Electric light source is the instrument or device to convert the electric energy to light energy. It is widely used in daily lighting, industry, agriculture, national defense and scientific research, etc. Human began the research on electric light source near the end of 18th century. Nowadays the electric light source has entered into the new era of miniaturization, energy conservation.

Electric light source classification:

• Incoherent light source: It can be further divided into two categories: light source and radiation.
• Coherent light source(Laser): Two sources of light are said to be coherent if the waves emitted from them have the same frequency and are 'phase-linked'; that is, they have a zero or constant phase difference.