(12) United States Patent
`Stam et al.
`
`USOO64984.40B2
`(10) Patent No.:
`US 6,498,440 B2
`45) Date of Patent:
`Dec. 24, 2002
`
`9
`
`(54) LAMPASSEMBLY INCORPORATING
`OPTICAL FEEDBACK
`
`(75) Inventors: Joseph S. Stam, Holland, MI (US);
`John K. Roberts, East Grand Rapids,
`MI (US)
`(73) Assignee: Gentex Corporation, Zeeland, MI (US)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/818,958
`(22) Filed:
`Mar 27, 2001
`(65)
`Prior Publication Data
`US 2002/0047624 A1 Apr. 25, 2002
`Related U.S. Application Data
`(60) Provisional application No. 60/192,484, filed on Mar. 27,
`2000.
`(51) Int. Cl." ........................ H05B 37/02; G05B 37/00;
`s GO5F 1700
`(52) U.S. Cl. .......................... 315,291; 315/316; 11/292
`(58) Field of Search ................................. 315/291, 316,
`315/318, 292, 295, 362,309, 293,317;
`340/825.07, 825.18, 815.45; 362/800
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`5,350,977 A * 9/1994 Hamamoto et al. ......... 315/291
`5,420,482 A 5/1995 Phares ........................ 315/292
`6,016,038 A * 1/2000 Mueller et al. ............. 315/291
`6,166,496 A * 12/2000 Lys et al. ................... 315/292
`6,285,140 B1
`9/2001 Ruxton ....................... 315/291
`
`* cited by examiner
`
`Primary Examiner Don Wong
`ASSistant Examiner-Chuc Tran
`(74) Attorney, Agent, or Firm-Price, Heneveld, Cooper,
`DeWitt & Litton; James E. Shultz Jr.
`(57)
`ABSTRACT
`An illuminator assembly that is capable of utilizing a
`plurality of light Sources to produce a desired resultant hue,
`includes a processor, a memory, a plurality of light Sources
`and a detector. The memory is coupled to the processor and
`Stores data and information. Each of the plurality of light
`Sources are coupled to the processor and produce a different
`color. The processor is capable of independently controlling
`the intensity of each light Source So as to produce a desired
`resultant hue. The detector is also coupled to the processor.
`The detector provides the processor with information which
`the processor utilizes in determining how to adjust the
`intensity of each of the light Sources to provide the desired
`resultant hue.
`
`4992,704 A 2/1991 Stinson ...................... 315/312
`
`19 Claims, 7 Drawing Sheets
`
`
`
`
`
`
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`
`
`PROCESSOR
`PORT 0
`
`PORT 1
`
`PORT 2
`
`l,01
`
`02
`
`VWGoA EX1020
`U.S. Patent No. 9,955,551
`
`

`

`U.S. Patent
`U.S. Patent
`
`Dec. 24, 2002
`Dec. 24, 2002
`
`Sheet 1 of 7
`Sheet 1 of 7
`
`US 6,498,440 B2
`US 6,498,440 B2
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`100
`100
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`101
`101
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`102
`102
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`103
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`FIG. 1
`FIG. 1
`
`
`
`

`

`Dec. 24, 2002
`Dec. 24, 2002
`
`Sheet 2 of 7
`Sheet 2 of 7
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`US 6,498,440 B2
`US 6,498,440 B2
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`
`
`U.S. Patent
`
`U.S. Patent
`
`

`

`U.S. Patent
`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 3 of 7
`
`US 6,498,440 B2
`US 6,498,440 B2
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`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 4 of 7
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`US 6,498,440 B2
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`DETECTOR
`SIGNAL
`
`s' s' s' s
`
`1
`
`0
`
`F.G. 5A
`
`507 508
`
`509 510
`
`511 512
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`SOS 506
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`Director - - - - - - - - - - -
`si"
`||
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`PORT 0
`
`SIGNAL —t- - SS
`(RED)
`\
`513
`
`PORT 1
`SIGNAL - SS- S
`(GREEN)
`514
`
`PORT 2
`SIGNAL -S-S-S
`(BLUE)
`sis
`
`FG. SB
`
`

