A black body or calibrated reference source is an actively, temperature-controlled device. They typically provide a reference source for calibrating thermal cameras and other optical temperature sensors, such as pyrometers. These devices consist of an active surface with a special high emissivity coating, an internal temperature sensor and a closed loop (PID) temperature controller. Some have an adjustable temperature controller, simpler devices have a single, fixed temperature. For special high temperature applications, there are cavity style models available. The name black body comes from physics – black body radiation. The name was given because the idealized version of a black body absorbs all radiation of all wavelengths. However, some practical limitations to this exist. A perfect black body would have an emissivity value of 1. However, most good black bodies only achieve an emissivity value of 0.98 or lower.

Planck’s law describes black-body radiation. The higher the radiated energy, the shorter the wavelength. This phenomenon can be seen when heating up a piece of metal. The heat cannot be seen until it reaches a certain energy level, then the piece of metal starts to faintly glow red. As the energy further increases, red becomes orange, orange becomes bright yellow. The wavelength shifts from the infrared region into the visible region and becomes perceptible by human vision (400 nm to 700 nm).