1. The principle of the optical flux sphere>
The Lucisphere> is a hollow spherical cavity covered with a diffuse white reflective coating. There are one or several holes on the wall, which are used for the light entrance hole and the hole for receiving light and placing the light receiving device. The inner wall of the light flux sphere should be a good spherical surface; usually the deviation from the ideal spherical surface is required to be no more than 0.2% of the inner diameter. The inner walls of the sphere are coated with an ideal diffuse material, which is a material with a diffuse reflectance close to 1. A commonly used material is BaSO4. Mix it evenly with the adhesive, and then spray it on the inner wall. The BaSO4 coating has a spectral reflectance of up to 99% in the visible spectrum. The light entering the lumen sphere is reflected multiple times by the inner wall coating, resulting in uniform illumination on the inner wall. In order to obtain higher measurement accuracy, the aperture of the light flux sphere should be as small as possible. The aperture ratio is defined as the ratio of the area of the sphere at the opening of the integrating sphere to the total inner wall area of the sphere.
There are generally two types of structures in the optical flux sphere. One is a 2π structure and the other is a 4π structure. The IS-*MA new optical flux sphere with a stage launched by Lisun can perform 4π tests on various types of light sources, and the IS-*M**P photometric optical flux sphere (side opening) can perform both 4π tests and 2π test. Simply put, the 4π test is to place the lamp in the middle of the integrating sphere for testing, and the 2π test is to place the lamp on the side opening for testing. The 4π test is suitable for all types of SSL including all directions of emission or only one direction of emission (ignoring the direction), the 2π test is suitable for forward emitters (ignoring the direction), high power LEDs with large heat sinks and non-directional emission, suitable for not With rear emitting LEDs.
Second, the role of the optical flux sphere>
1. Optical receiver>
The light to be measured enters the ball through the small hole on the Luminous Flux Ball>, and one or two photodetectors, such as selenium photocells or photomultiplier tubes, are installed on the inner wall. from the photodetectorThe output photocurrent is proportional to the illuminance of the inner wall of the integrating sphere, that is, it is proportional to the luminous flux entering the luminous flux sphere. In this way, the change of the luminous flux entering the luminous flux sphere can be known according to the change of the output photocurrent.
2. Evenly illuminated object surface>
Several light bulbs (usually four or six) are evenly arranged on the inner wall of the luminous flux sphere> symmetrically with the light exit hole. 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 are basically coincident). The luminous flux sphere is used to measure the vignetting coefficient of the photographic objective lens and the uniformity of illumination on the image plane.
3. Spherical collimator>
Open two holes at both ends of the sphere horizontal axis of the lumen 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 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. Thus, the aperture plug together with the extinction tube forms a black body, so that for the collimating objective the sphere will simulate 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. A light flux 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 the measurement, the illuminance of the blackbody target image and the Beiser image are respectively measured by the photodetector, that is, the corresponding indication values measured by the photodetector respectively, and the stray light coefficient of the telescope under test can be obtained through calculation. Because, if the telescope’s image of a black body target in the bright sky is not completely black, it means that in addition to the target’s imaging, the telescope also has stray light hitting the image surface.