Although the measurement system using photoelectric integrating sphere> with a photometric probe has the advantages of simplicity, reliability, and stable operation, it is inconvenient to measure colors and is not suitable for the measurement of discontinuous spectra. Use less. Nowadays, the preferred method for measuring the light and color of LED lamps is to use the measurement system of the photoelectric integrating sphere spectrum analyzer. This system is based on the measurement theory of the photoelectric integrating sphere. Light color parameters such as wavelength, half width, red ratio, luminous flux, CCT, CRI, SDCM, Duv, X, Y, etc.
1. Test method of photoelectric integrating sphere spectrometer>
Spectrophotometry and full-spectrum method to measure light color parameters of light source are currently the measurement methods adopted by most manufacturers, testing institutions and laboratories. These two measurement methods use an integrating sphere to connect to a spectrum analyzer, and compare the standard lamp with the lamp to be measured to obtain the light color parameters of the measured light source. The two test methods are described below.
The spectrophotometric method is used to measure the measured light source, and the photometric method is used to measure the luminous flux and the spectroscopic method is used to measure the chromaticity parameters.
Simply speaking, the photometric method of measuring luminous flux is to use a standard lamp with known luminous flux (the value can be traced to the China Metrology Institute) in the photoelectric integrating sphere to compare with the measured light source, so as to obtain the luminous flux of the measured light source.
The basic principle of luminous flux measurement is to place the light source to be measured in the photoelectric integrating sphere, and coat the inner wall of the photoelectric integrating sphere with a white diffuse reflection layer (spectral reflectance ρ≥0.98), and the light emitted by the light source is reflected by the sphere wall multiple times Finally, the illuminance on the entire spherical wall is uniformly distributed, and then the luminous flux projected onto the photodetector through the hole on the spherical wall should be proportional to the total luminous flux emitted by the light source. In order to make the relative spectral sensitivity of the photodetector on the spherical wall conform to the spectral luminous efficiency of the human eye, it is generally corrected by adding a filter group. By calculating the propagation and conditions of light in the filter glass group, according to the typical transmission of known colored glass typesFor the emission characteristic curve, select the colored glass group that matches the curve, and then calculate the appropriate thickness of each color glass required for the matching curve according to the formula, and finally correct it to obtain the photometric value. Spectrometry is used to measure chromaticity parameters. A spectrometer is generally composed of a monochromator spectroscopic system, a photometric detection system, and a data processing part. First calibrate the spectrum analyzer with a standard lamp with known radiance of each wavelength, then put the measured light source, and use a monochromator to measure the correction of each corresponding wavelength, the spectrum of each wavelength of the measured light source Radiation intensity, and then divide the calculated spectral radiation intensity of each wavelength by the maximum spectral radiation intensity value to obtain the relative spectral power distribution of the light source to be tested. Because the relative spectral power distribution of the standard lamp is different from the spectral power distribution of the measured light source, the luminous flux will be generated, and then the chromaticity parameters such as color coordinates, chromaticity tolerance, correlated color temperature, and color rendering index will be obtained.
2. Full spectrum method
The full spectrum method requires that the absolute spectral power distribution corresponding to every 5nm wavelength in the visible band of 380nm~780nm must be known, and the absolute spectral power corresponding to each wavelength must be calibrated by the National Institute of Metrology of China within the specified time At the same time, the luminous flux is calibrated. After the corresponding absolute spectral power distribution of each wavelength is known, the absolute spectral power distribution list is made into the absolute spectral power distribution data of the standard lamp that can be read by the software, which can remove the photoelectric detection on the window of the spherical wall. The measuring instrument is directly connected to the inner window of the sphere wall by the optical fiber, and the other end of the optical fiber is connected to the incident slit of the spectrum analyzer. The light is introduced into the grating monochromator, which can be tested to obtain the ratio of the optical power corresponding to each wavelength of the standard lamp. After being amplified by the PMT, the photocurrent ratio is obtained, and then the LA absolute spectral power distribution P of the standard lamp is relatively calculated. Measure the absolute spectral power distribution of the lamp. According to the conversion formula of radiant quantity and luminous quantity, for the luminous flux of the standard lamp and the lamp to be tested, the relative spectral power distribution is calculated from the absolute spectral power distribution, and then the color coordinates and chromaticity are obtained by the same method as the spectrophotometric method. Tolerance, correlated color temperature, color rendering index and other photoelectric parameters.