WO2013008157A1 - Method of manufacturing a phosphor-enhanced light source - Google Patents

Method of manufacturing a phosphor-enhanced light source Download PDF

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Publication number
WO2013008157A1
WO2013008157A1 PCT/IB2012/053460 IB2012053460W WO2013008157A1 WO 2013008157 A1 WO2013008157 A1 WO 2013008157A1 IB 2012053460 W IB2012053460 W IB 2012053460W WO 2013008157 A1 WO2013008157 A1 WO 2013008157A1
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WIPO (PCT)
Prior art keywords
light
phosphor
reflecting optical
optical layer
enhanced
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PCT/IB2012/053460
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French (fr)
Inventor
Coen Adrianus Verschuren
Christian Kleijnen
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Koninklijke Philips Electronics N.V.
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Publication of WO2013008157A1 publication Critical patent/WO2013008157A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/44—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the coatings, e.g. passivation layer or anti-reflective coating
    • H01L33/46—Reflective coating, e.g. dielectric Bragg reflector
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V13/00—Producing particular characteristics or distribution of the light emitted by means of a combination of elements specified in two or more of main groups F21V1/00 - F21V11/00
    • F21V13/02—Combinations of only two kinds of elements
    • F21V13/08—Combinations of only two kinds of elements the elements being filters or photoluminescent elements and reflectors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V9/00—Elements for modifying spectral properties, polarisation or intensity of the light emitted, e.g. filters
    • F21V9/30—Elements containing photoluminescent material distinct from or spaced from the light source
    • F21V9/32—Elements containing photoluminescent material distinct from or spaced from the light source characterised by the arrangement of the photoluminescent material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
    • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
    • F21K9/60—Optical arrangements integrated in the light source, e.g. for improving the colour rendering index or the light extraction
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V14/00—Controlling the distribution of the light emitted by adjustment of elements
    • F21V14/04—Controlling the distribution of the light emitted by adjustment of elements by movement of reflectors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V23/00—Arrangement of electric circuit elements in or on lighting devices
    • F21V23/04—Arrangement of electric circuit elements in or on lighting devices the elements being switches
    • F21V23/0442—Arrangement of electric circuit elements in or on lighting devices the elements being switches activated by means of a sensor, e.g. motion or photodetectors
    • F21V23/0457—Arrangement of electric circuit elements in or on lighting devices the elements being switches activated by means of a sensor, e.g. motion or photodetectors the sensor sensing the operating status of the lighting device, e.g. to detect failure of a light source or to provide feedback to the device
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0008—Processes
    • H01L2933/0025—Processes relating to coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0095—Post-treatment of devices, e.g. annealing, recrystallisation or short-circuit elimination

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • General Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Led Device Packages (AREA)

Abstract

A method (100) of manufacturing a phosphor-enhanced light source, a phosphor-enhanced light source, and a multitude of phosphor-enhanced light sources are provided. The phosphor-enhanced light source has a predefined color characteristic. The method (100)comprises the steps of:(i) receiving (102) a phosphor-enhanced lighting module, the phosphor-enhanced lighting module comprises a light emitter, a luminescent material and a light exit window, the light emitter configured to emit light in a first spectral range, the luminescent material configured to absorb a portion of the light in the first spectral range and to convert at least a part of the absorbed light to light of a second spectral range, the phosphor-enhanced lighting module configured to emit a specific light emission distribution comprising light of the first spectral range and light of the second spectral range through the light exit window, (ii) selecting (104) a partially back-reflecting optical layer having a specific back-reflection characteristic being related to the specific light emission spectrum of the received phosphor-enhanced lighting module, the partially back-reflecting optical layer partially reflects back light that impinges on the partially back-reflecting optical layer and partially transmits light that impinges on the partially back-reflecting optical layer, the back-reflection characteristics being defined as a ratio between the amount of back- reflected light and the amount of transmitted light, (iii) assembling (106) the selected partially back-reflecting optical layer in front of the light exit window to partially reflect emitted light back to the luminescent material.

Description

METHOD OF MANUFACTURING A PHOSPHOR-ENHANCED LIGHT SOURCE
FIELD OF THE INVENTION
The invention relates to manufacturing methods of phosphor-enhanced light sources. BACKGROUND OF THE INVENTION
Phosphor-enhanced light sources have a light emitter which emits light in a first spectral range and have phosphor material to convert a part of the light in the first spectral range towards light in a second spectral range. The light emission of the phosphor- enhanced light source partly consists of light of the first spectral range and partly consists of light of the second spectral range. The combination determines the color point in a color space, and thus also the correlated color temperature, of the emitted light. The light emitter is often a Light Emitting Diode (LED). LEDs manufactured in the same process under equal processing conditions have often a slightly different light emission spectrum. Thus, the phosphor-enhanced light sources have slightly different light emissions and, thus, each emit a slightly different color (expressed in color point or in correlated color temperature).
Traditionally the LEDs were binned and only LEDs emitting a predefined specific light emission spectrum were used to manufacture the phosphor-enhanced light sources.
Published patent application US2011/0031516 discloses a manufacturing method to manufacture phosphor-enhanced light sources which all emit light of the same predefined color. In the disclosed manufacturing process the emitted color of each LED is measured and a specific phosphor layer having a specific thickness or a specific phosphor density is selected to obtain a light emission of the predefined color. Thus, for each LED it is determined what characteristics the phosphor layer should have to obtain the predefined light emission. As such a relatively large amount of phosphor layers having slightly different characteristics needs to be manufactured and needs to be kept in stock. Manufacturing many phosphor layers having slightly different characteristics and continuously keeping a stock of these slightly different phosphor layers is relatively expensive. SUMMARY OF THE INVENTION
It is an object of the invention to provide a method to cost-effectively manufacture a phosphor-enhanced light source being configured to emit light in a predefined color range.
A first aspect of the invention provides a method of manufacturing a phosphor-enhanced light source as claimed in claim 1. A second aspect of the invention provides a phosphor-enhanced light source as claimed in claim 12. A third aspect of the invention provides a multitude of phosphor-enhanced light sources as claimed in claim 13. Advantageous embodiments are defined in the dependent claims.
A method of manufacturing a phosphor-enhanced light source being configured to emit light having a predefined color characteristic in accordance with the first aspect of the invention comprises the steps of: (i) receiving a phosphor-enhanced lighting module, the phosphor-enhanced lighting module comprises a light emitter, a luminescent material and a light exit window, the light emitter configured to emit light in a first spectral range, the luminescent material configured to absorb a portion of the light in the first spectral range and to convert at least a part of the absorbed light to light of a second spectral range, the phosphor-enhanced lighting module configured to emit a specific light emission distribution comprising light of the first spectral range and light of the second spectral range through the light exit window, (ii) selecting a partially back-reflecting optical layer having a specific back-reflection characteristic being related to the specific light emission spectrum of the received phosphor-enhanced lighting module, the partially back-reflecting optical layer partially reflects back light that impinges on the partially back-reflecting optical layer and partially transmits light that impinges on the partially back-reflecting optical layer, the back- reflection characteristics being defined as a ratio between the amount of back-reflected light and the amount of transmitted light, (iii) assembling the selected partially back-reflecting optical layer in front of the light exit window to partially reflect emitted light back to the luminescent material.
