as) United States
`a2) Patent Application Publication 0) Pub. No.: US 2010/0259182 Al
`
` MANet al. (43) Pub. Date: Oct. 14, 2010
`
`
`US 20100259182A1
`
`(54) LIGHT SOURCE INTENSITY CONTROL
`SYSTEM AND METHOD
`Jul. 18,2006=(CA) oo cence 2552685
`(75)
`Inventors:
`Kwong MAN,Vancouver (CA);
`Ian ASHDOWN,West Vancouver
`(CA)
`Correspondence Address:
`Philips Intellectual Property and Standards
`P.O. Box 3001
`Briarcliff Manor, NY 10510-8001 (US)
`
`Publication Classification
`
`(51)
`
`Int.Cl.
`(2006.01)
`HOSB 37/02
`(52) US. Ch. eccccccecceeeetetetetenetenenes 315/250; 315/297
`
`(57)
`
`ABSTRACT
`
`(30)
`
`Foreign Application Priority Data
`
`(73) Assignee:
`
`TIR TECHNOLOGYLP,
`Burnaby, BC (CA)
`
`(21) Appl. No.:
`
`12/161,812
`
`(22) PCT Filed:
`
`Feb. 9, 2007
`
`PCT/CA07/00188
`
`The light source comprises one or morefirst light-emitting
`elements for generating light havinga first wavelength range
`and one or more secondlight-emitting elements for generat-
`ing light having a second wavelength range. Thefirst light-
`emitting elements and second light-emitting elements are
`responsive to separate control signals provided thereto. A
`control system receives a signal representative of the operat-
`ing temperature from one or more sensing devices and deter-
`(86) PCT No.:
`minesfirst and second control signals based on the desired
`colouroflight and the operating temperature. The light emit-
`§ 371 (©)(),
`
`
`(2), (4) Date: ted by thefirst and second light-emitting elementsasaresultJul. 23, 2008
`+
`as
`ofthe received first and second control signals can be blended
`Related U.S.Application Data
`to substantially obtain the desired colour oflight. The desired
`(60) Provisional application No. 60/772,458,filed on Feb.
`colour of light generated can thus be substantially indepen-
`dent ofjunction temperature induced changesin the operating
`10, 2006, provisional application No. 60/830,196,
`filed on Jul. 11, 2006.
`
`characteristics of the light-emitting elements.
`
`1
`
`APPLE 1053
`Apple v. Masimo
`IPR2022-01299
`
`APPLE 1053
`Apple v. Masimo
`IPR2022-01299
`
`1
`
`

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`Patent Application Publication
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`US 2010/0259182 Al
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`Patent Application Publication
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`Patent Application Publication
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`Oct. 14,2010 Sheet 5 of 5
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`US 2010/0259182 Al
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`Oct. 14, 2010
`
`LIGHT SOURCE INTENSITY CONTROL
`SYSTEM AND METHOD
`
`FIELD OF THE INVENTION
`
`[0001] The present invention pertains to the field of illumi-
`nation and in particular to an intensity control system for a
`light source.
`
`BACKGROUND
`
`[0002] Recent advances in the development of semicon-
`ductor light-emitting diodes (LEDs) and organic light-emit-
`ting diodes (OLEDs) have madethese devices suitablefor use
`in general illumination applications, including architectural,
`entertainment, and roadwaylighting, for example. As such,
`these devices are becoming increasingly competitive with
`light sources such as incandescent, fluorescent, and high-
`intensity discharge lamps.
`lighting characteristics, white
`[0003] Due to its natural
`light is typically the preferred choice for lighting. An impor-
`tant consideration for LED-based luminaires used for ambi-
`ent lighting and LED-based backlighting for liquid crystal
`displays (LCDs) is the need to produce natural white light.
`White light can be generated by mixing the light emitted from
`different colour LEDs.
`
`[0004] Various standards have been proposed to character-
`ize the spectral content of light. One wayto characterize light
`emitted by a test light source is to compare it with the light
`radiated by a black body and identify the temperature of the
`black body at which its perceived colour best matches the
`perceived colour ofthe test light source. That temperature is
`called correlated colour temperature (CCT) and is usually
`measured in Kelvin (K). The higher the CCT, the bluer, or
`cooler the light appears. The lower the CCT,the redder, or
`warmerthe light appears. An incandescent light bulb has a
`CCTof about 2856 K, and fluorescent lamps can have CCTs
`in the range of about 3200Kto 6500 K.
