a2) United States Patent
`US 7,055,986 B2
`(10) Patent No.:
`Littleton
`(45) Date of Patent:
`Jun. 6, 2006
`
`
`US007055986B2
`
`(54) PROGRAMMABLE LED SPECTRAL LIGHT
`SOURCE
`
`(75)
`
`Inventor: Roy T. Littleton, Woodbridge, VA (US)
`
`(73) Assignee: The United States of America as
`represented by the Secretary of the
`Army, Washington, DC (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`atent is extended or adjusted under 35
`Pp
`i
`US.C. 154(b) by 216 days.
`
`(21) Appl. No.: 10/792,850
`(22)
`Filed:
`Mar. 5, 2004
`(65)
`Prior Publication Data
`
`US 2005/0194516 Al
`
`Sep. 8, 2005
`
`(51)
`
`Int. Cl.
`(2006.01)
`F2IV W16
`(2006.01)
`F2IV 29/00
`(52) U.S. Che ccccsesseven 362/231; 362/235; 362/251:
`362/276; 362/294; 362/373
`,
`,
`,
`(58) Field of Classification Search........ 362/230-231,
`362/235-236, 276, 373, 800, 802, 249,251,
`oo.
`. 362/294
`See application file for complete search history.
`.
`References Cited
`U.S. PATENT DOCUMENTS
`5,608,213 A *
`3/1997 Pinkus et al. ss. 250/252.1
`5,679,949 A * 10/1997 Task et al.
`....
`. 250/252.1
`
`eee 430/30
`5,686,210 A * 11/1997 Sharman 0...
`
` 7/1998 Hochstein ............. 315/159
`
`5,783,909 A *
`........00.. 382/312
`5,982,957 A * 11/1999 DeCaro et al.
`
`(56)
`
`6,127,783 A * 10/2000 Pashley et al... 315/149
`6,441,558 B1*
`8/2002 Muthuet al.
`......
`
`7/2004 Vogel et al. we. 315/312
`6,759,814 BL*
`2003/0233138 A1l*
`12/2003 Spooner oo... eee 607/93
`OTHER PUBLICATIONS
`
`J. Res. Natl. Inst. Stand. Technol. 107, 363-371 Jul. 2002,
`Development of a Tunable LED-Based Colorimetric Source,
`Steven W. Brown,et.al.
`Nist Tech Beat Apr. 23, 2004, http:/Avww.nist.gov/
`ublic__affairs/techbeat/th2004__0423 htm Portable ‘Rain-
`Pp
`bow’ Source Improves Color Calibrations, Laura Ost.
`
`* cited by examiner
`Pri
`Examiner—Alan
`Cari
`Assistant Examiner—Jason Han
`(74)Attorney: Agent, or Firm—Arthur Samora; Andrew
`
`(57)
`ABSTRACT
`An apparatus for emulating various known night sky illu-
`.
`ot
`ve
`:
`:
`mination conditions. The apparatus comprises a plurality of
`electrically-powerable LEDs which are disposed in an arra
`y-powers
`P
`mamey
`and have respective spectral curves centered at different
`.
`Lo
`:
`wavelengths in the visible to the short wave infrared wave-
`bands, and meansforfixing the temperatures ofthe LEDsto
`avoid temperature-induced changesin their spectral curves.
`Additionally, the apparatus includes means for varying the
`y.
`pp
`rying
`light intensities of the individual LEDs so that the combi-
`nation of their spectral curves matches the spectrum of the
`known night sky illumination condition to be emulated, and
`meansfor regulating the total amountof light collected from
`th
`that th
`lati
`t.
`has
`th
`intensityasthe known nightskyilluminationcomlitinntobo
`emulated
`&
`
`.
`
`18 Claims, 1 Drawing Sheet
`
`
`
`
`Light
` Temperature
`Contraller Controller
`
`
`
` Intensities
`
`2?
