U.S. patent application number 14/412942 was filed with the patent office on 2015-06-18 for illumination device comprising a phosphor arrangement and a laser.
The applicant listed for this patent is OSRAM GMBH. Invention is credited to Peter Hoehmann.
Application Number | 20150167907 14/412942 |
Document ID | / |
Family ID | 48782312 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150167907 |
Kind Code |
A1 |
Hoehmann; Peter |
June 18, 2015 |
Illumination Device Comprising A Phosphor Arrangement And A
Laser
Abstract
A lighting device comprising a phosphor arrangement (2) having a
phosphor region; (31-33), a first laser (5) for irradiating a part
of the phosphor region (31-33) with a first laser radiation;
wherein the phosphor region (31-33) comprises at least one phosphor
which can be irradiated by the first laser radiation and re-emits
said first laser radiation at least partly in a manner
wavelength-converted into colored light having a first light color;
a second laser (6) configured for emitting a second laser radiation
having a second light color, wherein the second light color of the
second laser radiation is identical in color to the first light
color of the wavelength-converted colored light; and wherein the
lighting device is configured to simultaneously emit the second
laser radiation and the wavelength-converted colored light of
identical color emitted by the phosphor.
Inventors: |
Hoehmann; Peter; (Berlin,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OSRAM GMBH |
Munich |
|
DE |
|
|
Family ID: |
48782312 |
Appl. No.: |
14/412942 |
Filed: |
July 5, 2013 |
PCT Filed: |
July 5, 2013 |
PCT NO: |
PCT/EP2013/064306 |
371 Date: |
January 5, 2015 |
Current U.S.
Class: |
362/84 |
Current CPC
Class: |
F21V 13/14 20130101;
F21S 41/16 20180101; F21V 9/08 20130101; F21V 14/08 20130101; G03B
21/204 20130101; F21V 9/35 20180201; G02B 26/008 20130101; F21Y
2115/10 20160801; F21Y 2113/13 20160801; G03B 33/12 20130101; F21K
9/64 20160801; F21V 9/45 20180201; F21V 5/04 20130101; F21V 7/0091
20130101; G03B 33/08 20130101; F21Y 2115/30 20160801; F21V 3/08
20180201 |
International
Class: |
F21K 99/00 20060101
F21K099/00; F21V 7/00 20060101 F21V007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 2012 |
DE |
10 2012 211 837.3 |
Claims
1. A lighting device comprising: a phosphor arrangement having at
least one phosphor region; at least one first laser for irradiating
in each case at least one part of the phosphor region with a first
laser radiation; wherein the at least one phosphor region comprises
at least one phosphor which can be irradiated by the first laser
radiation and re-emits said first laser radiation at least partly
in a manner wavelength-converted into colored light having a first
light color; at least one second laser configured for emitting a
second laser radiation having a second light color, wherein the
second light color of the second laser radiation is identical in
color to the first light color of the wavelength-converted colored
light; and wherein the lighting device is configured to
simultaneously emit the second laser radiation and the
wavelength-converted colored light of identical color emitted by
the at least one phosphor.
2. The lighting device as claimed in claim 1, comprising an optical
unit, for superimposing the second laser radiation and the
wavelength-converted colored light of identical color emitted by
the at least one phosphor.
3. The lighting device as claimed in claim 2, wherein the optical
unit comprises an optical integrator.
4. The lighting device as claimed in claim 3, wherein the optical
integrator is a TIR rod.
5. The lighting device as claimed in claim 1, wherein the spectra
of first laser radiation and second laser radiation are
different.
6. The lighting device as claimed in claim 1, wherein the laser
radiation of the at least one second laser comprises red laser
radiation.
7. The lighting device as claimed in claim 1, wherein the laser
radiation of the at least one first laser comprises blue laser
radiation and/or blue-violet and/or ultraviolet laser
radiation.
8. The lighting device as claimed in claim 1, wherein the phosphor
arrangement is embodied as a rotatable phosphor wheel.
9. The lighting device as claimed in claim 1, wherein the lighting
device comprises at least one reflector disposed optically
downstream of the phosphor wheel, and a light emission area of the
phosphor region that is generated by the laser radiation is
situated in or at a focal point of the at least one reflector.
10. The lighting device as claimed in claim 9, wherein the optical
unit comprises an optical integrator, and, wherein the reflector is
elliptically shaped, and the optical integrator is situated in or
at the second focal point of the at least one elliptical
reflector.
