EP2554018B1

EP2554018B1 - Light emitting diode light source

Info

Publication number: EP2554018B1
Application number: EP11716052.3A
Authority: EP
Inventors: Hong Zhong; Yi MEI; Roger Cornelis Petrus Hoskens
Original assignee: Philips Lighting Holding BV
Current assignee: Signify Holding BV
Priority date: 2010-04-02
Filing date: 2011-03-23
Publication date: 2017-05-10
Anticipated expiration: 2031-03-23
Also published as: RU2012146737A; WO2011121489A1; EP2554018A1; RU2557016C2; JP2013524427A; CN102812782B; CN102812782A; PL2554018T3; JP5805175B2

Description

TECHNICAL FIELD

This invention relates generally to lighting technology, and more particularly to light emitting diode (LED) light sources.

BACKGROUND

In the LED light source field, warm white light having a color temperature of 2700K and 3000K (abbreviated to "2700/3000K" in the following paragraphs) can be obtained from a mix of blue light, yellow/green light and a huge amount of red light. In one approach, by coating nitride red fluorescent powder and phosphor, for example yttrium aluminum garnet (YAG), onto gallium nitride (GaN)-based blue LED chips, for example, warm white light can be produced by mixing the yellow/green light and the red light, which are generated by activating the nitride red fluorescent powder and phosphor with a portion of blue light emitted from the blue LED, with the unabsorbed blue light which passes through the nitride red fluorescent powder and phosphor. However, in this approach, there may be a great deal of energy loss during light conversion from blue to red, and therefore the lighting efficiency of this type of warm white LED light source is low.
In order to improve the lighting efficiency of a warm white LED light source, in another approach, the warm white LED light source can be constituted by packaging an array of phosphor-coated blue LEDs, for example a YAG-coated GaN-based blue LED array, with a red LED array, for example an aluminum indium gallium phosphide (AlInGaP) LED array. Compared with the preceding approach of converting blue light to red light, the lighting efficiency of this approach is much higher, because the red LED array directly emits the red light, and the quality of the mixed warm white light is better. US7213940B1 discloses a lighting device comprising first and second groups of solid state light emitters which emit light having dominant wavelengths in ranges from 430nm to 480nm and from 600nm to 630nm, respectively, and a first group of lumiphors which emit light having dominant wavelengths in the range from 555nm to 585nm. By supplying current to a power line, a combination of light exiting the lighting device emitted by the first group of emitters, and light exiting the lighting device emitted by the first group of lumiphors produces, in absence of any additional light, a sub-mixture of light having x, y color coordinates within an area on a 1931 CIE Chromaticity Diagram defined by points having coordinates (0.32, 0.40), (0.36, 0.48), (0.43, 0.45), (0.42, 0.42), (0.36, 0.38).
However, since a blue LED has a different temperature-dependence of the lumen output as compared to that of the red LED, i.e. the lumen degradation of the red LED is much stronger than that of the blue LED as the junction temperature rises. Thus, when the LED light source is in operation, that is, the junction temperature reaches a high level, a color point of the warm white light, mixed from the cold white light emitted from the phosphor-coated blue LED array and the red light emitted from the red LED array, may shift greatly. When the color point of the mixed warm white light shifts away from 5 MacAdam ellipses of a color temperature of 2700/3000K on the black-body locus, the observer may observe that the color of the warm white light source is more greenish or reddish.
Normally, when the LED light source is in the operational state, and if the ratio of the lumen output of the phosphor-coated blue LED array to the lumen output of the red LED array is within a range of 4.8:1 to 3.8:1, the color point of the warm white light, mixed from the cold white light emitted from the phosphor-coated blue LED array and the red light emitted from the red LED array, can locate within 5 MacAdam ellipses of a color temperature of 2700/3000K on the black-body locus.
Usually, a warm white LED light source constituted by packaging the phosphor-coated blue LED array with the red LED array is driven by a dual-channel driver. Besides the dual-channel driver, the lighting system having the LED light source is generally further equipped with a temperature sensor. When the LED light source is in the operational state, the temperature sensor measures the junction temperature of the LED array and sends the temperature information to the dual-channel driver. Based on the received temperature information, the dual-channel driver adjusts the currents supplied to the phosphor-coated blue LED array and the red LED array, respectively, so that the ratio of the lumen output thereof remains in the range of 4.8:1 to 3.8:1.
The warm white LED light source driven by the dual-channel driver can make sure that the ratio of the lumen output of the phosphor-coated blue LED array to the lumen output of the red LED array remains in the range of 4.8:1 to 3.8:1 during its operation, however, since this type of lighting system adopting LED light sources includes the temperature sensor and the dual-channel driver, it is complicated in structure and the cost is higher.