`

`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 5 of 7
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`US 6,498,440 B2
`
`601
`
`602
`
`
`
`
`
`LAMP TURNED ON
`
`MEASURE
`AMBIENT LIGHT
`
`MEASURE LED SET 1
`(RED)
`
`
`
`MEASURE LED SET 2
`(GREEN)
`
`MEASURE LED SET 3
`(BLUE)
`
`
`
`DETERMINE COLOR PROPORTIONS
`TO ACHIEVE DESIRED HUE
`
`SET PWM DUTY CYCLES TO
`EACH LED SET
`
`
`
`
`
`
`
`OPERATE LAMP UNTIL
`NEXT CALIBRATIONCYCLE
`
`F.G. 6
`
`

`

`U.S. Patent
`
`Dec. 24, 2002
`
`Sheet 6 of 7
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`US 6,498,440 B2
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`380 430 480 530 580 630 680 730 780
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`WAVELENGTH (nm)
`
`FG. 7
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`
`
`0
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`0 1
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`0.2
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`0.3
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`0.5
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`

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`U.S. Patent
`U.S. Patent
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`Dec. 24, 2002
`Dec. 24, 2002
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`Sheet 7 of 7
`Sheet 7 of 7
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`US 6,498,440 B2
`US 6,498,440 B2
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` U
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`FIG. 9
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`

