Title of Invention

A LIGHTING SYSTEM

Abstract

The invention relates to a lighting system having at least two light-emitting diodes), each of said light-emitting diodes emitting, in operation, visible light in a preselected wavelength range, characterized in that the lighting system has conversion means for converting a part of the visible light emitted by one of the light-emitting diodes into visible light in a further wavelength range so as to optimize the color rendition of the lighting system.

Full Text

The invention relates to a lighting system comprising at least two light-emitting diodes, each of said light-emitting diodes emitting, in operation, visible light in a preselected wavelength range. Lighting systems based on light-emitting diodes (LEDs) are used as a source of white light for general lighting applications. A lighting system of the type mentioned in the opening paragraph is known. In recent years, apart from red light-emitting diodes based on GaP, also efficient, blue light-emitting diodes and green light-emitting diodes based on GaN have been developed. In order to produce white light, in principle, three LEDs are necessary as the primary light source, namely a blue, a green and a red LED. It is a drawback of such lighting systems that a combination of three LEDs as the primary light source does not always lead to the desired color rendition, which can be attributed to the fact that LEDs with spectral maxima in the desired spectral regions which at the same time are sufficiently energy-efficient are not available or short. It is an object of the invention to provide a lighting system, which exhibits an improved color rendition. The invention further aims at improving the luminous efficacy of the lighting system. To achieve this, the lighting system includes conversion means for converting a part of the visible light emitted by one of the light-emitting diodes into visible light in a further wavelength range so as to optimize the color rendition of the lighting system. The conversion means are excited by light originating from one of the at least two LEDs. A part of this light is converted by the conversion means, for example via a process of absorption and emission, into visible light in the further wavelength range. This results in a lighting system which comprises, in fact, three light sources, namely two primary light sources which are formed by the at least two LEDs, which primary light sources each emit visible light in a preselected wavelength range, and one so-called secondary light source which emits visible light in the further wavelength range. By a suitable choice of the wavelength ranges in which these two primary light sources and the secondary light source emit visible light, a lighting system is obtained having an improved color rendition relative to a lighting system based on the two primary light sources. Since the application of a third primary light source (for example a green LED or a red LED) is avoided, an improved color rendition of the lighting system is obtained. Preferably, the conversion means comprise a luminescent material. Such materials are very suitable because they generally have a high quantum efficiency and a high lumen equivalent (expressed in Im/W), so that a high luminous efficacy of the lighting system is obtained. In addition, many varieties of (stable) inorganic and organic luminescent materials (phosphors) are known, so that the selection of a material for achieving the aim in accordance with the invention (improving the color rendition) is simplified. The color rendition of the lighting system can be influenced in two ways. On the one hand, the spatial color rendition is improved by optimally mixing the light originating from the LEDs and the conversion means. On the other hand, the color rendition of the lighting system is improved by taking measures which make sure that the light output of the LEDs is independent of time. Such dependence is obtained, for example, if the light output of a LED changes as a function of the temperature of the LED. In this case, the use of temperature-independent LEDs has advantages. In accordance with a first aspect of the invention, the luminescent material can be preferably excited by light originating from the wavelength range of 400 to 500 nm. By virtue of this sensitivity, the luminescent material can very suitably be used to absorb, in particular, blue light. This absorbed light is very efficiently converted by the luminescent material into visible light in the further wavelength range, for example green light. Suitable luminescent materials are (Sr, Ca)2 SiO4 :Eu2+, Ba2 SiO4 :Eu2+, SrGa2 S4, ZnS:Cu+, ZnS:Au+, ZnS:Al3+, (Zn,Cd)S:Ag+ and CaS:Ce3+. Said materials have a relatively high quantum efficiency and light absorption at 450 nm. These materials further exhibit a relatively very high lumen equivalent when blue light is converted to the desired green light. A very attractive embodiment of the lighting system in accordance