Intensity, Quality, and Contrast
There are four primary attributes used to describe the illumination quality and type of light source. Intensity is the simplest attribute to define. It’s simply how bright the source is. There is not much control over intensity when we are taking pictures using only available light, other than to adjust the ISO, shutter speed, or f/stop.
The other options include modifying the existing light or waiting for different conditions. Waiting for the right conditions may sound extreme, but is not always that difficult if you have the time. Many professionals time their portrait sessions to coincide with the soft light found in the three hours before sunset. Light intensity is divided into two categories. Specular light is generated from a direct bright source point that casts hard shadows. The sun shining in a clear sky is a specular source. So is an unshielded light bulb, a fire, and a spotlight. The picture is an example of a scene lit by specular light. Specular light sources generally produce images with high-to-medium contrast.
Diffused light is generated by broad light sources, or specular sources that have been softened and scattered before they reach the subject. Fog, haze, cloud cover, and large reflective surfaces generate diffused light. Diffused light sources generally produce images with softer shadows and lower contrast than specular light sources. The foggy light here is an example of diffused light. Keep in mind that most scenes in nature are illuminated with a mix of both specular and diffused light. That’s because specular light is reflected off of surfaces, creating secondary illumination.
Contrast is a term used to define both the range of tones (tonal contrast) from lightest to darkest, and/or the way colors in an image relate to each other and the overall composition (color contrast). The human eye can distinguish about 256 shades of gray. Tonal contrast is usually divided into three categories, based on the number of shades in the image. High-contrast images contain mostly blacks and whites, with few middle tones. Medium-contrast (also called normal contrast) images have a range of tones from blacks to whites. Low-contrast images contain mostly middle tones. Specular light sources, with their hard shadows and bright highlights, tend to produce high contrast in images, while the soft shadows created by diffuse lighting are associated with lower tonal contrast. Color contrast is more subjective. It’s the way colors are perceived in relation to each other and the composition. Reddish tones are “warm,” while blue is considered “cool.” The viewer senses the cool air in the bluish tone imparted by the fog in the previous image.
Cool and warm colors, and complementary colors placed close to each other in a picture, build color contrast. The next photo shows a color wheel. The smaller wheels on the right of the photo show examples of the various relationships. Colors that are on opposite sides of the wheel are complementary.
A color’s brightness and the color saturation (which are affected by lighting) modifies its visual contrast. Johan Aucamp contrasted a rainbow and the warmth of a bright golden mountain top with cold blue sky and a dark sea in his landscape seen here.
Less can be more when creating impact with color contrast. Adding more colors into an image tends to decrease the overall color contrast, and to diminish the visual importance of any one color. Below, Carla Hoskins isolated one flower and used a shallow depth of field with color contrast to make it stand out in the composition.
Color saturation makes a color appear more intense that’s not the same as bright. The glow of the sky at the setting sun in this image is saturated, as are the blues and greens from before. Bright light produces bright, rather than saturated colors, and overexposure can wash the color out of a picture’s highlights. Color temperature identifies the color of a light source. Our sun is a yellow star. The atmosphere filters the light, changing its color during the day, and under different weather conditions.
The hour just before sunrise and the one before sunset are very warm. Passing through cloud cover it becomes scattered and increasingly cool. Artificial light comes in various shades based on the source, from lamps that mimic the sun at noon, to reddish tungsten bulbs, to fluorescent fixtures with a greenish glow. Our brains compensate for the variations; sensors and film do not. So photographers can use color temperature to impart mood to our images.