Visible spectrum includes those wavelengths which can stimulate the sense of sight but there is no basic difference between light waves and the electromagnetic waves produced by electrical oscillating circuits. The term electromagnetic spectrum is used for the range of wavelengths from 10⁸ to 1Å. The frequency of an alternating current generator can be made as low as possible by decreasing the speed of the generator. Waves of shorter wavelength can be produced by electrical oscillators. X rays and gamma rays represent the waves are very short wavelengths.