Characterization of Materials Using Integrating Sphere Spectrophotometer

I. Overview of the Development of Integrating Sphere Spectrophotometer Analysis System
In spite of the advantages of simplicity, reliability and stability of the measuring system of integrating sphere with photometric probe, the inconvenience of measuring color and the impossibility of measuring non-continuous spectra make it less used nowadays. The primary method for measuring the light color of LED lamps nowadays is the measurement system of integrating sphere spectrophotometer, which is based on the measurement theory of integrating sphere, and can calculate the parameters of main wavelength, peak wavelength, half-width, red ratio, flux, CCT, CRI, SDCM, Duv, X, Y and other light colors by measuring therelative spectral power distribution at a certain point of the spherical surface. There are two methods for testing with integrating sphere spectrophotometer, namely spectrophotometric method and full spectrum method.

LISUN LPCE-2 Integrating Sphere Spectroradiometer LED Testing System is for single LEDs and LED lighting products light measurement. LED’s quality should be tested by checking its photometric, colorimetric and electrical parameters. According to CIE 177, CIE84,  CIE-13.3, IES LM-79-19, Optical-Engineering-49-3-033602, COMMISSION DELEGATED REGULATION (EU) 2019/2015, IESNA LM-63-2, IES-LM-80 and ANSI-C78.377, it recommends to using an array spectroradiometer with an integrating sphere to test SSL products. The LPCE-2 system is applied with LMS-9000C High Precision CCD Spectroradiometer or LMS-9500C Scientific Grade CCD Spectroradiometer, and a-molding integrating sphere with holder base. This sphere is more round and the test result is more accruate than the traditional integrating sphere.

II. Testing methods for a Integrating Sphere Spectrophotometer

1. Spectrophotometric Method of Integrating Sphere Spectrophotometer
Spectrophotometric method measures the flux and Chromaticity parameters of the test light source respectively by photometric method and spectrophotometric method. In photometric method, the flux of the test light source is measured by comparison with the standard lamp with known flux in the integrating sphere. The basic principle of flux measurement is to put the test light source in the integrating sphere and coat a white diffuse reflecting layer (spectral reflectance ρ ≥ 0.98) on the wall of the integrating sphere. The light emitted by the light source is reflected by the wall of the integrating sphere multiple times, so that the illumination on the whole wall is evenly distributed, and then the flux is projected to the photoelectric detector through the hole on the wall, which is proportional to the total light flux emitted by the light source. In order to make the relative spectral sensitivity of the photoelectric detector on the sphere wall conform to the spectral visual efficiency of the human eye, the method of adding filter glass group is generally used to modify it. After computing the propagation of light in the filter glass group and the relevant conditions, the suitable colored glass group with matching curve shall be selected according to the typical transmission ratio curves of known colored glass, and then the suitable thickness of each colored glass shall be calculated according to the formula, and finally the luminous value shall be modified to obtain the luminous value. In spectrophotometric method, the spectrophotometer is usually composed of monochromator spectral system, photometry detection system and data processing part. Firstly, the absolute spectral power distribution corresponding to each wavelength is calibrated by the standard lamp with known radiation at each wavelength.

Then the test light source is used to measure the corrected absolute spectral radiation intensity corresponding to each wavelength of the measured light source. Then the absolute spectral radiation intensity calculated for each wavelength is divided by the maximum absolute spectral radiation intensity to obtain the relative spectral power distribution of the measured light source. After obtaining the relative spectral power distribution of the measured light source, the correction of different spectral power distributions shall be carried out first. Because the relative spectral power distribution of the standard lamp and the spectral power distribution of the measured light source are different, the flux will be generated, and then the chromatic coordinates, chromaticity tolerances, correlated color temperature, color rendering indexes and other photometric parameters will be obtained.

2. Full Spectrum Method of Integrating Sphere Spectrophotometer
Full spectrum method requires that the absolute spectral power distribution corresponding to each 5nm wavelength in the visible
wavelength range 380nm-780nm must be known in the measurement, and the absolute spectral power distribution corresponding to each wavelength must be calibrated by the Chinese National Institute of Metrology within a certain period of time, and the flux must be calibrated at the same time. After knowing the absolute spectral power distribution corresponding to each wavelength, the absolute spectral power distribution list shall be made into the standard lamp absolute spectral power distribution data which can be read by the software, and the photoelectric detector on the window of the sphere wall can be removed, and the light can be directly led into the window in the sphere wall through the fiber optic cable. The test process is the same as burning the standard lamp and the test light source in succession in the integrating sphere, and the fiber optic cable on the sphere wall leads the light into the single colorimeter on the grating. The relative light power at each wavelength corresponding to the standard lamp can be tested, and then the light power ratio is amplified by the PMT to obtain the absolute spectral power distribution of the test light. According to the conversion formula of radiant flux and luminous flux, the absolute spectral power distribution of the test lamp is calculated from the relative spectral power distribution after the absolute spectral power distribution of the standard lamp, and then the chromatic coordinates, chromaticity tolerances, correlated color temperature, color rendering index and other photometric parameters are obtained in the same way as in spectrophotometric method.

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

Our main products are Goniophotometer, Integrating Sphere, Spectroradiometer, Surge Generator, ESD Simulator Guns, EMI Receiver, EMC Test Equipment, Electrical Safety Tester, Environmental Chamber, Temperature Chamber, Climate Chamber, Thermal Chamber, Salt Spray Test, Dust Test Chamber, Waterproof Test, RoHS Test (EDXRF), Glow Wire Test and Needle Flame Test.

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Tags：LPCE-2 (LMS-9000)