Integrating sphere is a cavity sphere with a white diffuse reflection material on its inner wall, also called as photometric sphere, luminous bulb and so on. There are usually one or several apertures on the sphere which are used as the light port, light receiving port and sample port. Some of them are also equipped with sample holder, lens holder, port plug, light trap, adapter and standard whiteboard and other accessories to meet a variety of optical measurement requirements. The inner wall is coated with an ideal diffuse reflection material, and the light entering the integrating sphere pass through the inner wall coating repeatedly to form a uniform illuminance on the inner wall, thereby eliminating the influence of the unevenness of the outgoing beam due to the characteristics of the light source itself. In order to obtain higher measurement accuracy, the aperture of the integrating sphere should be as small as possible. The aperture ratio is defined as the ratio at the opening of the integrating sphere to the area of the inner wall for the entire sphere.