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Patent Issued for Tunable White Color Methods and Uses

July 16, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Tu, Qifei (Shanghai, CN); Leung, Wa-Hing (Hong Kong, CN), filed on June 10, 2011, was published online on July 1, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8766555 is assigned to Huizhou Light Engine Ltd (Huizhou, CN).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to lighting devices and methods. In particular, devices and methods which use one or more light emitting devices and one or more luminescent materials.

"In current illumination systems, white light typically covers the Correlated Color Temperature ('CCT') range of from 2700K to 6500K.

"In order make CCT adjustments to current light sources, such as halogen or HID lamps, users are required to use color filters or gels to block unwanted color. In these cases, 20%-50% of light and electrical power is wasted.

"Illuminating sources, e.g., lighting devices, may produce 'white' light by adding two (or more) distinctly different combinations of colors. While the light emitted by any of these devices will appear white, if the devices are used to illuminate a colored object, which selectively absorbs certain colors, the object might look different when viewed with the two different 'white' lights. For this reason, different 'white' lights will reproduce colors of objects differently, depending upon the nature of the object.

"Color reproduction is typically measured using Color Rendering Index ('CRI'). CRI is a relative measurement of how the color rendition of an illumination system compares to that of a blackbody radiator. The CRI equals 100 if the color coordinates of a set of test colors being illuminated by the illumination system are the same as the coordinates of the same test colors being irradiated by the blackbody radiator. Natural daylight has the highest CRI (of 100), and is considered the aspiring standard for color reproduction ability. In order to quantify color rendering performance, the International Lighting Committee (CIE) originally defined 8 test color samples (TSC) and evaluated the color difference of the TSCs when lit by black body radiator and the light source to be evaluated.

"The color difference resulting for each TSC is termed as Ri (where i indicates the number of the TSC, initially set by the CIE from TSC1 to TSC8). CRI is an average value of R1 to R8 (the color difference values for TSC1 to TSC8, respectively) and is considered to be a general indicator of color rendering performance. Later, it was considered that 8 TSCs were not enough and 7 more TSCs (TSC9 to TSC15) were added.

"Characteristics of a lighting device can be represented on a 1931 CIE (Commission International de I'Eclairage) Chromaticity Diagram. Those skilled in the art are familiar with this Diagram, which represents the mapping of human color perception as a function of two CIE parameters 'x' and 'y.' These two parameters create chromaticity coordinates (x, y) which can be plotted in the Diagram. The spectral colors and their associated wavelengths are distributed along the edge of the outlined space, which includes all of the hues perceived by the human eye. The boundary line represents maximum saturation for the spectral colors.

"Deviation from a point on the 1931 CIE Chromaticity Diagram can be expressed in either in terms of coordinates, or, in order to indicate as to the extent of the perceived differences in color, in terms of MacAdam ellipses. MacAdam ellipses are, by way of example, a locus of points defined as being ten MacAdam ellipses from a specific hue defined by a particular set of chromaticity coordinates consists of hues which would each be perceived as differing from the specified hue to a common extent (and likewise for loci of points defined as being spaced from a particular hue by other quantities of MacAdam ellipses).

"The 1931 CIE Chromaticity Diagram also maps out a blackbody locus or 'Planckian' locus, wherein the chromaticity coordinates that lie along the blackbody locus obey Planck's equation: E(.lamda.)=A.sup.-5/(e.sup.(B/T)-1), where E is the emission intensity, .lamda. is the emission wavelength, T the color temperature of the blackbody and A and B are constants. The human eye perceives white light when chromaticity coordinates lie near or on the Planckian locus. The Diagram was revised in 1976 such that the distance between points on the diagram is approximately proportional to the perceived color difference. Duv represents the distance to the closest point on the Planckian locus on the CIE 1960 (uv) diagram.

"Correlated color temperature ('CCT') is the temperature of the blackbody whose perceived color most resembles that of the light source in question. Chromaticities falling on the black body or Planckian locus are identified by true color temperature while chromaticities near the locus are identified by CCT. In current illumination systems, white light typically covers CCT range of from 2700K to 6500K.