11. The lighting device as claimed in claim 1, wherein the phosphor
arrangement is a phosphor layer arranged on a carrier with a TIR
optical element disposed upstream.
12. The lighting device as claimed in claim 1, wherein the second
laser radiation emitted by the at least one second laser comprises
two or more laser emission wavelengths.
13. A method for operating a lighting device as claimed in claim 1,
wherein the laser radiation of the at least one second laser is
emitted at least occasionally simultaneously with the irradiation
of the at least one phosphor with the laser radiation of the at
least one first laser.
14. The method as claimed in claim 13, wherein the at least one
first laser and the at least one second laser are operated
simultaneously in continuous-wave operation.
15. The method as claimed in claim 13, wherein the laser radiation
of the at least one second laser is clocked with temporal overlap
with respect to a cyclically repeating phase of a phosphor
conversion.
16. The method as claimed in claim 13, wherein the
wavelength-converted colored light emitted by the at least one
phosphor and the second laser radiation of identical color are fed
simultaneously into the optical integrator.
Description
TECHNICAL FIELD
[0001] The invention relates to a lighting device comprising at
least one laser and a phosphor arrangement that is irradiated by
the laser radiation of the at least one laser. Furthermore, the
invention relates to a method for operating said lighting
device.
[0002] The invention is applicable in particular to projection
devices, for example for film and video projecting gear in
industrial and medical image recognition, in technical and medical
endoscopy, for lighting effects in the entertainment industry, for
medical irradiations and in the automotive sector, in particular
for headlights for motor vehicles.
PRIOR ART
[0003] Light sources having a high luminous flux and a high
luminance are employed in a wide variety of fields, for instance in
endoscopy and likewise in projection apparatuses, wherein gas
discharge lamps are currently the most widely used for this
purpose. In lighting applications, for example projection or
endoscopy, on the basis of LARP ("Laser Activated Remote Phosphor")
technology, which is known in principle, a phosphor is excited by a
laser arranged at a distance from said phosphor. In this case, the
laser radiation that impinges on the phosphor is at least partly
converted into wavelength-converted useful light by means of
wavelength conversion by the phosphor.
[0004] The term laser radiation hereinafter encompasses both
non-visible, e.g. ultraviolet (UV) or infrared (IR), laser
radiation and visible, e.g. blue-violet, blue, red, etc., laser
radiation. A suitable phosphor or a phosphor mixture converts the
invisible or visible laser radiation into corresponding visible
electromagnetic radiation, i.e. light. Hereinafter the term "color"
phosphor, where "color" here is representative of a concrete color,
for example one of the primary colors red, green, blue, yellow,
etc., or a mixed color composed of two or more primary colors,
characterizes a phosphor which, upon excitation with suitable laser
radiation, converts the latter into light having the relevant
"color", i.e. what is meant here is a light color, rather than a
body color. A red phosphor thus converts suitable laser radiation,
for example blue laser radiation of a blue laser diode having an
emission wavelength of approximately 460 nm, into light having the
light color "red" (red light), a green phosphor converts the laser
radiation into light having the light color "green" (green light),
etc. The invention is not restricted to the visible range for the
superimposed light, although this is preferred from a present-day
perspective for practically relevant applications.
[0005] For video projecting, in particular, the corresponding
phosphors for the projector color channels red, green and blue
(possibly also further color channels, e.g. yellow) are usually
applied to a rotating wheel in order to distribute the laser power
over a larger area on average over time and thus to reduce the
phosphor degradation. In addition, static phosphor arrangements are
also
known, in which the phosphors are applied on a heat sink. At all
events the light wavelength-converted by a phosphor is collected by
means of an optical device, e.g. reflector, converging lens or TIR
optical element (TIR: Total Internal Reflection; e.g. conical glass
rod), and used further for the relevant application.
[0006] What is disadvantageous is that red phosphors have a lower
conversion efficiency in comparison with yellow and green phosphors
if they are irradiated with laser radiation having high surface
power densities (e.g. 10-50 W/mm.sup.2). As a result, for red
light, in particular, limits are imposed on the luminous fluxes and
luminances that can be achieved with LARP technology.
SUMMARY OF THE INVENTION
[0007] The object of the present invention is to provide a lighting
device on the basis of LARP technology having an improved luminous
flux and high luminance for at least one light color.
