Until the middle of the 1800's, the generally accepted theory of light was the particle picture. In this viewpoint, advocated by Newton, light was considered to be a stream of tiny particles. However, in the late 1800's, the particle picture was replaced by the wave theory of light. This was because certain phenomena associated with light, namely refraction, diffraction and interference, could only be explained using the wave picture.
Visible light is just one particular type of electromagnetic radiation.
The different types of radiation are distinguished by their wavelength, or frequency, as shown in Fig. Radiation outside the visible spectrum with wavelengths longer than red light is called infrared, while radiation with wavelength shorter than blue is called ultraviolet. The theory which accurately describes the wave-like properties of all types of electromagnetic radiation is called Maxwell's Theory of Electromagnetism . In the early 20th century, experiments revealed that there were some phenomena associated with light that could only be explained by a particle picture. Thus, light as it is now understood, has attributes of both particles and waves.