"Semiconductor light emitting diodes (LEDs) produce light by exciting electrons across the band gap between a conduction band and a valence band of the semiconductor light-emitting layer. The wavelength of the light generated, when the LED is driven by current, depends upon the semiconductor materials of the light-emitting layers of the LED. Thus, the emission spectrum of any particular LED is concentrated around one wavelength. Because white light is a blend of light of more than one color, it is impossible to produce white light with a single light emitting diode. Prior art devices have achieved reproduction of white light by, for example, employing a pixel made of respective red, green and blue light emitting diodes. Other conventional devices have used a combination of light emitting diodes, e.g., emitting blue light, and a luminescent material that emits, e.g., yellow light, in response to excitation from the light from the LED.

"As can be seen in FIG. 1, when white light is produced by combining two colors, the possible perceivable light that can be produced by such a combination graphs as a single line on the 1931 CIE Chromaticity Diagram. In FIG. 1, a hypothetical two color light source can produce light along the dotted line connecting the respective wavelength points of the two light sources along the outer outline edge of the Diagram. In the illustrated hypothetical case, white light could be produced by such a combination of light sources at the point at which the dotted line crosses the Planckian locus, at about 3000K.

"On the other hand, when three color light sources are used, the range of possible colors that can be produced is shown on the Diagram as a triangle having vertices corresponding to the wavelengths of the three color sources. For example, FIG. 1 shows a dashed triangle that is typical of a standard RGB (red, green, and blue) device, such as for example in a CRT for a television or computer monitor. Such a device can produce any color within the area of the dashed triangle. As for white light, the RGB display could also produce white at 3000K, as in the two color light, but is not limited to this CCT value. For example, in the illustrated example, white colors ranging from 2700K to 6500K can be produced by the RGB solution. However, as discussed above, while the appearance of the mixed light itself will be similar regardless of the component colors making up the light, the appearance of an object illuminated by various lighting devices, whether two or three color devices, will differ depending upon the component colors of the light source.

"While various combinations of phosphors (or 'lumiphors') and light emitting devices have conventionally been utilized to create white light, it has been difficult using solid state light emitters to produce light that will complement natural skin tones, for example in lamps used for makeup mirrors and other similar uses.

"U.S. Pat. No. 7,213,940 to Van de Ven et al. (the ''940 patent') attempts to address the problems relating to the production of pleasing white light by utilizing a device consisting of two types of LEDs and a lumiphor. In particular, Van de Ven proposed a lighting device that includes first and second groups of solid state light emitters, which, when illuminated, emit light having dominant wavelength in ranges of from 430 nm to 485 nm and from 600 nm to 630 nm, respectively, and a first group of lumiphors, which, when excited, emit light having dominant wavelength in the range of from 555 nm to 585 nm.

"In the device defined in the '940 patent, the combination of light from the two LED sources and the lumiphor produces a mixture of light having coordinates on the 1931 CIE Chromaticity Diagram that define a polygon shaped area. This area from the '940 patent is shown as area 5 in FIG. 2.

"FIG. 2 of the present application shows this area 5 plotted against a Planckian locus. As can be seen from FIG. 2, in the lighting device taught by the '940 patent, the combination of light sources produces a mixture of light having x and y coordinates that defines a point that is within ten MacAdam ellipses of at least one point on the Planckian locus. For example, area 5 as shown on FIG. 2 is defined by five lines, two of which are shown as dashed lines in FIG. 2. As can be seen from FIG. 2, with the two groups of light emitters used in the '940 patent, only white light with a CCT of between 2700K.about.4000K can be produced.

"There exists a need to provide a lighting device that achieves improved CRI values using solid state light emitters, e.g., LEDs, in order expand their usage in fields such as film, theater, cosmetics, fashion and apparel. There is also a need for a highly efficient white light source using solid state light emitters with improved CRI values and a flexible, wide gamut, i.e., range of accessible colors."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "In consideration of the above problems, in accordance with one aspect of the present invention, a method of achieving a tunable white light from a solid state light emitting lighting apparatus, the method comprising: illuminating a first group of one or more solid state light emitters which emit light having a dominant wavelength in the range of from 430 nm to 485 nm; exciting a first group of one or more lumiphors which emit light having a dominant wavelength in the range of from 555 nm to 585 nm; illuminating a second group of one or more solid state light emitters which emit light having a dominant wavelength in the range of from 430 nm to 485 nm; and illuminating a third group of one or more solid state light emitters which emit light having a dominant wavelength in the range of from 600 nm to 635 nm such that: a combination of light exiting the solid state emitting lighting apparatus which was emitted by (1) the first group of solid state light emitters, (2) the first group of lumiphors, (3) the second group of solid state light emitters, and (4) the third group of solid state light emitters produces a mixture of light having x, y coordinates on a 1931 CIE Chromaticity Diagram which defines a point which is within three (3) or less MacAdam ellipses of at least one point on the Planckian locus on a 1931 CIE Chromaticity Diagram.

