The OED defines spectrum as "The entire range of wavelengths of electromagnetic radiation, from the longest radio waves to the shortest gamma rays of which the range of visible light is only a small part."
Dicţionarul Oxford defineşte spectru ca fiind "Totalitatea lungimilor de undă a radiaţiei electromagnetice, de la cele mai lungi, unde radio, la cele mai scurte, raze gamma, din care spectrul luminii vizibile e doar o mică parte."