Patent Application
20100172120
The invention relates to a color-tunable illumination system comprising a first light source, a second light source and a layer of first luminescent material.
The invention also relates to a luminaire comprising the illumination system.
Such illumination systems are known per se. They are used, inter alia, as luminaire for general lighting purposes, for example, for office lighting, for shop lighting or, for example, for in-home general lighting purposes.
The luminescent material generally absorbs part of the light emitted by a light source of the color-tunable illumination system and converts the absorbed light into light of a different color. The luminescent material is often arranged at a distance from the light source. This configuration is also referred to as a remote phosphor configuration. A benefit when using the remote phosphor configuration is that the conversion efficiency and the life-time of the luminescent material are improved and that the range of luminescent materials to choose from is improved.
Such a color-tunable illumination system is known from US 2005/0041424. In an embodiment of the known color-tunable illumination system the illumination system comprises at least a first blue light emitting diode emitting light having the color blue, and at least a second blue light emitting diode emitting light having the same color blue. The known illumination system comprises luminescent material which is arranged in so called carrier material. The carrier material is arranged in strips covering portions of a housing which surrounds the first and second light emitting diodes. The strips of carrier material may be arranged such that the illumination from at least one of the light emitting diodes is projected through the carrier material. By modulating the power of the separate light emitting diodes, the illumination conditions can be adapted, thus tuning a color of the known illumination system.
A disadvantage of the known illumination system is that light emitted from the known illumination system creates colored shadows.
It is an object of the invention to provide a color-tunable illumination system which reduces the occurrence of colored shadows.
According to a first aspect of the invention the object is achieved with a color-tunable illumination system according to claim 1. According to a second aspect of the invention, the object is achieved with a luminaire as claimed in claim 13. The color-tunable illumination system according to the invention comprises a first light source, a second light source and a layer of first luminescent material being arranged inside a light mixing chamber,
the light mixing chamber having a light exit window for emitting the light from the light mixing chamber,
the first light source and the second light source each comprising at least one light emitting diode and emitting light of a first predefined color into the light mixing chamber,
the first luminescent material absorbing light of the first predefined color and converting the absorbed light into light of a second predefined color different from the first predefined color, the first luminescent material being arranged remote from the first light source and the second light source, the first light source being positioned with respect to the first luminescent material for illuminating the first luminescent material with a first relative flux of light being a part of the light emitted by the first light source into the light mixing chamber, the second light source being positioned with respect to the first luminescent material for illuminating the first luminescent material with a second relative flux of light being part of the light emitted by the second light source into the light mixing chamber (60), the first relative flux being different from the second relative flux, and
the color-tunable illumination system further comprising a controller for controlling an intensity of the light emitted by the first light source relative to the intensity of the light emitted by the second light source and/or for controlling a position of the first light source with respect to the luminescent material relative to the position of the second light source with respect to the luminescent material.
The effect of the color-tunable light source according to the invention is that the use of the light mixing chamber generates substantially homogeneously mixed light emitted from the illumination system which prevents the occurrence of colored shadows. By using the controller, the intensity of the light emitted by the first light source can be tuned relative to the second light source which alters a flux of light of the first predefined color through the first luminescent material. Because the first relative flux is different from the second relative flux, the contribution of the light of the second predefined color to the mixed light emitted from the light mixing chamber can be controlled, thus tuning the light emitted by the color-tunable illumination system according to the invention. Consequently the color of the light emitted by the color-tunable illumination system may be altered while preventing colored shadows to occur.
In the known color-tunable illumination system, the different colors are produced by different light sources which are arranged in an array. When using these known color-tunable illumination systems in general lighting applications, the shadow of an object illuminated by the color-tunable illumination system will be constituted of a multiple of shadows originating from the different colored light sources and thus will have different colors resulting in colored shadows. In the color-tunable illumination system according to the invention the light from the different light sources and from the first luminescent material is mixed inside the light mixing chamber such that the light emitted by the color-tunable illumination system is substantially homogeneously mixed. When illuminating the object with light originating from the color-tunable illumination system according to the invention, the colored shadows will be reduced.
