Method and Device For Adjusting the Color or Photometric Properties of an Led Illumination Device

• US 20100301777A1
• Filed: 09/08/2008
• Published: 12/02/2010
• Est. Priority Date: 09/07/2007
• Status: Active Grant

• Current Assignee: Arnold & Richter Cine Technik GmbH & Co., Betriebs KG (Stahl Beteiligungs- GmbH)
• Original Assignee: Arnold & Richter Cine Technik GmbH & Co., Betriebs KG (Stahl Beteiligungs- GmbH)
• Inventors: Kraemer, Regine
• Granted Patent: US 8,708,560 B2
• Time in Patent Office: Days
• US Class Current: 315/312
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/28 using temperature feedback
• CPC Class Codes: H05B 45/325 Pulse-width modulation [PWM]

Abstract

The invention relates to a method for the temperature-dependent adjustment of the color properties or the photometric properties of an LED illuminating device having LEDs emitting light of different colors or wavelengths or LED color groups emitting light of the same color or wavelength within a color group, the luminous flux portions thereof determine the color of light, color temperature and/or the chromaticity coordinates of the light mixture emitted by the LED illuminating device.

Claims

1-57. -57. (canceled)

58. A method for the temperature-dependent adjustment of the color properties or the photometric properties of an LED illuminating device having LEDs emitting light of different colors or wavelengths or LED color groups emitting light of the same color or wavelength within a color group, the luminous flux portions thereof determining the color of light, color temperature and/or the chromaticity coordinates of the light mixture emitted by the LED illuminating device, comprising the steps of:

a basic setting of the light mixture onto a specified color of light by adjusting the luminous flux portions for the variously colored LEDs at an initial temperature of the LED illuminating device,

determining the initial emission spectra E_A(λ

) being dependent on the wavelength of the variously colored LEDs of the variously colored LEDs at the basic setting,

measuring the actual value of the temperature at and/or within the LED illuminating device, in particular the board temperature of the LEDs arranged on a circuit board and/or the junction temperature of at least one LED,

determining at least one temperature-dependent value determining or codetermining the emission spectra E(λ

) of the variously colored LEDs at the measured temperature, the emission spectra being dependent on the wavelengths of the variously colored LEDs, from calibration data stored for each of the variously colored LEDs,

determining the emission spectra E(λ

) being dependent on the wavelength of the variously colored LEDs at a measured temperature of the LED illuminating device differing from the initial temperature,

determining the luminous flux portions of the variously colored LEDs for a light mixture having the specified color of light, color temperature and/or the chromaticity coordinate at the measured temperature depending on the at least one temperature-dependent value determined and

adjusting the determined luminous flux portions of the variously colored LEDs at the LED illuminating device.

59. The method of claim 58, wherein at least one temperature-dependent value consists of the peak wavelength (λ

_p) of the LED emission spectrum and/or the half-width (w₅₀) of the LED emission spectrum and/or the brightness (Y) and in that calibration data for the peak wavelength (λ

_p) of the LED emission spectrum and/or the half-width (w₅₀) of the LED emission spectrum and/or the brightness (Y) is determined for each of the variously colored LEDs as a function of the temperature (T) and is stored as function or table.

60. The method of claim 58, wherein the emission spectra of the variously colored LEDs for the measured temperature are approximated by the Gaussian distribution by either

simulating the Gaussian bell-shaped curve

61. The method of claim 58, wherein the emission spectra E(λ

) being dependent on the wavelength of the variously colored LEDs are approximated at a measured temperature of the LED illuminating device differing from the initial temperature by a temperature-dependent normalization and shift of the initial emission spectra E_A according to

E_T(λ

)=f_L(T)·

E_A(λ

−

Δ

λ

_p(T)),

wherein

f_L(T) denotes a temperature-dependent conversion factor (brightness of the spectrum relative to the brightness of the initial spectrum) representing the relative change in brightness over the whole temperature range and

Δ

λ

_p(T) denotes a temperature-dependent shift of the peak wavelength with respect to the initial spectrum.

