversion element 30 receives the primary light 25 on the back side 32, and emits a secondary light 35 on the front side 31.

(12) FIG. 2 shows another lighting device 100, which is designed for remission operation or reflectance operation. The light emitting unit 200 beams primary light 250 onto the front side 310 of the light conversion element 300, whereby the front side is illuminated in the region of a primary light receiving surface 330, (compare, for example, FIG. 4). The light conversion element 300 emits the secondary light 350 on the front side 310, preferably in the region of the entire front side 310 or in the region of a secondary light emitting surface 340 (see, for example, FIG. 4).

(13) FIG. 3 shows a lighting device 100 having a light conversion element 300, which is arranged on a base body 120. On its back side, the base body 120 has cooling elements 122 in the form of cooling ribs. The light emitting unit 200 provides primary light 250, which can radiate onto the primary light receiving surface 330 on the front side 310 of the light conversion element 300. The light emitting unit 200, that is, for example, a laser light source, is arranged on the front side 310 at an angle to the normal line 110, such as, for example, at an angle of 60 degrees to the normal line 110. For example, the light also impinges at an angle to the normal line 110 on the front side of the light conversion element 300, such as, for example, in a angular range of 60±10 degrees.

(14) FIG. 4 shows a top view onto a light conversion element 300 with an outlined primary light receiving surface 330, a primary light emitting surface 332, and a secondary light emitting surface 340. The primary light emitting surface 332 is slightly larger and, furthermore, is configured such that the primary light emitting surface 332 completely encloses the primary light receiving surface 330. This is not necessary and is solely a readily understood design. In the region of the primary light emitting surface 332, primary light is emitted from the surface 310 of the light conversion element 300. For example, light that is emitted from the primary light emitting surface 332 is light of the same wavelength as the primary light 250 that is irradiated onto the primary light receiving surface 330 and, for example, is emitted as a beam of light at the front side 310 based on reflectance. For example, on its front side 310, the light conversion element 300 has a degree of reflectance of 2% for the incident beam of primary light 250 for the assumed angle of 60±5 degrees.

(15) Furthermore, the secondary light emitting surface 340, within which the secondary light 350 that is produced or converted in the light conversion element 300 is emitted, is arranged on the light conversion element 300. The three outlined regions, primary light receiving surface 330, primary light emitting surface 332, and secondary light emitting surface 340, typically overlap; in one example, as is shown in FIG. 4, they are arranged so that the primary light emitting surface 332 comprises the primary light receiving surface 330, and is arranged approximately concentric thereto. Further, as is also shown in FIG. 4, the secondary light emitting surface 340 can comprise or enclose the primary light receiving surface 330 and/or the primary light emitting surface 332.

(16) The light conversion element 300 or also the phosphor is typically provided as an yttrium aluminum garnet YAG.

(17) FIG. 5 shows an embodiment of the lighting device 100 having a light emitting unit 200 with a plurality of light sources 202, 204, 206, which jointly illuminate the primary light receiving surface 330. In this example, each light source 202, 204, 206 comprises a diode laser. The second diode laser 204 is arranged adjacent to the first diode laser 202 and irradiates into the light conversion element 300 at a slightly altered angle of irradiation. It is clear that the second diode laser 204 can also be arranged spatially behind the first diode laser 202 and then can irradiate a beam of light into the light conversion element 300 at an identical angle when this is advantageous. In this example, the third diode laser 206 is optional and is therefore illustrated with dotted lines; it is arranged on an opposite-lying side in relation to the first diode laser 202. In spatial arrangement, it is possible to arrange all of the light sources 202, 204, 206 in such a way that all of them irradiate a beam of light at the same angle or at a similar angle into the primary light receiving surface 330, because the degree of reflectance of the front side 310 depends on the angle of irradiation, as needed, so that, for different angles of irradiation, the degree of reflectance could increase and, as a result, more radiant power would be lost or less radiant power of the primary beam of light 250 would be available for the production of the secondary beam of light 350.