`[0005]
`Furthermore the properties of light can be charac-
`terized in terms of luminousflux and chromaticity. Luminous
`flux is used to define the measurable amountof light and
`chromaticity used to define the perceived colour impression
`of light, irrespective of its perceived brightness. Chromaticity
`and luminous flux are measured in units according to stan-
`dards ofthe Commission Internationale de I’Eclairage (CIE).
`The CIE chromaticity standards define hue and saturation of
`light based on chromaticity coordinates that specify a posi-
`tion in a chromaticity diagram. The chromaticity coordinates
`of light are derived from tristimulus values and expressed by
`the ratio of the tristimulus valuesto their sum; ie. x=X/(X+
`Y+Z), y=Y/(X+Y+Z), Z=Z/(X+Y+Z), where x,y and zare the
`chromaticity coordinates and X, Y, and Z arethe tristimulus
`values. Because x+y+z=1, it is only necessary to specify two
`chromaticity coordinates such as x and y, for example. Any
`CCTvalue can be transformed into corresponding chroma-
`ticity coordinates.
`[0006]
`In spite of their success, LED-based light sources
`can be affected by a numberof parameters in a complex way.
`Chromaticity and luminousflux output of LEDs can greatly
`depend on junction temperature, which can have undesirable
`effects on the CCT and moregenerally the chromaticity ofthe
`emitted light.
`[0007]
`Ignoring temperature dependencies, the amount of
`light emitted by an LED is proportional to its instantaneous
`forward current. If the LEDsare pulsed at a rate greater than
`
`about 60 Hz, the human visual system perceives a time-
`averaged amountoflight as opposedto individual pulses. As
`aresult, light source dimming can be achieved by varying the
`amount of time-averaged forward current, using such tech-
`niques as pulse width modulation (PWM) or pulse code
`modulation (PCM). However, changesin the average forward
`current can affect the junction temperature ofthe LED, which
`can alter the spectral power distribution and in consequence
`the CCTor chromaticity and luminousflux of the light emit-
`ted by the LED. The compensation ofthis effect can become
`complex when various coloured LEDs are used to generate
`mixed light of a desired chromaticity. As discussed by M.
`
`Dyble, in “Impact of Dimming White LEDs: Chromaticity
`Shifts Due to Different Dimming Methods,” Fifth Interna-
`tional Conference on Solid State Lighting, Bellingham,
`Wash.; SPIE Vol. 5941, 2005, colour appearanceofthe result-
`ant mixed light can shift unacceptably when dimming,as the
`spectral power distribution of the individual LEDs can
`change.
`[0008] LED junction temperature variations can also cause
`undesired effects in the spectral power distribution of the
`resultant output light. Variations in junction temperature not
`only can reduce the luminousflux output, but can also cause
`undesirable variations in the CCT ofthe mixedlight. Further-
`more, overheating of LEDs can also reduce the life span of
`LEDs.
`
`In order to overcome these limitations, various
`[0009]
`methods for generating natural white light have been pro-
`posed. U.S. Pat. No. 6,448,550 to Nishimura teachesa solid-
`state illumination device having a plurality of LEDsof dif-
`ferent colours and use optical feedback. Light from the LEDs
`is measured by photosensitive sensors mountedin close prox-
`imity with LEDs and compared with a reference set of
`responses to a previously measured spectral powerdistribu-
`tion. The amountofvariation betweenthe sensor responses to
`the light from the LEDsandthe previously measured spectral
`powerdistribution is used as a basis for adjusting the current
`to the LEDsin order to maintain the light from the LEDs as
`close as possible to the pre-determinedspectral powerdistri-
`bution. While the Nishimura reference provides a way to
`achieve control of the spectral powerdistribution of the out-
`put light with a desired colour property, it uses a complex
`optical feedback system.
