The Nature of Light Light is a form of energy that transmits from one place to another at finite velocity. It is detectable with our eyes. Visible light constitutes a small portion of a continuous spectrum of radiation ranging from cosmic rays to radio waves (Fig–1.1). White or visible light, which our eye detects, is only a fraction of the complete spectrum. The wavelength of rays in white light ranges from 380 mm to 770 mm. Theory of Light There are two theories put forwarded to explain the behaviour and travel of light. 1. Particle theory – Release of a small amount of energy as a photon when an atom is excited. Moreover, just like photons (Light quanta) behave like properties of matter, electrons also behave like group of waves. 2. Wave theory – Radiant energy travels as a wave from one point to another. Waves possess both electric and magnetic properties and thus, light is an electromagnetic phenomenon. Wave theory can only explain the phenomena of polarization, reflection, refraction and interference that form the basis for optical mineralogy.