SUMMARY

In order to simplify the design and reduce the cost, it would be desirable to use a single-channel driver to drive the phosphor-coated blue light emitting diode array and the red light emitting diode array, that is, the phosphor-coated blue light emitting diode array and the red light emitting diode array are driven by the same current.
To better address the above concern, in one embodiment of the present invention, a light emitting diode light source is provided. The light source comprises: a red light emitting diode array; a phosphor-coated blue light emitting diode array, a color point of the mixed light emitted from the phosphor-coated blue light emitting diode array falling into a quadrilateral of the CIE chromaticity diagram, wherein coordinates of four vertices of the quadrilateral are (0.375, 0.427), (0.390, 0.456), (0.366, 0.430), (0.38, 0.46); wherein, when the junction temperature of the light emitting diodes of the phosphor-coated blue light emitting diode array and the light emitting diodes of the red light emitting diode array is substantially equal to room temperature, the ratio of the lumen output of the phosphor-coated blue light emitting diode array to the lumen output of the red light emitting diode array is within a range of 4:1 to 1.5: 1; and wherein, in operation, the red light emitting diode array and the phosphor-coated blue light emitting diode array are driven by the same current. According to an embodiment, when the light emitting diode light source is in the operational state, that is, a junction temperature of light emitting diodes of the phosphor-coated blue light emitting diode array and light emitting diodes of the red light emitting diode array is for example between 70°C and 100°C, the ratio of the lumen output of the phosphor-coated blue light emitting diode array to the lumen output of the red light emitting diode array may be within a range of 4.8:1 to 3.8:1, so that the color point of the warm white light, mixed from the cold white light emitted from the phosphor-coated blue light emitting diode array and the red light emitted from the red light emitting diode array, can locate within 5 MacAdam ellipses of a color temperature of 2700/3000K on the black-body locus, and thus the quality of the warm white light emitted from the light emitting diode light source is efficiently improved.
Advantageously, the quantity ratio and/or area ratio of the light emitting diodes of the phosphor-coated blue light emitting diode array to the light emitting diodes of the red light emitting diode array is adjusted such that the ratio of the lumen output of the phosphor-coated blue light emitting diode array to the lumen output of the red light emitting diode array is within a range of 4:1 1 to 1.5:1.
Advantageously, the component ratio and/or grain size of the phosphor is adjusted such that the color point of the mixed light emitted from the phosphor-coated blue light emitting diode array falls within the quadrilateral.
Advantageously, the peak emission wavelength of the blue light emitting diode array is set within a range of 440nm to 460nm. Advantageously, the blue light emitting diode array is a gallium nitride-based blue light emitting diode array.
Advantageously, the peak emission wavelength of the red light emitting diode array (110) is set within a range of 600nm to 620nm. Advantageously, the red light emitting diode array is an AlInGaP light emitting diode array.
Advantageously, the phosphor comprises YAG or TAG.
According to another embodiment of the present invention, a lighting apparatus is provided. The lighting apparatus comprises a single-channel driver and any of the light emitting diode light sources described above, wherein the light emitting diode light source is driven by the single-channel driver.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic view of a light emitting diode light source 100 according to an embodiment of the present invention;
Figure 2 is a schematic view of a lighting apparatus 10 according to an embodiment of the present invention;
Figure 3 is a CIE chromaticity diagram according to an embodiment of the present invention;
Figure 4 shows a layout of respective light emitting diodes of the light emitting diode light source 100 according to an embodiment of the present invention. Corresponding numerals and symbols in different Figures generally refer to corresponding parts unless otherwise indicated.