`[0010] U-S. Pat. No. 6,507,159 to Muthu discloses a control
`method and system for an LED-based luminaire having a
`plurality of red, green and blue light LEDs for generating a
`desired light by colour mixing. Muthuseeksto alleviate the
`unwanted variations in the luminous flux output and CCT of
`the desired light by providing a control system with a feed-
`back system includingfiltered photodiodes, a mathematical
`transformation for determining tristimulus values of the
`LEDs, and a reference-tracking controller for resolving the
`difference between the feedback tristimulus values and the
`
`desired reference tristimulus values in order to adjust the
`forward current of the LEDs, such that the difference in
`tristimulus values is reduced to zero. The calculations as
`required by Muthu for the mathematical transformations can,
`however, makeit difficult to implement an optical feedback
`control system with a response time that is fast enough to
`avoid visual flicker during dimming operations, for example.
`[0011] U.S. Pat. No. 6,576,881 to Muthu et al. discloses a
`method and system for controlling the output light generated
`by red, green, and blue LEDs. Sensors positioned proximate
`to the LEDsto detect a first set of approximate tristimulus
`
`7
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`

`US 2010/0259182 Al
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`Oct. 14, 2010
`
`values of the outputlight. Thefirst set of tristimulus valuesis
`communicated to a controller, which converts these values
`into a second set of tristimulus values representative of a
`standard colourimetric system. The relative luminous flux
`output of the LEDsis adjusted on the basis of the difference
`between the secondset of the tristimulus values and a set of
`
`the output light with a desired colour property, it uses a
`complex optical feedback system. In addition, a drawback of
`this procedure as disclosed by Muthu et al. is the excessive
`amount of thermal stress imposed on the LEDs during ON
`and OFF cycles at low frequencies which are required for the
`optical feedback system.
`[0015] Therefore, there is a need for a relatively simple
`light source intensity control system and method that can
`account for device junction temperature effects on the light
`emitted by the light source.
`[0016] This background information is provided to reveal
`information believed by the applicant to be of possiblerel-
`evanceto the present invention. No admission is necessarily
`intended, nor should be construed, that any of the preceding
`information constitutespriorart againstthe present invention.
`
`SUMMARYOF THE INVENTION
`
`user-specifiedtristimulus values. Based on this configuration,
`as with some previously identified prior art, the calculations
`required for the mathematical transformations can make it
`difficult to implement an optical feedback control system
`with a response timethatis fast enough to avoid visualflicker
`during dimmingoperations, for example.
`[0012] U.S. Pat. No. 6,630,801 to Schuurmansprovides a
`method and system for sensing the colour point of resultant
`light produced by mixing coloured light from a plurality of
`LEDsin the RGBcolours. The system comprises a feedback
`unit for generating feedback values corresponding to the
`chromaticity of the resultant light based on values obtained
`[0017] An object of the present invention is to provide a
`from filtered and unfiltered photodiodes that are responsive to
`light source intensity control system and method.In accor-
`the light from the LEDs. The system also comprises a con-
`dance with an aspect of the present invention, there is pro-
`troller which adjuststhe resultant light based uponthe differ-
`vided a light source for generating a desired colour oflight,
`ence between the feedback values and values representative
`said light source comprising: one or morefirst light-emitting
`of the chromaticity of a desired resultant light. While the
`elements for generating first light havingafirst wavelength
`Schuurmans reference provides a wayto achieve control of
`range, the one or morefirst light-emitting elements respon-
`the spectral power distribution of the output light with a
`sive toafirst control signal; one or more secondlight-emitting
`desired colour property, it also uses a complex optical feed-
`elements for generating second light having a second wave-
`back system.
`length range, the one or more secondlight-emitting elements
`responsive to a second control signal; one or more sensing
`[0013] U.S. Patent Publication No. 2003/0230991 to
`devices for generating one or more signals representative of
`Muthuetal. discloses an LED-based white-light backlighting
`operating temperaturesof the one or morefirst light-emitting
`system for electronic displays. The backlighting system of
`elements and the one or more secondlight-emitting elements;
`Muthuet al. includes a plurality of LEDs of different light
`and a control system operatively coupled to the one or more
`colours arranged such that the combination of light colours
`first light-emitting elements, the one or more second light-
`produces white light. The system also comprises a micropro-
`cessor which monitors the luminousflux, radiant flux, or
`emitting elements and the one or more sensing devices, the
`control system configured to receive the one or moresignals
`tristimulus levels of the white light and controls the luminous
`and configured to determinethe first control signal and the
`flux and chromaticity of the white light by feedback control.