with a first aspect of the invention is characterized in that the two light-emitting diodes at least comprise a blue light-emitting diode and at least a red light-emitting diode, and that the conversion means comprise a (green light-emitting) luminescent material for converting a portion of the light emitted by the blue light-emitting diode into green light. In this manner, a lighting system in accordance with a first aspect of the invention is obtained which emits white light with a high color rendering index on the basis of three basic colors (red, blue and green), in which only two primary light sources are employed, namely blue and red light, and green light is obtained by converting a portion of the blue light. Preferably, the maximum of the spectral emission of the blue light-emitting diode lies in the wavelength range from 460 to 490 nm, the maximum of the spectral emission of the red light-emitting diode lies in the wavelength range from 610 to 630 nm, and the maximum of the spectral emission of the (green light-emitting) luminescent material lies in the wavelength range from 510 to 530 nm. In accordance with a second aspect of the invention, the luminescent material can be preferably excited by light originating from the wavelength range of 500 to 560 nm. By virtue of this sensitivity, the luminescent material can very suitably be used to absorb, in particular, green light. This absorbed light is very efficiently converted by the luminescent material into visible light in the further wavelength range, for example red light. Suitable luminescent materials are CaS:Eu,Mn; CaS:Eu; SrS:Eu; (Zn,Cd)S:Ag; SrO:Eu; Sr3B2O6 : Eu; Sr2Mg(BO3)2; CaS:Eu, Mn; CaS:Eu or SrS:Eu. Said materials have a relatively high quantum efficiency and light absorption. These materials further exhibit a relatively very high lumen equivalent when blue light or green light is converted to the desired red light. A very attractive embodiment of the lighting system in accordance with a second aspect of the invention is characterized in that the two light-emitting diodes at least comprise a blue light-emitting diode and at least a green light-emitting diode, and that the conversion means comprise a luminescent material for converting a portion of the light emitted by the blue and/or green light-emitting diode to red light. An important advantage of the use of blue and green LEDs as the primary light source is that both diode chips can be manufactured by means of the GaN technology known per se. Unlike red GaP diode chips, such blue and green GaN diode chips are not temperature-dependent, so that the use of relatively expensive electronics to compensate for the temperature-dependence of such diode chips can be dispensed with. A further advantage resides in that said blue and green GaN diode chips can be contacted on the same side, so that they can be readily arranged in series. The use of a green-excited luminescent material emitting red light has the additional advantage with respect to a blue-excited luminescent material emitting red light that the quantum deficit is smaller. Preferably, the maximum of the spectral emission of the blue light-emitting diode lies in the wavelength range from 460 to 490 nm, the maximum of the spectral emission of the green light-emitting diode lies in the wavelength range from 510 to 550 nm, and the maximum of the spectral emission of the red light-emitting luminescent material lies in the wavelength range from 610 to 630 nm. The color rendering index (Ra) of the lighting system in accordance with a first and a second aspect of the invention is preferably at least equal to or greater than 80 (Ra > 80). By a suitable combination of the spectral emissions of two primary light sources, which are formed by the at least two LEDs, and the spectral mission of one so-called secondary light source which, after conversion by the conversion means, emits visible light in the further wavelength range, a lighting system having a high color rendering index is obtained. A point of special interest in the lighting system in accordance with the invention is that upon blending light originating from LEDs with light originating from the conversion means, the direction-dependence of light originating from LEDs (primary light sources) may differ from the direction-dependence of light originating from the conversion means (secondary light source). In general, LEDs emit highly directional light, while the conversion means, in this case the luminescent material, emit (diffuse) light in accordance with a Lambert radiator. The invention fiirther aims at improving the blending of light by the lighting system. To achieve this, an alternative embodiment of the lighting system in accordance with the invention is characterized in that the lighting system is fiirther provided with reflection means. The LEDs are provided in the lighting system in such a manner that a substantial part of the light originating from the LEDs cannot directly leave the lighting