[0008] This object is achieved by means of a lighting device, at
least comprising a phosphor arrangement having at least one
phosphor region, at least one first laser for irradiating in each
case at least one part of the phosphor region with a first laser
radiation, wherein the at least one phosphor region comprises at
least one phosphor which can be irradiated by the first laser
radiation and re-emits said first laser radiation at least partly
in a manner wavelength-converted into colored light having a first
light color, at least one second laser designed for emitting a
second laser radiation having a second light color, wherein the
second light color of the second laser radiation is identical to
the first light color of the wavelength-converted colored light,
and wherein the lighting device is designed to simultaneously emit
the second laser radiation and the wavelength-converted colored
light identical color emitted by the at least one phosphor.
[0009] Particularly advantageous configurations are found in the
dependent claims.
[0010] In addition, the object is achieved with regard to its
aspects for operating the device according to the invention by
means of a method comprising the features of patent claim 13.
[0011] The at least one laser can comprise in particular at least
one semiconductor laser, in particular diode laser or laser diode.
Moreover, laser diodes can be operated together in groups in a
simple manner, e.g. as a stack ("laser stack") or matrix.
[0012] The phosphor region can comprise, in particular, a phosphor
layer comprising one or a plurality of phosphors. A phosphor layer
of the phosphor region can be settable with regard to the thickness
thereof and/or a concentration of the at least one phosphor in a
targeted manner such that a wavelength-converted portion is thus
also settable in a targeted manner. In particular, by means of a
sufficiently high phosphor concentration and/or a sufficiently
large thickness, the incident first laser radiation can be
substantially completely wavelength-converted. This can correspond,
in particular, to a degree of conversion of at least approximately
95%, in particular of at least approximately 98%, in particular of
at least approximately 99%.
[0013] The wavelength conversion can be carried out for example on
the basis of a luminescence, in particular photoluminescence or
radioluminescence, in particular phosphorescence and/or
fluorescence.
[0014] However, the phosphor region can also serve (only) as a
diffuser for the incident second laser radiation. The spectrum of
the second laser radiation scattered by the phosphor region
diffusely and without phosphor conversion thus remains
unchanged.
[0015] Besides the at least one first laser radiation, it is also
possible to use one or a plurality of further laser radiations
having mutually different laser spectra for exciting the at least
one phosphor region, i.e. for the phosphor conversion into colored
light having a light color. By way of example, it can be
advantageous to irradiate a first phosphor (e.g. red phosphor) with
a laser radiation having a first laser spectrum (e.g. blue laser
radiation) and a second phosphor (e.g. blue phosphor) with a laser
radiation having a second laser spectrum (e.g. blue-violet or
ultraviolet laser radiation). Likewise, for the superimposition
with unconverted laser radiation, it can be advantageous to
provide, in addition to the at least one second laser radiation,
one or a plurality of further laser radiations having mutually
different laser spectra but in each case the same light color as
the colored light converted by a phosphor.
[0016] Within the meaning of the present invention, the terms "the
same light color" and "light of identical color" or the like should
be understood such that the dominant wavelength of the second laser
radiation differs from the dominant wavelength of the
simultaneously superimposed wavelength-converted light (by means of
phosphor conversion of the first laser radiation) in terms of
absolute value not more than, with increasing preference in this
order, by 20%, 15%, 10%, 5%. The dominant wavelength of light
having a light color (colored light) is defined in the CIE
chromaticity diagram (standard chromaticity diagram) by the point
of intersection between the straight line, extended from the white
point via the determined color locus of the colored light, and the
spectrum locus of the closest edge of the CIE chromaticity
diagram.
[0017] The basic concept of the invention consists, in the case of
high luminances, in increasing the luminous flux of a colored light
portion of the useful light of an LARP-based lighting device by the
broadband colored light generated by means of phosphor conversion
in a known manner and having a light color corresponding to the
phosphor used being simultaneously superimposed with a narrowband
laser radiation having the same light color. It is only as a result
of the simultaneous superimposition of converted colored light with
laser radiation having the same light color that a high luminous
flux, required for projection applications, in particular, and also
a high luminance are achieved for the respective light color. To
express it in a simplified way, therefore, by way of example, the
broadband red light generated by a red phosphor is simultaneously
superimposed with narrowband red laser radiation, thus resulting in
superimposed red light (R) having the lighting properties according
to the invention. It can also be advantageous for the broadband red
light generated by a red, phosphor to be simultaneously
superimposed with narrowband red laser radiation having two or more
different laser emission wavelengths, for example having a laser
emission wavelength of 638 nm and 670 nm. This concept is also
suitable, in principle, for other light colors, e.g. green (G),
yellow (Y) or blue (B). However, for the other light colors, with
the currently available phosphors and laser diode wavelengths, this
is not (yet) possible with the same efficiency as for red
light.
