What Is an Integrating Sphere?

The integrating sphere is a cavity sphere coated with white diffuse reflection material on the inner wall, which is also called a luminosity sphere or a luminous sphere. One or more window holes are opened in the ball wall, which are used as light entrance holes and receiving holes for placing light receiving devices. The inner wall of the integrating sphere should be a good spherical surface. Generally, the deviation from the ideal spherical surface should not be greater than 0.2% of the inner diameter. The inner wall of the ball is coated with an ideal diffuse reflection material, that is, a material with a diffuse reflection coefficient close to 1. The commonly used material is magnesium oxide or barium sulfate. After mixing it with a gel binder, spray it on the inner wall. The spectral reflectance of the magnesium oxide coating in the visible range is above 99%. In this way, the light entering the integrating sphere is reflected multiple times by the inner wall coating to form a uniform illuminance on the inner wall. In order to obtain higher measurement accuracy, the aperture ratio of the integrating sphere should be as small as possible. The opening ratio is defined as the ratio of the area of the ball at the opening of the integrating sphere to the area of the entire inner wall of the ball.