system, but instead is incident on the reflection means. An advantage of the use of reflection means is that the light originating from the two primary light sources (the blue and red LEDs or the blue and green LEDs) and the secondary (green or red) light originating from the conversion means is blended. The reflection means are preferably diffusely reflecting reflection means. By directing the light originating from the LEDs to the diffusely reflecting reflection means, the reflected light also acquires the characteristics of a Lambert radiator. This results in a further improvement of the blending of the various color components and hence of the color rendition of the lighting system. Furthermore, the light is preferably reflected by the reflection means without a change of the color rendition (white-reflecting reflection means). In this manner, undesirable color deviations in the light emitted by the lighting system are precluded. Preferably, the diffusely reflecting reflection means comprise a material chosen from the group formed BaSO4, ZnS, ZnO and TiO2. Such materials are very suitable because their reflection coefficient in the wavelength range from 400 to 800 nm is above 98%, and they reflect the light in a diffuse and wavelength-independent manner. An attractive embodiment of the lighting system in accordance with the invention is characterized in that the conversion means are provided in or on the diffusely reflecting reflection means. In this manner, the light originating from the LEDs is effectively blended, obtains the desired direction characteristic, and the conversion means additionally receive sufficient suitable light for the conversion to visible light in the further wavelength range, which converted light has the same direction characteristic as the diffusely reflected light of the LEDs. The blending of colors and/or the direction characteristic of the emitted light can be improved in an alternative manner by covering the LEDs with a relatively thin layer of the luminescent material, whereby particles in the luminescent material act as diffusor. It is further desirable that the color temperature of the lighting system is variable. An alternative embodiment of the lighting system in accordance with the invention is characterized in that the color temperature of the lighting system can be adjusted by separately driving the light-emitting diodes. The color temperature is (electrically) adjustable by separately driving the LEDs. A suitable embodiment of such an adjusting element includes a first diode chain of red and blue LEDs and a second diode chain of exclusively blue (or exclusively red) LEDs. A further suitable embodiment of such an adjusting element includes a first diode chain of blue and green LEDs and a second diode chain of exclusively blue (or exclusively green) LEDs. As a result thereof, an adjustable color temperature range from 2000 to 6300 K is achieved. The color temperature adjustment is partly determined by the quantity of luminescent material (conversion means). Accordingly the present invention provides a lighting system comprising at least two light-emitting diodes, each of said light-emitting diodes emitting, in operation, visible light in a preselected wavelength range, characterized in that the lighting system has conversion means for converting a part of the visible light emitted by one of the light-emitting diodes into visible light in a further wavelength range so as to optimize the color rendition of the lighting system. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the Drawings: FIG. 1A is a partly cross-sectional view and a side view of an embodiment of the lighting system in accordance with a first aspect of the invention; FIG. IB is a cross-sectional view taken on the line I-I of a detail of the lighting system shown in FIG. lA; FIG. 2 shows the transmission spectrum of an embodiment of the lighting system in accordance with the invention; FIG. 3 A is a cross-sectional view of an alternative embodiment of the lighting embodiment of the lighting system in accordance with a first aspect of the invention, and FIG. 3B is a cross-sectional view of a side view of the alternative embodiment of the lighting system shown in FIG. 3 A; FIG. 4 is a circuit diagram of LEDs for use in a lighting system in accordance with the invention having an adjustable color temperature, and FIG. 5 is a cross-sectional view of an embodiment of the lighting system in accordance with a second aspect of the invention. The Figures are purely schematic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. In the Figures, like reference numerals refer to like parts, whenever possible. FIG. lA is a partly cross-sectional view and a side view of an embodiment of the lighting system in accordance with a first aspect of the invention. A lighting system 1 comprises a housing 2 accommodating drive electronics (not shown in FIG. lA) for the light-emitting diodes (LEDs) and a screen 3. In this example, the housing