`
`1
`
`APPLE 1054
`Apple v. Masimo
`IPR2022-01299
`
`APPLE 1054
`Apple v. Masimo
`IPR2022-01299
`
`1
`
`

`

`U.S. Patent
`
`Jun. 6, 2006
`
`US 7,055,986 B2
`
`15
`
`Programmable
`Computer
`
`29
`
`23
`
`
`
`Light
`Intensities
`Temperature
`
`Controller
`
`27
`
`2
`
`

`

`US 7,055,986 B2
`
`1
`PROGRAMMABLE LED SPECTRAL LIGHT
`SOURCE
`
`GOVERNMENTINTEREST
`
`The invention described herein may be manufactured,
`used, sold, imported, and/or licensed by or for the Govern-
`ment of the United States of America.
`
`BACKGROUND OF THE INVENTION
`
`This invention relates in general to light sources, and
`moreparticularly, to programmable light sources.
`The performance of passive low-light-level imaging sys-
`tems that operate in the visible, near infrared, and short
`wavelength infrared spectral bands has been investigated for
`the past several years. Although such devices operate under
`low power, exhibit low dark current, and retain high system
`resolution under moonlight conditions,
`they are limited
`under low light level conditions.
`Typically, their performance is evaluated in a laboratory
`setting using a 2856° K blackbody—atungsten filament—as
`the radiation source, which can correlate reasonably well
`with night sky measurements below 1 micron. However, it
`does not correlate reasonably well with night sky measure-
`ments above 1 micron. Night sky spectral irradiance data
`indicate that a moonless sky produces over an order of
`magnitude more photons in the short-wave infrared (1 to 2
`micron) wavebandthan in the visible and near infrared (0.4
`to 1.0 micron) waveband. Therefore, the use of a single
`broadband 2856° K source in a laboratory to evaluate
`imaging systems that operate beyond 1 micron is insuffi-
`cient.
`
`SUMMARY OF THE INVENTION
`
`It is therefore an object of this invention to accurately
`evaluate in a laboratory setting passive low-light-level imag-
`ing systems that operate in the visible, near infrared, and
`short wavelength infrared spectral bands.
`This and other objects of the invention are achieved in one
`aspect by an apparatus for emulating various knownspectral
`signatures, particularly night sky illumination conditions.
`The apparatus comprises a plurality of electrically-power-
`able LEDs which are disposed in an array and have respec-
`tive spectral curves centered at different wavelengths in the
`visible to the short wave infrared wavebands, and meansfor
`fixing the temperatures of the LEDs to avoid temperature-
`induced changes in their spectral curves. Additionally, the
`apparatus includes means for varying the light intensities of
`the individual LEDsso that the combination oftheir spectral
`curves matches the spectrum of the known night sky illu-
`mination condition to be emulated, and meansfor regulating
`the total amountof light collected from the array so that the
`cumulative spectrum has the same intensity as the known
`night sky illumination condition to be emulated.
`Another aspect of the invention involves a method of
`emulating various spectral signatures comprising the steps
`of: (a) electrically-powering a plurality of electrically-pow-
`ered LEDsin an array, the LEDs having respective spectral
`curves centered at different wavelengths in the visible to the
`short wave infrared wavebands; (b) fixing the temperatures
`of the LEDs to avoid temperature-induced changesin their
`spectral curves;
`(c) varying the light
`intensities of the
`individual LEDs so that the combination of their spectral
`curves matches the spectrum of the known night sky illu-
`mination condition to be emulated; and (d) regulating the
`
`10
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`total amount of light collected from the array so that the
`cumulative spectrum has the same intensity as the known
`night sky illumination condition to be emulated.
`The invention can accurately emulate various night sky
`illumination conditions by emitting spectra in a laboratory
`setting to matchthat of full moon,partial moon,starlight and
`overcast starlight conditions.
`Additional advantages and features will become apparent
`as the subject
`invention becomes better understood by
`reference to the following detailed description when con-
`sidered in conjunction with the accompanying drawings
`wherein:
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The sole FIGURE is a schematic illustration of an illu-
`mination conditions-emulating apparatus embodying the
`invention.