Thus, the phosphor-enhanced light sources that are manufactured with the method according to the invention use the partially back-reflecting optical element to redirect a part of the light that is emitted by the phosphor-enhanced lighting module back towards the luminescent material. The luminescent material absorbs some of the back-reflected light and converts the absorbed light towards light of the second spectral range. Consequently, the ratio between light of the second spectral range and light of the first spectral range become larger and the color characteristic of the light that is emitted by the phosphor-enhanced light source changes. By carefully selecting a specific partially back-reflecting optical layer, phosphor- enhanced light sources are manufactured that have the predefined color characteristic.
The manufacturing method allows the use of phosphor-enhanced lighting modules which each have a slightly different light emission spectrum. If, according to the invention, slightly different light emission spectra are corrected with the partially back- reflecting optical layers, the average manufacturing costs of the phosphor-enhanced lighting modules significantly drop. If phosphor-enhanced lighting modules have to be manufactured according to a tight specification, no tolerances can be accepted in the components of the phosphor-enhanced lighting modules or expensive manufacturing methods have to be used as discussed in the background of the art section. The method of manufacturing a phosphor- enhanced light source according to the invention only adds a relatively cheap additional element to the phosphor-enhanced lighting modules such that the phosphor-enhanced light source emits light that has the required predefined color characteristic. Partially back- reflecting optical elements are in general relatively cheap optical elements, even if they have to fulfill a relatively tight back-reflection reflection characteristic. The cost savings with respect to allowing the use of phosphor-enhanced lighting modules having slightly different light emission spectra are larger than the cost increase of assembling an additional optical element. Thus, a cheaper phosphor-enhanced light source emitting light having a predefined color characteristic may be manufactured.
It is to be noted that the obtained light emission by the phosphor-enhanced light source has the predefined color characteristic, which means that within a predefined deviation interval the color characteristic of the light emitted by the phosphor-enhanced light source is equal to the predefined color characteristic.
It is further to be noted that the phosphor-enhanced lighting module may also comprise a further luminescent material which is configured to absorb light of the first color range or of the second color range and to convert a part of the absorbed light towards a third color range. More than two different luminescent materials may also be comprised in the phosphor-enhanced lighting module. The luminescent materials may be organic or inorganic luminescent materials which are provided in, for example, a coating to a substrate, a solid sheet of sintered phosphor in a ceramic binder, particles of an inorganic phosphor are dispersed in a matrix polymer, or molecules of an organic phosphor are molecularly dissolved in the matrix polymer.
Optionally, the color characteristic is one of: a color point of the emitted light in a color space, a correlated color temperature of the emitted light. Optionally, the step of selecting a partially back-reflecting optical layer comprises the steps of (i) measuring a color characteristic of the received phosphor-enhanced lighting module, (ii) determining a required back-reflection characteristic on basis of the measured color characteristic by using a model which represents relations between the measured color characteristics, back-reflection characteristics and the color characteristics of the phosphor-enhanced lighting module for different phosphor-enhanced light modules of a specific type of a phosphor-enhanced lighting module, (iii) obtaining the partially back- reflecting optical layer which has a specific back-reflection characteristic that matches the required back-reflection characteristic.
By measuring the color characteristic of the received phosphor-enhanced lighting module it is possible to determine the back-reflection characteristic which is required to obtain a light emission by the phosphor-enhanced light source especially if the model comprises the relations between the different characteristics of different components of the phosphor-enhanced light source, the measured color characteristic and the final light emission by the phosphor-enhanced light source for the type of phosphor-enhanced light modules. If the required back-reflection characteristic is known, a partially back-reflecting optical layer, which fulfills this requirement, may be obtained. These optional steps allow the selection of the best fitting partially back-reflecting optical layer and as such it results in a phosphor-enhanced light source which has exactly the predefined color characteristic.
Optionally, the model is based on previously executed color characteristic measurements of different phosphor-enhanced lighting modules of different phosphor- enhanced lighting modules of the type of phosphor-enhanced lighting modules which are provided with and without different partially back-reflecting optical layers. Obtaining a model may be based on a mathematical model of the physics of the phosphor-enhanced lighting model and the partially back-reflecting optical layer, however, in many situations it is more cost-effective to obtain an empirical model which is based on several measurements of different phosphor-enhanced lighting modules of the same type which were provided with different back-reflecting optical layers or were not provided with the back-reflecting optical layer. Especially when specific characteristics of the phosphor-enhanced lighting modules and the partially back-reflecting optical layers are often changed in the production process it may be advantageous to obtain after every change a new model calibration step instead of consulting a team of scientists who build the new theoretical model.
Optionally, the step of obtaining the partially back-reflecting optical layer comprises the step of (i) manufacturing the partially back-reflecting optical layer having the required back-reflection characteristic in response to determining the back-reflection characteristic, or (ii) selecting an earlier manufactured partially back-reflecting optical layer from a stock of different partially back-reflecting optical layers having different back- reflection characteristics. Depending on specific characteristics of the partially back- reflecting optical layers it may be advantageous in specific manufacturing processes to keep a stock of different partially back-reflecting optical layers of which one is selected that fulfills the required back-reflection characteristics most, and in other situations it may be
advantageous to manufacture a partially back-reflecting optical layer after determining the required back-reflection characteristics. It is to be noted that the step of manufacturing the partially back-reflecting optical layer is a step which is often referred to as "manufacturing on demand". In specific manufacturing processes the manufacturing of the partially back- reflecting optical layer may be done relatively quick such that the whole manufacturing process is not delayed, and in other specific manufacturing processes, it may take some time before the specific partially back-reflecting optical layer is ready for use, which means that the phosphor-enhanced lighting module has to be kept in stock for some time. Manufacturing the partially back-reflecting optical layer on demand often results in very accurate partially back-reflecting optical layers having the required back-reflection characteristic.
The manufacturing of a specific partially back-reflecting optical layer may be done by printing (inkjet, plotting, dispensing, gravure, etc.) a partially reflective pattern on an optical layer, or by applying specific coatings on a light-transmitting substrate by means of spin-coating, spray coating, blade or slot coating, a sputter coating or evaporation process, or plasma-enhanced chemical vapor deposition (PECVD).