[0018] By suitably mixing the colored light superimposed according
to the invention with one or a plurality of further colored light
portions, it is possible to set mixed light having a cumulative
color locus appropriate for the respective application of the
lighting device. As necessary, the further color portions can in
turn likewise be generated by superimposition of broadband light
having a light color from a phosphor conversion with laser
radiation of identical color.
[0019] For projection applications, in particular, the individual
color channels of an image generating unit require corresponding
colored light portions, for example in the primary colors--spanning
a color space (gamut)--red, yellow, green, blue, the dominant
wavelengths of which lie within specific wavelength ranges.
[0020] The red channel of a video projector, for example, requires
red light having a dominant wavelength in the range of
approximately 600 to 620 nm. The inventor has found that the
simultaneous superimposition of broadband red light--generated by a
red phosphor excited with laser radiation--and narrowband red laser
radiation--for example from a red laser diode having an emission
wavelength of approximately 638 nm--is advantageously suitable for
this purpose. It is only the simultaneous superimposition of the
conversion light generated by means of LARP technology with laser
radiation of identical color that makes it possible to achieve not
only a high luminous flux but also a high luminance for the
resulting colored light. Light emitting diodes (LEDs) are
incidentally not suitable for the high luminances sought, on
account of their high etendue. Some significant insights are
summarized in the table further below, wherein the respective red
phosphor RL was irradiated with a blue laser diode and a surface
power density of 10 W/mm.sup.2. The red laser diode LD had an
emission wavelength of approximately 638 nm.
TABLE-US-00001 Power [W] Luminous Dominant No. RL LD flux [lm]
wavelength [nm] 1 1 (L0) -- 210 600.2 2 1 (L1) -- 270 596.2 3 0.75
(L0) 0.25 190 604.7 4 0.75 (L1) 0.25 235 600.3 5 1 (L1) 0.33 315
600.3
[0021] As can be discerned from a comparison of rows 1 and 4, given
the same optical power (1 W) and the same dominant wavelength
(approximately 600 nm), but with an additional red laser diode LD
(25% of the optical power), a luminous flux is achieved which is
approximately 10% higher than without. In order to be able to keep
the dominant wavelength constant, a standard phosphor L0 was used
in the configuration in No. 1 without a red laser diode, and a
correspondingly adapted phosphor L1 was used with a red laser
diode. Alternatively, given the same phosphor L0 and in addition a
red laser diode LD, it is possible to achieve a higher dominant
wavelength (604.7 nm instead of 600.2 nm) (cf. rows 1 and 3).
[0022] Comparison of rows 1 and 5 reveals that, given the same
dominant wavelength (approximately 600 nm), but with 33% additional
optical power from a red laser diode LD, a luminous flux which is
almost 50% higher is achieved. These results reveal the potential
for increasing the luminous flux in the red color channel if, given
correspondingly high surface power densities of the pump laser
radiation on the red phosphor, the maximum conversion of the red
phosphor has been reached, i.e. if increasing the pump laser power
no longer enables a higher colored luminous flux solely by means of
the corresponding phosphor conversion.
[0023] What is crucial in this connection is that the colored light
converted by means of a phosphor and the laser radiation of
identical color are generated or superimposed simultaneously. It is
only then that an increase in the luminous flux in the relevant
color channel is possible.
[0024] For further details concerning the simultaneous generation
and subsequent superimposition of broadband light from a phosphor
conversion and laser radiation of identical color, reference should
be made to the following exemplary embodiments. The configuration
possibilities, features and their advantages described for the
lighting device according to the invention hold true analogously,
in so far as applicable, for the method according to the invention
as well.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention will be explained in greater detail below on
the basis of exemplary embodiments. In the figures:
[0026] FIG. 1 shows a lighting device in accordance with a first
embodiment comprising a rotatable phosphor wheel,
[0027] FIG. 2 shows in plan view one possible embodiment of the
phosphor wheel of the lighting device from FIG. 1,
[0028] FIG. 3 shows a lighting device in accordance with a second
embodiment comprising a rotatable phosphor wheel,
[0029] FIG. 4 shows a variant of the lighting device shown in FIG.
