LASER light has three main properties that distinguishes it from normal, everyday light we meet: it is monochromatic, collimated, and coherent. Here we will learn about the property of collimation, first. Here, the light rays are parallel to one another. They do not spread out as they leave the light source. It is called as collimated rays. Now we will learn about monochromatic light. What is colour? Color is a property defined by the wavelength of light. Different colours of light have different wavelengths. When you look at a red object, it looks red because the object is reflecting red light. When light consists of only one wavelength of light, we say it is monochromatic (from ancient Greek, mono meaning “alone” or “single”, and chromatic meaning colour. Then we come to the definition of coherence. A beam of light consists of several rays of light. Each ray of light can be represented as a wave, like a wave in the ocean, also called a transverse wave. When all the waves of light in a beam are in step, or in phase, we say the light is coherent. If two rays of light are in step or in phase, it means their crests (and troughs) synchronize up. If not, they are termed as incoherent light waves.