The measurement of concentrated solar radiation is often done by using the Lambertian target and video camera technique. With these instruments the recording of two-dimensional flux maps is performed by moving a white and diffuse reflecting target into the beam and taking an image of the reflection pattern with the camera. Many of the present and past instruments are based on this principle, e.g. for analyzing dish, tower, or solar furnace performance. The method relies on white, temperature resistant target materials with good Lambertian scattering properties. Solid ceramic material, powder coatings (alumina, magnesia), or other kinds of paints may be used. Recently, Lambertian transmitting diffusers have also found application. The investigations reported in the paper revealed that many of the tested samples show good diffuse reflection and transmission properties. Only a flat PTFE sheet and two white temperature resistant paints show a distinct directional reflectance component or a higher deviation from Lambertian property. In transmission, a pronounced directional component is shown by an etched glass plate. As mainly all of the coatings or solid materials were selected with respect to sufficient thermal stability, the good Lambertian diffusers are able to meet the requirements of high flux density measurement.

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