We as photographers use light as our main ingredient for image making. Without light there is no photograph, and light plays a very direct role in the emotional response one has to an image. At the most basic level light is necessary for a correct exposure, but the impact of light and lighting on the making of a photograph goes much the physics of image making and into the message and emotional content of the photo. Depending on the quality of the light, harsh or soft, shadowless, or dramatic, concentrated or filling, a portrait produces very different impressions on the viewer.
In addition to light at the time of exposure, color and tonal manipulation as part of digital processing are critical elements in defining the mood of a photograph. Hard contrast, combined with hard light, creates a raw feeling, whereas soft, low contrast light is soothing and pretty.
I show a couple of examples here from a recent shoot.
This first image above uses delicately soft light created with a very large octagonal softbox. Note how shadows are low contrast and soft, while at the same time the light contours the shape of the face and produces a pleasant impression of three-dimensionality or volume. The message that the simple composition, designer glasses and carefully done makeup send is that of calmness, self-confidency and beauty.
This second image above of the same model is the opposite. A white background is used, but instead of using soft, gentle light, harsh lights have been used - they generate high contrast shadows projected against the white background. The shadows are not only very visible, but the upper body shadow is disjointed from the lower body shadow, as two different flash heads were used for this effect. The gradation of light to shadow on her face is really harsh, almost as an illustration - due to additional contrast added in postprocessing. The mood here is drama and raw sensuality, as opposed to soft femininity.
The photographer can use light to help define the emotional content of a photograph, not only to create the exposure. The “quality” of light is decisive in defining the mood of an image.