`second control signal based upon the operating temperatures
`The backlighting system of Muthu et al. uses photodiodes
`and the desired colourof light; wherein thefirst light and the
`with filters to determine approximatetristimulus valuesofthe
`second light are blended to create the desired colouroflight.
`LEDsand adjusts the luminousflux and chromaticity of the
`[0018]
`In accordance with another aspect of the present
`white light. While the Muthu et al. reference provides a way
`invention there is provided a method for generating a desired
`to achieve control of the spectral power distribution of the
`colourof light, the method comprising the steps of: determin-
`output light with a desired colour property, it uses a complex
`ing a first operating temperature of one or morefirst light-
`optical feedback system.
`emitting elements which providefirst light having a first
`[0014] U-S. Pat. No. 6,441,558 also to Muthuet al. dis-
`spectrum; determining a second operating temperature of one
`closes a multi-colour LED-based luminaire for generating
`or more secondlight-emitting elements which provide sec-
`light at different colour temperatures. The desired luminous
`ondlight having a second spectrum;providing a first spectral
`flux outputfor each array ofcolour LEDsis achieved by using
`radiant intensity model indicative of effects of the first oper-
`a controller system that adjusts the current supplied to the
`ating temperature on thefirst spectrum; providing a second
`LEDsbased on the chromaticity of the desired light and the
`spectral radiant intensity model indicative of effects of the
`junction temperature of the LEDs. Oneof the shortcomings
`associated with the LED-based luminaire of Muthuetal. is
`second operating temperature on the second spectrum;deter-
`mininga first control signal and a secondcontrol signal based
`upon the first spectral radiant intensity model, the second
`spectral radiant intensity model, the desired colour of light
`and the first operating temperature and secondoperating tem-
`perature; providingthe first control signal to the one or more
`first light-emitting elements; providing the second control
`signal to the one or more secondlight-emitting elements; and
`blending the first light and the secondlight into mixed light
`having the desired colouroflight.
`
`that in order to measure the luminous flux of an array of
`LEDs, an optical feedback sensor is used to obtain the lumi-
`nousflux from the LEDs which is communicated to the con-
`
`troller by a polling sequence. According to Muthuetal., the
`measurement sequence begins by measuring the luminous
`flux output of the all LED arrays in operation. Each array of
`LEDsis alternately switched “OFF”briefly, and a further
`measurement is taken. The difference between the initial
`measurement and the next measurement provides the light
`output from the LED array that was turned OFF. The mea-
`surement of the light output is repeated for the remaining
`LEDarrays. Again, while the Muthuetal. reference provides
`a way to achieve control of the spectral powerdistribution of
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`FIG. 1 illustrates a light source according to one
`[0019]
`embodimentof the present invention.
`
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`
`FIG. 2 illustrates both the measuredspectral radiant
`[0020]
`intensity and double Gaussian modelled spectral radiant
`intensity of a blue light-emitting diode according to one
`embodimentof the present invention.
`[0021]
`FIG. 3 illustrates the temperature dependent varia-
`tions of the parameters for a double Gaussian model of the
`spectral radiant intensity of a red light-emitting diode accord-
`ing to one embodimentof the present invention.
`[0022]
`FIG.4 illustrates the temperature dependent varia-
`tions of the parameters for a double Gaussian model of the
`spectral radiant intensity of an amber light-emitting diode
`according to one embodimentofthe present invention.
`[0023]
`FIG. 5 illustrates the colour gamut for the three
`colouredlight-emitting elements as defined by the CIE 1931
`x,y Chromaticity Diagram.
