Integrating spheres are widely used to measure total luminous flux of LED light sources. Their detector heads are required to have a directional response matched to Lambert's cosine law on the principle of the integrating sphere. It is approved on IES-LM79, the measurement method provisions, that the directional response, f2, has a value less than 15 . In practice, for cosine response a small integrating sphere (satellite integrating sphere) is used as a light receiving system of many sphere photometers. However, this also creates several problems such as attenuation of the photometer signals passing through the satellite sphere and anisotropic response caused by the baffle inside the satellite sphere. An optical system with directional response matched to the cosine law is considered a detector head of a sphere photometer. As a result, we found that by equipping a photometer head consisting of a transparent PTFE diffuse plate, a probe f2 value of less than 10 can be provided. This indicates the possibilities of optical systems that have a smaller anisotropic response caused by a baffle and brighter throughput than a traditional satellite integrating sphere.
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