When ever we use a light source to illuminate an object, that object is being hit with multiple “rays” of light. Some of those rays are hitting the object in the place which is nearest to the light source, and some of the rays are hitting the subject where is furthest from the light source. OK, nothing new until now.
As a crude generalization one can argue that the light that falls on the closer side to the light source will be brighter then the light hitting the furthest side. This is because the light will scatter more when it makes it long journey to the far side. (This is not true for focused beams and laser, but this thumb rule can be applied to most studio lights and strobes).