The inventors have realized that the position of the first luminescent material with respect to the first and second light source may be used to define a relative flux of the light of the first predefined color through the first luminescent material which may be used to alter a contribution of the converted light by the first luminescent material to the light emitted by the illumination system. To alter the color of the light emitted by the illumination system the controller, for example, alters the intensity of the light emitted by the first light source relative to the second light source. Alternatively, the controller alters a position of the first light source and/or of the second light source with respect to the luminescent material. The changing of the position alters the difference between the first relative flux with respect to the second relative flux and thus tunes the color of the emitted light by tuning the contribution of the light of the second predefined color to the mixed light emitted from the light mixing chamber. the intensity of the light emitted by the first light source relative to the second light source.
In this context, light of a predefined color typically comprises light having a predefined spectrum. The predefined spectrum may, for example, comprise a primary color having a specific bandwidth around a predefined wavelength, or may, for example, comprise a plurality of primary colors. The predefined wavelength is a mean wavelength of a radiant power spectral distribution. In this context, light of a predefined color also includes non-visible light, such as ultraviolet light. The light of a primary color, for example, includes Red, Green, Blue, Yellow and Amber light. Light of the predefined color may also comprise mixtures of primary colors, such as Blue and Amber, or Blue, Yellow and Red. By choosing, for example, a specific combination of the Red, Green and Blue light substantially every color can be generated by the illumination system, including white. Also other combinations of primary colors may be used in the light projection system which enables the generation of substantially every color, for example, Red, Green, Blue, Cyan and Yellow. The number of primary colors used in the color-tunable illumination system may vary.
In an embodiment of the color-tunable illumination system, the first light source is arranged for directly illuminating the first luminescent material, and the second light source is shielded from directly illuminating the first luminescent material By shielding the light emitted by the second light source from directly illuminating the first luminescent material the efficiency of the tuning of the light emitted by the color-tunable illumination system can be improved. Using the light mixing chamber generally homogeneously mixes the light from all light sources to generate a substantially homogeneously mixed light beam emitted from the light exit window of the light mixing chamber. Shielding to prevent direct illumination of the first luminescent material by the second light source can be achieved by proper placement of the first luminescent material and the first and second light source. Indirect illumination however will generally always be present to some extent, since light from the first luminescent material has to enter the mixing chamber, so light can travel in the opposite direction as well.
In an embodiment of the color-tunable illumination system, dichroic shielding means are arranged for shielding the second light source from illuminating the first luminescent material. The dichroic shielding means may, for example, transmit light of the second predefined color, and may reflecting light from the first predefined color.
In an embodiment of the color-tunable illumination system, the light mixing chamber comprises a further luminescent material converting light of the first predefined color into a further predefined color different from the first predefined color and the second predefined color. The further predefined color preferably is visible light, for example, white light. The light of the first predefined color, for example, may have a central wavelength in a range between 200 and 400 nanometers. Light in a range between 200 and 400 nanometers is also known as ultraviolet light. A benefit when using ultraviolet light as light of the first predefined color is that the color point of the light leaving the mixing chamber is only determined by a mixture of phosphors in the luminescent material because the light of the first predefined color does not contribute to the visible light. This as opposed to using blue light as light of the first predefined color, where the color point of the light leaving the light mixing chamber is also determined by thickness of the applied luminescent material since the thickness of the luminescent material determines an extent of the conversion of the blue light into light of the second predefined color. This means that the phosphor thickness when using blue light needs to be properly controlled, whereas this is not necessary for using light.