`
`the controller. The controller can optionally include one or
`more storage media collectively referred to herein as
`“memory”. The memory can be volatile and non-volatile
`computer memory such as RAM, PROM, EPROM,and
`EEPROM,floppy disks, compact disks, optical disks, mag-
`netic tape, or the like, wherein control programs (such as
`software, microcodeor firmware) for monitoring or control-
`ling the devices coupled to the controller are stored and
`executed by the CPU. Optionally, the controller also provides
`the meansof converting user-specified operating conditions
`into control signals to control the peripheral devices coupled
`to the controller. The controller can receive user-specified
`commands by way of a user interface, for example, a key-
`board, a touchpad, a touch screen, a console, a visual, acoustic
`input device, or other device as is well knownto those skilled
`in this art.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`Definitions
`
`[0031] As used herein, the term “about”refers to a +/-10%
`variation from the nominal value. It is to be understoodthat
`such a variation is always included in any given value pro-
`vided herein, whetheror not it is specifically identified.
`[0024] The term “light-cmitting clement” (LEE) is used to
`[0032] Unless defined otherwise, all technical and scien-
`define any device that emits radiation in any region or com-
`tific terms used herein have the same meaning as commonly
`bination of regions of the electromagnetic spectrum for
`understood by one of ordinary skill in the art to which this
`example, the visible region, infrared and/orultraviolet region,
`invention belongs.
`whenactivated by applying a potential difference across it or
`passing a current through it, for example. Therefore a light-
`[0033] The present invention provides a light source for
`emitting element can have monochromatic or quasi-mono-
`generating a desired colour of light. The light source com-
`chromatic spectral emission characteristics. Examples of
`prises one or morefirst light-emitting elements for generating
`light-emitting elements include semiconductor, organic, or
`light havingafirst wavelength range and one or more second
`polymer/polymeric light-emitting diodes, blue or UV
`light-emitting elements for generating light having a second
`pumped phosphor coated light-emitting diodes, optically
`wavelength range. Thefirst light-emitting elements and sec-
`pumped nanocrystal light-emitting diodes or any other simi-
`ondlight-emitting elements are responsive to separate control
`lar devices as would be readily understood by a worker skilled
`signals provided thereto. The light source further includes a
`in the art. Furthermore, the term light-emitting element is
`sensing device for sensing operating temperature or tempera-
`used to define the specific device that emits the radiation, for
`tures ofthefirst and secondlight-emitting elements. A control
`example a LED die, and can equally be used to define a
`system receives a signal representative of the operating tem-
`combination of the specific device that emits the radiation
`perature(s) from the sensing device and determinesthefirst
`together with a housing or package within which the specific
`and second control signals based onthe desired colouroflight
`device or devices are placed.
`and the operating temperatures. The light emitted bythefirst
`[0025] The term “luminous flux” is used to define the
`and secondlight-emitting elements as a result of the received
`amountof light emitted by a light source according to stan-
`first and second control signals can be blended to substan-
`dards ofthe Commission Internationale de l’Eclairage (CIE).
`tially obtain the desired colour of light. In this manner, the
`Where the wavelength regime of interest includes infrared
`desired colour of light generated by the light source can be
`and/or ultraviolet wavelengths, the term “luminous flux”is
`substantially independent of junction temperature induced
`used to include radiant flux as defined by CIE standards.
`changes in the operational characteristics of the light-emit-
`[0026] The term “chromaticity” is used to define the per-
`ting elements.
`ceived colour impression oflight according to CIE standards.
`[0034]
`In another embodiment, the light source can addi-
`[0027] The term “intensity” is used to define the measured
`tionally comprise one or morethirdlight-emitting elementfor
`photometric brightness of a light source according to the
`generating light having a third wavelength range, one or more
`standards of the Commission Internationale de 1’Eclairage
`fourth light-emitting elements for generating light having a
`
`(CIE).
`fourth wavelength, etc, as would be readily understood by a
`[0028] The term “spectral radiant intensity” is used to
`worker skilled in the art. In this embodiment, the sensing
`define the radiant intensity of light at a given wavelength
`device may be configured to sense the operating temperature
`emitted by a light source according to the standards of the
`of the one or morethird light-emitting elements, one or more
`CIE.
`fourth light-emitting elements etc, which would be received
`by the control system enabling subsequent determination of
`control signals for these third and fourth light-emitting ele-
`ments.