62. The method of claim 58, wherein the emission spectra of the variously colored LEDs for the measured temperature are determined by a measurement.

63. The method of claim 58, wherein the luminous flux portions for the variously colored LEDs are determined by a program-controlled device or pulse-width modulating signals corresponding to the luminous flux are provided from the program-controlled device into which the measured or approximated emission spectra of the used LED colors are imported and several optimization parameters are put in and from which luminous flux portions for the variously colored LEDs optimized towards different target parameters being effected in advance by the program-controlled device or pulse-width modulating signals corresponding to the luminous flux portions are provided.

64. The method of claim 63, wherein the optimization parameters are generated by either

setting the desired color temperature of the light mixture generated by the variously colored LEDs, the mixed-light capability and the reference illuminant for which a good mixed-light capability is to be achieved or

entering the recording medium, in particular the film type or the camera sensor used for which good mixed-light capability is to be achieved

whereby the target parameters for optimizing the luminous flux portions consist of one or more of the following parameters:

color temperature,

distance from the Planckian locus,

color rendering index,

mixed-light capability with film or digital camera.

65. The method of claim 58, wherein for correcting the color properties or photometric properties of the LED illuminating device depending on the temperature of the LEDs or of the LED illuminating device

the temperature values at an LED of each LED color group or a temperature value of an illuminating module being representative for all LED colors is measured,

the parameters f_L and Δ

λ

_p are determined for each color group via a linear or quadratic dependency on the temperature,

the new, temperature-dependent emission spectra being calculated either via the Gaussian distribution or via an overlay of a plurality of Gaussian distributions by means of the temperature-dependent parameters, the emission spectra for white LEDs being approximated by more than three Gaussian distributions and the emission spectra of the colored LEDS are approximated by several, preferably by 5 to 9 Gaussian distributions

or by shifting and normalizing the stored initial spectrum.

66. The method of claim 65, wherein

the temperature-dependent emission spectra are imported into the program-controlled processing unit and pulse-width modulated signals corresponding to the luminous flux portions are calculated for the light mixture,

the pulse-width modulated signals for the variously colored LEDs are adjusted at the LED illuminating device and

a brightness measurement and an adaptation of the light intensity emitted from the LED illuminating device to the brightness set point is effected by correspondingly increasing or decreasing the electric power fed to the variously colored LEDs.

67. The method of claim 65, wherein

the temperature-dependent emission spectra E_T(λ

) are imported into the program-controlled processing unit and pulse-width modulated signals corresponding to the luminous flux portions are calculated for the light mixture,

the pulse-width modulated signals for the variously colored LEDs are adjusted at the LED illuminating device and

optionally a brightness measurement and an adaptation of the light intensity emitted from the LED illuminating device to the brightness set point is effected by correspondingly increasing or decreasing the electric power fed to the variously colored LEDs.

68. The method of claim 58, wherein a brightness measurement is performed and the difference between the measured actual value of brightness and a set point of brightness is determined after correction of the color properties or photometric properties of the LED illuminating device and in that the light intensity emitted from the LED illuminating device is adjusted to the set point of brightness by correspondingly increasing or decreasing the electric power fed to the variously colored LEDs.

69. The method of claim 58, wherein the output signals of a color sensor or a spectrometer being additionally installed at the LED illuminating device are regarded during the determination of the relative brightness of the LED color groups by providing the output signals of the color sensor or the spectrometer to the program-controlled processing unit for the determination of the luminous flux portions or the pulse-width modulated control signals of the LED color groups corresponding to the luminous flux portions of the light mixture.

