by Roger N. Clark
Lighting has many factors. It can be directional or diffuse, with multiple or single sources, have different colors and direction to the viewer and camera.
The Lighting, Composition and Subject Series:
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Types of Lighting
Understanding the direction and color of light sources is key to learning how, when, and where to photograph a subject. Figure 1 illustrates two basic types of lighting: 1) the directional reflection from a mirror, and 2) diffuse reflection of light from white paper. It was difficult to make this photograph because the light from the sun reflected in the mirror was so bright. Which reflects more light: the mirror or the paper?
The light from the mirror and the paper reflect nearly the same total light (the paper about 2% more light), but the mirror appears brighter because it reflected most of the light towards the camera, whereas the paper reflected the light in all directions. There is a continuous range from collimated direct reflection to completely diffuse reflection. It is the directionality of direct versus diffuse light, whether the light is reflected or transmitted that contributes to the huge dynamic range we see in the natural world.
Figure 2 shows several kinds of light: direct light (the lights from the city; stars are natural direct lights as is the sun in sunrise/sunset photos), reflected sunlight off of the moon, and transmitted light through the thin clouds. There are also different types of color: continuous spectrum and emission line sources. The moon is a continuous spectrum light source as it is reflected sunlight. The lights from the city are incandescent and emission line sources like neon signs and low pressure sodium lights.
The Moonrise image, Figure 2, illustrates another property of light: directionality. The clouds in front of the moon scatter light mostly in the same direction as the moonlight. This is called forward scattering. Compare that to the pad of paper in Figure 1. if the pad of paper were thick enough, no light would be transmitted and the light would be scattered only in the hemisphere above the paper. That is called backscatter. Thin clouds forward scatter light and that forward scattering can be as much as a million times (20 photographic stops) or more in the forward direction as it is in the side or backward directions. This makes it difficult to photograph toward the sun on some days as clouds in the sky can be so bright they saturate the film or electronic sensor.
Types of Lighting Important in photography (light can be any/all combinations of these in various proportions)
Polarized Light. Light from a clear blue sky is polarized where the maximum polarization is 90 degrees from the sun. Light from the clear blue sky is also a diffuse light source. Light directionally reflected off of non-metallic surfaces can be strongly polarized, depending on angle, including glass, water, and leaves on trees. (Metallic surfaces are also weakly polarized, but the effect is usually small in photography.) Rainbows are polarized (Figure 3). When photographing a landscape at a phase angle of 90 degrees, a polarizing filter can darken the blue sky and reduce the effects of light scattered from haze between you and the subject, making the subject appear clearer.
The sun is both a continuous spectrum light source, an emission line light source, an absorption line light source, and is slightly diffuse. For example, in a telephoto image of a sunset, the sun appears large, but in a wide angle image of the sun, the sun appears small and can be considered a point source. This is also true of shadows: they can appear sharp if the shadow is cast only a short distance, for example the shadows cast by facial features on a person's face. But shadows from the sun can have a soft edge, e.g. cast by a distant mountain. Light from the sun reaches the Earth transmitted and diffusely scattered through our atmosphere and clouds, and some of that light gets polarized. Absorption of the light as it passes though the atmosphere changes its color.
The night sky is often dominated by emission line light sources: molecules in the upper atmosphere excited by solar ultraviolet radiation during the day and emits that energy as light at night at specific wavelengths, usually in the red and green (Figure 4). This is the reason the dark, moonless night sky is not black. See The Color of the Night Sky for more information.
The Lighting, Composition and Subject Series:
First Published May 5, 2009
Last updated November 1, 2014.