A light that qualifies as soft or hard is quite simple, it is the transition from light to shadow on a subject. This is also called the graduation of the “falloff”. If the transition is sharp and quick, then it is a hard light. This sharpness can be clearly distinguished from the shadow under the chin. Another example of a hard light source would be the noonday Sun. The shadow to light edge is so stark that many pictures taken without modification will be extremely hard lit.