Optionally, the step of selecting the partially back-reflecting optical layer comprises (i) positioning a first back-reflecting optical layer in front of the light exit window of the received phosphor-enhanced lighting module, the back-reflection characteristic of the first back-reflecting optical layer increases in a specific direction, (ii) positioning a second back-reflecting optical layer in front of the first back-reflection optical layer, the back- reflection characteristic of the second back-reflecting optical layer decreases in the specific direction, (iii) measuring a color characteristic of the light emitted by a combination of the received phosphor-enhanced lighting module, the first back-reflecting optical layer and the second back-reflection layer, (iv) moving the first back-reflecting optical layer relatively to the second back-reflecting layer and/or relatively to the light exit window while still measuring the color characteristic until the measured color characteristic is substantially equal to the predefined color characteristic, and (v) forming the selected partially back- reflecting optical layer from a first subarea of the first back-reflecting optical layer and a second subarea of the second back-reflection layer, the first subarea and the second subarea respectively are selected from the first back-reflecting optical layer and the second back- reflecting layer, the selected respective subareas are the subareas which result in the predefined color characteristic In other words, the first subarea and the second subarea were in front of the light exit window of the phosphor-enhanced lighting module at the moment when the measured color characteristic was substantially equal to the predefined color characteristics.
With the above optional steps of selecting the partially back-reflecting optical layer the correct partially back-reflecting optical layer is obtained via measuring the color characteristic and moving the first partially back-reflecting optical layer and/or second partially back-reflecting optical layer and/or the phosphor-enhanced lighting module until the correct color characteristic is measured. This allows the exact selection of the first subarea of the first back-reflecting optical layer and the second subarea of second back-reflecting optical layer such that the required back-reflection characteristic of the partially back-reflecting optical layer is obtained and thereby the light emission by the phosphor-enhanced light source has the required predefined color characteristic. The first back-reflecting optical layer may be a foil which has a back-reflecting gradient in a specific lateral direction, and the second back-reflecting optical layer may be the same foil which is rotated 180 degrees. This allows the use of a single foil having the back-reflecting gradient and, thus, because of the relatively large numbers in which this foil is to be manufactured, the price of the foil can be kept low.
Optionally, the partially back-reflecting optical layer is one of, or a
combination of: (i) one or more parallel arranged plates of a light transmitting material having a refractive index that is larger than 1.4, (ii) a light transmitting substrate provided with a dielectric coating, the light transmitting substrate has a first refractive index and the dielectric coating has a second refractive index which is at least 0.2 larger than the first refractive index, (iii) diffusing layer, (iv) wavelength selective reflective layer.
A plate of a light transmitting material may be glass or a plate of a transparent synthetic material. Such materials are available in high quantities at relatively low prices. A back-reflection characteristic, expressed as a percentage, of a single plate varies between 5.4% and 20% depending on the angle of incidence of the light and depending on the polarization of the light which impinges on the plate. By applying multiple plates on top of each other, larger back-reflection characteristics may be obtained. If multiple plates are used they may not be in optical contact, which means that the interface between the plates cannot be ignored from an optical standpoint of view. Layers of a transparent material do not absorb much light and as such do not contribute to an inefficiency of the phosphor-enhanced light source.
By using a low-cost transparent, but stable, substrate on which a dielectric coating with a high refractive index is provided, an effective and cost-effective partially back-reflecting optical layer may be obtained. Such a dielectric coating is, for example, SiNx and can easily be deposited with sputter coating or plasma-enhanced chemical vapor deposition (PECVD). Layers with the dielectric coating have typically low absorption value and hardly scatter the light.
A diffusing layer is, for example, a transparent substrate on which a coating with specific scattering particles is applied. The particles are, for example, particles of Ti02 (Anatase) or A1203. The diffusing layer may also be a synthetic transparent material in which the particles are dispersed. An advantage of diffusing layer is that the light output of the phosphor-enhance light source is more uniform, the color-over-angle of the light output is more uniform, and that the color appearance of the luminescent material of the phosphor- enhanced lighting module is reduced.
Optionally, the wavelength selective reflective layer is one of: a dichroic filter or a filter of a matrix polymer comprising scattering nanoparticles.
An advantage of the wavelength selective reflective layer is that more light in a predefined spectral range to which the luminescent material is sensitive is back-reflected, in other words, by selecting a specific wavelength selective layer light of the first spectral range is mainly back-reflected and, consequently, converted to light of the second spectral range. Thus, it is prevented that back-reflected light to which the luminescent material is not very sensitive is absorbed. A dichroic filter can be tuned to have a more discrete back-reflection profile such that it reflects back a very specific color range, while the matrix polymer comprising scattering nanoparticles has a continuous back-reflection profile wherein some wavelengths are back-reflected to a higher extent than other wavelengths. A matrix material such as solgel which comprises particles of about 200nm of Ti02 reflects back more blue light than yellow/orange light, which is advantageous if the light emitter of the phosphor- enhanced lighting module emits blue light and the luminescent material converts blue light towards yellow/orange light. Optionally, the step of assembling the selected partially back-reflecting optical layer in front of the exit window comprises the creation of gap between a layer forming the light exit window and the selected partially back-reflecting optical layer.
A gap is a space with a transparent material having a refractive index of about 1, thus, the space may be filled with environmental air or another transparent gas. For some specific partially back-reflecting optical layers it is required that the difference between the refractive index of the gap and the refractive index of the partially back-reflecting optical layers is large enough to obtain enough back-reflection of light.
A further advantage of the gap is that, especially if the light exit window of the phosphor-enhanced lighting module is formed by a layer that comprises the luminescent material, the partially back-reflecting optical layer does not directly receive heat from the luminescent material. The luminescent material can become relatively warm because of conversion inefficiencies. If the partially back-reflecting optical layer is made of a synthetic material, for example, when it is a foil, it must be prevented that the partially back-reflecting optical layer becomes deteriorated because of the heat that it received from the luminescent material.
Optionally, the creation of the gap comprises the step of creating spacing structures between the layer forming the light exit window and the selected partially back- reflecting optical layer.
Especially if the partially back-reflecting optical layer is a foil it is advantageous to put spacing structures in between the light exit window and the partially back-reflecting optical layer to keep the partially back-reflecting optical layer at the required distance from the light exit window. It prevents, for example, that the foil bends towards the light exit window and that the foil comes in contact with the light exit window. The back- reflection characteristic may change when the foil is bent. Further, the phosphor-enhanced light source does not have the required appearance when the foil is bent.
The spacing structures may be formed by positioning or gluing small light transmitting components between the two layers, or by printing a synthetic material at specific locations such that the two layers are sufficiently separated. For foils, the spacing structures may also be formed by means of hot embossing techniques.
Optionally, the phosphor-enhanced lighting module has an absorption coefficient that is lower than 0.2. The absorption coefficient is the ratio between an amount of light that is absorbed by the phosphor-enhanced lighting module of an amount of light that impinges on the light exit window and the amount of light that impinges on the light exit window of the phosphor-enhanced lighting module.