In an embodiment of the color-tunable illumination system, the first predefined color is within a ranged between 400 nanometers and 490 nanometers. Light having a central wavelength in a range between 400 and 490 nanometers is also known as blue light. A benefit when using blue light as light of the first predefined color is that this light is visible to humans and thus can directly be mixed into the output of the color-tunable illumination system without conversion. Any conversion using luminescent materials to convert light from one color to another introduces some loss of energy due to a Stokes-shift involved in the conversion. Using blue light as light of the first predetermined color some of the light emitted by the color-tunable illumination system does not need to be converted which increases the efficiency of the system. Furthermore, the Stokes-shift when converting blue light into light of the second predefined color is less than when converting ultraviolet light into light of the second predefined color, further increasing the efficiency. Furthermore, the color blue is one of the primary colors which may be used to mix with other primary colors such as red and green or such as yellow to obtain white light. For example, when choosing the further luminescent material to absorb part of the blue light emitted by the first and second light source and emits the further predefined color being the color yellow, and the amount of luminescent material is chosen properly so as to obtain the proper extent of conversion of light of the first predefined color, the light emitted from the color-tunable illumination system basically is the color white (due to the combination of remainder of the blue light and yellow light emitted by the further luminescent material). Adding the light of the second predefined color to the substantially white light will enable the color temperature of the light emitted by the color-tunable illumination system to be altered. Omitting the use of ultraviolet light in the color-tunable illumination system by using blue light as light of the first predefined color provides a further benefit that an additional UV-filter may be omitted. The UV-filter is typically required to prevent ultraviolet light from being emitted by the color-tunable illumination system. When the color-tunable illumination system is used in, for example, general lighting applications, the emission of ultraviolet light must be avoided because it is harmful to the human eye. When the light of the first predefined color is ultraviolet light, the light exit window typically contains the UV-filter which absorbs or reflects ultraviolet light before it is emitted. When using light emitting diodes which emit light of the color blue the UV-filter may be omitted which again increases the efficiency of the system and which reduces the cost of the color-tunable illumination system.
In an embodiment of the color-tunable illumination system, the color-tunable illumination system further comprises a third light source and a third luminescent material,
the third light source comprising at least one light emitting diode emitting light of the first predefined color into the light mixing chamber, the third light source being arranged for directly illuminating the third luminescent material while the first light source and second light source being shielded from directly illuminating the third luminescent material,
the third luminescent material absorbing light of the first predefined color and converting the absorbed light into light of a third predefined color different from the first predefined color and second predefined color. A benefit of this embodiment is that the use of the third luminescent material increases a range within which the color of the light emitted by the color-tunable illumination system can be tuned. For example, the adding of the light of the second predefined color may shift the color of the light emitted by the color-tunable illumination system from blue to yellow (or part thereof), while the adding of the light of the third predefined color may shift the color of the light emitted by the color-tunable illumination system from green to red (or part thereof). In another embodiment, the third light source and third luminescent material may be used to “fine-tune” the changing of the color temperature to properly follow, for example, the black body locus, which is a curved line in the color space. To follow a curved line in color space, three light sources with controlled relative intensities are needed.
In an embodiment of the color-tunable illumination system, the first luminescent material and/or the further luminescent material and/or the third luminescent material comprises a phosphor composition being a mixture of phosphors, each phosphor composition of the first luminescent material, the further luminescent material and/or the third luminescent material being different. For example, in the embodiment in which the first predefined color is ultraviolet light, the further luminescent material may, for example, be a mixture of phosphors providing substantially white light having a predefined color temperature and the first luminescent material and third luminescent material may convert the absorbed ultraviolet light into light of the second predefined color and of the third predefined color, respectively, which changes the color of the light emitted by the color-tunable illumination system, for example, to higher, respectively lower color temperature.
In an embodiment of the color-tunable illumination system, the first light source and/or the second light source comprises a series arrangement of a plurality of light emitting diodes. A benefit of this embodiment is that the use of a light source comprising a plurality of light emitting diodes enables an increase in the intensity of the light emitted by the color-tunable illumination system. Furthermore, the use of a plurality of light emitting diodes enables a more uniform distribution of the light emitting diodes inside the light mixing chamber which further improves a mixing of the light of the different light emitting diodes, resulting in an improved mixture of the light emitted by the color-tunable illumination system.
In an embodiment of the color-tunable illumination system, the light emitting diodes of the first light source are arranged in a further light mixing chamber comprising the first luminescent material or in a plurality of further light mixing chambers comprising the first luminescent material, the further light mixing chamber or the plurality of further light mixing chambers being arranged inside the light mixing chamber. A benefit of this embodiment is that the use of the further light mixing chamber or the plurality of further light mixing chambers pre-mixes the light of the first light source with the light of the second predefined color which improves the overall color mixing inside the light mixing chamber. The wall of the first light mixing chamber may, for example, be constituted of dichroic shielding means allowing light of the second predefined color to pass and reflecting light of the first predefined color. This arrangement substantially shields light of the second light source from impinging on the first luminescent material which enhances the color-tunability efficiency of the color-tunable illumination system according to the invention.
