This video glossary covers the terminology and defines the meaning of common video terms related to cameras, codecs, lighting, film set lingo, post-production workflows, and everything else you ever wanted to know about film and video production.
This term refers to light that is defined by its quality, or how hard or soft a light source is. The way that you measure the quality of the light is by how close the source of the light is to the subject. An easy shorthand is to measure how harsh, or hard, the shadows are.
If the shadows cast by or cast onto your subject are large and have hard, defined edges to them, that would qualify as hard light. This happens when the light source is too small or too close to your subject.
Compare that to softer, smaller shadows, and you have soft quality light. This is usually because the light source is farther away, more spread out, or more encompassing of your subject.
A good example of this would be the shadows cast by the sun on a clear day versus a cloudy day. On a clear day, you get harsh shadows from a single source of light, versus a cloudy day where the light is diffused by the clouds, resulting in softer (if any) shadows.