DETAILED DESCRIPTION OF illustrative embodiments

Embodiments of the present invention are described in detail hereinbelow with reference to the accompanying drawings.
Figure 1 is a schematic view of a light emitting diode light source 100 according to an embodiment of the present invention.
Figure 2 is a schematic view of a lighting apparatus 10 according to an embodiment of the present invention. The lighting apparatus 10 comprises a single-channel driver 200 and the light emitting diode light source 100 of Figure 1.
As shown in Figures 1 and 2, the light emitting diode light source 100 comprises a red light emitting diode array 110 and a phosphor-coated blue light emitting diode array 120. The red light emitting diode array 110 may include one or more red light emitting diodes, and similarly the blue light emitting diode array 120 may include one or more red light emitting diodes.
In an embodiment, the peak emission wavelength of the blue light emitting diode array 120 is set within a range of 440nm to 460nm. Advantageously, the blue light emitting diode array 120 comprises a gallium nitride-based blue light emitting diode array.
The gallium nitride-based blue light emitting diode array includes, but is not limited to, a GaN blue light emitting diode array, a GaAlN blue light emitting diode array, an InGaN light emitting diode array, or an InAlGaN blue light emitting diode array.
In an embodiment, the peak emission wavelength of the red light emitting diode array 110 is set within a range of 600nm to 620nm. Advantageously, the red light emitting diode array 110 comprises an AlInGaP light emitting diode array.
In an embodiment, the phosphor comprises YAG (Yttrium Aluminum Garnet) . In another embodiment, the phosphor comprises TAG (Terbium Aluminum Garnet).
As illustrated in Figure 2, the red light emitting diode array 110 and the phosphor-coated blue light emitting diode array 120 are coupled in series, and the operational current thereof is supplied by the single-channel driver 200.
When the light emitting diode light source 100 is in the operational state, the operational current supplied by the single-channel driver 200 flows through the red light emitting diode array 110 and the phosphor-coated blue light emitting diode array 120, so that the arrays 110 and 120, respectively, are activated to emit light. A portion of the blue light emitted from the blue light emitting diode array 120 activates the phosphor coated thereon to emit yellow/green light, and the yellow/green light is mixed with unabsorbed blue light passing through the phosphor to generate cold white light. Then, the cold white light emitted from the phosphor-coated blue light emitting diode array 120 is mixed with the red light emitted from the red light emitting diode array to form warm white light.
In the embodiments of Figures 1 and 2, the color point of the mixed light emitted from the phosphor-coated blue light emitting diode array 120 falls within a quadrilateral of a CIE chromaticity diagram of Figure 3. The coordinates of four vertices of the quadrilateral are (0.375, 0.427), (0.390, 0.456), (0.366, 0.430), (0.38, 0.46).
In an embodiment, the component ratio of the phosphor may be adjusted such that the color point of the mixed light emitted from the phosphor-coated blue light emitting diode array 120 falls within the quadrilateral.
In another embodiment, the grain size of the phosphor may be adjusted such that the color point of the mixed light emitted from the phosphor-coated blue light emitting diode array 120 falls within the quadrilateral.
In a further embodiment, both the component ratio of the phosphor and the grain size of the phosphor may be adjusted such that the color point of the mixed light emitted from the phosphor-coated blue light emitting diode array falls within the quadrilateral.
Furthermore, in the embodiments of Figures 1 and 2, when the junction temperature of the light emitting diodes of the phosphor-coated blue light emitting diode array 120 and the light emitting diodes of the red light emitting diode array 110 is substantially equal to room temperature, the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is within a range of 4:1 to 1.5:1.
Advantageously, the room temperature is 25°C.
It will be appreciated that the room temperature of the present invention may allow a minor deviation from 25 °C.
In an embodiment, a predetermined duration of operational current supply to the phosphor-coated blue light emitting diode array 120 and the red light emitting diode array 110 is in the form of pulses, and the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is measured. Then, the quantity ratio of the blue light emitting diodes of the phosphor-coated blue light emitting diode array 120 to the red light emitting diodes of the red light emitting diode array 110 is adjusted such that the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is within a range of 4:1 to 1.5:1.
Since the predetermined duration of operational current supply to the phosphor-coated blue light emitting diode array 120 and the red light emitting diode array 110 is in the form of pulses, the junction temperature of the light emitting diodes is substantially equal to room temperature, so that the accuracy of the measured ratio of the lumen output is ensured and thus the accuracy of the following adjustment to the ratio of the lumen output is ensured.
Optionally, the predetermined duration is from 5 to 100 ms, and advantageously, the predetermined duration is 25 ms.