3,
[0030] FIG. 5 shows a lighting device in accordance with a further
embodiment comprising a static phosphor arrangement,
[0031] FIG. 6a shows the temporal profile of the phosphor segments
of the phosphor wheel of the lighting device from FIG. 1,
[0032] FIG. 6b shows the temporal profile of the blue laser
radiation of the lighting device from FIG. 1,
[0033] FIG. 6c shows the temporal profile of the red laser
radiation of the lighting device from FIG. 1.
PREFERRED EMBODIMENT OF THE INVENTION
[0034] Identical reference signs in different exemplary embodiments
hereinafter denote features that are identical or of identical
type.
[0035] FIG. 1 shows, as a schematic sectional illustration in side
view, a lighting device 1 comprising a phosphor wheel 2, which is
rotatable about a rotation axis W, as indicated by the curved
arrow. FIG. 2 shows in plan view one possible embodiment of the
phosphor wheel 2. The lighting device 1 is suitable for example for
application in a video projector with an image generating unit
having the color channels red (r), green (g) and blue (b).
[0036] The phosphor wheel 2 comprises three luminous regions 31, 32
and 33 embodied as adjacent ring segments on a ring that is
concentric with respect to the rotation axis W. The lighting device
1 furthermore comprises a first laser 5 for irradiating the three
luminous regions 31 to 33 and also a second laser 6 for irradiating
in each case only the luminous region 31 (R), which both irradiate
a top side O of the phosphor wheel 2. The first laser 5 emits
ultraviolet laser radiation or at least blue-violet laser radiation
b, and the second laser 6 emits red laser radiation r. The
respective laser radiation b, r of the two lasers 5, 6 is combined
via an optical element 7 onto a shared irradiation zone on the top
side O of the phosphor wheel 2 and forms there the laser radiation
spot L--shared during the red phosphor segment R--, below which the
phosphor wheel 2 rotates.
[0037] The luminous regions 31 to 33 are covered here with a first
phosphor layer R, a second phosphor layer G and a third phosphor
layer B, which convert the blue-violet laser radiation b of the
first laser 5 with a high degree of conversion, e.g. of more than
95%, temporally successively into red (red phosphor), green (green
phosphor) and respectively blue light (blue phosphor) by "down
conversion". The red, green and respectively blue light is then
scattered in each case into an upper half-space OH above the
irradiated top side O of the phosphor wheel 2. The luminous regions
31 and 33 therefore serve as different phosphor regions R, G, B for
the laser radiation of the first (blue-violet) laser 5. For the
irradiation of the complete concentric ring formed by the luminous
regions 31 to 33, therefore, the first (blue-violet) laser 5 is
operated in continuous-wave operation.
[0038] By contrast, the second (red) laser 6 is preferably operated
in a clocked fashion, to be precise in such a way that it emits
only red laser radiation r, while the luminous region 31, i.e. the
phosphor layer R comprising the red phosphor, rotates past below
the laser radiation spot L(r, b). For this purpose, it is
advantageous to correspondingly synchronize the driving of the red
laser 6 with the phosphor wheel (not illustrated, for the sake of
clarity). In other words, the phosphor layer R is irradiated at the
same time (simultaneously) both by the first laser 5 with
blue-violet laser radiation b and by the second laser 6 with red
laser radiation r, i.e. the red laser radiation beam spot covers
the blue laser radiation beam spot during the red phosphor segment
R to form the common laser beam spot L(r, b). While the blue-violet
laser radiation b is converted into red light by the red phosphor,
the red laser radiation r is scattered by the red phosphor with
only low absorption losses. As a result of the simultaneous
combination of red laser radiation scattered in an unconverted
fashion and wavelength-converted red light, a higher luminous flux
is thus achieved--for the red color channel. The temporal
synchronization between phosphor wheel 2 and blue-violet laser
radiation b and also red laser radiation r is illustrated
schematically in FIGS. 6a-c. FIG. 6a illustrates the temporal
succession of the phosphor segments R (red phosphor), G (green
phosphor) and B (blue phosphor) of the phosphor wheel 2 which
rotate through below the laser beam spot L. FIG. 6b shows,
beginning with a point in time corresponding to the beginning of
the red phosphor segment R in the example shown, the
continuous-wave power I.sub.b of the blue-violet laser radiation b
with a temporally constant value of greater than zero. Finally FIG.
