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 known as a hollow sphere with a highly reflective inner surface. It is mainly a high-efficiency device for scattering or emitting light from a sample placed inside or outside the sphere and near a certain window, or collecting 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.
The working principle of the photometric integrating sphere is:>
The light is collected by the integrating sphere through the sampling port, and after multiple reflections inside the integrating sphere, the light will be Presented very uniformly at various locations 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 the integrating sphere structure is that it can reduce and eliminate the measurement errors caused by the shape of the light, the divergence angle, and the difference in responsivity at different positions on the detector.
The function of the photometric integrating sphere>
1. Light receiver
The light to be measured enters the sphere through the small hole on the integrating sphere and is on the inner wall Set up one or two light detectors, such as selenium photocells or photomultiplier tubes. The photocurrent output by the photodetector is proportional to the illumination on the inner wall of the integrating sphere, that is, proportional to the light flux entering the integrating sphere. In this way, the change of the light flux entering the integrating sphere can be known based on the change of the output photocurrent.
2. Uniformly illuminated object surface
Arrange several light bulbs (usually four or six) evenly on the inner wall of the integrating sphere symmetrically with the light outlet. . The light emitted by the bulb is diffusely reflected by the inner wall many times to form a uniform and bright luminous spherical surface, which can be used as the object surface of the optical system under test with uniform brightness and large field of view (2w>140 degrees) (the entrance pupil of the optical system and the The light exit holes basically overlap). This integrating sphere is used to measure the vignetting coefficient and image plane illumination uniformity of photographic objectives.
3. Spherical parallel light pipe
Open two holes at both ends of the horizontal axis of the integrating sphere. A collimating objective lens is installed in one hole, and the focal length of the collimating objective lens 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 mounted on the other hole, and a horn-shaped extinction tube whose inner wall is coated with a black absorbing layer is plugged outside the plug, so that the light entering the extinction tube through the plug hole is completely absorbed.
Therefore, the aperture plug together with the extinction tube constitutes a blackbody, so that the sphericalWill simulate having a completely black 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 measured telescope can be obtained The stray light coefficient. 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 the risk of uneven distribution of the incident light source on the detector or slight deviation of the beam during measurement. The slight error caused by the shift can improve the accuracy of the measurement. 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 photometric integrating sphere mainly include the following four aspects:>
1. Preparation: Prepare the integrating sphere of appropriate size, requirements and lamps The luminous flux of the light source is close to the standard light source, the ambient temperature is kept at about 25 degrees, and no wind blows into the integrating sphere;
2. Inspection: Install the standard light source in the center of the integrating sphere, and connect the current source and power meter, then light the standard light source. In the integrating sphere software operation interface, adjust to continuous testing until the luminous flux reaches stability, and record the luminous flux value;
3. Calibration: The calibration operation is similar to the inspection, except that calibration must be performed before lighting the standard light source. zero. 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 sample: Install the sample into the integrating sphere, turn on 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 LEDs should be tested by checking their photochromatic and electrical parameters. 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 Photometry and Color degree testing 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.