Abstract: There has been a heated debate about the nature of light for centuries. The wave-particle duality of light is the result of mutual compromise between the two theories. Some phenomena, such as interference and diffraction, are explained by wave theory, while others, such as photoelectric effect, are explained by particle theory. The coexistence of particles and waves is really unacceptable in concept, because so far, there is no theory that can well unify fluctuations and particles in one mode. This paper discusses the essence of light from such a starting point.