`

`1
`LAMPASSEMBLY INCORPORATING
`OPTICAL FEEDBACK
`
`US 6,498,440 B2
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`2
`intensity and color variance, one must measure the output of
`the blue-green and amber LEDs and adjust their initial
`proportions during assembly of the lamp.
`Yet another method of creating white light using LEDs is
`to combine the colors of three or more LEDs in a particular
`ratio to form white light. A typical System may combine light
`from red, blue and green LEDs to form an RGB system that
`is capable of producing not only white light but any other
`color of light as well (by adjusting the intensity of the red,
`blue and green LEDs, independently). Another advantage of
`Such a System is the potential for an improved color ren
`dering indeX and thus an increase in the brilliance of colors
`on the object being illuminated. The primary difficulty in
`implementing an illuminator using a plurality of LEDs,
`especially where there are three or more colors, is accom
`modating the large intensity variance present in modern
`LEDs. The high variance in intensity of the individual color
`LEDs leads to wide variance in the output color. To solve
`this problem, LEDs are typically sorted by color and inten
`sity. Frequently, further measurements of individual assem
`blies are needed to insure accurate color calibration. These
`methods may partially correct an initial problem but do not
`Solve problems associated with differential brightness decay,
`which occurs with aging or changes in intensity of the
`individual constituent colors which can occur with changes
`in temperature of the die or the ambient environment.
`AS Such, an illuminator assembly that adapts to light
`Source component variability, to produce a desired resultant
`hue of illumination, is desirable.
`SUMMARY OF THE INVENTION
`An embodiment of the present invention is directed to an
`illuminator assembly that produces light of a desired result
`ant hue. In one embodiment, the illuminator assembly
`includes a processor, a memory, a plurality of light Sources
`and a detector. The memory is coupled to the processor and
`Stores data and information. Each of the plurality of light
`Sources are coupled to the processor and produce a different
`primary color. The processor is capable of independently
`controlling the intensity of each light Source So as to produce
`a desired hue resulting from the mixing of the light emitted
`from each light Source. The detector is also coupled to the
`processor. The detector provides the processor with
`information, which the processor utilizes in determining
`how to adjust the intensity of each of the light Sources to
`provide the desired resultant hue.
`These and other features, advantages and objects of the
`present invention will be further understood and appreciated
`by those skilled in the art by reference to the following
`Specification, claims and appended drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`In the drawings:
`FIG. 1 is a drawing of an illuminator assembly
`constructed, according to an embodiment of the present
`invention;
`FIG. 2A shows a leadframe for an LED lamp, which may
`be used in conjunction with the present invention;
`FIG. 2B shows an encapsulated LED lamp, which may be
`used in conjunction with the present invention;
`FIG. 3A shows another leadframe for an LED lamp,
`which may be used in conjunction with the present inven
`tion;
`FIG. 3B shows another encapsulated LED lamp, which
`may be used in conjunction with the present invention;
`FIG. 4 shows a control circuit for implementing an
`embodiment of the present invention;
`
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`This application claims priority based on U.S. Provi
`sional Patent Application Ser. No. 60/192,484, entitled
`“LAMP ASSEMBLY IN CORPORATING OPTICAL
`FEEDBACK," by Joseph S. Stam et al., filed Mar. 27, 2000,
`the disclosure of which is hereby incorporated by reference.
`BACKGROUND OF THE INVENTION
`The present invention is directed to a lamp assembly and,
`more specifically, to a lamp assembly that incorporates
`optical feedback.
`Recent advances in light emitting diode (LED) technol
`ogy has led to the development of Several high-brightness
`LED lamps for use in automobiles and other applications.
`Many of these applications require a Substantially white
`colored illumination when providing light for taskS Such as,
`for example, reading a map or book. A common method of
`producing white light using LEDs is to deposit a yellow
`phosphor on top of a InGaN Blue LED die. Some of the blue
`light emitted by the LED is absorbed by the phosphor
`causing it to emit yellow light. The combination of the blue
`light from the LED and the yellow light from the phosphor
`combines to produce a metameric white light.
`This technique is relatively simple and leads to a single