"In a second aspect of the present invention, a method of achieving a tunable white light from a solid state light emitting lighting apparatus, the method comprising: illuminating a first group of solid state light emitters, the first group includes at least one solid state light emitter, such that each solid state light emitter in the first group emits light having a dominant wavelength in the range of from 430 nm to 485 nm; exciting a first group of one or more lumiphors which emit light having a dominant wavelength in the range of from 555 nm to 585 nm; illuminating a second group of solid state light emitters, the second group includes at least one solid state light emitter, such that each solid state light emitter in the second group emits light having a dominant wavelength in the range of from 430 nm to 485 nm; and illuminating a third group of solid state light emitters, the third group includes at least one solid state light emitter, such that each solid state light emitter in the third group emits light having a dominant wavelength in the range of from 600 nm to 635 nm such that: a combination of light exiting the solid state emitting lighting apparatus which was emitted by (1) the first group of solid state light emitters, (2) the first group of lumiphors, (3) the second group of solid state light emitters, and (4) the third group of solid state light emitters produces a mixture of light having x, y coordinates on a 1931 CIE Chromaticity Diagram which defines a point which is within three (3) or less MacAdam ellipses of at least one point on the Planckian locus on a 1931 CIE Chromaticity Diagram.

"In another aspect of the present invention, if all of the first group of solid state light emitters are illuminated, at least one of the lumiphors in the first group of lumiphors is excited by light emitted by the first group of solid state light emitters.

"In another aspect, resultant white light produced by the combination of the light emitters of the first and the respective first group of lumiphors is above the Planckian locus in the 1931 CIE chromaticity Diagram, and more than 7 MacAdam ellipses away from any point on the Planckian locus, and has a CCT between 3200K and 6000K, with a duv of >0.006.

"In another aspect of the present invention, if all of the first group of solid state light emitters are illuminated, all of the lumiphors in the first group of lumiphors is excited by light emitted by the first group of solid state light emitters.

"In another aspect of the present invention, the tunable white light from the solid state light emitting lighting apparatus has a CCT range of from 2700 k to 4500 k, from 2700 k to 6500 k, or between 2700 k to 6500 k.

"In another aspect of the present invention, the tunable white light from the solid state light emitting lighting apparatus has a CRI of more than 85.

"In another aspect of the present invention, the tunable white light from the solid state light emitting lighting apparatus has a CRI of more than 90.

"In another aspect of the present invention, the tunable white light from the solid state light emitting lighting apparatus has a CCT range of from 2700K to 6500K and a CRI of more than 85.

"In another aspect of the present invention, the tunable white light from the solid state light emitting lighting apparatus has a CCT range of from 2700K to 5500K and a CRI of more than 90.

"In another aspect of the present invention, a combination of (1) light exiting the solid state light emitting lighting apparatus which was emitted by the first group of solid state light emitters, and (2) light exiting the solid state light emitting lighting apparatus which was emitted by the first group of lumiphors would, in the absence of additional light, produce a sub-mixture of white light which is above the Planckian locus in a 1931 CIE Chromaticity Diagram and more than seven (7) MacAdam ellipses from any point on the Planckian locus.

"In another aspect, each solid state light emitter in the third group emits light that has a dominant wavelength in the range of from 615 nm to 620 nm.

"In another aspect, each solid state light emitter in the second group emits light that has a dominant wavelength in the range of from 460 nm to 475 nm.

"In another aspect, the relative flux ratios of the first, second and third groups are controlled by a current controller such that the first group of LEDs accounts for no less than 75% of the total lumen output, the second group accounts for no more than 10% of the total lumen output, and the third group accounts for no more than 25% of the total lumen output.

"In another aspect, the CCT of the solid state light emitting lighting apparatus is adjusted by varying the driving currents of the LEDs, while maintaining a constant lumen output for any given CCT.

"In another aspect, the CCT of the solid state light emitting lighting apparatus is adjusted by varying the total lumen output of the apparatus for different CCT options.