6c shows the temporal profile of the clocked red laser radiation r,
the laser power I.sub.b of which is greater than zero only in the
phases in which the red phosphor segment R rotates through below
the laser beam spot L. The method for operating the lighting device
1 illustrated in FIG. 1 can therefore be summarized with reference
to FIGS. 6a-c as follows: [0039] rotating the phosphor wheel 2,
[0040] operating the blue-violet laser 5 in continuous-wave
operation, [0041] irradiating the phosphor wheel 2 with the
blue-violet laser radiation b of the blue-violet laser 5 such that
the blue-violet laser radiation b forms a laser beam spot L on the
phosphor wheel 2 rotating through, as a result of which the
phosphor segments R, G, B are successively repeatedly irradiated by
the blue-violet laser radiation b, [0042] operating the red laser 6
in clocked operation, [0043] irradiating the phosphor wheel 2 with
the red laser radiation r of the red laser 6 such that, during the
switch-on phases of the red laser 6, the red laser radiation r
forms a laser beam spot L on the phosphor wheel 2 rotating through
at the same location as the blue-violet laser radiation b, [0044]
synchronizing the switch-on phases of the red laser 6 with the
phosphor wheel 2 such that the red laser radiation r irradiates the
red phosphor segment R.
[0045] What is achieved by the irradiation of the phosphor wheel 2
both with the blue-violet laser radiation b and with the red laser
radiation r at the same location L, firstly, and the temporal
synchronization of the switch-on phases of the red laser 6 with the
red phosphor segment R rotating through, secondly, is that the
phosphor conversion of the incident blue-violet laser radiation b
(that is to say the generation of broadband red light) and the
unconverted scattering of the incident red (narrow band) laser
radiation r are carried out simultaneously by means of the red
phosphor segment R.
[0046] The synchronization of the switch-on phases of the red laser
with the red phosphor segment R rotating through is omitted if the
red laser 6 alternatively--like the blue-violet laser 5--is also
operated in continuous-wave operation. However, clocked operation
is generally preferable for reasons of energy efficiency for the
red laser 6. What is crucial at any rate is that at least a
temporal overlap of the converted (broadband) red light and the
unconverted (narrow band) red laser radiation is achieved.
[0047] The method explained above functions, in principle,
analogously also with other light colors, in particular also with
the combination of green phosphor conversion and green laser
radiation and also blue phosphor conversion and blue laser
radiation.
[0048] A reflector 8 here in the form of an elliptical half-shell
reflector is disposed optically downstream of the phosphor wheel 2.
The reflector 8 covers a part of the irradiated side of the
phosphor wheel 2, including the region irradiated by the two lasers
5 and 6, or the laser radiation spot L, and is thus positioned in
the upper half-space OH. There is an opening 4 in the reflector 8,
through which opening the laser radiation of the two lasers 5 and 6
can enter the interior of the reflector 8 and irradiate the
luminous regions 31 to 33 there. The phosphor wheel 2 is arranged
partly outside the reflector 8, which facilitates a positioning of
a drive motor for the rotation axis W and a cooling of the phosphor
wheel 2.
[0049] A focal point F of the reflector 8 is situated in or near
the light emission area or laser radiation spot L generated by the
laser radiation of the two lasers 5 and 6 on the phosphor wheel 2
or the luminous regions 31 to 33 thereof.
[0050] A filter wheel 9 is arranged at the second focal point F' of
the reflector 8, which filter wheel blocks the non-converted blue
laser radiation synchronously with the irradiation of the red and
green phosphors and thus improves the color purity of the red and
green color channels, respectively. Arranged directly downstream of
the filter wheel 9 or the second focal point F' of the reflector 8
is an optical integrator 10, for example a conical TIR optical
element (TIR=Total Internal Reflection), which collects the
abovementioned color portions of the useful light and forwards them
for further use, for example--as mentioned in the introduction--for
the image generating unit of a video projector.
[0051] The light emitted by the reflector 8 via the optical
integrator 10 (including the red laser radiation backscattered
without being converted by the red phosphor) is perceived as a
mixed light having red, green and blue color portions given a light
sequence implemented sufficiently rapidly, e.g. given a rotation of
the phosphor wheel 2 of at least 25 revolutions per second.
[0052] Alternatively (not illustrated), the blue phosphor can be
dispensed with if a laser that emits blue laser radiation is used
for the first laser (instead of blue-violet laser radiation or UV
laser radiation). The blue laser radiation can then be used
directly for the blue portion of the useful light of the lighting
device. For this purpose, the luminous region comprises a material
which is applied on a reflective base and which scatters blue
light, said material scattering the blue laser radiation of the
first laser into the upper half-space OH without wavelength
conversion. With regard to the functioning of the green and red
phosphors, the explanations already given above hold true here as
well.