`component Solution. However, this technique relies entirely
`on an InGaN emitter as the Source of energy for the
`illuminator. Currently, most InCaN LED systems are less
`efficient and more expensive than other alternatives, Such as
`AlInGaP LED emitters. As such, a system that relies pri
`marily on an InGaN die, as the Source of optical radiation,
`is typically more expensive to produce. Additionally, the use
`of a phosphor typically shortens the useful life of the device
`as an illuminator. This is because the phosphor typically
`decays at a faster rate than the underlying InGaN die.
`Additionally, as the phosphor decays, the relative proportion
`of yellow light emitted is reduced, which results in a color
`shift in the light output.
`Another technique for producing white light is to combine
`the outputs of an amber AlInGaP LED and a blue-green
`InGaN LED in appropriate proportions. Such an approach is
`outlined in U.S. Pat. No. 5,803,579 entitled, ILLUMINA
`TOR ASSEMBLY INCORPORATING LIGHT EMITTING
`45
`DIODES, to Turnbull, et. al., commonly assigned with the
`present invention, and hereby incorporated by reference.
`Using this approach, the outputs of the LEDs are combined
`in different proportions to produce white light of different
`color temperatures. An increase in the proportion of amber
`light (or a corresponding decrease in the proportion of
`blue-green light) will produce a warmer white light corre
`sponding to a lower color temperature. An increase in the
`proportion of blue-green light produces a cooler white light
`corresponding to a higher color temperature.
`Although the two types of LED dies decay at a rate that
`is more Similar than the rates of InCiaN die and phosphors,
`the AlInGaP and InCaN dies still exhibit a difference in
`decay rates. These differences in decay rates lead to a
`difference in color temperature over the life of the device.
`However, Since a change in relative proportion of one of the
`constituent colorS Still produces a resultant color, which is
`typically accepted as white light, the Severity of this effect
`is acceptable in many applications. Unfortunately, this effect
`is typically increased due to the wide variance in intensity
`and Somewhat lesser variance in color that is typical of
`modern LED production. In order to accommodate for
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`3
`FIG. 5A is a diagram of a waveform for operating a
`detector, according to an embodiment of the present inven
`tion;
`FIG. 5B is a diagram of four waveforms for operating a
`detector to measure the ambient light and intensity of LEDs,
`according to an embodiment of the present invention;
`FIG. 6 is a flow chart showing the operation of the present
`invention;
`FIG. 7 is a plot of the relative spectral power vs. wave
`length for LEDs which may be used to implement the
`present invention, according to an embodiment of the
`present invention;
`FIG. 8 is a CIE 1976 UCS diagram showing the format
`ting of white light by the mixing of two complementary hues
`from LEDs that may be used in the present invention; and
`FIG. 9 is a CIE 1976 UCS diagram showing the format
`ting of any color light by the mixing of three hues from
`LEDs that may be used in the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The present invention is directed to a lamp (e.g., LED)
`assembly that utilizes a detector (to provide optical
`feedback), preferably located within the LED assembly, to
`determine how to adjust drive currents provided to a plu
`rality of LEDs that are grouped according to color. The
`detector is preferably positioned Such that it can receive light
`radiated from each LED group. A control circuit receives
`input from the detector and based on the input, adjusts the
`drive current of each group of LEDs to produce a desired
`resultant hue. The control circuit can also adjust the intensity
`of the entire assembly. In addition, the control circuit is
`preferably capable of determining an ambient light level,
`which can be utilized in determining the actual light output
`of an LED group.
`FIG. 1 depicts a lamp assembly 100 that includes a
`plurality of light emitting diodes (LEDs) 110, according to
`an embodiment of the present invention. Each LED may be
`of a unique color, there may be Several LEDs of one color
`or there may be multiple groups of LEDs, each group being
`a unique color. FIG. 1 shows three groups of LEDs 110 with
`each group containing two LEDs (two red LEDs 101, two
`green LEDs 102 and two blue LEDs 103). By independently
`controlling the intensity of each of these groups, any color
`illumination (including white light) can be produced. The
`use of three colors or the colorS Specifically mentioned
`herein are merely exemplary and are not intended to be
`limiting.
`LEDs 110 may be of a variety of types. The LEDs 110
