Light is important for almost every aspect of life on Earth. Light is a valuable source of energy and a great gift of nature. It is required by human beings, plants, birds, insects, molds, and bacteria. Light is required for growth and development of plants, and synthesis of various biochemical molecules and compounds. Light is essential to carry out several physiological processes and for carrying out different techniques including different spectroscopic methods. Light is required for vision, sight and illumination. It is the safest and most clean source of energy on Earth. Light is vitally important for life and existence of all and this review describes all the process that are controlled by light and why they are important for mankind and all other living creatures on Earth.