If you've attended a few seminars on lighting or portraiture, you've likely heard an audience member ask about exposure for people with dark skin. Invariably, the speaker announces that exposure is exposure and there is no need for compensation. The argument is often supported by an example consisting of an image of several people of differing skin tone. If the exposure is biased for the skin of any one person, an unfavorable skin rendition will result for the others. The argument is irrefutable, but for the inquirer, the answer is often unsatisfying. They want more detail in the photographic rendition of dark skin, something closer to what they see with the naked eye. And, they're not alone. Shortly before digital capture overtook film as the medium of choice, Kodak was marketing a special portrait film for deep-complected skin. If Kodak thought this was an issue, maybe there is something to it.
Dark vs. Light
The subject of skin tone is a very interesting one. It can be approached from both a technical and social angle. In my conversations with people from around the world, I have been surprised by how often darker skin is associated with lower social standing. No doubt, some of this bias is a vestige of Western hegemony. While it would be foolish to assume that a dark-skinned customer will want a lighter rendition of their skin, it can sometimes be an issue. I'm not qualified to talk about the social aspect, so I'll take a stab at the technical.
Diffuse vs. Direct Reflection
In general, the darker the skin, the more it absorbs light and the less it reflects it diffusely. Direct (specular) reflection, however, is dependent primarily on the sheen of the skin surface, and not tone. So, while light and dark skin may produce very similar levels of specular reflection, there will be a big difference in the diffuse reflection. As a result, direct reflections make up a greater proportion of the light reflected from dark-toned skin and the implications of this are many.
Defining Form with Shadow and Highlight
On light skin, the specular highlights ride on top of the glowing skin (diffuse highlight). These specular patches may enhance form, but that are not usually the primary feature that defines form and depth. On light skin, it is the difference in the areas of diffuse highlight and the surrounding shadows that give the face form. With extremely dark skin, shadows and diffuse highlights may be so dark that distinguishing between them becomes difficult. At this extreme, form is rendered by the differences between the specular highlights and the surrounding areas, both shadow and diffuse highlight. Simply, or perhaps over-simply put, with light skin you create form and depth with shadows. With dark skin, you do so with highlights.
If you are not quite getting the picture, take a look at some real-world renditions of people with very deep and very fair complexions. One of the best examples of dark African beauty comes in the form of model Alek Wek. A much photographed model, you'll find plenty of images of her on the web. Notice how areas of specular reflection on her cheeks, forehead, nose, and chin often define the form of her face. At the other extreme, take a model with fair skin. Nicole Kidman or Taylor Swift are two examples. Notice how form on these faces is created by shadows around the cheeks, nose, brow, and jaw.
Lighting Strategies for Dark Skin
There is no one right way to light a face, but here are some things you might want to keep in mind when planning your lighting for dark skin. Specular highlights are inevitably more prominent for darker skin. Controlling them is key to achieving the desired result. You'll probably be leaning one of two ways to control specular highlights: minimizing them or making them as large and prominent as possible.
Minimizing specular highlights is not always easy. One approach is to place your lighting, preferably smaller or controllable lights, at oblique angles so that much of the direct reflection is aimed away from camera view. Feathering is another technique that can help, as feathering can decrease both the apparent size and intensity of the source's specular reflection. These techniques were used in the second example from the prior post. By reducing specular reflection, you let the diffuse reflection do more of the talking, and increase tonal richness in the process.
The other approach is to define form by painting the face with large and soft specular highlights. By using very large light sources, you create large specular highlights that can cover the greater part of many facial features. As the light source is large, the energy of the specular highlight will be distributed over a large area, resulting in a pleasant glow. The following picture, as corny as it is, demonstrates the approach. The main light for this image was a large 3' X 4' softbox placed in close.