`may contain Solid State Semiconductor radiation emitters that
`have at least one PN junction (in which photons are emitted
`upon the passage of current through the junction). The Solid
`State Semiconductor radiation emitter may be referred to
`hereinafter as an LED chip, an LED die or an emitter. Such
`LED chips may be composed of materials such as InGaN,
`AlInGaP, GaP. GaN, GaAs, AlGaAs, SiC or others. LED
`chips of this type are available from Such companies as
`LumiLEDs, Cree, Uniroyal Technology Corporation,
`Nichia, Toyoda Gosai, Tyntec and others. The LED chip
`may be packaged by a variety of means, including bonding
`of the chip onto a leadframe and encapsulating the leadframe
`and chip with a transparent encapsulant material. The lead
`frame may be designed for Surface mount or thru-hole
`assembly onto a printed circuit board or may not be designed
`for circuit board assembly. Packages of this type are referred
`to by common names such as T-1, T-134, T-5, poly-LED,
`chip-LED, Super-flux, piranha TM, Snap-LED and others.
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`Alternatively, the LED chips need not be packaged at all and
`may be directly attached to a circuit board 104 using
`chip-on-board assembly techniqueS or the like. An LED die
`package using one of the above mentioned techniques may
`be referred to hereinafter as a light Source, an LED device,
`an LED lamp or simply an LED. LED lamps are available
`from numerous companies Such as LumiLEDs, Nichia,
`Stanley, Osram, Panasonic and Unity Optoelectronics, to
`name a few.
`In a preferred embodiment LEDs 110 are constructed as
`described in U.S. patent application Ser. No. 09/426,795,
`filed Oct. 22, 1999, entitled SEMICONDUCTOR RADIA
`TION EMITTER PACKAGE, to Roberts et al., commonly
`assigned with the present invention and hereby incorporated
`by reference. Alternatively, the LEDs may be constructed
`according to U.S. Provisional Patent Application Ser. No.
`(60/265,487) filed on Jan. 31, 2001, entitled HIGHPOWER
`LED LIGHT ENGINE to Roberts et al.; U.S. Provisional
`Patent Application Ser. No. (60/265,489), filed on Jan. 31,
`2001, entitled LIGHT EMITTING DIODES AND
`METHOD OF MAKING THE SAME to Roberts et al.; and
`U.S. Provisional Patent Application Ser. No. 60/27005 45,
`filed on Feb. 19, 2001, entitled RADIATION EMITTER
`DEVICE HAVING AMICROGROOVE LENS to Roberts,
`commonly assigned with the present invention and hereby
`incorporated by reference. U.S. patent application Ser. No.
`09/426,795 to Roberts et al. discloses an LED chip that is
`mounted onto a leadframe containing a heat extraction
`member and encapsulated with a transparent encapsulant.
`Roberts et al. also discloses an LED lamp which is config
`urable as a thru-hole or Surface-mount device compatible
`with traditional electronic assembly methods. The presence
`of the heat extraction member allows the LED chips to be
`operated at greater currents by dissipating heat in a more
`efficient manner than is possible with conventional LED
`packages.
`Roberts et al. also discloses a plurality of LED chips that
`are incorporated into a single LED package that provides
`Sufficient heat dissipation to operate the LED chips at a high
`enough current for illumination applications. FIG. 2A shows
`a thru-hole configuration of a Roberts et al. leadframe 201
`prior to encapsulation. AS shown, the leadframe 201 con
`tains a heat extraction member 202 and two LED chips 203
`and 204. LED chips may be of the same or different types
`or colors. The current to each of the LED chips can be
`controlled separately through electrical leads 205 and 207
`with a common chip Substrate connection provided by
`electrical lead 206. If LED chips 203 and 204 are of different
`colors, the resultant hue, which is Synthesized by the com
`bination of the two colors, can be dictated by varying the
`current to these two leads 205 and 207. FIG. 2B Shows the
`leadframe 201 of FIG.2A after it has been encapsulated with
`encapsulant 209, with tiebars 208 removed.
`Another configuration disclosed in Roberts et al. is shown
`in FIGS. 3A and 3B. FIG. 3A illustrates a Surface mount
`configuration of a leadframe 301 with three emitters 302,
`303 and 304 mounted onto a heat extraction member 305
`and connected with electrical leads 306, 307 and 308 and a
`Substrate electrical lead 309. FIG. 3B shows the device of
`FIG.3A with encapsulation 310. As above, the three emitters
`302, 303 and 304 may be of the same type or of different
`types and may be controlled independently. If the three
`emitters 302, 303 and 304 are red, green and blue,
`respectively, the device can produce light of any hue if the
`current to each of the emitters 302, 303 and 304 is changed
`independently.
`In addition to Solid State Semiconductor optical radiation
`emitters, the present invention may be adapted equally to
`
`