"In a third aspect of the present invention, a lighting apparatus comprises a first group of one or more solid state light emitters which emit light having a dominant wavelength in the range of from 430 nm to 485 nm; a first group of one or more lumiphors which emit light having a dominant wavelength in the range of from 555 nm to 585 nm; a second group of one or more solid state light emitters which emit light having a dominant wavelength in the range of from 430 nm to 485 nm; and a third group of one or more solid state light emitters which emit light having a dominant wavelength in the range of from 600 nm to 635 nm; and at least first, second and third power lines, the first group of solid state light emitters, the second group of solid state light emitters, and the third group of solid state light emitters are each electrically coupled to at least one of the first, second and third power lines, wherein when current is supplied to at least one of the first, second and third power lines, a combination of light exiting the lighting apparatus which was emitted by (1) the first group of solid state light emitters, (2) the first group of lumiphors, (3) the second group of solid state light emitters, and (4) the third group of solid state light emitters produces a mixture of light having x,y coordinates on a 1931 CIE Chromaticity Diagram which defines a point which is within three (3) or less MacAdam ellipses of at least one point on the Planckian locus on a 1931 CIE Chromaticity Diagram.

"In a fourth aspect of the present invention, a lighting apparatus comprises a first group of solid state light emitters; a first group of lumiphors; a second group of solid state light emitters; a third group of solid state light emitters; and at least first, second and third power lines, the first group of solid state light emitters, the second group of solid state light emitters, and the third group of solid state light emitters are each electrically coupled to at least one of the first, second and third power lines, wherein the first group of solid state light emitters includes at least one solid state light emitter, such that each solid state light emitter in the first group, if illuminated, emits light having a dominant wavelength in the range of from 430 nm to 485 nm; the first group of lumiphors includes at least one lumiphor, such that each lumiphor in the first group, when excited, emits light having a dominant wavelength in the range of from 555 nm to 585 nm; the second group of solid state light emitters includes at least one solid state light emitter, such that each solid state light emitter in the second group, if illuminated, emits light having a dominant wavelength in the range of from 430 nm to 485 nm; and the third group of solid state light emitters includes at least one solid state light emitter, such that each solid state light emitter in the third group, if illuminated, emits light having a dominant wavelength in the range of from 600 nm to 635 nm; if current is supplied to the first power line, a combination of light exiting the solid state emitting lighting apparatus which was emitted by (1) the first group of solid state light emitters, (2) the first group of lumiphors, (3) the second group of solid state light emitters, and (4) the third group of solid state light emitters produces a mixture of light having x,y coordinates on a 1931 CIE Chromaticity Diagram which defines a point which is within three (3) or less MacAdam ellipses of at least one point on the Planckian locus on a 1931 CIE Chromaticity Diagram.

"In another aspect, if current is supplied to a power line, a combination of (1) light exiting the lighting apparatus which was emitted by the first group of solid state light emitters, (2) light exiting the lighting apparatus which was emitted by the first group of lumiphors, (3) light exiting the lighting apparatus which was emitted by the second group of solid state light emitters, and (4) light exiting the lighting apparatus which was emitted by the third group of solid state light emitters would, in an absence of any additional light, produce light having x, y color coordinates within an area on a 1931 CIE Chromaticity Diagram defined by points having coordinates (x=0.3863, y=0.4713); (x=0.1319, y=0.0747); (x=0.6867, y=0.3132).

"In another aspect, the first group of solid state light emitters comprise a plurality of LEDs, the second group of solid state light emitters comprise a plurality of LEDs, and the third group of solid state light emitters comprise a plurality of LEDs.

"In another aspect, the lighting apparatus is tunable as to CCT level by adjusting the current levels applied to one or more of the first, second and third groups of solid state light emitters.

"In another aspect, the lighting apparatus is tunable to achieve a Ra>90, at CCT=2700K, 4500K and 6500K, and R13 and R15>90 on color samples corresponding to the color of human skin.

"In another aspect, the lighting apparatus is tunable to achieve a Ra>90, at CCT in a range of 2700K.about.6500K, and R13 and R15>90 on color samples corresponding to the color of human skin.

"In another aspect, the lighting apparatus further comprises: first, second and third current sources, corresponding to the first, second and third groups of solid state light emitters, respectively, and a controller that controls the current applied to the first, second and third groups of solid state light emitters, the controller being adapted to control the first, second and third current sources such that the lighting apparatus can achieve a Ra>90, at CCT=2700K, 4500K and 6500K, and R13 and R15>90 on color samples corresponding to the color of human skin.