(18) FIG. 6 shows another embodiment of the lighting device 100, whereby—as is the case for all figures of this application—it applies that the same reference numbers show the same or at least similar objects. The three light sources 202, 204, 206 of the light emitting unit 200 are arranged adjacent to one another and couple into a light guide 210. In this example, the three light sources 202, 204, 206 couple into the free beam, although an in-coupling via three separate light guides and a bundling within the light guide 210 is also technically feasible. Each of the light sources 202, 204, 206 thus emits a partial primary light 244, 246, 248, which is bundled in or bundled by the light guide 210 to form the bundled primary light 350. This bundled primary light 350 is directed from the light emitting unit 200 or from the light guide 210 onto the primary light receiving surface 330. By means of the light guide 210, it is possible to arrange the distance of the exit opening 212 of the light guide 210 even more precisely and, in particular, even closer to the front side 310 of the light conversion element 300. Thus, the light guide 210, for example, is made with a smaller diameter than that of a light source 202, 204, 206 and, for this reason, has less interference in the region of emission of the secondary beam of light 350. By means of the light guide 210, it is also possible to adjust a variable distance between the exit opening 212 of the light guide 210 and the primary light receiving surface 330 and for the distance to be variably adjustable as needed in an automated manner. Thus, through the variable adjustment of the distance d between the exit opening 212 and the primary light receiving surface 330, it is potentially possible to compensate for any shift in color or for any shifting or degrading of the power. This connection between the distance d and the emitted power of the light conversion element will be illustrated more clearly on the basis of FIG. 9.

(19) Furthermore, FIG. 6 shows an alternative embodiment to the cooling element 122 on the back side of the base body 120. Here, it is a full-surface copper body 124 arranged for further transfer or dissipation of the heat that is introduced into the light conversion element 300. Furthermore, it would also be possible to arrange another form of cooling 122 on the back side of the base body 120, such as, for example, a fluid cooling and, for example, also a liquid cooling, in order to dissipate the heat from the light conversion element 300.

(20) FIG. 7 shows another embodiment of the lighting device 100, whereby the light emitting unit 200 comprises a first, second, and third light source 202, 204, 206 and the light sources couple the respective partial primary light 244, 246, 248 into an optical light guide 210. An optical element 220 is consequently arranged in the exit opening 212 of the light guide in the beam path of the primary light 250 and, in this case, is a converging lens. The optical element 220 bundles the primary light 250, so that the size of the primary light receiving surface 330 on the light conversion element 300 can be adjusted or reduced in size. Through the reduction in size of the primary light receiving surface 330, it is also possible to reduce in size the secondary light emitting surface 340. The light flux of the secondary light 350 that leaves the secondary light emitting surface 340 is thereby concentrated. It is therefore possible to achieve a higher luminance of the secondary light 350.

(21) The size of the secondary light emitting surface 340 as a function of the size of the primary light receiving surface 330 can also be adjusted, however, in the case of the previously described embodiments of FIGS. 3, 5, 6 or also in the case of FIG. 8 by, for example, adjusting or altering the distance of the exit opening 214 of the light emitting unit 200 or the exit opening 212 from the light conversion element 300. Furthermore, it is also possible to fix or to influence an exit angle of the primary light 250 out of the exit opening 212, 214 in order to adjust the irradiated primary light receiving surface 330. The size of the secondary light emitting surface is also determined by, among other things, the material composition, the density, the thickness, the scattering properties, and the temperature. For example, the light emitting surface increases with increasing scattering of the material.

(22) FIG. 8 shows yet another embodiment of the lighting device 100 having a light emitting unit 200, which comprises a laser source 202 and an optical element 220 in order to provide the high-density primary light spot 330 on the light conversion element 300. The laser source 202 is arranged in FIG. 8 in such a way that it radiates the beam of primary light 250 onto the light conversion element 300 at an angle of 60 degrees to the normal line 110.

(23) The secondary light 350 exits from the light conversion element 300 in a large solid angle, such as, for example, in a cone-shaped solid angle that centrally encloses the normal line 110 at an angle of 30 degrees, or also, for example, 45 degrees. In this cone, which, for example, can also be 60 degrees relative to the normal line 110 or 80 degrees relative to the normal line 110, the luminous flux of the secondary beam of light 350 that is emitted from the light conversion element 300 is therefore distributed approximately uniformly. In this example, only a portion of the emitted luminous flux of the secondary beam of light 350 enters the secondary optics 352, in which the light can be further processed in order to be formed into an output beam 354, such as, for example, into a headlight beam of a motor vehicle headlight. In other words, only a portion of the amount of light 350 produced in the secondary light emitting surface 340 enters the secondary optics 352 and, accordingly, only a portion of the secondary light 350 is used for producing the output beam 354. More precisely, the secondary light 350 is directed from only a portion of the secondary emitting surface 340 into the secondary optics 352, whereas the remaining portion of the secondary emitting surface 340 radiates out a beam of the secondary light 350 in another direction, where it is not received by the secondary optics 354 and transmitted further.

