Sources of light are hot bodies, lightning, electric discharges, insects, and fire. Light stimulates vision. So much for the definition, frankly speaking nobody found the truth about light. Our course is geared towards a bird's eye view of physicist's light. You should realize that you will begin a course about Light which pervades such diverse subjects as physics, astronomy, chemistry, mathematics, theology, psychology, biology and medicine.
Light is the most ancient object of all things created.
Mentioned in the Bible in its beginning verses, started on the eve of creation of the universe which physicists believe, credit goes to Einstein who gave us a working principle in his Big Bang Theory of the Universe. The oldest object reaching the earth is light, which may have started its journey at a distant star in a galaxy billions of years ago. When light moves, it moves with the greatest speed of all things, its speed is 186,000 miles per second. When it stops, it no longer exists. We say it is absorbed.