Tests have shown that very efficient phosphor-enhanced light sources can be manufactured if the phosphor-enhanced lighting modules have a relatively low absorption coefficient. The partially back-reflecting optical layer reflects back a part of the light that is emitted by the phosphor-enhanced lighting module to allow a portion of the back-reflected light to be converted by the luminescent material. If the absorption coefficient of the phosphor-enhanced light source is relatively low, another portion of the back-reflected light that is not absorbed by the luminescent material is reflected and emitted once again. Thus, the back-reflection of light does not contribute much to an inefficiency of the phosphor-enhanced light source, because the back-reflected light is recycled or it is converted to light of the second color range.
Optionally, the phosphor-enhanced lighting module has an absorption coefficient that is lower than 0.1
According to a second aspect of the invention, a phosphor-enhanced light source is provided which is obtained by the method of manufacturing the phosphor-enhanced light source according to the first aspect of the invention.
The phosphor-enhanced light source according to the second aspect of the invention provides the same benefits as the phosphor-enhanced light source manufactured with the method according to the first aspect of the invention and has similar embodiments with similar effects as the corresponding options discussed in the context of the
manufacturing method.
According to a third aspect of the invention, a multitude of phosphor-enhanced light sources is provided for emitting light having a predefined color characteristic. Each phosphor-enhanced light source comprises a phosphor-enhanced lighting module and a partially back-reflecting optical layer. The phosphor-enhanced lighting module comprises a light emitter, a luminescent material and light exit window. The light emitter is configured to emit light in a first spectral range. The luminescent material is configured to absorb a portion of the light in the first spectral range and to convert at least a part of the absorbed light to light of a second spectral range. The phosphor-enhanced lighting module is configured to emit a specific light emission distribution comprising light of the first spectral range and light of the second spectral range through the light exit window. The partially back reflecting optical layer is assembled in front of the light exit window. The partially back-reflecting optical layer has a specific back-reflection characteristic that is related to the specific light emission spectrum of the phosphor-enhanced lighting module. The partially back-reflecting optical layer partially reflects back light that is received from the phosphor-enhanced lighting module. The light is reflected back towards the luminescent material of the phosphor- enhanced lighting module. Further, the partially back-reflecting layer partially transmits light that is received from the phosphor-enhanced lighting module. The back-reflection
characteristic is defined by a ratio between the amount of back-reflected light and the amount of transmitted light. The phosphor-enhanced lighting modules of a plurality of the multitude of phosphor-enhanced light sources each emit a different specific light emission distribution if the phosphor-enhanced lighting modules are in use without a partially back-reflecting optical layer, and each partially back-reflecting optical layer of the plurality of the multitude of phosphor-enhanced light sources has a different back-reflection characteristic.
The multitude of phosphor-enhanced light sources according to the third aspect of the invention provide the same benefits as the phosphor-enhanced light source manufactured with the method according to the first aspect of the invention and has similar embodiments with similar effects as the corresponding options discussed in the context of the manufacturing method.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
It will be appreciated by those skilled in the art that two or more of the above- mentioned options, implementations, and/or aspects of the invention may be combined in any way deemed useful.
Modifications and variations of the method, which correspond to the described modifications and variations of the method, can be carried out by a person skilled in the art on the basis of the present description.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Fig. 1 schematically shows a method of manufacturing a phosphor- enhanced light source according to the first aspect of the invention, Fig. 2 schematically shows another embodiment of the method, Fig. 3 schematically shows a cross-section of a phosphor-enhanced light source, Fig. 4 schematically shows equipment that is being used in a specific
embodiment of the method,
Fig. 5 schematically shows different color points in a color space of light emitted by a plurality of phosphor-enhanced light sources which are based on two types of phosphor-enhanced lighting module,
Fig. 6 schematically shows the efficiency of the different phosphor- enhanced light sources of Fig. 5.
It should be noted that items denoted by the same reference numerals in different Figures have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item have been explained, there is no necessity for repeated explanation thereof in the detailed description.
The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly
DETAILED DESCRIPTION OF THE EMBODIMENTS
A first embodiment is shown in Fig. 1. A method 100 of manufacturing a phosphor-enhanced light source is schematically presented. The phosphor-enhanced light source will be manufactured by the method such that the phosphor-enhanced light source is configured to emit light that has a predefined color characteristic. In step 102 of the method 100 a phosphor-enhanced lighting module is received. The phosphor-enhanced lighting modules comprise a light emitter, a luminescent material and a light exit window. The light emitter emits light of a first color. The luminescent material absorbs light of the first color and converts (a part of) the absorbed light towards light of the second color. The phosphor- enhanced lighting module emits, in use, light of a specific light emission distribution which comprises light of the first color and light of the second color.
Because of manufacturing deviations, the light emitter and the used luminescent material may have slightly different characteristics and, consequently, the color characteristic of the specific light emission of individual phosphor-enhanced lighting modules may differ from the predefined color characteristic. For example, the predefined color characteristic is that the phosphor-enhanced light source has to emit light of a correlated color temperature of about 3000 Kelvin, while the light that is emitted by the different phosphor-enhanced lighting module has a correlated color temperature in the range from 3000 to 3500 Kelvin. In step 104 of the method 100 a partially back-reflecting optical layer is selected which has a specific back-reflection characteristic that is related to the specific light emission spectrum of the phosphor-enhanced lighting module that was received in step 102. The partially back-reflecting optical layer partially reflects back light that impinges on the partially back-reflecting optical layer and transmits a portion of the light that is not refiected back through the layer. The back-reflection characteristic of the partially back-reflecting optical layer is related to a ratio between the amount of back-reflected light and the amount of the transmitted light.
In step 106 of the method the selected partially back-reflecting optical layer is assembled in front of the light exit window of the received phosphor-enhanced lighting module such that it partially reflects light back that is emitted by the phosphor-enhanced lighting module. The light is refiected back towards the luminescent material of the phosphor-enhanced lighting module.
Thus, a specific portion of the light that is emitted by the phosphor-enhanced lighting module is reflected back to the luminescent material which, subsequently, absorbs a portion of the back-reflected light and converts a part of this absorbed light towards light of the second color. This additional light of the second color is also emitted into the direction of the light exit window and, thus, into the direction of the partially back-reflecting optical layer. Consequently, the relative amount of light of the second color increases in the total light emission of the phosphor-enhanced light source.
In specific embodiments, the light emitter of the phosphor-enhanced lighting module emits blue light, and the luminescent material converts a part of the blue light towards yellow-orange light such that the obtained light emission is a color point near the black body line in a color space. By reflecting some light back with the partially back- reflecting optical layer, the relative amount of yellow-orange light is increased in the total light emission of the phosphor-enhanced light source and, consequently, the color point slightly shifts in the color space along a vector in the yellow-orange direction.