`
`WRITTEN DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`The FIGURE shows the apparatus 11 for emulating
`various known spectral signatures such as night sky illumi-
`nation conditions. The apparatus 11 comprises an electri-
`cally-powered array 13 of LEDs which have respective
`spectral curves centered at different wavelengths in the
`visible to the short wavelength infrared wavebands, specifi-
`cally in the 0.4 to 2.5 micron range, and meansforfixing the
`temperatures of the LEDs to avoid temperature-induced
`changes in their spectral curves. Additionally, the apparatus
`11 includes means for varying the light intensities of the
`individual LEDs so that the combination of their spectral
`curves matches the spectrum of the known night sky illu-
`mination condition to be emulated, and meansfor regulating
`the total amountoflight collected from the array so that the
`cumulative spectrum has the same intensity as the known
`night sky illumination condition to be emulated.
`While the temperature-fixing means maytake a variety of
`forms, conveniently it may take the form shown of a
`programmable computer 15, a copper plate 17 thermally
`connected to the LED array 13, a temperature sensor 19 that
`is in thermal communication with copper plate 17 and
`electrically connected to temperature controller 23. A plu-
`rality of thermo-electric coolers 21 connected to the copper
`plate for providing an input to the programmable computer,
`a temperature controller 23 connected to the computer, to the
`temperature sensor 19 and to the coolers, a heat sink 25
`connected to the coolers, and a cooling fan 27 disposed next
`to the coolers.
`
`While the light-intensities-varying means may take a
`variety of means, conveniently it may take the form shown
`of the programmable computer 15, and a light-intensities
`controller 29 connected between the LED array 13 and the
`computer.
`While the light-regulating means maytake a variety of
`forms, conveniently it may take the form shown of the
`programmable computer 15, an integrating sphere 31
`attached to the LED array 13, the sphere having an input
`opening 33 and an output opening 35, and aniris 37 mounted
`on the output opening of the sphere and connected to the
`programmable computer.
`For the materials of the present invention, the preferred
`temperature sensor is a Model W2142 platinum resistance
`thermometer device manufactured by Omega. The preferred
`thermo-electric coolers are model CP1.0-71-05L-1 coolers
`
`made by Melcor, while LEDs manufactured by Roithner
`
`3
`
`

`

`US 7,055,986 B2
`
`3
`Lasertechnik, of Vienna can be used. The preferred inte-
`grating sphere is a custom six-inch sphere mad by Spectra-
`Physics. The light intensity controller and temperature con-
`troller
`can be manufactured using readily available
`commercial electronic components in a manner known by
`the skilled artisan.
`In operation, the array 13 of LEDsiselectrically-powered
`and the temperatures of the LEDSare fixed to avoid tem-
`perature-induced changes in their spectral curves. This is
`done by monitoring heat-generated temperature changes in
`the temperature of the copper plate 17 and thus in the
`temperature of the LED array 13 with the temperature sensor
`19. Temperature sensor 19 provides an input to the tempera-
`ture controller according to the temperature of the copper
`plate. The temperature sensor, in response to a command
`from programmable computer 15 to maintain a predeter-
`mined temperature, uses the temperature sensor input to
`drive the thermo-electric coolers 21 and cool the LEDarray,
`by removing heat generated by the thermo-electric coolers
`with the heat sink 25 and the cooling fan 27. With this
`configuration, the LED array temperature is continuously
`driven to be equal to a fixed predetermined temperature.
`Next, the integrating sphere 31 collects at its input open-
`ing 33 light from the LED array 13 and outputsat its output
`opening 35 a uniform distribution of the light collected from
`the array. The light intensities controller 29 controls the
`electric power provided to the individual LEDs from their
`power supply (not shown), and thustheir light intensities, in
`response to commandsfrom the programmable computer 15
`so that the combination of their spectral curves matches the
`knownnight sky illumination condition to be emulated, and
`the iris 37 adjusts the size of the output opening 35 of the
`integrating sphere 31 in response to commands from the
`programmable computer 15 so that the cumulative spectrum
`has the same intensity as the known night sky illumination
`condition to be emulated.
`
`Itis obvious that many modifications and variations of the
`present invention are possible in light of the above teach-
`ings. It is therefore to be understood that within the scope of
`the appended claims, the invention may be practiced other-
`wise than as described.
