When describing the quality of a light source, the term Contrast is synonymous with quality. What we are describing is the relative hardness (or softness) of a light source. Hard light is high contrast, which produces clearly defined shadows that are dark and have a hard edge. Soft light is low contrast, which produces faint shadows that gently feather at the edges. The softer the light source, the more difficult it will be to see shadows.
Here is an example of hard light. This photograph was taken with a snooted monolight. The snoot is a funnel like modifier that fits over the light to reduce the effective size of the light source. In this case it is 2-¼ inches (57 mm) in diameter. The light source is about 3 ft. (0.9 m) from the subject. Note how the shadow is well defined with edges that mimic the shape of the subject.
In part two I will show the underlying principle behind this characteristic of light using diagrams that will hopefully shed light on the subject and explain why to a photographer, size does matter.
Next we have an example of soft light. This photograph was taken with the same monolight, but fitted with a 46” umbrella. The farthest bounce surface of the umbrella is about 4-½ ft. (1.4 m) from the subject. Note how the shadow is very soft with barely discernible edges.