`

`S
`other types of Semiconductor radiation emitters, Such as
`polymer LEDs or organic LEDs (OLEDs). Additionally, the
`present invention should not be construed as limited to any
`particular configuration of LED chip or LED lamp or
`packaging technique. Nor should the present invention be
`construed as limited to any number of LED lamps or any
`number of LED lamp colors.
`An optical radiation detector 106 is preferably configured
`to measure the optical radiation from any of LEDs 110 and
`is optionally configured to measure ambient lighting condi
`tions. As shown in FIG. 1, light from LEDs 110 is radiated
`onto a diffuser 105. While most of the light from LEDs 110
`passes through the diffuser 105 and onto the illuminated
`scene, some of the light is scattered from the diffuser 105
`back towards detector 106 and thus allows detector 106 to
`measure the relative output of the LEDs 110. Additionally,
`the detector 106 can optionally measure the ambient light
`through diffuser 105.
`Diffuser 105 may be constructed as a frosted piece of
`glass or plastic. Alternatively, diffuser 105 may be an
`engineered diffuser Such as a Holographic Light Shaping
`Diffuser'TM, available from Physical Optics Corporation of
`Torrance, Calif. Such diffusers typically provide a controlled
`amount of diffusion and maximum efficiency. Detector 106
`may be used to provide additional functionality to lamp 100.
`For example, detector 106 may be used as an optical receiver
`for communication of data or instructions from an optical
`transmitter, Such as is common in IRDA Systems. The
`instructions can be, for example, from an infrared remote
`control and may include commands Such as to turn on/off
`lamp 100, vary the brightness of lamp 100 or vary the color
`of lamp 100. Instructions can also be communicated to other
`devices, which may be coupled to lamp 100 via a network.
`For example, multiple lamps 100 may be positioned
`throughout a house and networked together and may serve
`as receivers for infrared remote controls, which control other
`appliances Such as a Stereo or television Set. In addition,
`LEDs 110 may be used to encode a response to a remote
`control or may be used to communicate data optically to
`other devices. Further, instructions may be communicated to
`lamp 100 by other techniques such as by radio frequency
`transmissions, using protocols Such as BlueTooth". Instruc
`tions may alternatively by communicated over a separate
`network or as a current line carrier Signal.
`The detector 106 may be of various types including
`silicon photodiodes or CdS photoresistors. In a preferred
`embodiment, the detector is constructed according to U.S.
`patent application Ser. No. 09/307,191, filed on May 7,
`1999, entitled PHOTODIODELIGHTSENSOR to Nixon et
`al., commonly assigned with the present invention and
`hereby incorporated by reference. The Nixon et al. detector
`collects light over a variable integration time and provides a
`digital output indicative of the amount of light collected. The
`Nixon et al. detector includes a direct digital connection to
`a microcontroller that is adaptable to operate over a wide
`range of light levels and is typically Small and inexpensive.
`However, one of ordinary skill in the art will appreciate that
`the present invention can be implemented advantageously
`with a large variety of optical detectors, provided that a
`detector is capable of measuring the relative optical output
`of any of the LEDs.
`In addition to the embodiment illustrated in FIG. 1, it is
`possible to configure detector 106 in multiple ways. The
`detector may be configured to directly view the output of one
`or more of the LEDs 110 either by mounting it separate from
`circuit board 104 or by optically redirecting light from any
`of LEDs 110 to the detector using light pipes or mirrors.
