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Integrating sphere test system is also called photometric integrating sphere or integrating sphere spectrum analyzer. What is a photometric integrating sphere:
An integrating sphere is also called a hollow sphere with a highly reflective inner surface. It is mainly a high-efficiency device that collects the light scattering or emission from a sample inside the ball or placed outside the ball and close to a window, or the light emitted by the light source itself. It can be used to accurately measure the optical reflection and transmission properties of materials, the radiance, brightness or chromaticity of light sources, etc.
The working principle of the photometric integrating sphere is:
The light is collected by the integrating sphere through the sampling port. After multiple reflections inside the integrating sphere, the light will appear very evenly at various positions inside the integrating sphere. When using the light inside the integrating sphere to measure, it can make our measurement results more reliable. The advantage of using an integrating sphere structure is that it can reduce and eliminate measurement errors caused by light shapes, divergence angles, and differences in responsivity at different locations on the detector.
The role of photometric integrating sphere
1. Optical receiver
The light to be measured enters the sphere through the small hole on the integrating sphere, and one or two photodetectors, such as selenium photocells or photomultiplier tubes, are arranged on the inner wall. The photocurrent output by the photodetector is proportional to the illuminance of the inner wall of the integrating sphere, that is, proportional to the luminous flux entering the integrating sphere. In this way, the change of the luminous flux entering the integrating sphere can be known according to the change of the output photocurrent.
2. Uniformly illuminated object surface
Several light bulbs (usually four or six) are evenly arranged on the inner wall of the integrating sphere symmetrically with the light exit hole. The light emitted by the bulb is diffusely reflected multiple times by the inner wall to form a uniform and bright luminous spherical surface. It can be used as the object surface of the optical system under test with uniform brightness and a large field of view (2w>140 degrees) (the entrance pupil of the optical system and The light exit holes basically overlap). The integrating sphere is used to measure the vignetting coefficient of the photographic objective lens and the uniformity of illumination on the image plane.
3. Spherical parallel light tube
Open two holes at both ends of the horizontal axis of the integrating sphere. One hole is fitted with a collimating objective lens whose focal length is equal to the diameter of the inner wall of the sphere. Several light bulbs are arranged symmetrically with the horizontal axis on the housing near the objective lens side, requiring that the light they emit cannot directly impinge on the objective lens. A plug with a central opening is installed on the other hole, and a horn-shaped extinction tube with an inner wall coated with a black absorbing layer is inserted outside the plug, so that the light entering the extinction tube through the plug hole is completely absorbed.
Thus, the aperture plug, together with the extinction tube, forms a blackbody, so that for a collimating objective the sphere will simulate a completely dark target in a bright sky. Remove the hole plugs and matting tubes and replace them with white plugs, and the sphere will simulate a sky with uniform brightness. An integrating sphere with a collimating objective lens, a bulb, and black and white plugs is called a spherical collimator, and it is used to measure the stray light coefficient of the telephoto factor.
During measurement, the illuminance of the blackbody target image and the white plug image are respectively measured through the photodetector, which is the corresponding indicated value measured by the photodetector. After calculation, the stray light coefficient of the telescope under test can be obtained. . Because if the telescope's image of a blackbody target in a bright sky is not completely black, it means that in addition to imaging the target, the telescope also has stray light hitting the image surface.
Why use a photometric integrating sphere?
Generally speaking, when used carefully, optical diffusers can reduce slight errors caused by uneven distribution of the incident light source on the detector or slight deviation of the light beam during measurement, thereby improving measurement accuracy. But for more precise measurements, you must use an integrating sphere as an optical diffuser to minimize the above errors.
Using a photometric integrating sphere to measure luminous flux (Lumen) can make the measurement results more reliable. The integrating sphere can reduce and eliminate the measurement error caused by the shape of the light, the divergence angle, and the difference in responsivity at different positions on the detector. The integrating sphere can also be used with a spectrometer. The light output hole of the integrating sphere is connected in front of the incident grating of the spectrometer to ensure that the angles of the light sources to be measured enter the spectrometer at the same angle, greatly improving the reproducibility of measurement.
The specific measurement and use methods of the photometric integrating sphere mainly include the following four aspects:
1. Preparation: Prepare an integrating sphere of appropriate size, a standard light source that is close to the luminous flux of the lamp, keep the ambient temperature at about 25 degrees, and do not allow wind to blow into the integrating sphere;
2. Inspection: Install the standard light source in the center of the integrating sphere, connect the current source and power meter, and then turn on the standard light source. Adjust to continuous test on the operating interface of the integrating sphere software until the luminous flux reaches a stable value, and record the luminous flux value;
3. Calibration: The operation of calibration is similar to that of inspection, the difference is that zero calibration must be performed before lighting the standard light source. After the luminous flux reaches stability, enter the standard color temperature and standard luminous flux of the standard light source in the integrating sphere software operation interface, and then click to start calibration. The integrating sphere tester will automatically complete the calibration;
4. Test the sample: Install the sample into the integrating sphere, light the sample, close the integrating sphere, and start the test. After the luminous flux stabilizes, record the value.
LPCE-2 high-precision spectroradiometer integrating sphere system mainly tests energy-saving lamps, fluorescent lamps, HID lamps (such as high-pressure sodium lamps and high-pressure mercury lamps), cold cathode fluorescent lamps and LED lamps. The quality of the LED should be checked by checking itsPhotochromic and electrical parameters were tested. The test results of this system meet CIE177, CIE-13.3, CIE-84, ANSI-C78.377, IOS 24824, IESNA-LM-63-2, Optical-Engineering-49-3-033602, (EU) 2019/2015 , LM-80 and LM-79 photometric and colorimetric test requirements. The LPCE-2 system adopts LMS-9000C high-precision fast spectroradiometer or LMS-9500C scientific grade fast spectroradiometer, a new integrating sphere with stage produced by one-time molding technology, and other related equipment. The testing accuracy of the once-molded integrating sphere is much higher than that of the traditional spliced integrating sphere.
LPCE-2 (LMS-9000) CCD fast photochromatic and electrical comprehensive testing system