Optionally, the duty ratio of the operational current supplied in the form of pulses ranges from 1% to 20%.
In another embodiment, the area ratio/total area ratio of the blue light emitting diodes of the phosphor-coated blue light emitting diode array 120 to the red light emitting diodes of the red light emitting diode array 110 may be adjusted such that the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is within the range of 4:1 to 1.5:1.
In a further embodiment, both the quantity ratio and the area ratio of the blue light emitting diodes of the phosphor-coated blue light emitting diode array 120 to the red light emitting diodes of the red light emitting diode array 110 may be adjusted such that the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is within the range of 4:1 to 1.5:1.
When the junction temperature of the light emitting diodes of the phosphor-coated blue light emitting diode array 120 and the red light emitting diode array 110 is substantially equal to room temperature, the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is within the range of 4:1 to 1.5:1. Thus, when the light emitting diode light source is in the operational state, that is, the junction temperature of the light emitting diodes of the phosphor-coated blue light emitting diode array 120 and the light emitting diodes of the red light emitting diode array 110 is for example between 70°C and 100°C, the ratio of the lumen output of the phosphor-coated blue light emitting diode array 120 to the lumen output of the red light emitting diode array 110 is within a range of 4.8:1 to 3.8:1, so that the color point of the warm white light, mixed from the cold white light emitted from the phosphor-coated blue light emitting diode array 120 and the red light emitted from the red light emitting diode array 110, can locate within the 5 MacAdam ellipses of a color temperature of 2700/3000K on the black-body locus as shown in Figure 3.
Figure 4 illustrates a layout of respective light emitting diodes of the light emitting diode light source 100 according to an embodiment of the present invention. The red light emitting diode array 110 of the light emitting diode light source 100 comprises a first red light emitting diode 1101 and a second red light emitting diode 1102, and the phosphor-coated blue light emitting diode array 120 comprises a first phosphor-coated blue light emitting diode 1201 and a second phosphor-coated blue light emitting diode 1202. As illustrated in Figure 4, four light emitting diodes of the light emitting diode light source 100 are set asymmetrically on a substrate. The first phosphor-coated blue light emitting diode 1201 is set on the left side of the substrate, the first red light emitting diode 1101 and the second red light emitting diode 1102 are symmetrically set respectively on the upper side and lower side of the substrate, and the second phosphor-coated blue light emitting diode 1202 is set on the right side of the substrate.
It is to be noted that the layout of Figure 4 is an illustrative example, and it will be appreciated that the layout of the light emitting diodes of the light emitting diode light source 100 is not limited to the layout described above.
In an embodiment, the phosphor-coated blue light emitting diode array 120 and the red light emitting diode array 110 are packaged onto a carrier substrate, for example a ceramic substrate with a single silicone lens encapsulation on all these two light emitting diode arrays.
In another embodiment, the phosphor-coated blue light emitting diode array 120 and the red light emitting diode array 110 are packaged onto a carrier substrate, for example a ceramic substrate with a silicone lens encapsulation on each individual light emitting diode array.
Although it is described in the previous embodiments that a light emitting diode light source 100 according to embodiments of the present invention is driven by a single-channel driver, the light emitting diode light source is not limited to be driven by a single-channel driver, and it may also be driven by a dual-channel driver. As mentioned above, when the light emitting diode light source is driven by the dual-channel driver, it is relatively complicated in structure and the cost is higher. The light emitting diode light source of embodiments of the present invention, driven by the single-channel driver, has the same lighting performance, further reduces the cost and simplifies the structure.
Although the present invention has been described above in detailed descriptions and with reference to the accompanying drawings, it should be understood that such descriptions are merely illustrative and are not to be construed in a limiting sense; therefore, the present invention is not limited to such embodiments.
It will also be readily understood that those skilled in the art may understand and implement other variations of the disclosed embodiments by studying the specification, disclosed contents, accompanying drawings and appended claims. In the claims, the verb "to comprise" and its conjugations does not exclude other elements and steps, and the indefinite article "a/an" does not exclude a plurality. In practical applications of the present invention, the function of a plurality of technical features in the claims may be implemented by a single component. It should be understood that any of the reference numbers in the accompanying drawings and in the claims does not limit the scope of the present invention.

