n (ca. 1890) That form of energy consisting of the electromagnetic spectrum which travels at 115.890 km (186,500 miles/s) through a vacuum, reducing this speed in denser media (air, water, glass, etc.). The nature of radiant energy is described by its wavelength or frequency although it also behaves as distinct quanta (“corpuscular theory”). The various types of energy may be transformed into other forms of energy (electrical, chemical, mechanical, atomic, thermal, and radiant) but the energy itself cannot be destroyed (Serway RA, Faugh JS, Bennett CV (2005) College physics. Thomas, New York).