When two objects at different temperatures come within proximity of each other, heat is exchanged. This occurs through electromagnetic radiation emitted from one object and absorbed by the other. The hot object will experience a net heat loss and the cold object, a net heat gain as a result of the temperature difference. This is called thermal radiation. Radiation heat loads are usually considered insignificant when the system is operated in a gaseous environment since the other passive heat loads are typically much greater in magnitude. Radiation loading is usually significant in systems with small active loads and large temperature differences, especially when operating in a vacuum environment.