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where24-26 September 2008, Rome, ItalyY AW :relative spectral distribution of the test LEDS t (λ):S r (λ): relative spectral distribution of the referenceLEDs D (λ) rel : relative spectral responsivity of the spherephotometerV(λ) :CIE spectral luminous efficiency function ofthe photopic visionThe final equation for the luminous flux of the test LED canbe given in the following form:whereYTYAStΦT= ΦSt⋅ ⋅ xF(3)Y YStY T : Detector current of the Test LEDY St : Detector current of the Standard LEDY AT : Detector current of the Auxiliary LED, whenthe Test LED is in the sphereY ASt : Detector current of the Auxiliary LED, whenthe Standard LED is in the sphereF: Color correction factorIf the flux different to the luminous flux is to measured,then instead of a V(λ) the detector head is to be equippedwith a filter with the corresponding characteristic. For measuringthe radiometric flux, a detector with a flat spectral responseis to be used, if color coordinates are to be measured,filters realizing the functions X1-X2 and Z CIE color matchingneed to be used. That is, the corresponding filter characteristicshould appear in Eq. (3) instead of the V(λ) function,resulting different types of color correction factors.The substitution method has a disadvantage, which is thetime of the measurements. Before the measurement of a testLED, the sphere has to be calibrated for the proper wavelengthrange by a standard LED with appropriate spectraldistribution. In case of large number of measurements it isvery difficult to perform this process from time to timemanually. So, the calibration of the sphere and the measurementhas to be divided both in time and space and the calibrationof the integrating sphere for the relevant wavelengthranges based on the following theory:SΦYATSt ASt= ⋅(4)YStYAWwhereS: Absorption corrected sensitivityФ St : Certificate value of the Standard LEDY St : Detector current of the Standard LEDY ASt : Detector current of the Auxiliary LED, whenthe Standard LED is in the sphere – self absorptionmeasurementDetector current of the Auxiliary LED,when the DUT port is covered with awhite cover cap – self absorption and ageingmeasurementDuring the calibration process the standard LEDs are usedfor obtaining a so called absorption corrected sensitivity factorused as multiplier constant in the calculation of the totalflux of the DUT LED. So, the total flux of the DUT LED canbe given in the following form:whereYAWΦT = S ⋅YT⋅ ⋅ K ⋅ F (5)YATФ T Total flux of the DUT LEDS: Absorption corrected sensitivityY T : Detector current of the Auxiliary LED,when the Test LED is in the sphereY AT : Detector current of the Auxiliary LED,when the DUT LED is in the sphere – selfabsorption measurementY AW : Detector current of the Auxiliary LED,when the DUT port is covered with awhite cover cap – self absorption measurementK: Correction for ageingF : Color correctionThe calculation of the total flux of the test LED is thecomparison of the certain detector currents induced by standardLED and test LED. In the equation the self-absorptionvalue of the measured LED is also considered and the calculatedtotal flux is multiplied with correction factors for ageingand color. The accuracy of the further measurements isdetermined by the stability and accuracy of the used standardLEDs.We have designed and manufactured a thermoelectriccooler based, fast calibrator equipment, mounted with fivedifferent colored standard LEDs, the spectral distribution ofwhich are closely matched to the test LEDs in order to securesmall color mismatch error. The auto calibrator kit issuitable for the calibration of the integrating sphere in anautomated way only within some minutes’ time.The fast calibrator is a computer controllable electroniccircuit for high power LED current control and forward voltagemeasurement. This device is able to source current in therange of 0 to 500 mA on five different channels, one at atime. The resolution is 0.125mA. The circuit uses a single5V power supply. The maximum output voltage at the LEDunder test can be more than 4V − this makes the circuit suitablefor the measurement of a large scale of different powerLEDs. The device can be connected to a PC via the USB interface.Fig. 3 shows the block diagram of the fast spherecalibrator.In the design of this calibrator tool we took advantage ofknowing the thermal time-constant distribution of the appliedpower LEDs. In short, we can say, that the junction©EDA Publishing/THERMINIC 2008 91ISBN: 978-2-35500-008-9