Integrating spheres are used especially for measuring divergent light sources such as LEDs. The light is introduced through the input port, then reflected many times by the highly reflective interior of the sphere until it illuminates the inner surface uniformly. A detector samples a small fraction of this light to measure the total power input. Ophir integrating spheres have a highly reflective diffuse white coating for measurements independent of beam size, position and divergence. There are several sphere sizes, apertures and wavelength regions available. The large IS6 series has 2 configurations for measuring divergent or parallel beams (see diagram).