70. The method of claim 58 comprising the steps of:

a. turning on the LED illuminating device,

b. measuring the brightness (Y₀) of the LED color groups with a brightness sensor immediately after turning on the LED illuminating device by subsequent individual activation of each single LED color group or by measuring the brightness (Y_t) and color of the LED color groups by an RGB or color sensor or spectrometer immediately after turning on the LED illuminating device by subsequent individual activation of each single LED color group and detecting additionally modifications of the peak wavelength (λ

_p) and half-width (w₅₀),

c. measuring the initial temperature (Tu) within the housing of the LED illuminating device and/or within the area of at least one LED of the variously colored LED color groups immediately after turning on the LED illuminating device,

d. determining temperature-dependent factors for the initial temperature (Tu) from the characteristic lines Y₀=f(Tu) stored for each LED color group in the calibration data,

e. calculating ageing-dependent and color-dependent temperature factors (f_k) from the ratio of the characteristic line Y₀=f(Tu) stored in the calibration data and the measured actual brightness (Y_t) of each LED color group according to

f_k=Y_t(T)/Y₀(T),

f. measuring the actual temperature (T) within the housing of the LED illuminating device and/or within the area of at least one LED of the variously colored LED color groups,

g. determining the temperature-dependent peak wavelength (λ

p), half-width (w₅₀) and/or brightness (Y) for each LED color group from characteristic lines λ

_p=f(T), w₅₀=f(T) and Y₀=f(T) stored for each LED color group in calibration data,

h. approximation of the emission spectra of the variously colored LED color groups for the measured actual temperature (T) via the Gaussian distribution,

i. multiplication of the emission spectra of the variously colored LEDs approximated by the Gaussian distribution with the ageing-dependent and color-dependent temperature factors (f_k),

k. calculation of luminous flux portions as well as of pulse-width modulated control signals for each LED color group from the approximation of the emission spectra of the variously colored LED color groups depending on the actual temperature (T),

l. controlling the LEDs of each LED color group by the new pulse-width modulated control signals and

m. returning to method step f.

71. The method of claim 58, wherein

a. the peak wavelength (λ

_p), half-width (w₅₀) and brightness (Y₀) are measured for each LED color group dependently on the temperature (T) of a specified temperature range and are determined as function or table λ

_p=f(T), w₅₀=f(T) and Y₀=f(T) for each LED color group,

b. the emission spectra of the variously colored LED color groups are approximated by the Gaussian distribution for the measured temperature,

c. temperature-dependently optimized PWM control signals PWM(T) for the pulse-width modulated control signals of each LED color group are calculated for light mixing ratios with specified settings for color temperature or chromaticity coordinates and

d. the temperature-dependently optimized PWM control signals PWM(T) for the pulse-width modulated control signals of each LED color group are stored for light mixing ratios with specified settings for color temperature or chromaticity coordinates.

72. A method for the temperature-dependent adjustment of the color properties or the photometric properties of an LED illuminating device having LEDs emitting light of different colors or wavelengths, the luminous flux portions thereof determine the color of light, color temperature and/or chromaticity coordinates of the light mixture emitted by the LED illuminating device and are adjusted by controlling the variously colored LEDs consisting of colored and white LEDs and being grouped together to LED color groups having the same color in each case by pulse-width modulated control signals, comprising the steps of

measuring the temperature, in particular of the temperature within the LED illuminating device, of a board containing the LEDs or the junction temperature of at least one LED and

basic setting of the light mixture onto a specified color of light, color temperature and/or chromaticity coordinates by adjusting pulse-width modulated control signals corresponding to the luminous flux portions of the LED color groups of the light mixture at an initial temperature and

modifying the pulse-width modulated control signals corresponding to the luminous flux portions of the LED color groups of the light mixture adjusted to a specified color of light, color temperature and/or chromaticity coordinates, the modulation being dependent on the measured temperature.