In an embodiment of the color-tunable illumination system, when the color-tunable illumination system comprises the further luminescent material, the plurality of light emitting diodes are arranged to substantially uniformly illuminate the light exit window of the light mixing chamber and wherein the further luminescent material is arranged at the light exit window of the light mixing chamber. A benefit of this embodiment is that it enables the color-tunable illumination system to be relatively compact. The light of the further predetermined color emitted by the further luminescent material is emitted substantially in all directions, and thus also emitted back into the light mixing chamber. Due to this emission of the light from the further luminescent material, part of the light of the further predetermined color is mixed in the light mixing chamber, further improving the color mixing of the color-tunable illumination system. Light generated by the first luminescent material must be transmitted through the light exit window and thus through the further luminescent material. Preferably the further luminescent material does not absorb light of the second predefined color or only absorbs a very small part of the light of the second predefined color.
In an embodiment of the color-tunable illumination system, the first and the second light source are arranged on an edge of the light mixing chamber next to the light exit window, each of the first and the second light source emitting light away from the light exit window preventing direct illumination of the light exit window by the first and the second light sources A benefit of this embodiment is that the light emitting diodes of the first and second light sources do not directly illuminate the light exit window which ensures good mixing of light and reduces a glare of the light source. An additional benefit is that the first and the second light source may be cooled without the use of active cooling arrangements such as fans or Peltier elements. The first and the second light source comprise a light emitting diode. Typically, light emitting diodes require some kind of cooling. When the first and the second light source is arranged on the edge of the light mixing chamber of the color-tunable illumination system next to the light exit window, the cooling of the light emitting diodes may be provided via cooling fins arranged, for example, on the outside of a housing of the color-tunable illumination system. This enables the color-tunable illumination system to be built into a luminaire or, for example, into a ceiling of a house, office or shop, while cooling the light emitting diodes via the cooling fins protruding from the luminaire or ceiling.
In an embodiment of the color-tunable illumination system, the first predefined color is the color blue, the first luminescent material converts the absorbed light of the first predefined color into amber light being the second predefined color, and the further luminescent material converts the absorbed light of the first predefined color into yellow light being the further predefined color. A benefit of this embodiment is that using a first luminescent material emitting amber, a further luminescent material emitting yellow together with the first predefined color being blue, the color-tunable illumination system according to the invention can tune the color of the emitted light from relatively cold white to warm white, for example, between 6500K and 2700K substantially along the black-body locus. For example, the first luminescent material comprises a mixture of Y3Al5O12:Ce3+ and CaS:Eu2+, and the further luminescent material (52) comprises Y3Al5O12:Ce3+. Alternatively, the first luminescent material comprises (Ba,Sr)2Si5N8:Eu2+, and the further luminescent material comprises Y3Al5O12:Ce3+. In a third embodiment, the first luminescent material comprises a mixture of Lu3Al5O12:Ce3+ and CaS:Eu2+, and the further luminescent material comprises a mixture of Lu3Al5O12:Ce3+ and CaS:Eu2+ with a different phosphor ratio. The first luminescent material may, for example, comprise a mixture of 85% w/w Y3Al5O12:Ce3+ (further also referred to as YAG:Ce) and 15% w/w CaS:Eu2+, (further also referred to as CaS:Eu) which mixture emits the second predefined color amber. The luminescent material (Ba,Sr)2Si5N8:Eu2+ (further also referred to as BSSN:Eu) emits the second predefined color amber. The luminescent material Lu3Al5O12:Ce3+ (further also referred to as LuAG:Ce) emits the second predefined color green, and the luminescent material CaS:Eu2+ (further also referred to as CaS:Eu) emits the second predefined color red. The embodiments using BSSN:Eu and YAG:Ce with blue light, and using two mixtures of LuAG:Ce and CaS:Eu with blue light can realize substantially the same effect. Other phosphors that convert blue light into red light, such as (Ba,Sr,Ca)2Si5N8:Eu2+, (Sr,Ca)S:Eu2+, and (Ca,Sr)AlSiN3:Eu2+, can be used instead of CaS:Eu, reaching substantially the same effect. Other phosphors that convert blue light into green light, such as Sr2Si2N2O2:Eu2+, and SrGa2S4: Eu2+, can be used instead of LuAG:Ce, reaching substantially the same effect. The garnet luminescent materials YAG:Ce and LuAG:Ce can be replaced by (Y3-x-yLuxGdy)(Al5-zSiz)(O12-zNz):Ce having 0<x≦3, 0≦y≦2.7, 0<x+y≦3 and 0<z≦2.