`
`What is claimed as new and desired to be secured by
`Letters Patent of the united statesis:
`
`1. An apparatus for emulating spectral signatures com-
`prising:
`a plurality of electrically-powerable LEDs disposed in an
`array, the LEDs having respective spectral curves cen-
`tered at different wavelengths in the visible to the short
`wave infrared wavebands;
`means for fixing the temperatures of the LEDs to avoid
`temperature-induced changes in their spectral curves;
`means for varying the light intensities of the individual
`LEDsso that the combination of their spectral curves
`matchesthe spectrum of an illumination condition to be
`emulated; and
`means for regulating the total amount oflight collected
`from the array so that the cumulative spectrum has the
`same intensity as the illumination condition to be
`emulated,
`wherein the light-regulating means includes an integrat-
`ing sphere attached to the LEDarray, the integrating
`sphere having an input opening for collecting light
`from the array and an output opening for outputting a
`uniform distribution of the collected light, and
`an iris mounted on the output opening of the integrating
`sphere for adjusting the size of the output opening.
`
`25
`
`40
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`45
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`50
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`60
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`65
`
`4
`2. The apparatus recited in claim 1 where the temperature-
`fixing means includes a programmable computer.
`3. The apparatus recited in claim 2 wherein the tempera-
`ture-fixing means includes a copper plate thermally con-
`nected to the LED array.
`4. The apparatus recited in claim 3 wherein the tempera-
`ture-fixing means includes a temperature sensor connected
`to the copper plate and to the computer for monitoring
`heat-generated changes in the temperature of the LED array
`and feeding the information to the computer.
`5. The apparatus recited in claim 1 wherein the light-
`intensities-varying means includes a programmable com-
`puter.
`6. The apparatus recited in claim 5 wherein the light-
`intensities-varying meansincludesa light intensity control-
`ler connected to the LED array and to the programmable
`computer for varying the light intensities of the individual
`LEDs in response to commands from the computer.
`7. The apparatus recited in claim 1 wherein the light-
`regulating means includes a programmable computer.
`8. An apparatus for emulating various known spectral
`signatures comprising:
`a plurality of electrically-powerable LEDs disposed in an
`array, the LEDs having respective spectral curves cen-
`tered at different wavelengths in the visible to the short
`wave infrared wavebands;
`means for fixing the temperatures of the LEDs to avoid
`temperature-induced changes in their spectral curves;
`means for varying the light intensities of the individual
`LEDsso that the combination of their spectral curves
`matches the spectrum of a known night sky illumina-
`tion condition to be emulated; and
`means for regulating the total amount of light collected
`from the array so that the cumulative spectrum has the
`same intensity as the known night sky illumination
`condition to be emulated,
`wherein the temperature-fixing means includes;
`a programmable computer,
`a copperplate thermally connected to the LED array,
`a temperature sensor connected to the copper plate and to
`the computer for monitoring heat-generated changes in
`the temperature of the LED array and feeding the
`information to the computer, and
`a plurality of thermo-electric coolers connected to the
`copper plate for cooling the LEDarray.
`9. The apparatus recited in claim 8 wherein the tempera-
`ture-fixing means includes a temperature controller con-
`nected to the computer andto the thermo-electric coolers for
`driving the coolers in response to commands from the
`computer to cool the LED array.
`10. The apparatus recited in claim 9 wherein the tempera-
`ture-fixing means includes a heat sink connected to the
`thermo-electric coolers for removing heat generated by the
`coolers.
`
`11. The apparatus recited in claim 10 wherein the tem-
`perature-fixing means includes a cooling fan disposed next
`to the thermo-electric coolers for removing heat generated
`by the coolers.
