Rimmer: In simple terms as you move further away from a source of light or other form of energy it gets weaker based on a formula. "In physics, an inverse-square law is any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity." Arnold On 11/06/15, Rimmer deVries wrote: What is this inverse-square law for light ? Rimmer