73. The method of claim 72, wherein

the dependency of the pulse-width modulated control signals on the temperature is determined from the brightness of the LED color groups linearly or quadratically varying over the relevant temperature range.

a factor (f_PWM) corresponding to the reciprocal of the relative brightness modification of the LED color groups with respect to the basic setting is determined and in that the multiplication of the basic-setting relating value of the pulse-width modulating control signals (PWM_A) of each LED color group with the factor (f_PWM) being dependent on the measured temperature (T) results in the value of the pulse-width modulated control signals (PWM(T)) of each LED color group corresponding to the measured temperature according to the equation

PWM(T)=PWM_A*f_PWM(Ts).

the pulse-width modulated signals (PWM(T)) of each LED color group are adjusted at the LED illuminating device, in that a brightness measurement is done and the difference between the measured brightness actual value and a brightness set value is determined and in that the light intensity emitted from the LED illuminating device is adapted to the brightness set point by correspondingly increasing or decreasing the electric power fed to the LED color groups.

74. The method of claim 72 comprising the steps of:

a. turning on the LED illuminating device,

b. measuring the brightness (Y₀) of the LED color groups with a brightness sensor immediately after turning on the LED illuminating device by subsequent individual activation of each single LED color group or by measuring the brightness (Y_t) and color of the LED color groups by an RGB or color sensor or spectrometer immediately after turning on the LED illuminating device by subsequent individual activation of each single LED color group and detecting additionally modifications of the peak wavelength (λ

_p) and half-width (w₅₀),

c. measuring the initial temperature (Tu) within the housing of the LED illuminating device and/or within the area of at least one LED of the variously colored LED color groups immediately after turning on the LED illuminating device,

d. determining temperature-dependent factors for the initial temperature (Tu) from the characteristic lines Y_o=f(Tu) stored for each LED color group in the calibration data,

e. calculating ageing-dependent and color-dependent temperature factors (f_k) from the ratio of the characteristic line Y₀=f(Tu) stored in the calibration data and the measured actual brightness (Y_t) of each LED color group according to

f. f_k=Y_t(T)/Y₀(T),

g. measuring the actual temperature (T) within the housing of the LED illuminating device and/or within the area of at least one LED of the variously colored LED color groups,

h. determining the temperature-dependent peak wavelength (λ

p), half-width (w₅₀) and/or brightness (Y) for each LED color group from characteristic lines λ

_p=f(T), w₅₀=f(T) and Y₀=f(T) stored for each LED color group in calibration data,

i. approximation of the emission spectra of the variously colored LED color groups for the measured actual temperature (T) via the Gaussian distribution,

j. multiplication of the emission spectra of the variously colored LEDs approximated by the Gaussian distribution with the ageing-dependent and color-dependent temperature factors (f_k),

k. calculation of luminous flux portions as well as of pulse-width modulated control signals for each LED color group from the approximation of the emission spectra of the variously colored LED color groups depending on the actual temperature (T),

l. controlling the LEDs of each LED color group by the new pulse-width modulated control signals and

m. returning to method step f.

75. The method of claim 72, wherein a brightness balance is done after method step g and before method step h, by

g1. measuring the total brightness Y_ist of all LED color groups,

g2. calculating correction factors f_Y=Y_soll/Y_ist for each LED color group from the ratio of the specified set value Y_soll and the measured total brightness Y_ist of all LED color groups,

g3. calculating new pulse-width modulated control signals for the LEDs of each LED color group corresponding to each LED color group from the product of the pulse-width modulated control signals calculated in method step d for each LED color group and the correction factors f_Y,

g4. controlling the LEDs of each LED color group by pulse-width modulating current impulses corresponding to the new pulse-width modulated control signals for each LED color group;

and after method step 1 by

l1. measuring the total brightness Y_ist of all LED color groups,

l2. calculating correction factors f_Y=Y_soll/Y_ist for each LED color group from the ratio of the measured total brightness Y_ist of all LED color groups and a specified set value Y_soll for the brightness,

l3. calculating new pulse-width modulated control signals for the LEDs of each LED color group corresponding to each LED color group from the product of the pulse-width modulated control signals calculated in method step k for each LED color group and the correction factors f_Y,

l4. controlling the LEDs of each LED color group by the corresponding pulse-width modulated current impulses for each LED color group.

