The arc created excites the molecular deuterium contained within the bulb to a higher energy state. The deuterium then emits light as it transitions back to its initial state. This continuous cycle is the origin of the continuous UV radiation. This process is not the same as the process of decay of atomic excited states (atomic emission), where electrons are excited and then emit radiation. Instead, a molecular emission process, where radiative decay of excited states in molecular deuterium (D2), causes the effect.