"In another aspect, the lighting apparatus further comprises: first, second and third current sources, corresponding to the first, second and third groups of solid state light emitters, respectively, and a controller that controls the current applied to the first, second and third groups of solid state light emitters, the controller being adapted to control the first, second and third current sources such that the lighting apparatus can achieve a Ra>90, at CCT in a range of 2700K.about.6500K, on color samples corresponding to the color of human skin.

"In another aspect, the lighting apparatus further comprises a current controller that controls the relative flux ratios of the first, second and third groups, the controller having a look-up table associated therewith, the controller being programmed to: accept commands from a user, including a command to set a CCT and a total flux output in response to receipt of the command, retrieve a set of data that contains information of the required flux output of each group of LEDs from the look-up table, and based on the 100% duty cycle (full power) flux output of each group, generate pulse width modulation (PWM) signals to control current supplied to each group to alter the flux output of each group in order to achieve a desired CCT and total flux output.

"In another aspect, the apparatus further comprises first, second and third current sources, corresponding to the first, second and third groups, respectively, the controller controlling the current supplied to each group via the first, second and third current sources.

"In another aspect, the first, second and third current sources each have a temperature sensor to sense the temperature of groups, respectively, wherein currents supplied by the current sources are adjusted by the temperature sensors to compensate the flux variation due to temperature changes, allowing the 100% duty cycle flux output of each group of LEDs to be maintained irrespective of temperature changes.

"In a fifth aspect of the present invention, a lighting apparatus comprises: a first group of solid state light emitters; a first group of lumiphors; a second group of solid state light emitters; a third group of solid state light emitters; at least first, second and third power lines, the first group of solid state light emitters, the second group of solid state light emitters, and the third group of solid state light emitters each being electrically coupled to at least one of the first, second and third power lines; and a current controller that controls the relative flux ratios of the first, second and third groups, the controller having a look-up table associated therewith, the controller being programmed to: accept commands from a user, including a command to set a CCT and a total flux output in response to receipt of the command, retrieve a set of data that contains information of the required flux output of each group of LEDs from the look-up table, and based on the 100% duty cycle, (full power) flux output of each group, generate pulse width modulation (PWM) signals to control current supplied to each group to alter the flux output of each group in order to achieve a desired CCT and total flux output.

"In another aspect, the lighting apparatus further comprises first, second and third current sources, corresponding to the first, second and third groups, respectively, the controller controlling the current supplied to each group via the first, second and third current sources.

"In a sixth aspect of the present invention, a method is provided on a solid state lighting apparatus comprising: a first group of solid state light emitters; a first group of lumiphors; a second group of solid state light emitters; a third group of solid state light emitters; at least first, second and third power lines, the first group of solid state light emitters, the second group of solid state light emitters, and the third group of solid state light emitters each being electrically coupled to at least one of the first, second and third power lines; and a current controller that controls the relative flux ratios of the first, second and third groups, the controller having a look-up table associated therewith. The method comprises the controller: accepting commands from a user, including a command to set a CCT and a total flux output in response to receipt of the command, retrieving a set of data that contains information of the required flux output of each group of LEDs from the look-up table, and based on the 100% duty cycle (full power) flux output of each group, generating pulse width modulation (PWM) signals to control current supplied to each group to alter the flux output of each group in order to achieve a desired CCT and total flux output.

"In a seventh aspect of the present invention a lighting apparatus comprises: first, second and third groups of solid state light emitters; a first group of lumiphors; at least first, second and third power lines, the first, second and third group of solid state light emitters each being electrically coupled to at least one of the first, second and third power lines. A current controller controls the relative flux ratios of the first, second and third groups, the controller being programmed to, in response to receipt of a command, retrieve a set of data from a look-up table that contains information of the required flux output of each group of LEDs and generate pulse width modulation (PWM) signals to control current supplied to each group to alter the flux output of each group in order to achieve a desired CCT and total flux output."

URL and more information on this patent, see: Tu, Qifei; Leung, Wa-Hing. Tunable White Color Methods and Uses. U.S. Patent Number 8766555, filed June 10, 2011, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8766555.PN.&OS=PN/8766555RS=PN/8766555

Keywords for this news article include: Electronics, Semiconductor, Light-emitting Diode, Huizhou Light Engine Ltd.

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