Definitions
Inverse Square Law- A law stating that the intensity of an effect such as illumination or gravitational force changes in inverse proportion to the square of the distance from the source.
Guide Numbers- A measure of the power of a flashgun expressed in meters or feet.
Angle Of Incidence= Angle of Reflection- The angle that a reflected ray, as of light, makes with a normal to the surface at the point of reflection. angle of reflection. The angle formed by a ray or wave reflected from a surface and a line perpendicular to the surface at the point of reflection.