Using light sources emitting ultraviolet light and a first and a further luminescent material comprising for example a mixture of BaMgAl10O17:Eu2+ (converting ultraviolet light into blue light), Ca8Mg(SiO4)4Cl2: Eu2+, Mn2+ (converting ultraviolet light into green light), and Y2O3:Eu3+, Bi3+ (converting ultraviolet light into red light) with different phosphor ratios can enable a shift from relatively cold white to warm white, for example between 6500K and 2700K substantially along the black body locus. Any other color change is possible as well, determined by the phosphor ratio. Any other phosphor converting ultraviolet light into blue, green or red light or any other color can be used instead of the phosphors mentioned above.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
In the drawings:
The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the figures are denoted by the same reference numerals as much as possible.
In the embodiment of the color-tunable illumination system 10, 12 as shown in
In an embodiment of the color-tunable illumination system 10, 12, the first predefined color has a predefined wavelength in a range between 400 and 490 nanometers. This light of the first predefined color is also known as light of a primary color blue which is visible light to a human. Using, for example, YAG:Ce as further luminescent material 52 emits light of a primary color yellow when illuminated by light of the primary color blue. Combining the primary color blue and the primary color yellow inside the light mixing chamber 60 results in substantially cool white light which is emitted from the color-tunable illumination system 10, 12. The amount of the further luminescent material 52 inside the light mixing chamber 60 determines the color temperature of the white light emitted from the light mixing chamber 60. The first luminescent material 50 may, for example, comprise a mixture of the phosphors YAG:Ce and CaS:Eu, wherein the YAG:Ce contributes to the primary color yellow and wherein the CaS:Eu emits light of the primary color red which are mixed inside the light mixing chamber 60. By varying, for example, the weight percentages of the mixture of phosphors constituting the first luminescent material 50, the rate of change of the color of the light emitted by the light mixing chamber 60 of the color-tunable illumination system 10, 12 can be manipulated. Thus a specific range within which the color-tunable illumination system 10, 12 can be tuned can be preset. The combination of YAG:Ce and CaS:Eu enables the range of the change of color of the color-tunable illumination system 10, 12 to be near the black-body locus defined in the color-space. This embodiment is especially beneficial when using these color-tunable illumination systems 10, 12 in luminaires used in general illumination applications, because these color variations may, for example, be ultraviolet light which illuminates the further luminescent material 52 to most closely resemble variations in white light, as in sunlight throughout a day from morning to evening.
The light of the first predefined color produce, for example, substantially white light. Using light sources emitting ultraviolet light and a first and a further luminescent material comprising for example a mixture of BaMgAl10O17:Eu2+ (converting ultraviolet light into blue light), Ca8Mg(SiO4)4Cl2: Eu2+,Mn2+ (converting ultraviolet light into green light), and Y2O3: Eu3+,Bi3+ (converting ultraviolet light into red light) with different phosphor ratios can enable a shift from relatively cold white to warm white, for example between 6500K and 2700K.
Alternatively, other phosphors and/or phosphor mixtures may be used to obtain a change of color of the color-tunable illumination system according to the invention.
In a preferred embodiment of the color-tunable illumination system 10, 12 according to the invention, the light source 21, 22, 31, 32, 41 comprises light emitting diodes 21, 22, 31, 32, 41. However, the light source 21, 22, 31, 32, 41 may be any suitable light source, such as an organic LED, a low-pressure discharge lamp, a high-pressure discharge lamp, an incandescent lamp or a laser light source.
Alternatively, the colors of the first predetermined color, the second predetermined color and the third predetermined color may be any other color which is mixed in the light mixing chamber 60 to obtain a color-tunable light emission of the color-tunable illumination system 14 according to the invention. A benefit of the embodiment shown in
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. 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07108844.7 | May 2007 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB08/51972 | 5/20/2008 | WO | 00 | 11/17/2009 |