76. The method of claim 72 comprising the steps of:

a. turning on the LED illuminating device,

b. measuring the temperature (T) within the housing of the LED illuminating device and/or within the area of at least one LED of the variously colored LED color groups,

c. determining the temperature-dependent factors f_Y=f_PWM for each LED color group from characteristic lines stored for each LED color group in calibration data,

f_Y=f_PWM=Y₀(T₀)/Y₀(T),

with Y₀=f(T),

d. calculation of new pulse-width modulated control signals PWM(T) to control the LEDs of each LED color group from the multiplication of PWM control signals PWM(A) specified for a basic temperature (T_o) to control the LEDs of each LED color group with the determined temperature-dependent factors f_Y=f_PWM for each LED color group,

PWM(T)=PWM(A)*f_PWM,

e. controlling the LEDs of the variously colored LED color groups by the new pulse-width modulated control signals PWM(T) for each LED color group and

f. returning to method step b;

the pulse-width modulated control signals PWM(A) specified for a basic temperature being determined for the pulse-width modulated control signals for each LED color group for light mixing ratios with specified color temperatures (CCT) or chromaticity coordinates (x,y) as well as the brightness (Y0) dependently on the temperature (T) of a specified temperature range as calibration data and are stored for each LED color group as function or table Y₀=f(T) and PWM(A)=f(CCT) or PWM(A)=f(x,y).

77. The method of claim 72, wherein

a. the peak wavelength (λ

_p), half-width (w₅₀) and brightness (Y₀) are measured for each LED color group dependently on the temperature (T) of a specified temperature range and are determined as function or table λ

_p=f(T), w₅₀=f(T) and Y₀=f(T) for each LED color group,

b. the emission spectra of the variously colored LED color groups are approximated by the Gaussian distribution for the measured temperature,

c. temperature-dependently optimized PWM control signals PWM(T) for the pulse-width modulated control signals of each LED color group are calculated for light mixing ratios with specified settings for color temperature or chromaticity coordinates and

d. the temperature-dependently optimized PWM control signals PWM(T) for the pulse-width modulated control signals of each LED color group are stored for light mixing ratios with specified settings for color temperature or chromaticity coordinates.

78. The method of claim 72, wherein

a. the temperature-dependent spectra of the LED color groups are measured,

b. temperature-dependently optimized PWM control signals PWM(T) for the pulse-width modulated control signals of each LED color group are calculated for light mixing ratios with specified settings for color temperature or chromaticity coordinates and

c. the temperature-dependently optimized PWM control signals PWM(T) for the pulse-width modulated control signals of each LED color group are stored for light mixing ratios with specified settings for color temperature or chromaticity coordinates.

79. The method of claim 72 comprising the steps of:

a. turning on the LED illuminating device,

b. measuring the temperature (T) within the housing of the LED illuminating device and/or within the area of at least one LED of the variously colored LED color groups,

c. determining actual temperature-dependent PWM control signals PWM(T) for each LED color group from the stored temperature-dependent optimized PWM control signals for the pulse-width modulated control signals of each LED color group for light mixing ratios with specified settings for color temperature or chromaticity coordinates,

d. controlling the LEDs of the variously colored LED color groups by the temperature-dependent PWM control signals PWM(T) and

e. returning to method step b.

80. A method for the temperature-dependent adjustment of the color properties or the photometric properties of an LED illuminating device having LEDs emitting light of different colors or wavelengths, the luminous flux portions thereof determine the color of light, color temperature and/or the chromaticity coordinates of the light mixture emitted by the LED illuminating device and are adjusted by controlling the variously colored LEDs consisting of colored and white LEDs and being grouped together to LED color groups having the same color in each case by pulse-width modulated control signals, by controlling the color of the LED illuminating device by a temperature characteristic line (Y=f(Tb)) of the LED illuminating device representing the brightness (Y) depending on the board temperature (Tb) of the LEDs being arranged on a board and/or the junction temperature of at least one LED for each LED color or LED color group at a specified current in the steady state and determining the temperature characteristic lines of the LED illuminating device by

