Soft Light vs. Diffuse Light: Some Tips To Help You Tell The Difference

Often times we photographers get so wrapped up in our gear and the misleading jargon that comes along with it that we tend to forget the basics of light quality. What do I mean by that? I’ll tell you, but before I do that I’d like to first review the differences between soft and diffused light.

Light, as it relates to our photo, has three main components. Highlight, midtone, and shadow. We control these with the type/quality of light that hits our subject. It’s the transition from shadow to midtone and from highlight to midtone that we will be concentrating on for this discussion.

Let’s first start by defining the midtone of the photo. The midtone is what we consider to be the “correct” exposure. Whether we meter the light or use our own artistic judgement, the midtone is what we’re looking at to decide exposure. Once we know our exposure, we can now look at the shadow and highlight components of our photo. For purposes of this discussion shadow will simply be the light falling away from correct exposure to black or no light at all and the highlight will be the transition from our correct exposure to bright and then to white. Now that we know the three components of the light in our photo we can now get to the transitions between them.

The way we control the quality of the light is by modifying the light source used on our subject. So how do we do that? Well there are two ways. The first is to modify the light to affect the shadow transition. This is done by the size of the light as it relates to our subject. In other words, if the light source is larger than our subject the transition will be gradual or soft but if the light is smaller than our subject the transition will be sharper or hard.

This brings us to the highlight transition. This is where some confusion can occur and where the misleading jargon gets started. A highlight is described one of two ways. Specular or diffuse. For example, if you are driving down the road and the sun reflects off of the car in front of you or you see tiny points of light dancing on the surface of a lake, these are a specular highlights. In order to modify a specular condition, there is only one way and that is to diffuse it.

If we look at any standard softbox, we will see a couple of different things. First is that it’s typically large. Much larger than a person if that is our subject. That will give a soft light for the shadows. That’s a good thing. It also, in many cases will have a silver reflective surface on the inner walls. This is to help amplify the light but it will make the light specular. Some photographers call this punchy or crispy light, good for showing texture in clothing and that sort of thing. But what if we get a “hot spot” on our models’ face as a result? The solution is to add diffusion to the softbox. Most softboxes come with one or two layers of diffusion material that can be added to the front of it. Now you’ve controlled the highlight transition.

Oh the confusion? Yeah I almost forgot. I often hear people say the light is soft when a specular highlight is gone because they used a large softbox. Which is only partially correct as we have just learned. Here are a couple of things you can try to help demonstrate the quality of light for yourself. Take a very large silver umbrella take a portrait with it fairly close to your subject. Look at the shadow transition. It will be soft because of its relative size. Now look at the highlight. Your subject will probably appear shiny. That is because the umbrella doesn’t have any diffusion material only the silver surface. Then put the diffusion cover known as a “shower cap” on the umbrella and notice how the shine is gone. Now try this experiment with a small light like a speedlight for example. Use it as is and look at the shadow transition. It will be hard and the highlight will be specular. Now place diffusion in front of it. You can use a tissue or something like that if you don’t have an actual diffusion cover for it. The shadow will still be hard but the highlight will not be specular anymore.

So to summarize, when we talk about light being hard or soft, we are talking about shadows and the size of the light as it relates to the subject. And when we are talking about light being specular or diffuse, we are talking about the highlights. I hope this has helped clear up some of the confusing things people say about the quality of light in a photograph.

Please comment below and let me know if you have tried these experiments. I’d love to hear from you. And if you have questions about anything in this article, please ask them below as well.