Lighting patterns creates dimension & expression to face, but it is the lighting ratio that can make or break the portrait.
What is this Lighting Ratio?
In mathematical language, a ratio is a comparison of one thing to another. The dictionary definition states, the quantitative relation between two amounts showing the number of times one value contains or is contained within the other.
Lighting Ratio in photography refers to the comparison of key light (the main source of light from which shadows fall) to the fill light (the light that fills in the shadow areas). Therefore the higher the lighting ratio, the higher the contrast of the image will be and the lower the ratio, the lower the contrast. Since the lighting ratio is the ratio of the light levels on the brightest lit to the least lit parts of the subject, and the brightest lit are lit by both key (K) and fill (F), therefore the lighting ratio is properly (K+F):F although for contrast ratios of 4:1 or more, then K:F is sufficiently accurate.
What is the art of Photography?
One can do it with the built-in meter in the camera; it is much easier to use a handheld incident light meter. The in-camera meter is a reflective style meter which takes a measurement of the light reflecting ‘off’ of your subject. A handheld meter is an incident meter which measures the amount of light falling ‘on’ the subject and is a more accurate way of measuring lighting ratios.
In respect to lighting ratios, one measure the light falling on the light or highlight side of the face, and compare it to the shadow side to arrive at the lighting ratio. The trick is to add brilliance to your highlights. This is achieved by the use of careful lighting. The highlights when brilliant, highlights within the main highlight. This further enhances the illusion of great depth in a portrait.
Considering lighting ratios is important for portrait photography. The four most common lighting ratios for portrait photography are 1:1, 2:1, 3:1, and 4:1. Generally somewhere between 2:1 and 4:1 is the commonly used ratio for most portraiture.
Note: The term ‘portraiture’ refers to a word picture that presents or portrays a person’s appearance and character.