What does light ratio mean in photography? Pingguang, what else? Thank you very much

The light ratio is usually used to compare the brightness between the main lamp and the auxiliary lamp.

If the brightness of the main lamp is three times that of the auxiliary lamp when taking black-and-white photos, it will be 3: 1, and four times it will be 4: 1.

The light ratio of color photography is usually twice that of the main lamp and the auxiliary lamp, which is 2: 1.

Flat light can also be called front light, that is, the main light is placed on the front of the lens, and the shooting effect has no outline, no hierarchy, and no three-dimensional sense of light and shadow.