[0053] In a variant that is not illustrated, the two lasers are
embodied as a laser diode matrix. The laser diode matrix consists
of 4 times 5 laser diodes each having a laser beam power of 1 watt.
Of the total of 20 laser diodes, 16 are embodied as laser diodes
which emit blue laser radiation and four are embodied as laser
diodes which emit red laser radiation. With the use of a blue
phosphor, blue-violet laser diodes having an emission wavelength of
approximately 405 nm are appropriate; in the case of the variant
without a blue phosphor, laser diodes having an emission wavelength
of approximately 460 nm are suitable. Laser diodes having an
emission wavelength of approximately 638 nm are suitable as red
laser diodes. The red and blue laser diodes can be arranged either
in a mixed fashion or in a spatially grouped fashion, i.e. in the
form of an areal color pattern, for example inner red and outer
blue laser diodes, or vice versa. Preferably, the laser radiation
of the laser diode matrix is specularly reflected by 90.degree.
with respect to the optical axis of the laser diode matrix with the
aid of a so-called TIR stepped mirror and in this case the area
distribution of the 20 laser beams is compressed in one or two
mutually perpendicular axes and subsequently focused onto the
phosphor wheel with the aid of a focal lens. The compression
enables the use of a focal lens having a smaller diameter than
without compression.
[0054] The following phosphors are appropriate, for example:
Red phosphor (R): CaAlSiN.sub.3:Eu, Green phosphor (G):
YAG:Ce(Y.sub.0.96Ce.sub.0.04).sub.3Al.sub.3.75Ga.sub.1.25O.sub.12,
Blue phosphor (B): BaMgAl.sub.10O.sub.17:Eu.sup.2+.
[0055] Furthermore, numerous further suitable phosphors can be used
for the invention. Depending on the application, phosphors having a
conversion spectrum comparable to those shown, that is to say red,
green and blue, are appropriate or alternatively those having a
different conversion spectrum.
[0056] FIG. 3 shows in a schematic illustration a further lighting
device 101 according to the invention comprising the colored light
channels red, green and blue. In contrast to the lighting device 1,
here the unconverted red laser radiation is fed in a separate beam
path for the superimposition with the converted red light. Here,
therefore, the phosphor regions 131 of the phosphor wheel 102 are
irradiated only with the blue laser radiation of a first laser 105
in order thus to generate red and green converted light. For this
purpose, the phosphor wheel 102 has a sector comprising a red
phosphor and a sector comprising a green phosphor. A dichroic
mirror 11 that reflects blue light directs the blue laser radiation
onto the phosphor wheel 102. Depending on which of the two phosphor
sectors it is currently rotating past below the blue laser
radiation spot, the converted red or green light backscattered from
the red or green phosphor, respectively, is collected by a
collimator lens 12 and directed through the dichroic mirror 11,
which is transparent to red or green light, via a converging lens
13 onto an optical integrator 110, for example a conical TIR rod.
For the blue color channel, the phosphor wheel 102 has a sector
having a slot 15 besides the red and green phosphor sectors.
Whenever this slot sector 15 moves through the blue laser beam
coming from one side of the dichroic mirror 11, the blue laser beam
can pass through the slot and is reflected back via three
deflection mirrors 16-18 onto the other side of the dichroic mirror
11. The dichroic mirror 11 finally concentrates the blue laser
radiation via the converging lens 13 onto the input aperture of the
optical integrator 110. In addition, in a separate beam path, red
laser radiation of a red laser diode 106 is imaged via a collimator
lens 14 and the collimator lens 13 onto the input aperture of the
optical integrator 110 and is simultaneously superimposed there
with the red converted light. In this way, the luminous flux is
increased in conjunction with high luminance for the red colored
light channel. For the simultaneous superimposition, the blue laser
105 is operated in continuous-wave operation. By contrast, the
second red laser 106 is operated in a clocked fashion, to be
precise in such a way that it emits only laser radiation, while the
luminous region 31, i.e. the phosphor layer R comprising the red
phosphor, rotates past below the laser radiation spot L, that is to
say ultimately in the phase in which red converted light is also
generated and directed into the optical integrator 110. In this
respect, the temporal control and synchronization of the method for
operating the lighting device 101 corresponds to the already
explained method for operating the lighting device 1 (see FIGS. 1
and 6).
