What is light ratio? What is the definition of light ratio?

Light ratio is one of the important parameters of photography, which refers to the ratio of the brightness of the light receiving surface to the brightness of the shadow surface of the object being photographed. Under the distribution of natural light and artificial light, the brightness of the light-receiving surface of the object is high, and although the shadow surface does not receive light directly (or less), it still has a certain brightness due to scattered light (or auxiliary light). The light ratio is often expressed in the form of "light receiving surface brightness/shadow surface brightness". Light ratio also refers to the ratio of brightness of adjacent parts of an object and the contrast between light and shade of the main part of the object. Large light ratio, large contrast, small light ratio and small contrast. The light ratio determines the contrast between light and shade of the picture, forming different light and shade and tone. When shooting portraits, clever use of light ratio can effectively show the characteristics of "rigidity" and "softness" of the subject. For example, women and children often use a small light ratio, and men and the elderly often use a large light ratio. Direct light tends to form a large light ratio, and scattered light tends to form a small light ratio.