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`Numerous optical configurations are possible So long as the
`detector 106 is capable of receiving at least a portion of
`radiation from any of LEDs 110, which it is intended to
`CSUC.
`More than one detector 106 may be utilized. When
`multiple detectors 106 are utilized, they are typically con
`figured to view different LEDs 110. A detector 106 may be
`configured with a filter which allows a single color of light
`from LEDs 101, 102 or 103 to be detected and thus greatly
`reduces the sensitivity of the detector 106 to light which is
`not emitted from the desired color of LED. In this case,
`another detector 106 may contain a filter, which allows light
`of another color of light to be detected.
`In another embodiment, one of LEDs 101,102 or 103 may
`actually be used as detector 106. For example, one of LEDs
`101 can be reverse-biased and operated as a photodiode to
`detect light from other LEDs 101 of the same color.
`FIG. 4 shows a control circuit utilized in conjunction with
`illuminator assembly 100 that contains three groups of two
`LEDs, each group being of a different color. The LEDs are
`powered from a common supply labeled VCC. The LEDs in
`each set are driven independently by ports 0, 1 and 2 of
`processor 401 through transistors Q1 through Q6. In this
`context, the term processor may include a general purpose
`processor, a microcontroller (i.e., an execution unit with
`memory, etc., integrated within a single integrated circuit) or
`a digital Signal processor. TransistorS Q1, Q3 and Q5 may be
`of type MPSAO6 and transistors Q2, Q4 and Q6 may be of
`type O2N3904. Processor 401 may be of a variety of types,
`for example, one of a number of PIC microcontrollers
`available from Microchip of Chandler, Ariz.
`The operation of this type of LED drive circuit is
`explained in detail in U.S. Pat. No. 5,803,579, previously
`incorporated. In summary, when port 0 of processor 401 is
`asserted, LEDs D1 and D2 are turned on. When port 1 is
`asserted, LEDs D3 and D4 are turned on. When port 2 is
`asserted, LEDs D5 and D6 are turned on. The current for
`each set of LEDs is limited by resistors R1,R2 and R3. By
`rapidly turning ports 0, 1 and/or 2 on and off at a rate faster
`than is perceivable to the human eye, it is possible to vary
`the apparent brightness of the LEDS. This technique is
`commonly referred to as pulse width modulation (PWM).
`The percentage of time that each LED group is on is the duty
`cycle of the LED group. The greater the duty cycle, the
`brighter the LEDs of a given LED group. In order to remain
`unperceivable to the human eye, the frequency at which the
`LEDs are pulse width modulated should be greater than 15
`HZ, more preferably greater than 30 Hz and most preferably
`greater than 60 Hz.
`Although FIG. 4 illustrates three groups of two LEDs,
`wherein the two LEDs within the group are in Series, one of
`ordinary skill in the art will appreciate that other configu
`rations are possible. The LEDs may be in parallel or in a
`series/parallel combination. The number of LEDs which
`may be placed in Series is dependent on the forward Voltage
`of the specific type of LED and the Supply voltage. For
`example, if the circuit is powered from an automotive
`vehicle power Supply, it is only possible to power two
`InGaN blue LEDs in series because the forward voltage of
`a InGaN LED is typically 3.5 volts each, plus 1.2 V for the
`current sink transistor for a total of 8.2 V (automotive design
`requirements mandate that a device be functional down to
`9.0 V). For the same conditions, using an AlInGaP amber
`LED with a forward voltage of 2.5 V three series coupled
`LEDs, can be utilized.
`Techniques other than pulse width modulation can be
`utilized to vary the brightness of LEDs 110. For example, a
`
`