`
`[0029] The term “emission spectrum”is used to define the
`distribution of spectral radiant intensity ofall wavelengths of
`visible light.
`[0030] The term “controller” is used to define a computing
`device or microcontroller having a central processing unit
`(CPU) and peripheral input/output devices (such as A/D or
`D/A converters) to monitor parameters from peripheral
`devices that are operatively coupled to the controller. These
`input/output devices can also permit the CPU to communicate
`and control peripheral devices that are operatively coupled to
`
`FIG.1 illustrates a block diagram ofa light-emitting
`[0035]
`element light source according to one embodiment of the
`present invention. The light source includesarrays 20, 30, 40
`each having one or more light-emitting elements that are in
`thermal contact with one or more heatsinks or heat extraction
`mechanisms (not shown). The combination of coloured light
`generated by each ofthe red light-emitting elements 22, green
`
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`Oct. 14, 2010
`
`light-emitting elements 32 and blue light-emitting elements
`42 can generate light of a specific chromaticity, for instance
`white light. In one embodiment, the light source includes
`mixing optics (not shown) to spatially homogenize the output
`light generated by mixing light from the red light-emitting
`elements 22, greenlight-emitting elements 32, and bluelight-
`emitting elements 42.
`[0036] Current drivers 28, 38, 48 are coupledto arrays 20,
`30, 40, respectively, and are configured to supply current to
`the red light-emitting elements 22, green light-emitting ele-
`ments 32, and blue light-emitting elements 42 in arrays 20,
`30, 40. The current drivers 28, 38, 48 control the luminous
`flux outputs ofthe red light-emitting elements 22, green light-
`emitting elements 32, and blue light-emitting elements 42 by
`regulating the flow of current through the red light-emitting
`elements 22, greenlight-emitting elements 32, and bluelight-
`emitting elements 42. The current drivers 28, 38, 48 are
`configured to regulate the supply of current to arrays 20, 30,
`40 interdependently so as to control the chromaticity of the
`combinedlight as described hereinafter.
`[0037] A controller 50 is coupledto currentdrivers 28, 38,
`48. The controller 50 is configured to interdependently adjust
`the amount of average forward current by adjusting the duty
`factor of the current drivers 28, 38, 48, thereby providing
`control of the luminousflux output of the red light-emitting
`elements 22, green light-emitting elements 32, and bluelight-
`emitting elements 42.
`[0038]
`In one embodimentofthe present invention, a tem-
`perature sensor 26, 36 or 46 is in thermal contact with all
`arrays 20, 30 and 40 and coupled to controller 50, thereby
`providing a means for measuring the operating temperature
`of the arrays 20, 30, 40. The operating temperature of the
`arrays 20, 30, 40 can be correlated to the junction temperature
`of red light-emitting elements 22, green light-emitting ele-
`ments 32 and blue light-emitting elements 42. In one embodi-
`ment, each array 20, 30 and 40 has a separate temperature
`sensor 26, 36 and 46 respectively, in order to measure each
`array’s individual operating temperature.
`[0039]
`In one embodimentof the present invention,alter-
`nately, or in combination with one or more temperature sen-
`sors, voltage sensors 27, 37, 47 are coupled to the output of
`current drivers 28, 38, 48 and measure the instantaneous
`forward voltage of light-emitting element arrays 20, 30, 40.
`Controller 50 is coupled to voltage sensors 27, 37, 47 and
`configured to monitor the instantaneous forward voltage of
`light-emitting element arrays 20, 30, 40. The forward voltage
`of the arrays 20, 30, 40 can be correlated to the junction
`temperature of red light-emitting elements 22, green light-
`emitting elements 32 and bluelight-emitting elements 42. For
`example, experimentally derived correlations between junc-
`tion temperature and LED peak wavelength, spectral width or
`output powerare disclosed by Chhajed,S. et al., 2005, “Influ-
`ence of Junction Temperature on Chromaticity and Colour-
`Rendering Properties of Trichormatic White-Light Sources
`Based on Light-Emitting Diodes”, Journal of Applied Phys-
`ics 97, 054506, herein incorporated by reference.