(24) FIG. 9 shows the achievable luminances of the secondary light 350 that can be produced using a light conversion element 300 versus the distance of the exit opening 212, 214 from the primary light receiving surface 330 for different operating currents of the light emitting unit 200 used at an operating temperature of 25° C. The operating currents are 500 mA, 1000 mA, 1500 mA, 2000 mA, 2100 mA, 2200 mA, 2300 mA, 2400 mA, 2500 mA, 2600 mA, and 2700 mA. For all of the curves illustrated, it can be seen, first of all, that they show a decreasing luminance with increasing distance. This can be explained by the fact that, with increasing distance of the exit opening 212, 214 from the primary light receiving surface 330, owing to spreading of the primary light beam 250, a larger primary light receiving surface 330 is illuminated, as a result of which the produced luminance of the secondary light 350 decreases. For decreasing distance, however, at and above an operating current of 2100 mA, there results an irregular course of the curve in the direction of smaller distances, so that the luminance decreases as the distance decreases.

(25) This can be explained by the occurrence of quenching, during which the incident energy is transformed into heat and is not available as luminosity for the secondary light 350. For various operating currents of the light source 202, it is thus possible to determine a maximum in the luminance in each case, just before the onset of quenching with a further decline in the distance. Accordingly, on the basis of FIG. 9, it is possible, in a simple way, to explain that an arbitrary increase in the operating current of the light source 202 as well as a further decrease in the distance of the exit opening 212, 214 from the primary light receiving surface 330 do not lead per se and without inventive intervention to a further increase in the luminance of the secondary light 350, but rather this is subject to physical limits, which are subject to further elaboration or exploration in an inventive way. Thus, by use of suitable parameters, it was possible in a well elaborated design, composed of the primary light emitting unit 200, the thickness of the light transformation element 300, the improvement of the cooling thereof, and the adjustment of the size of the primary light receiving surface 330, to adjust a significant increase in the luminance in comparison to known lighting assemblies. For example, by means of the lighting device described in this application, it is possible to realize a luminance in ranges of above 2000 cd/mm.sup.2, preferably above 500 cd/mm.sup.2, and above 800 cd/mm.sup.2, and luminances of nearly 1600 cd/mm.sup.2 have been achieved. A luminance in ranges of 300 cd/mm.sup.2 and above seems realistic for serial operation.

(26) It is self-evident to the person skilled in the art that the above-described embodiments are to be understood as being given by way of example and that the invention is not limited to them, but rather they can be varied in diverse ways without leaving the protective scope of the claims. Furthermore, it is self-evident that the features, regardless of whether they are disclosed in the description, the claims, the figures, or elsewhere, also individually, define key constituent parts of the invention, even when they are described jointly with other features, and can thus be regarded as having been disclosed independently of one another. In all figures, the same reference numbers represent the same objects, so that descriptions of objects that are mentioned as needed in only one figure or, in any case, not in regard to all figures, can also be extended to the figures in regard to which the object is not explicitly described in the description. The description of features of one exemplary embodiment applies appropriately in each case also to the other exemplary embodiments.

(27) TABLE-US-00001 LIST OF REFERENCE NUMBERS  10 lighting device  20 light emitting unit  25 primary light  30 light conversion element  31 front side  32 back side  35 secondary light 100 lighting device 110 normal line 120 base body 122 cooling element or cooling ribs 124 copper body 200 light emitting unit 202 first light source 204 second light source 206 additional light source 210 light guide 212 exit opening of the light guide 214 exit opening of the light emitting unit 220 optical element 244 partial primary light 246 partial primary light 248 partial primary light 250 primary light 300 light conversion element 310 front side 330 primary light receiving surface 332 primary light emitting surface 340 secondary light emitting surface 350 secondary light 352 secondary optics 354 output beam of light