Visible light region of electromagnetic spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye.
Electromagnetic radiation in this range of wavelengths is called visible light or simply light.
A typical human eye will respond to wavelengths from about 390 to 700 nm.
Theories of Light
Light is an electromagnetic phenomenon; visible light is a tiny part of a larger
electromagnetic spectrum of radiation ranging from cosmic rays to radio waves. Knowledge
of the nature of light and the emission and absorption processes are very important.
Two complimentary theories have been proposed to explain how light behaves and the
form by which it travels.
- Particle theory: Release of small amount of energy as a photon when an atom is excited.
- Wave theory: Radiant energy travels as a wave from one point to another.
Waves have electrical and magnetic properties (electromagnetic variations).
The scientific study of the behaviour of light covers reflection, refraction, polarization,
diffraction of light as it passes by the edge of an opaque object and interference
patterns resulting from diffraction. Newton proposed that light consists of small particles, with
which he could explain the phenomenon of reflection, refraction and splitting of
sunlight into a rainbow by a prism. Christian Huygens proposed wave theory of
light and demonstrated how waves might interfere to form a wave front, propagating
in a straight line.