The optical properties of the lining of the sphere greatly affect its accuracy. Different coatings must be used at visible, infrared and ultraviolet wavelengths. High-powered illumination sources may heat or damage the coating, so an integrating sphere will be rated for a maximum level of incident power. Various coating materials are used. Early experimenters used a deposit of magnesium oxide. Barium sulfate has a usefully flat reflectance over the visible spectrum. Finely-deposited gold is used for infrared measurements. Various proprietary PTFE compounds are also used for visible light measurements.An important requeriment for the coating material is the absence of flourecence. Flourecent materials absorb short wavelength light and reemit light at longer wavelengths. Due to the many scatterings this effect is much more pronounced in a integrating sphere than for materials irradiated normally.
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