S u r a j k i r a n
  The Sun makes its presence felt through the rays of light. The path of the rays can be modified in several ways such as reflection, refraction etc. The first experience of modification of light rays for school kids is through the experiment where a lens is used to burn a piece of paper. The modification of the path of light rays using lenses and the concept of measuring time using sunlight is brought together in 'Surajkiran', meaning 'sunray' in Hindi.  
  In this concept a planoconvex lens is held horizontally at a height equal to its focal length , with the convex surface facing the ground. The light from the Sun, after refraction in the lens, converge to form a bright spot on the ground. The spot falls at different places depending upon the position of the Sun relative to the lens. At noon the spot falls directly below the lens. In the evenings and mornings the spot is farthest from the noon position, on opposite ends. Concentric circles on the surface below the lens with the noon position of the bright spot as the centre is used to approximately gauge the time. At one level 'Surajkiran' is a simple device to gauge the time using the concept of refraction of light. At an other level it can be used as an educational tool to teach the principles of light.  
       Rishikesh Deshmukh