determining the function of the brightness (Y) depending on the board temperature (Tb) for each LED color at a specified current in the steady state (Y=f(Tb)),

normalizing the characteristic lines onto (Y(Tb1)=1), wherein (Tb1) is an arbitrarily chosen temperature value close to the later working point,

determining the parameters (a, b, c, d) for a linear function having the form

Y(Tb)=a+b*b,

a second-degree polynomial having the form

Y(Tb)=a+b*Tb+c*Tb²

or a third-degree polynomial having the form

Y(Tb)=a+b*Tb+c*Tb²+d*Tb³,

storing the parameters (a, b, c, d) in illuminating modules of the LED illuminating device, in the LED illuminating device or in an external controller.

81. The method of claim 80, wherein a color calibration of the LED illuminating device comprises the steps of:

measuring the spectrum and out of it derived brightness (Y) as well as chromaticity coordinates (x, y) for each LED color of the LED illuminating device,

converting the brightness of the spotlight to a board temperature (Tb1) via the characteristic line (Y=f(Tb)) and scaling the spectra onto (Y=Y(T_b1)),

calculating the optimum luminous flux portions of the LED colors from the measured spectra for N color temperature interpolation points using the program-controlled processing unit,

storing the luminous flux portions of the LED colors in table depending on the target chromaticity coordinates (x, y).

82. The method of claim 80, wherein a color regulation of the illuminating module of the LED illuminating device is effected by considering the stored calibration data for N color temperature interpolation points and/or as chromaticity coordinates table for the luminous flux portions of the LED colors, the temperature characteristic lines for each color and the brightness (Y) and the chromaticity coordinates (x, y) for each LED color by

determining the PWM control signals for the LED colors (PWM_A) for the desired chromaticity coordinates (x, y) and the desired brightness (Y),

measuring the board temperature (Tb),

determining the temperature-dependent PWM correction factors for each LED color for the approximated characteristic lines (fPWM=1/Y) stored in the memory,

capturing the total power of the LED illuminating device or the current intensity fed to the single LEDs of the LED illuminating device and

controlling the LEDs of the LED illuminating device by the PWM factors multiplied with correction factors at a total power of the LED illuminating device or a current intensity fed to the LEDs of the LED illuminating device smaller than the specified maximum value (Pmax, Imax) or

determining a cut-off factor (kCutoff) for limiting the current or power for all LED colors from

kCutoff=Pmax/Pneu

Or

kCutoff=Imax/Ineu

and controlling the LEDs of the LED illuminating device with new PWM factors according to PWM_T=PWMA*fPWM*kCutoff.

83. A method for determining temperature characteristic lines of an LED module for a temperature-dependent adjustment of the color properties or the photometric properties of an LED illuminating device having LEDs emitting light of different colors or wavelengths or LED color groups emitting light of the same color or wavelength within a color group, the luminous flux portions thereof determining the color of light, color temperature and/or the chromaticity coordinates of the light mixture emitted by the LED illuminating device, by determining the temperature characteristic lines randomly,

converting the characteristic line parameters onto the individual dominant wavelengths by means of interpolation or extrapolation

transferring the determined characteristic lines onto all LED modules and

storing the determined characteristic lines in the memory of said LED modules.

84. The method of claim 83 comprising the steps of:

recording several brightness-temperature characteristic lines at LED modules of different dominant wavelengths for each color,

determining several polynomial parameters for each color dependent on the dominant wavelength.

detecting the spectra of the LED colors and the according NTC temperature for each LED module

calculating the dominant wavelengths per color from this spectrum

correcting the polynomial parameters determined in advance at single modules according to the deviation of the individual dominant wavelength of the module to be calibrated from the dominant wavelength of the module from which the characteristic lines have been determined,

effecting a Conversion the polynomial parameters to an LED having certain dominant wavelengths by a linear interpolation of the polynomial parameters of two known curves of two LEDs having different dominant wavelengths to the new dominant wavelength.