Claims

A light emitting diode light source (100) comprising:
a red light emitting diode array (110); and

a phosphor-coated blue light emitting diode array (120),

characterized in that

a color point of the mixed light emitted from the phosphor-coated blue light emitting diode array (120) falling within a quadrilateral of the CIE chromaticity diagram, wherein coordinates of four vertices of the quadrilateral are (0.375, 0.427), (0.390, 0.456), (0.366, 0.430), (0.38, 0.46);

wherein, when the junction temperature of the light emitting diodes of the phosphor-coated blue light emitting diode array (120) and the light emitting diodes of the red light emitting diode array (110) is substantially equal to room temperature, the ratio of the lumen output of the phosphor-coated blue light emitting diode array (120) to the lumen output of the red light emitting diode array (110) is within a range of 4:1 to 1.5:1; and

wherein, in operation, the red light emitting diode array (110) and the phosphor-coated blue light emitting diode array (120) are driven by the same current.
The light emitting diode light source (100) of claim 1, wherein the quantity ratio and/or area ratio of the light emitting diodes of the phosphor-coated blue light emitting diode array (120) to the light emitting diodes of the red light emitting diode array (110) are adjusted such that the ratio of the lumen output of the phosphor-coated blue light emitting diode array (120) to the lumen output of the red light emitting diode array (110) is within a range of 4:1 to 1.5:1.
The light emitting diode light source (100) of claim 1 or 2, wherein, when light emitting diode light source is in the operational state, the ratio of the lumen output of the phosphor-coated blue light emitting diode array (120) to the lumen output of the red light emitting diode array (110) is within a range of 4.8:1 to 3.8:1.
The light emitting diode light source (100) of claim 3, wherein the junction temperature of the light emitting diodes of the phosphor-coated blue light emitting diode array (120) and the light emitting diodes of the red light emitting diode array (110) is between 70°C and 100°C.
The light emitting diode light source (100) of claim 1, wherein the component ratio and/or grain size of the phosphor are adjusted such that the color point of the mixed light emitted from the phosphor-coated blue light emitting diode array (120) falls within the quadrilateral.
The light emitting diode light source (100) of claim 1, wherein the peak emission wavelength of the blue light emitting diode array (120) is set within a range of 440nm to 460nm.
The light emitting diode light source (100) of claim 6, wherein the blue light emitting diode array (120) comprises a gallium nitride-based blue light emitting diode array.
The light emitting diode light source (100) of claim 1, wherein the peak emission wavelength of the red light emitting diode array (110) is set within a range of 600nm to 620nm.
The light emitting diode light source (100) of claim 8, wherein the red light emitting diode array (110) comprises an AlInGaP light emitting diode array.
The light emitting diode light source (100) of claim 1, wherein the phosphor comprises YAG or TAG.
The light emitting diode light source (100) of claim 7, wherein the gallium nitride-based blue light emitting diode array comprises a GaN blue light emitting diode array, a GaAlN blue light emitting diode array, an InGaN light emitting diode array, or an InAlGaN blue light emitting diode array.
A lighting apparatus (10) comprising a single-channel driver (200) and the light emitting diode light source (100) according to any one of claims 1 to 11, wherein the light emitting diode light source (100) is driven by the single-channel driver (200).