`12. An apparatus for emulating various known spectral
`signatures comprising:
`a plurality of electrically-powerable LEDs disposed in an
`array, the LEDs having respective spectral curves cen-
`tered at different wavelengths in the visible to the short
`wave infrared wavebands;
`means for fixing the temperatures of the LEDs to avoid
`temperature-induced changes in their spectral curves;
`
`4
`
`

`

`US 7,055,986 B2
`
`5
`means for varying the light intensities of the individual
`LEDsso that the combination of their spectral curves
`matches the spectrum of a known night sky illumina-
`tion condition to be emulated; and
`means for regulating the total amount oflight collected
`from the array so that the cumulative spectrum has the
`same intensity as the known night sky illumination
`condition to be emulated,
`wherein the light-regulating means includes an integrat-
`ing sphere attached to the LED array, the integrating
`sphere having an input opening for collecting light
`from the array and an output opening for outputting a
`uniform distribution of the collected light,
`a programmable computer, and
`an iris mounted on the output opening of the integrating
`sphere and connected to the programmable computer
`for adjusting the size of the output opening in response
`to commands from the computer.
`13. An apparatus for emulating various night sky illumi-
`nation conditions comprising:
`a plurality of electrically-powerable LEDs disposed in an
`array, the LEDs having respective spectral curves cen-
`tered at different wavelengths in the 0.4 to 2.5 micron
`range;
`a programmable computer;
`a copper plate thermally connected to the LED array;
`a temperature sensor connected to the copperplate and to
`the computer for monitoring changesin the temperature
`of the LED array resulting from generation of heat by
`the LED array and feeding the information to the
`computer;
`a plurality of thermo-electric coolers connected to the
`copper plate for cooling the LED array;
`a temperature controller connected to the computer and to
`the coolers for driving the coolers in response to
`commands from the computer to cool the LED array;
`a heat sink connected to the coolers for removing heat
`generated by the coolers;
`a cooling fan disposed next to the coolers for removing
`heat generated by the coolers;
`a light intensity controller connected between the LED
`array and the computer for varying the light intensities
`of the individual LEDs in response to commands from
`the computer;
`the
`an integrating sphere attached to the LED array,
`sphere having an input opening for collecting light
`from the array and an output opening for outputting a
`uniform distribution of the light collected front the
`array; and
`an iris mounted on the output opening of the integrating
`sphere and connected to the computer for adjusting the
`size of the output opening in response to commands
`from the computer.
`14. A method of emulating spectral signatures comprising
`the steps of:
`
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`(a) electrically powering a plurality of LEDs in an array,
`the LEDs having respective spectral curves centered at
`different wavelengths in the visible to the short wave
`infrared wavebands;
`(b) fixing the temperatures of the LEDs to avoid tempera-
`ture-induced changesin their spectral curves;
`(c) varying the light intensities of the individual LEDs so
`that the combination of their spectral curves matches
`the spectrum of an illumination condition to be emu-
`lated; and
`(d) regulating the total amountof light collected from the
`array so that the cumulative spectrum has the same
`intensity as the illumination condition to be emulated,
`wherein step (d) includes:
`collecting light from the array and outputting a uniform
`distribution of the collected light through an opening,
`and
`
`adjusting the size of the opening.
`15. The method recited in claim 14 wherein step (b)
`includes:
`
`monitoring heat-generated changes in the temperature of
`the LEDarray.
`16. The method recited in claim 15 wherein step (b)
`includes:
`
`feeding the monitored changes to a programmable com-
`puter.
`17. The method recited in claim 14 wherein step (b)
`includes:
`
`cooling the LED array.
`18. A method of emulating various spectral signatures
`comprising the steps of:
`(a) electrically powering a plurality of LEDs in an array,
`the LEDs having respective spectral curves centered at
`different wavelengths in the visible to the short wave
`infrared wavebands;
`(b) fixing the temperatures of the LEDs to avoid tempera-
`ture-induced changesin their spectral cvrves;
`(c ) varying the light intensities of the individual LEDs so
`that the combination of their spectral curves matches
`the spectrum of a known night sky illumination con-
`dition to be emulated; and
`(d) regulating the total amountof light collected from the
`array so that the cumulative spectrum has the same
`intensity as the known night sky illumination condition
`to be emulated,
`wherein step (d) includes:
`collecting light from the array and outputting a uniform
`distribution of the collected light through an opening,
`adjusting the size of the opening in response to commands
`from a programmable computer.
`
`5
`
`