is provided with a so-called E27 lamp cap 4 having mechanical and electrical contact means which are known per se. On a side of the lighting system 1 facing away from the lamp cap 4, there is a holder 5 on which a number of LEDs 6, 6', 7,7' 8, 8',. .. are provided. The LEDs 6, 6', 7, 7', comprise a collection of blue LEDs 6, 6', (maximum of the spectral emission lies in the wavelength range from 430 to 490 nm) and red LEDs 7, (maximum of the spectral emission lies in the wavelength range from 590 to 630 nm), which LEDs 6, 6', 7, 7' . . . are arranged so that the light that they emit is directed towards the screen 3. FIG. IB very schematically shows an example of a schematic, circular arrangement of the LEDs 6, 6', 7, 7' (sectioned via the line I—I in FIG. lA). On a side facing the LEDs 6, 6', 7, T the screen 3 is provided with (diffusely reflecting) reflection means 9 and conversion means 10. In this example, the reflection means 9 comprise a layer of BaSO4, which material has a (diffuse) reflection coefficient of at least substantially 100% for visible light. The conversion means 10 preferably comprise a luminescent material (phosphor) which bears the characteristic that it converts blue light (400-480 nm) originating from the blue LEDs 6, 6', into green light in the desired further wavelength range (530-565 nm). The conversion means 10 convert visible light emitted by one of the light-emitting diodes into visible light in a range having a longer wavelength. A collection of suitable luminescent materials is shown in Table I, where for each of the materials the quantum efficiency at 450 nm (QE450), the absorption coefficient at 450 nm (Abs450) and the lumen equivalent (LE) is indicated. TABLE I Luminescent materials (so-called green emitters) which can suitably be used as conversion means for the lighting system in accordance with a first aspect of the invention. To obtain sufficient green light and to avoid losses, the screen 3 is preferably embodied and arranged so that, dependent upon the degree of reflection of the luminescent material, only one reflection occurs or a number of reflections occur. It is further desirable that the luminescent material at least substantially completely reflects the light of the red LEDs. The light of the red and blue LEDs is effectively blended by the reflection means 9, the red and blue LEDs 6, 6', 7, 7', being positioned relative to the screen 3 in such a manner that these LEDs do not directly emit their light in a direction 11 of the light emitted by the lighting system 1, but that their light output is directed towards an inside of the screen 4 in such a manner that only reflected light is emitted in the direction 11. The red and blue LEDs can be separately driven, thus enabling the color temperature of the lighting system 1 to be varied and adjusted in accordance with the requirements. An example hereof is the application of a diode chain with red and blue LEDs and a further diode chain with exclusively blue LEDs (see also FIG. 4). This ordering of LEDs enables the portion of red light in the primary light source to be varied. Since the ratio of the blue emission relative to the green emission is fixed in such an ordering of LEDs [the blue LEDs 6, 6' are directly aimed at the layer with luminescent material (Ba2 SiO4 :Eu )], the example of FIG. lA also contains a number of further blue LEDs 8, 8', which emit very diffusely in the direction 11 of the light emitted by the lighting system 1. This measure enables the red and blue portion in the white light emitted by the lighting system 1 to be separately varied. This results in an additional setting possibility for adjusting the ratio of primary red and blue light and secondary green light, thus providing the lighting system 1 with an adjustable color temperature. By way of example, Table II shows a lighting system in accordance with a first aspect of the invention, which comprises: • blue GaN LEDs (make Nichia) with an emission maximum at 470 nm, FWHM=20 nm; • red GaP LEDs (make Hewlett Packard) with an emission maximum at 620 nm, FWHM=20 nm, two to four blue LEDs being used for each red LED; • and conversion means comprising a layer of Ba2SiO4:Eu . Column 1 of Table II lists various desirable values for the color temperature (Tc). The columns 2, 3 and 4 of Table II list the spectral contributions (x) of the three light components (sum of the three spectral contributions x amounts to 1). Column 5 in Table II lists the color rendering index (Ra) and column 6 lists the luminous efficacy (lum. eff.) of the lighting system. Table II shows that the proportion of green light (column 3) varies relatively little at the different color temperatures. The color temperature of the lighting system can be readily adjusted in a very wide range by only changing the distribution of the primary light sources (the blue and red light). In accordance with the measure of the invention, a lighting system having a relatively high color rendition (80 TABLE II