The size of the lightsource in relation to the size of the subject is what gives us soft light.
A small light source gives us sharp shadows – we call that ‘hard light’, while a large light source seems to wrap around the subject, softening the shadows… and we call that soft light.
It is the relationship of source size to subject size that makes it so.
A 2ft square softbox is plenty large for a shot of earrings but pitifully small for a car photograph.
On the left below, you can see the effect of a small light source on a cup of coffee. To the right, a large source provides a ‘softer’ light. Both are fine to use, just know how to use them and how to get the effect you want.
Understanding where to put the lights is a complex set of decisions… and all of them have a basis in both science and aesthetics. It is ultimately up to you, but there are some considerations in commercial photography that must be addressed.
While I believe in a concept I call “Subject Centric Lighting” for technically understanding how light works, the fundamental aesthetic of art belongs with the artist.
The “Arc of Beauty” is one of the most valuable concepts to understand.
In short: Front lighting flattens and backlighting defines. We use front lighting for portraits and people and some landscapes, but rarely for products, still life, or food.
We want to show texture, color, and definition on the table, while we want to show the detail of faces and wardrobe in portraits. Is that a huge over-simplification? No, but it is a bit of an oversimplification. Yes, there are photographers who use front lighting for still life, but that look is very unique and can be thought of as a signature look for those few who use it.
The arc of beauty is from sidelight to backlight. Once the angle is smaller than the 90-degree sidelight, it becomes front light and the difference can be dramatic.
