How does the black body in led related theory shine?

Black body: (1) An object that completely absorbs external radiation of any wavelength without any reflection under any conditions. (2) Objects with absorption ratio of 1. (3) An object that absorbs all incident radiation of any wavelength at any temperature. Black body is an ideal model, which does not exist in reality. So in reality, black cavity is used to simulate black body to carry out some feasible related experiments. Black body is an artificial object that can completely absorb external radiation. It is an ideal state and almost does not exist in reality. So, bold is a concept. In order to achieve this ideal state, people have designed a cavity, the inner wall of which is coated with carbon black and other substances.