Combination of blue and red LEDs and Ba2SiO4 :Eu as a luminescent material in an embodiment of the lighting system in accordance with a first aspect of the invention. FIG. 2 shows the transmission spectrum of an embodiment of the lighting system in accordance with the invention. The transmission T (arbitrary units) is plotted as a function of the wavelength λ(nm) of visible light for a combination of blue and red LEDs and Ba2SiO4 :Eu as the luminescent material at a color temperature Tc =4000 K (the spectrum in FIG. 2 corresponds to the data in column 4 of Table II). In FIG. 2, the spectral maximum of the blue LEDs is indicated by (a) and corresponds to a wavelength of 470 nm, and the spectral maximum of the red LEDs is indicated by (b) and corresponds to a wavelength of 620 nm. Furthermore, in FIG. 2, the spectral maximum of the light emitted by the luminescent material is indicated by (c) and corresponds to a wavelength of 550 nm. A further improvement of the color rendering index R.sub.a) in accordance with a first aspect of the invention is achieved by not only employing red and blue LEDs as sources of primary light but, for example, a combination of 4 different LEDs. A particularly suitable lighting system in accordance with a first aspect of the invention comprises: • blue GaN LEDs (make Nichia): emission maximum: 470 nm, FWHM=20 run; • blue-green GaN LEDs (make Nichia): emission maximum: 520 nm, FWHM=40 nm; • yellow GaP LEDs (make Hewlett Packard): emission maximum: 590 nm, FWHM=20 nm; • red GaP LEDs (make Hewlett Packard): emission maximum: 620 nm, FWHM=20 nm; 2+ • and conversion means comprising a layer of Ba2SiO4 :Eu A lighting system having such a combination of four light-emitting diodes and the conversion means in accordance with a first aspect of the invention has a color rendering index which, relative to the various color temperatures listed in Table II, is at least 10 points higher than in the case of a combination of two diodes (Ra lighting system is achieved by employing deep red LEDs with a spectral emission maximum in the wavelength range from 620 to 670 nm. FIG. 3 A shows an alternative embodiment of the lighting system in accordance with a first aspect of the invention. FIG. 3B is a cross-sectional view of a side elevation of the embodiment shown in FIG. 3A. The lighting system 101 comprises a housing 102 and a screen 103. This example includes an aperture angle a at which light leaves the lighting system 101 in a direction 111, which angle can be varied via adjusting screws 113, 113'. For this purpose, the screen is provided with adjusting plates 114, 114' having elongated or groove-shaped apertures 115, 115'. In the example shown in FIG. 3A, the aperture angle a is equal to 40o. The lighting system 101 comprises a holder 105 on which a number of LEDs 106, 106', 107, 107', 108, 108', are provided. The LEDs 106, 106', 107, 107' include an alternating collection of blue LEDs 106, 106' (spectral emission 430 LEDs 108, 108', which exhibit a very diffuse emission in the direction 111 of the light emitted by the lighting system 10 L FIG. 4 shows a circuit diagram of LEDs for use in a lighting system in accordance with the invention having an adjustable color temperature. A voltage is guided from a supply source 202 via a diode bridge 201 to an arrangement of blue LEDs 406, 406' and red LEDs 407, 407'. By means of a selector switch 203, further groups of blue LEDs 416, 416' and/or red LEDs 417, 417' can be switched on or off in accordance with the requirements. FIG. 5 is a cross-sectional view of an embodiment of the lighting system in accordance with a second aspect of the invention. The lighting system 201 comprises a housing 202, 202', which accommodates a holder 205 on which a number of LEDs 206;207 are provided. The LEDs 206; 207 include an alternating collection of blue LEDs 206 (spectral emission 430 A very suitable lighting system in accordance with a second aspect of the invention comprises: • blue GaN LEDs (make Nichia) with an emission maximum at 470 nm, FWHM=20 nm; • green GaN LEDs (make Nichia) with an emission maximum at 530 nm, FWHM=20 nm; • two or three green LEDs (dependent upon the required color temperature) being used for each blue LED; • and conversion means comprising a layer of CaS:Eu, Mn. The lighting system in accordance with the invention has the advantage that a high color rendition is achieved (Ra It will be obvious that within the scope of the invention many variations are possible to those skilled in the art. The scope of protection of the invention is not limited to the examples given in this document. The invention is embodied in each novel characteristic and each combination of characteristics. Reference numerals in the claims do not limit the scope of protection of said claims. The use of the term "comprising" does not exclude the presence of elements other than those mentioned in the claims. The use of the term "a" or "an" in front of an element does not exclude the presence of a plurality of such elements. WE CLAIM 1. A lighting system (1:101) comprising at least two light-emitting diodes (6, 6'..., 7, 7'....; 106, 106' ,107, 107' ; 206, 207), each of said light-emitting diodes emitting, in operation, visible light in a preselected wavelength range, characterized in that the lighting system (1; 101; 201) has conversion means (10; 110; 210) for converting a part of the visible light emitted by one of the light-emitting diodes (6, 6'.....; 106, 106' ; 206, 207) into visible light in a further wavelength range so as to optimize the color rendition of the lighting system 2. The lighting system as claimed in claim 1, wherein the conversion means (10; 110; 210) comprise a luminescent material. 