Different embodiments for the selected partially back-reflecting optical layers are:
(1) Parallel plates of, for example, glass or other (semi)transparent material with different refractive index n: from n = 1.4 to n = 2. The perpendicular reflection for a single plate increases from 5.4% up to 20%, with larger values for larger angles, depending on the polarization. Multiple plates stacks (without being in optical contact) easily provide larger reflectivity values without adding significant absorption. (2) A similar effect can be achieved at lower material cost by using a low-cost, transparent but stable substrate with n in the range between n = 1.5 and 1.6 (glass, plastic, etc.) with a thin dielectric coating with high n, such as SiNx. Such coatings have a typical refractive index around 2.0 and can be easily deposited using sputter coating or PECVD (plasma- enhanced chemical vapor deposition), etc. Depending on the thickness of the coating, the reflection increases (assuming a refractive index of 1.58 for the substrate) from 9.6% (no coat) to 22% (90 nm SiNx of n=2.0). Advantage in both cases is that scattering and absorption are very low. Larger reflectivity values can be obtained by a properly designed multi- layer stack with alternating high and low refractive index layers, or by stacking multiple coated substrates (not in optical contact).
(3) Alternative coating is a white diffusing coating, containing particles of Ti02 (Anatase) or A1203. Such coatings can be deposited by spin coating, printing or spraying in various thickness, at various densities (volume fraction), enabling a range of reflectivity with low absorption. Additional advantage of such coatings is that they improve the white appearance of the light module, effectively hiding the specific color appearance of the luminescent material. The scattering effect is also beneficial for improving the consistency of color over angle, especially when more transparent phosphors are used. The latter will have a beneficial effect on the system efficiency due to reduced losses in the phosphor layer.
(4) Instead of uniform coatings, the refiectivity can also be tuned by changing the area coverage. For example, dot patterns of varying diameter and spacing can be used.
(5) The above examples of partially back-reflecting optical layers assume a direct match between light module and optical element. By using two or more optical elements which can be adjusted with respect to each other, for example by translation or rotation, a mechanical adjustment of standard elements replaces the selection procedure, which can be advantageous in the production process and related costs. At least one of the optical elements would typically have a lateral gradient in reflection properties. For example, two linear but opposite gradients moved with respect to each other will give a variation in reflectivity which is uniform over the area.
(6) For improved efficiency, the optical element should preferably (partially) reflect the light of the first color (for example blue) light and transmit the light of the second color (for example yellow) This can be achieved by using a scattering material preferentially scattering blue light, such as a geld containing, for example, small Ti02 or similar nanoparticles. Alternatively, a simple dichroic coating can be applied, comprising a dedicated multi- layer stack with alternating high and low refractive index layers. This layer ideally has a specified reflectivity for blue (405 - 460 nm), and negligible reflection and high
transmission for larger wavelengths.
(7) Any combination of the above discussed options (1) to (6) In Fig. 2 another embodiment of a method 200 of manufacturing a phosphor- enhanced light source is schematically presented. In step 102 of method 200 is received a phosphor-enhanced lighting module. In step 104 a partially back-reflecting optical layer is selected. In step 106 the selected partially back-reflecting optical layer is assembled in front of a light exit window of the phosphor-enhanced light source.
In the step 104 of selecting the partially back-reflecting optical layer two alternative approaches could be applied.
In a first approach, in step 202, a color characteristic of the received phosphor- enhanced lighting module is measured. The measured color characteristic is used in step 204 to determine a required back-refiection characteristic. In step 204, a model which represents relations between the measured color characteristic, back-reflection characteristics and the light emission of the phosphor-enhanced light source. The model may a mathematical model which takes into account most of the optical parameters of the type of the use phosphor- enhanced lighting module and the available partially back-reflecting optical layers, or the model may be based on empirical data. The empirical data is, for example, obtained by measuring the color characteristics of different phosphor-enhanced lighting modules of type of used phosphor-enhanced lighting modules with or without different partially back- reflecting optical layers. Subsequently, in step 206 the partially back-reflecting optical layer is obtained which has a specific back-refiection characteristic that matches the required back- refiection characteristic. The step of obtaining the partially back-reflecting optical layer may be performed by manufacturing the partially back-reflecting optical layer in response to determining the back-refiection characteristic as schematically presented in step 208.
Alternatively, as schematically presented in step 210, an earlier manufactured partially back- reflecting optical layer is selected from a stock. In practical situations it is impossible to keep a stock of partially back-reflecting optical layers with all possible back-refiection
characteristics. Therefore, when the earlier manufactured partially back-reflecting optical layer is selected, the selected partially back-reflecting optical layer has a back-reflection characteristic that is within a predefined interval from the determined back-reflection characteristic. In a second approach, in step 212 a first back-reflecting optical layer is positioned in front of the phosphor-enhanced lighting module. The first back-reflecting optical layer has a gradually increasing back-reflection characteristic in a specific direction. In step 214 a second back-reflecting optical layer is positioned in front of the first back- reflecting optical layer and the phosphor-enhanced lighting module. The first back-reflecting optical layer has a gradually decreasing back-reflection characteristic in the specific direction. Subsequently, a color characteristic is measured. The color characteristic is of the light which is emitted by a combination of the received phosphor-enhanced lighting module, the first back-reflecting optical layer and the second back-reflecting layer. Subsequently, in step 218, the first back-reflecting optical layer is moved with respect to the second back- reflecting optical layer, or the second back-reflecting layer is moved with respect to the first back-reflecting optical layer, or both back-reflecting optical layers are moved with respect to each other. The moving may be based on the measured color characteristic, or may be based on trial-and-error. If the moving is based on the measured color characteristic, it is known in which direction which back-reflecting optical layer must be moved to get, for example, a higher or lower correlated color temperature. After the relative movements the color characteristic is once again measured in step 216, or the color characteristic is continuously measured while moving the first back-reflecting optical layer and/or the second back- reflecting layer. The alternation of steps 216 and 218, or the continuously execution of steps 216 and 218, is continued until the measured color characteristic is substantially equal to the predefined color characteristic, which means, that the measured color characteristic may be within a predefined error interval from the predefined color characteristic. If the measured color characteristic is substantially equal to the predefined color characteristic, the selected partially back-reflecting optical layer is formed by combining a subarea of the first back- reflecting optical layer with a subarea of the second back-reflecting optical layer. The subareas are the portions of the respective first and second back-reflecting optical layers that were in front of the light exit window at the moment when the measured color characteristic was substantially equal to the predefined color characteristic. The subareas may, for example, be cut out of the respective first and second back-reflecting optical layers and may be glued together to form the selected partially-reflected optical layer. In an example, the respective first and second back-reflecting optical layers may also be a foil with a back-reflection gradient. A foil may, for example, be cut by means of laser beam.
The step 106 of assembling the selected partially back-reflecting optical layer in front of the light exit window may comprise the step 222 of creating a gap between the selected partially back-reflecting optical layer and the light exit window. Further, the step 222 of creating the gap, may comprise the step of creating spacing structures in between the layer which forms the light exit window and the selected partially back-reflecting optical layer.
