A black body is a radiator, which absorbs all incoming radiation. It shows neither Reflection nor Transmissivity . A black body radiates the maximum energy possible at each Wavelength . The concentration of the radiation does not depend on angles. The black body is the basis for understanding the physical fundaments of non-contact temperature measurement and for calibrating the infrared thermometers. A thermal hollow body has a small hole at one end. If the body is heated and reaches a certain temperature, inside the hollow room a balanced temperature spreads. The hole emits ideal black radiation of this temperature.