3. The lighting system as claimed in claim 1 or 2, wherein the luminescent material can be excited by light originating from the wavelength range of 400 to 500 nm. 4. The lighting system as claimed in claim 2, wherein the luminescent material is chosen from the group formed by (Sr,Ca)2SiO4;Eu2+, Ba2SiO4:Eu2+, SrGa2S4, ZnS:Cu+, ZnS:Au+, ZnS:Al3+, (Zn,Cd)S:Ag+ and CaS:Ce3+. 5. The lighting system as claimed in claim 1 , wherein the two light-emitting diodes (6, 6'....; 7, 7' ; 106, 106' ; 107, 107'....) comprises at least a blue light-emitting diode (6, 6' ; 106, 106' ) and at least a red light-emitting diode (7, 7'...; 107, 107' ), and in that the conversion means (10; 110) has a luminescent material for converting a portion of the light emitted by the blue light-emitting diode (6,6'....; 106, 106' ) into green light. 6. The lighting system as claimed in claim 5, wherein the maximum of the spectral emission of the blue light-emitting diode (6, 6'....; 106, 106' ) lies in the wavelength range from 460 to 490 nm, the maximum of the spectral emission of the red light-emitting diode (7, 7'....; 107, 107' ) lies in the wavelength range from 610 to 630 nm, and the maximum of the spectral emission of the green light-emitting luminescent material lies in the wavelength range from 510 to 530 nm. 7. The lighting system as claimed in claim 2, wherein the luminescent material can be excited by light originating from the wavelength range from 500 to 560 nm. 8. The lighting system as claimed in claim 7, wherein the luminescent material is selected from the group formed by CaS: Eu,Mn; CaS:Eu; SrS:Eu; (Zn, Cd):S:Ag; SrO:Eu; SrsBsO6:Eu; Sr2Mg(BO3)2; CaS:Eu, Mn; CaS:Eu or SrS:Eu. 9. The lighting system as claimed in claim 1, wherein the two light-emitting diodes (206, 207) at least comprise a blue light-emitting diode (206) and at least a green light-emitting diode, and that the conversion means (210) comprise a luminescent material for converting a portion of the light emitted by the blue and/or green light-emitting diode (206, 207) to red light. 10. The lighting system as claimed in claim 9, wherein the maximum of the spectral emission of the blue light-emitting diode (206) lies in the wavelength range from 460 to 490 nm, the maximum of the spectral emission of the green light-emitting diode (207) lies in the wavelength range from 510 to 550 nm, and the maximum of the spectral emission of the red light-emitting luminescent material lies in the wavelength range from 610 to 630 nm. 11. The lighting system as claimed in claim 1 or 2, wherein a color rendering index of the lighting system (1; 101; 102) is at least equal to or greater than 80. 12. The lighting system as claimed in claim 1 or 2, wherein, in operation, a luminous flux of the light-emitting diodes (6, 6' , 7, 7'....; 106, 106'...., 107, 107'....; 205, 207) amounts to at least 5 1m. 13. The lighting system as claimed in claim 1 or 2, wherein the lighting system (1; 101; 201) is provided with reflection means (9; 109; 209). 14. The lighting system as claimed in claim 12, wherein the reflection means (9; 109; 209) comprises a material chosen from the group formed by BaSO4, ZnS, ZnO and TiO2. 15. The lighting system as claimed in claim 12 or 13, wherein the conversion means (10; 110; 210) are provided in or on the reflection means (9; 109; 209). 16. The lighting system as claimed in claim 1 or 2, wherein a color temperature of the lighting system (1; 101; 102) can be adjusted by separately driving the light- emitting diodes (6, 6', 7, 7' ; 8, 8' ; 106, 106'...., 107, 107' ; 108, 108' ; 206, 207). 17. A lighting system comprising at least two light-emitting diodes, substantially as hereinbefore described with reference to the accompanying drawings.

Documents:

in-pct-2000-088-che-abstract.pdf

in-pct-2000-088-che-claims filed.pdf

in-pct-2000-088-che-claims grand.pdf

in-pct-2000-088-che-correspondence others.pdf

in-pct-2000-088-che-correspondence po.pdf

in-pct-2000-088-che-dcescription complete filed.pdf

in-pct-2000-088-che-dcescription complete grand.pdf

in-pct-2000-088-che-drawings.pdf

in-pct-2000-088-che-form 1.pdf

in-pct-2000-088-che-form 19.pdf

in-pct-2000-088-che-form 26.pdf

in-pct-2000-088-che-form 3.pdf

in-pct-2000-088-che-form 5.pdf

in-pct-2000-088-che-pct.pdf