`

`US 6,498,440 B2
`
`15
`
`7
`variable current source could be used to vary the DC current
`to the LEDs 110. Alternatively, the function of processor 401
`may be replaced by a discrete logic circuit or an analog
`circuit.
`Detector 106 is connected to port 3 of processor 401. The
`operation of a photodiode light Sensor, according to U.S.
`patent application Ser. No. 09/307,191, is described with
`reference to FIG. 5A. Detector 106 (FIG. 4) may be con
`figured as an open-drain device with a high output produced
`by pull-up resistor R7. The rise time of edges 502 and 504
`of a detector output signal 500 is thus determined by the RC
`time constant of R7 and C1. To acquire a light measurement,
`processor 401 sets port 3 low for predetermined time period.
`At the end of the time period, the processor 401 tri-states
`port 3 and the detector signal 500 is pulled high by resistor
`R7. The time period between falling edge 501 and rising
`edge 502 defines the integration period over which photon
`generated charge is collected in detector 106. After a period
`of time, detector 106 generates an output pulse shown by the
`low pulse between edges 503 and 504. The time between
`edges 503 and 504 is indicative of the amount of charge
`collected over the integration period and thus the light level
`incident on detector 106.
`AS is described in greater detail in U.S. patent application
`Ser. No. 09/307,941, filed on May 7, 1999, entitled AUTO
`25
`MATIC DIMMING MIRROR USING SEMICONDUC
`TOR LIGHT SENSOR WITH INTEGRAL CHARGE
`COLLECTION, by Stam et al., commonly assigned with the
`present invention, and hereby incorporated by reference, the
`time between the rising edge of the integration pulse 502 and
`the falling edge of the output pulse 503 (called the pre-pulse
`time), is indicative of the dark current generated in the
`device and thus may be used as a measure of the temperature
`of the detector. A measure of temperature can be used to
`reduce the brightness of the LEDs 110, or inhibit their
`operation during high temperatures in order to prevent
`damage to the lamps.
`The use of the detector 106 to measure the output of the
`LEDs is further described with reference to FIG. 5B.
`Initially, detector 106 may acquire an ambient light reading
`which may then be subtracted from further readings of the
`LEDs 110 to prevent ambient light conditions from inter
`fering with the brightness readings of the LEDs.
`Alternatively, the ambient light reading can be used as a
`control input for the illumination System. An ambient read
`ing is taken with integration pulse 505 and received with
`output pulse 506. As mentioned above, the time between
`pulses can be used as a temperature measurement. Next, a
`measurement is taken of the output of one of the groups of
`LEDs, for example, the red group 101. The red group of
`LEDs 101 is turned on by setting port 0 of the processor 401
`high as indicated by pulse 513. Pulse 513 occurs simulta
`neously with integration pulse 507 and output pulse 508 is
`indicative of the output of the red LEDs 101, optionally after
`Subtracting the ambient light measurement. In a similar way,
`the green group of LEDs 102 is turned on with port 1, as
`indicated by pulse 514 which occurs with integration pulse
`509. The brightness of green LEDs 102 is indicated by
`output pulse 510. Finally, blue LEDs 103 are turned on with
`port 2, as indicated by 515 during integration pulse 511 with
`the brightness indicated by the width of pulse 512.
`If the lamp 100 is likely to be used in conditions where the
`ambient lighting is produced with fluorescent lamps or
`discharge lamps, it is desirable to take into account the 120
`HZ oscillation which occurs in these lamps as a result of
`being powered from a 60 Hz AC line source. To insure that
`the ambient light level measurement is constant and that the
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`35
`
`8
`amount of ambient light level present in a measurement of
`the LED brightness is consistent and can thus be accurately
`Subtracted from LED brightness measurements, it is useful
`to use an integration pulse width of /120th of a Second
`(0.0083 ms) or a multiple thereof. If shorter integration pulse
`widths are required, it is desirable to have the beginning of
`the ambient light integration pulse 505 and the beginning of
`any of the LED brightness measurement pulses 507, 509, or
`511 separated by /120th of a second or a multiple thereof.
`The operation of an LED illuminator assembly 100,
`according to the present invention, is best described with
`reference to FIG. 6. After the lamp is turned on in step 601,
`an ambient light measurement is taken in Step 602, accord
`ing to the procedure described above. Next, brightness
`measurements of each of the LED sets are taken in steps 603,
`604 and 605. If fewer groups of LEDs are present (such as
`would be the case in a binary-complementary white System)
`one or more of these Steps are omitted. If more groups of
`LEDs are present, additional measurement StepS can be
`added between steps 605 and 606.
`Once brightness measurements for all of the constituent
`LED colors are acquired, a duty cycle required to achieve a
`desired illumination hue is determined. This proceSS is best
`described with reference to FIGS. 7 and 8. For simplicity, a
`description of a binary-complementary two color System is
`described first. FIG. 7 illustrates the relative spectral output
`power of a blue-green InCaN LED 701 and an amber
`AlInGaP LED 702. As is readily evident from FIG. 7, both
`of these LEDs are highly monochromatic having the major
`ity of their optical output power contained in a narrow range
`of wavelengths (i.e., peak of ~483 nm for Blue-Green and
`~584 nm for Amber). Thus, these sources are highly satu
`rated and can be approximated as a single point on the
`monochromatic locus of the CIE 1976 UCS diagram (FIG.
`8).
`Point 801 defines the color coordinates of the blue-green
`(483 nm) LED and point 802 defines the color coordinates
`of the amber (584 nm) LED. An additive mixture of light
`from these two LEDs can produce any hue with color
`coordinates along line 803, which extends between points
`801 and 802. The proportion of light needed from each LED
`to achieve a hue along line 803 is inversely proportional to
`the distance between the color coordinate of the desired hue
`and the color coordinate of the LED. For example, CIE
`Standard illuminant A may be Synthesized with one propor
`tioned combination of ambe