What is Integrating Sphere?
An integrating sphere is a hollow spherical cavity with its interior covered with a diffuse white reflective coating, which is also known as photometric sphere or flux sphere etc.
There is one or several holes in the wall, which is used for light entrance hole and receiving hole to place light receiving devices. The inner wall of the integrating sphere should be a good spherical surface; it usually requires that the deviation from ideal spherical surface should not be larger than 0.2% of inside diameter. The inner wall of the sphere is coated with ideal diffuse material, which is the material with diffuse reflectance close to 1. The commonly used materials are MgO or BaSO4. Mix it with Glue Adhesive evenly and spray it on the inner wall. The spectral reflectance of MgO coating in the visible spectrum is above 99%. The light entering the integrating sphere is reflected by the inner wall coating multiple times to form uniform illumination on the inner wall. In order to obtain higher measurement accuracy, the aperture of integrating sphere should as small as possible. The aperture ratio is defined as the ratio of the sphere area at the opening of integrating sphere to the area of the sphere total inner wall.