Light is electro-magnetic energy that travels in a straight line through a medium or a vacuum at a constant speed. This means that light can be viewed as an electric field and a magnetic field that vibrate as they move along. When light encounters electrons that can move such as in a piece of metal it causes those electrions to vibrate in synch. The moving electrons create new light which is what we see reflected off a metal's surface. The direction of the new light is given by the law of reflection.
The electric fields of light cannot penetrate a metal but they can penetrate a material such as glass or water. In this case the speed at which the light can travel through is different. This causes the direction of the path to bend which gives us refraction.
The speed of light is constant through a uniform medium. Unlike water waves, sound waves or earthquake waves light does not need a material to carry the wave. Light can travel through a vacauum which is how we see the Sun and starts. Light travels fastest through a vacuum. No material thing can travel faster than light in a vacuum which is 186,000 miles per second or 3x10ee8 meters per second.
Since light acts like a wave it can interact with other waves. This causes diffraction patterns just as water or sound does. A water wave contains a continuous amount of energy. The waves striking an ocean shore gradually transport energy to erode and change the shore line. Unlike a water wave light contains a fixed amount of energy which is delivered all at once. Light acts more like a tidal wave which strikes once with the full amount . This is more like a material object and so we say light acts more like a particle. A paricle of light is called a photon. The amount of energy a photon contains is called a quantun of energy. To deal with this new understanding of light required a new branch of physics of the very small, called Quantum Mechanics.
The following are the properties of light:
a) Reflection--light reflected off the surface like mirror such that angle of incidence is equal to angle of reflection.
b) Refraction--bending of light as it passes between material of different optical density.
c) Dispersion--light-wave passing through a material gets refracted by different amounts because of different wave-lengths, giving rise to different colors seen through prism.
d) Diffraction--bending of light-waves around obstacles in its path.
Light is a range of electro-magnetic radiation having a dual nature as both particles and waves. The electro-magnetic wave has an amplitude, wavelength, and an angle at which it is vibrating. According to the modern Quantum Theory, light consists of particles, called photons.