`[0040] The controller 50, based on the detected tempera-
`tures and/or detected forward voltages can determine the
`junction temperature of each of the red light-emitting ele-
`ments 22, green light-emitting elements 32 and blue light-
`emitting elements 42 and based on a predetermined model of
`temperature dependenceto spectral output of each of the red
`light-emitting elements 22, green light-emitting elements 32
`and blue light-emitting elements 42, together with the desired
`
`colour of light to be created, the controller can determine
`control signals for the control of the operation of the red
`light-emitting elements 22, green light-emitting elements 32
`and blue light-emitting elements 42, in order that the desired
`colourof light is generated by the light source.
`
`Light-Emitting Elements
`
`[0041] The light-emitting elements can be selected to pro-
`vide a predetermined colour of light. The number, type and
`colourof the light-emitting elements within the light source
`can provide a means for achieving high luminousefficiency,
`a high Colour Rendering Index (CRI), and a large colour
`gamut. The light-emitting elements can be manufactured
`using either organic material, for example OLEDs or PLEDs
`or inorganic material, for example semiconductor LEDsor
`other device configurations as would be readily understood
`by a workerskilled in the art. The light-emitting elements can
`be primary light-emitting elements that can emit colours
`including blue, green, red or can emit another colour or
`colours. The light-emitting elements can optionally be sec-
`ondary light-emitting elements, which convert the emission
`of a primary source into one or more monochromatic wave-
`lengths or quasi-monochromatic wavelengths. Additionally,
`a combination of primary and/or secondary light-emitting
`elements can be employed. As would be readily understood
`by a worker skilledin theart, the one or more light-emitting
`elements can be mounted for example on a PCB (printed
`circuit board), a MCPCB (metal core PCB), a metallized
`ceramic substrate or a dielectrically coated metal substrate,or
`the like, that carries traces and connection pads. The light-
`emitting elements can be in unpackaged form suchasina die
`format or may be packaged parts such as LED packages or
`may be packaged with other components including for
`example drive circuitry, optics and control circuitry.
`[0042]
`In one embodiment, an array oflight-emitting ele-
`ments having spectral outputs centred around wavelengths
`corresponding to the colours red, green and blue can be
`selected, for example. Optionally, light-emitting elements of
`other spectral output can additionally be incorporatedinto the
`light source, for example light-emitting elements radiating at
`the red, green, blue and amber wavelength regions may be
`configured as arrays or optionally may include one or more
`light-emitting elements radiating at the cyan wavelength
`region, or other wavelength region as would be readily under-
`stood by a workerskilled in the art. The selection of light-
`emitting elements can be directly related to the desired colour
`gamutand/orthe desired maximum luminousflux and colour
`rendering index to be created by the lighting module.
`[0043]
`In one embodiment, multiple light-emitting ele-
`ments can be connectedelectrically in a plurality of configu-
`rations. For example, the light-emitting elements can be con-
`nected in series or parallel configurations or combinations of
`both. In one embodiment of the present invention, two or
`more light-emitting elements are connected in series as
`strings, wherein a string may comprise light-emitting ele-
`ments of the same colour bin.
`
`In another embodiment of the present invention,
`[0044]
`light-emitting elements are electrically connected in order
`that each individual light-emitting element can be individu-
`ally controlled. For example, a string of light-emitting ele-
`ments can be wired such that some light-emitting elements
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`Oct. 14, 2010
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`can be bypassedeitherpartially, or completely to allow this
`individualcontrol ofeach light-emitting element independent
`of one another.
`
`Sensing Device
`
`In one embodimentofthe present invention, a tem-
`[0045]
`perature sensor is configured to measure the junction tem-
`perature of the light-emitting elements in the arrays, wherein
`the single temperature sensor is strategically positioned to
`detect the operating temperature ofall colours of light-emit-
`ting elements. For example, in one embodiment, the light-
`emitting elements can be mounted on a common thermally
`conductive substrate upon which the temperature sensor is
`mounted.
`
`light-emitting element or colouroflight-emitting element, as
`a function of temperature. In this manner temperature modi-
`fied spectral output characteristics of the light-emitting ele-
`ments can be determined.
`
`[0053] The controller is further configured to evaluate con-
`trol signals for transmission to the light em