In Fig. 3, a cross-section of a phosphor-enhanced light source 300, which is obtainable by the method 100, 200, is presented. At the top end of Fig. 3 a cross-section of the phosphor-enhanced light source 300 is presented which comprises a phosphor-enhanced lighting module 302 to which a partially back-reflecting optical layer 312 is assembled. The phosphor-enhanced lighting module 302 comprises a light emitter 308 which emits light of a first color 306 which is, for example, blue light. The phosphor-enhanced lighting module 302 comprises a light exit window 316 which is formed by a luminescent layer 304 which comprises a luminescent material. The luminescent material absorbs a portion of the light of the first color 306 and converts a part of the absorbed light towards light of a second color 310, which is, for example, yellow/orange light. The light emission of the phosphor-enhanced lighting module 302 is a combination of light of the first color 306 and light of the second color 310. The light emission of the phosphor-enhanced lighting module 302 is emitted through a gap 314, which is filled with for example air, towards the partially back-reflecting optical layer 312. The partially back-reflecting optical layer 312 partly reflects light of the first color 306 and light of the second color 310 and partly transmits the respective light of the first color 306 and of the second color 310. The light that is reflected back impinges on the luminescent layer 304 and is, once again, partly absorbed and a part of the light that is absorbed is converted to light of the second color 310. As such, the total light emission of the phosphor-enhanced light source 300 comprises a larger amount of light of the second color 310 compared to the light emission of the phosphor-enhanced lighting module 302 without the partially back-reflecting optical layer 312. Consequently, the total light emission of the phosphor-enhanced light source 300 has another color characteristic than the light emission of the phosphor-enhanced lighting module 302 without the partially back-reflecting optical layer 312. By carefully tuning the amount of back-reflected light, the relative increase of light of the second color 310 in the total light emission can be carefully controlled to obtain the color characteristic that is within a predefined error interval from a predefined required color characteristic.
A part of the presented cross-section of the phosphor-enhanced light source is enlarged at the bottom end of Fig. 3. A section of the phosphor-enhanced lighting module 302 is presented which comprises a light emitter, for example, a blue emitting Light Emitting Diode (LED), which is provided on a substrate 376 which is assembled to the housing 378 of the phosphor-enhanced lighting module 302. The housing 378 encloses a light mixing cavity 374. Surfaces of the housing 378 and surfaces of substrate 376 which face towards the cavity 374 are, in an advantageous embodiment, light reflective. The partially back-reflecting optical layer 312 is assembled to the luminescent layer 304 by means of spacing structures 354. In the presented cross-section the spacing structures 354 are drawn at the edge of the partially back-reflecting optical layer 312 and the luminescent layer 304, however, in other embodiments, the spacing structures 354 may also be provided at other locations in between the partially back-reflecting optical layer 312 and the luminescent layer 304.
In the enlarged portion presented at the bottom end several flows of light are presented. The light emitter 308 emits light 306 of a first color. A portion 350 of the light of the first color is transmitted through the luminescent layer 304 towards the partially back- reflecting optical layer 312. A portion of the light of the first color is absorbed by the luminescent material of the luminescent layer 304 and is converted towards light 364 of the second color. The generated light 364 of the second color is emitted through the gap towards the partially back-reflecting optical layer 312. At the interface between the gap and the partially back-reflecting optical layer 312 a portion 356 of the light of the first color and another portion 360 of light of the second color are reflected back towards the luminescent layer 304.
The back-reflected portion 356 of light of the first color is partly absorbed by the luminescent material in the luminescent layer 304 and is emitted as additional light 358 of the second color. Some light 366 of the back-reflected portion 356 of light of the first color is transmitted through the luminescent layer 304. The transmitted light 366 impinges on the surfaces of the housing 378 or on surfaces of the substrate 376 and is reflected back to the luminescent layer 304 as indicated by arrow 370.
The back-reflected portion 360 of light of the second color may also be absorbed by the luminescent material in the luminescent layer 304 and may be emitted again as light 362 of the second color. This effect is called self-absorption, which means that the luminescent material may also absorb some light in the spectral range of the second color. However, this portion is in general relatively low, and depending on the specific luminescent material this amount may be neglected. A part of light 368 of the back-reflected portion 360 of light of the second color is transmitted through the luminescent layer 304. The transmitted light 368 impinges on the surfaces of the housing 378 or on surfaces of the substrate 376 and is reflected back to the luminescent layer 304 as indicated by arrow 372. The back-reflected portions 356, 360 of light which are transmitted into the cavity 374 are reflected by the surfaces which face the cavity 374 and, consequently, this light is recycled and gets another chance of being transmitted via the luminescent layer 304 and the partially back-reflecting optical layer 312 into the ambient. Also portions of this light may be absorbed and converted by the luminescent material and some portions of this light may be back-reflected another time. The recycling of light contributes to the efficiency of the phosphor-enhanced light source 300 because not much of the back-reflected light is absorbed at one of the surfaces of the housing 378 or of the substrate 376.
It is to be noted that the presented phosphor-enhanced lighting module 302 is just a possible example of such a phosphor-enhanced lighting module 302. In other embodiments other light emitters may be used, another number of light emitters may be present, the cavity may have another shape, and/or the luminescent material may be present at another position, etc. Phosphor-enhanced lighting modules 302, which are suitable for being used in the manufacturing method of the invention, at least comprise a light emitter, a luminescent material, and a light exit window, and the luminescent material is arranged such that, if light impinges on the light exit window, this impinging light is at least partly transmitted towards the luminescent material.
Fig. 4 schematically presents a manufacturing system 400 for performing a specific option of the manufacturing method of the invention.
The manufacturing system 400 comprises a controller 401, a color characteristic sensor 408, a first actuator 416, a second actuator 402, a first subarea selector 406 and a second subarea selector 410.
At the bottom end of Fig. 4, a cross-section of a received phosphor-enhanced lighting module 302 is presented. The phosphor-enhanced lighting module 302 has the same characteristics of earlier discussed phosphor-enhanced lighting modules in the context of, for example, Fig. 3.
A first back-reflecting optical layer 404 is positioned in front of the light exit window of the phosphor-enhanced lighting module 302 and the first back-reflecting optical layer 404 is brought in contact with the first actuator 416 which is capable of moving the first back-reflecting optical layer 404 to the left and to the right. The first back-reflecting optical layer 404 has a back-reflection characteristic which decreases from its left edge to its right edge, which is schematically presented with a diagonal line in the first back-reflecting optical layer 404. A second back-reflecting optical layer 414 is positioned in front of the first back-reflecting optical layer 404 and light exit window of the phosphor-enhanced lighting module 302 and the second back-reflecting optical layer 414 is brought in contact wit the second actuator 402 which is capable of moving the second back-reflecting optical layer 414 to the left and to the right. The second back-reflecting optical layer 414 has a back-reflection characteristic which increases from its left edge to its right edge, which is schematically presented with a diagonal line in the second back-reflecting optical layer 414.