[0057] FIG. 4 shows in a schematic illustration a further lighting
device 201 according to the invention, which is a variant of the
lighting device 101 shown in FIG. 3. Here the red and blue laser
radiation is generated with the aid of a common laser diode matrix
19. For this purpose, the laser diode matrix 19 has four times four
blue laser diodes 205 and also four red laser diodes 206. The four
red laser diodes 206 are arranged outside the 16 blue laser diodes
205 spanning a square field such that the red laser radiation can
pass a dichroic mirror 211, which reflects red light, on the
outside without being impeded. The red laser radiation thus passes
via the lens 12 onto the phosphor wheel 102, wherein the red laser
diodes 206 are driven in a clocked fashion such that the red laser
radiation impinges only on the red phosphor of the phosphor region
131 and is almost completely backscattered from there with only
very little absorption. The backscattered red laser radiation is
concentrated by the lens 12 onto the dichroic mirror 211, which
reflects red light and which directs the red laser radiation via
the converging lens 13 into the optical integrator 110. By
contrast, the blue laser radiation from the blue laser diodes 205
passes through the dichroic mirror 211 and is concentrated by the
lens 12 onto the phosphor wheel 102. In the course of a complete
rotation of the phosphor wheel 102, the blue laser radiation
impinges on the red phosphor and is converted to red light, the
green phosphor and is converted to green light, or the slot sector
and passes through the phosphor wheel 102 without conversion. The
blue laser radiation passing through the phosphor wheel 102 through
the slot 15 is directed via three deflection mirrors through the
dichroic mirror 211, which reflects red light, and via the
converging lens 13 into the optical integrator 110. The two colored
light portions red and green that are backscattered by phosphor
conversion by the corresponding phosphors of the phosphor wheel are
concentrated by the lens 12 onto the dichroic mirror 211 and
directed from there via the converging lens 13 into the optical
integrator 110. In order that the red light converted by the red
phosphor and the red unconverted laser radiation are superimposed
simultaneously in the optical integrator 110, the red laser diodes
206 are operated in a clocked fashion such that the red laser
radiation simultaneously with the blue laser radiation impinge on
the same red phosphor and are backscattered there in a converted
and an unconverted fashion, respectively. For the red colored light
channel, red light having a higher luminous flux in conjunction
with high luminance is achieved at the output of the optical
integrator in this way. If there is a need for a further colored
light channel, the phosphor wheel 102 can be provided with a
further sector-type phosphor region, for example with a yellow
phosphor for an additional yellow colored light channel.
[0058] FIG. 5 shows a further lighting device 301 according to the
invention in a schematic illustration. This involves a static
phosphor arrangement, i.e. without a phosphor wheel. Rather, the
phosphors for the different colored light channels are arranged on
a solid heat sink 20 as carrier in the form of a square phosphor
layer 21 having three juxtaposed strip-shaped sections (not
depicted by it) one each for the red, green and blue phosphors. A
first laser matrix 22 comprising 16 ultraviolet (UV) laser diodes
(not illustrated) supplies UV laser radiation which impinges on the
phosphor layer 21 via a dichroic mirror 311, which reflects UV
radiation, a lens 23 and a TIR optical element 24. The TIR optical
element 24 serves, firstly, to spatially homogenize the UV laser
radiation by means of multiple internal reflection and thereby to
uniformly irradiate the phosphor layer 21 with the three
strip-shaped phosphors. Secondly, it serves to collect the portion
of the UV laser radiation that is backscattered or diffusely
reflected and wavelength-converted by the phosphors. For this
purpose, the TIR optical element 24 substantially consists of a
conical quartz glass rod having a round cross section. The
converted colored light portions red, green and blue collected by
the TIR optical element 24, are concentrated by the lens 23, pass
through the dichroic mirror 311 and are fed into an optical
integrator 110 by a converging lens 13. In parallel with this beam
path of the converted colored light portions red, green, blue, red
laser radiation, generated by four red laser diodes of a red laser
diode matrix 25, is fed via the converging lens 13 into the optical
integrator 110. The red laser matrix and the UV laser matrix can
both be operated in continuous-wave operation or in a clocked
fashion, in the latter case in a synchronously clocked fashion,
however, in order that the red light converted by the red phosphor
is simultaneously superimposed with the unconverted red laser
radiation in the optical integrator 110. For the red colored light
channel, red light having a high luminance and a higher luminous
flux than without simultaneous superimposition is achieved at the
output of the optical integrator in this way.
* * * * *