The color characteristic sensor 408 measures a color characteristic of the light that is received from the phosphor-enhanced lighting module with the two back-reflecting optical layers in front of its light exit window. The color characteristic is, for example, the color point of emitted light, or in another embodiment, the correlated color temperature of the emitted light.
The measured color characteristic is communicated to the controller 401 which decides whether the measured color characteristic is within a predefined deviation interval from a predefined required color characteristic. If this is not the case, the controller 401 controls the first actuator 416 and/or the second actuator 402 to move, respectively, the first back-reflecting optical layer 404 and/or to move the second back-reflecting optical layer 414. The actuators 402, 416 may be controlled to move their respective back-reflecting optical layer to the left or to the right. If, for example, the first back-reflecting layer 404 is moved to the left, and the second back-reflecting layer 414 is moved to the right, the total back-reflection characteristic of subarea of the two respective back-reflecting layers 404, 414, which are in front of the light exit window, decreases and the color characteristic changes more towards the color characteristic of the light that is emitted by the phosphor- enhanced lighting module 302 without back-reflecting optical layers in front of its light exit window.
If the measured color characteristic is within a predefined deviation interval from a predefined required color characteristic, the controller 401 controls the actuators 402, 416 such that they do not move the respective back reflecting layers 404, 414 anymore and the first subarea selector 406 and the second subarea selector 410 are controlled to select subareas of respectively the first back-reflecting optical layer 404 and the second back- reflecting optical layer 414 that are in front of the light exit window of the phosphor- enhanced lighting module 302. The respective subarea selectors 406, 410 may use, for example, a sawing means to cut-off parts of the first back-reflecting optical layer 404 and the second back-reflecting optical layer 414 which extend outside the footprint of the phosphor- enhanced lighting module 302. In another embodiment, a laser beam is used to divide the first back-reflecting optical layer 404 and the second back-reflecting optical layer 414 into pieces. After selecting the subareas, the subareas are combined to form the selected partially back-reflecting optical layer.
Fig. 5 presents the results of some experiments. A CIE XYZ color space is presented in which different color points of light emitted by two types of a specific phosphor- enhanced lighting module without and with different partially back-reflecting optical layers.
The types of light emitting modules comprise at their light exit window two luminescent layers which each comprise a different luminescent material. In a first configuration, the luminescent layer, which provides light of a warm color, is the bottom layer which faces the light emitter of the phosphor-enhanced lighting module and not faces the ambient. Phosphor-enhanced lighting modules of the first type are indicated in the graph by "ww down" or "down. In a second configuration the luminescent layer, which provides light of a warm color, is the top layer which faces the ambient. This type is indicated in the graph by "ww up" or "up".
Two measurements were taken for each phosphor-enhanced lighting module without a partially back-reflecting optical layer, which are respectively indicated in the graph with "ref mixbox ww down" and "ref mixbox ww up".
The respective measurements for "down - glass" and "up - glass" are of phosphor-enhanced lighting modules provided with a layer of glass.
The respective measurements for "down - lx tape" and "up - lx tape" are of phosphor-enhanced lighting modules provided with one layer of Scotch tape. The Scotch tape operates as a scattering layer.
The respective measurements for "down - 2x tape" and "up - 2x tape" are of phosphor-enhanced lighting modules provided with two layers of Scotch tape.
The respective measurements for "down - Ti02 5.8 mu" are of phosphor- enhanced lighting modules provided with a glass plate which comprises a coating with Ti02 scattering nanoparticles. The thickness of the coating is 5.8 μιη.
The measurement of "up - A1203 is of a phosphor-enhanced lighting module of the second type which is provided with a glass plate with a coating comprising A1203 scattering particles.
The measurement of "up - Ti02 1.3 mu" is of a phosphor-enhanced lighting module of the second type which is provided with a glass plate with a coating with Ti02 scattering nanoparticles. The thickness of the coating is 1.3 μιη. The measurement of "up - Ti02 4.3 mu" is of a phosphor-enhanced lighting module of the second type which is provided with a glass plate with a coating with Ti02 scattering nanoparticles. The thickness of the coating is 4.3 μιη.
In the subsequent table, the results of the measurements are provided in a textual format:
Phosphor-enhanced lighting Color point Correlated
module type - Partially- X V color
reflective optical layer temperature
ww down - no partially-reflective 0.39 0.35 3381
optical layer
ww down - glass 0.40 0.37 3245
ww down - lx tape 0.42 0.38 3103
ww down - 2x tape 0.42 0.38 3062
ww down - Ti02 5.8 mu 0.46 0.41 2688
ww up - no partially-reflective 0.23 0.34 3844
optical layer
ww up - glass 0.40 0.40 3709
ww up - lx tape 0.41 0.41 3550
ww up - 2x tape 0.413 0.41 3500
ww up - A1203 0.414 0.415 3500
ww up - Ti02 1.3 mu 0.412 0.412 3509
ww up - Ti02 4.3 mu 0.44 0.43 3120
ww up - Ti02 5.8 mu 0.45 0.43 3036
Table 1 : experimental results
As may be seen in the table and in Fig. 5, glass is a good candidate for a partially back-reflective layer of glass if the correction of the color characteristic has to be small. It is further seen that a glass substrate with a 5.8 μιη layer comprising Ti02 is a good candidate for a partially back-reflective if the correction of the color characteristic has to be relatively large.
In Fig. 6 the results of efficiency measurement are presented. The efficiency of a plurality of the phosphor-enhanced light sources of the experiments of Fig. 5 was measured. Especially the presented efficiency value related to the phosphor-enhanced light sources which comprise the phosphor-enhanced lighting module of the second configuration. In the graph of Fig. 6 the relative efficiency of the phosphor-enhanced light sources compared to the reference phosphor-enhanced lighting module is drawn. It is seen that, the more light is reflected back, the lower the efficiency is. For example, the glass plate with the 5.8 μιη Ti02 coating results in the largest correction of the color characteristic of the reference phosphor- enhanced lighting module and also results in a phosphor-enhance light source having the lowest efficiency. However, the efficiency loss is relatively low and, as such, the efficiency loss is not a disadvantage compared to the advantage of the lower manufacturing costs of the phosphor-enhanced light sources.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.
In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and partly by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:
1. A method (100, 200) of manufacturing a phosphor-enhanced light source
(300) being configured to emit light having a predefined color characteristic, the method (100, 200) comprises the steps of
receiving (102) a phosphor-enhanced lighting module (302), the phosphor- enhanced lighting module (302) comprises a light emitter (308), a luminescent material and a light exit window (316), the light emitter (308) configured to emit light in a first spectral range, the luminescent material is configured to absorb a portion of the light in the first spectral range and to convert at least a part of the absorbed light to light of a second spectral range, the phosphor-enhanced lighting module (302) configured to emit a specific light emission distribution comprising light of the first spectral range and light of the second spectral range through the light exit window (316),
selecting (104) a partially back-reflecting optical layer (312) having a specific back-reflection characteristic being related to the specific light emission spectrum of the received phosphor-enhanced lighting module (302), the partially back-reflecting optical layer (312) partially reflects back light that impinges on the partially back-reflecting optical layer (312) and partially transmits light that impinges on the partially back-reflecting optical layer (312), the back-reflection characteristics being defined as a ratio between the amount of back-reflected light and the amount of transmitted light,
assembling (106) the selected partially back-reflecting optical layer (312) in front of the light exit window (316) to partially reflect emitted light back to the luminescent material.
2. A method (100, 200) according to claim 1, wherein the color characteristic is one of: a color point of the emitted light in a color space, a correlated color temperature of the emitted light.
3. A method (100, 200) according to claim 1, the step of selecting (104) a partially back-reflecting optical layer (312) comprises the steps of:
measuring (202) a color characteristic of the received phosphor-enhanced lighting module (302),
determining (204) a required back-reflection characteristic on basis of the measured color characteristic by using a model representing relations between the measured color characteristics, back-reflection characteristics and the color characteristics of the phosphor-enhanced lighting module (302) for different phosphor-enhanced light modules (302) of a specific type of a phosphor-enhanced lighting module (302),
obtaining (206) the partially back-reflecting optical layer (312) which has a specific back-reflection characteristic that matches the required back-reflection characteristic.
4. A method (100, 200) according to claim 3, wherein the model is based on previously executed color characteristic measurements of different phosphor-enhanced lighting modules (302) of the type of phosphor-enhanced lighting modules provided with and without different partially back-reflecting optical layers (312).
5. A method (100, 200) according to claim 3, wherein the step of obtaining (206) the partially back-reflecting optical layer (312) comprises the step of:
manufacturing (208) the partially back-reflecting optical layer (312) having the required back-reflecting characteristic in response to determining the back-reflection characteristic, or
- selecting (210) an earlier manufactured partially back-reflecting optical layer
(312) from a stock of different partially back-reflecting optical layers (312) having different back-reflecting characteristics.
6. A method (100, 200) according to claim 1, the step of selecting (104) the partially back-reflecting optical layer (312) comprises
positioning (212) a first back-reflecting optical layer (404) in front of the light exit window (316) of the received phosphor-enhanced lighting module (302), the back- reflection characteristic of the first back-reflecting optical layer (404) increases in a specific direction,
- positioning (214) a second back-reflecting optical layer (414) in front of the first back-reflecting optical layer (404), the back-reflection characteristic of the second back- reflecting optical layer (414) decreases in the specific direction,
measuring (216) a color characteristic of the light emitted by a combination of the received phosphor-enhanced lighting module (302), the first back-reflecting optical layer (404) and the second back-reflecting optical layer (414),
moving (218) the first back-reflecting optical layer (404) relatively to the second back-reflecting optical layer (414) and/or relatively to the light exit window (316) while still measuring the color characteristic until the measured color characteristic is substantially equal to the predefined color characteristic,
forming (220) the selected partially back-reflecting optical layer (312) from a first subarea of the first back-reflecting optical layer (404) and a second subarea of the second back-reflection optical layer (414), the first subarea and the second subarea being respectively selected from the first back-reflecting optical layer (404) and the second back- reflecting optical layer (414), the selected respective subareas are the subareas which result in the predefined color characteristic.
7. A method (100, 200) according to claim 1, wherein the partially back- reflecting optical layer (312) is one of, or a combination of:
- one or more parallel arranged plates of a light transmitting material having a refractive index that is larger than 1.4,
a light transmitting substrate provided with a dielectric coating, the light transmitting substrate has a first refractive index and the dielectric coating has a second refractive index being at least 0.2 larger than the first refractive index,
- diffusing layer,
wavelength selective reflective layer.
8. A method (100, 200) according to claim 7, wherein the wavelength selective reflective layer is one of: a dichroic filter or a filter of a matrix polymer comprising scattering nanoparticles.
9. A method (100, 200) according to claim 1, wherein the step of assembling (106) the selected partially back-reflecting optical layer (312) in front of the light exit window (316) comprises step of creating (222) of gap between a layer forming the light exit window (316) and the selected partially back-reflecting optical layer (312).
10. A method (100, 200) according to claim 9, wherein the step of creating (222) the gap comprises the step of creating (224) spacing structures between the layer forming the light exit window (316) and the selected partially back-reflecting optical layer (312).
11. A method (100, 200) according to claim 1, wherein the phosphor-enhanced lighting module (302) has an absorption coefficient that is lower than 0.2. , the absorption coefficient is a ratio between an amount of light that is absorbed by the phosphor-enhanced lighting module (302) of an amount of light that impinges on the light exit window (316) and the amount of light that impinges on the light exit window (316).
12. A phosphor-enhanced light source (300) obtained by the method (100, 200) of claim 1.
13. A multitude of phosphor-enhanced light sources (300) for emitting light having a predefined color characteristic, each phosphor-enhanced light source (300) comprising:
a phosphor-enhanced lighting module (302) comprising a light emitter (308), a luminescent material and light exit window (316), the light emitter (308) being configured to emit light in a first spectral range, the luminescent material being configured to absorb a portion of the light in the first spectral range and to convert at least a part of the absorbed light to light of a second spectral range, the phosphor-enhanced lighting module (302) being configured to emit a specific light emission distribution comprising light of the first spectral range and light of the second spectral range through the light exit window (316),
a partially back-reflecting optical layer (312) assembled in front of the light exit window (316), the partially back-reflecting optical layer (312) having a specific back- reflection characteristic related to the specific light emission spectrum of the phosphor- enhanced lighting module (302), the partially back-reflecting optical layer (312) is configured to partially reflect back light that is received from the phosphor-enhanced lighting module (302) towards the luminescent material of the phosphor-enhanced lighting module (302) and is configured to partially transmits light that is received from the phosphor-enhanced lighting module (302), the back-reflection characteristics being defined by a ratio between the amount of back-reflected light and the amount of transmitted light,
wherein the phosphor-enhanced lighting modules (302) of a plurality of the multitude of phosphor-enhanced light sources (300) each emit a different specific light emission distribution if the phosphor-enhanced lighting modules (302) are in use without a partially back-reflecting optical layer (312), and each partially back-reflecting optical layer (312) of the plurality of the multitude of phosphor-enhanced light sources (300) has a different back- reflection characteristic.
PCT/IB2012/053460 2011-07-14 2012-07-06 Method of manufacturing a phosphor-enhanced light source WO2013008157A1 (en)

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WO2016034469A1 (en) * 2014-09-02 2016-03-10 Koninklijke Philips N.V. Light source
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