How to control light ratio in photography?

Light ratio: As far as the total effect of two lamps used to illuminate an object is concerned, the intensity difference between them is called light ratio. —————————————————————————————————— This can usually be expressed in digital proportion. For example, the ratio of 3: 1 refers to the part of the main body that receives the total effect of two kinds of light, and its brightness is three times that of the part that only receives one kind of light. This can also be expressed in photometric units. For example, the highlight part is 300 feet/candle, and the shadow part is 100 feet/candle. However, the expression "3: 1" does not represent the aperture level. Usually, the two kinds of light that make up the light ratio are complementary light and main light. Supplementary light: The so-called supplementary light is the light source usually located at or near the camera axis, which is used to illuminate the subject as a whole, and its purpose is to expose the details of the shadow part properly. Only fill the light, the lighting it provides is quite dull. Due to illumination from the photographic optical axis, a satisfactory outline or shape of a three-dimensional object cannot be displayed. This kind of light cannot produce important highlights, so many photographers use relatively soft or diffuse light sources. White reflective umbrellas, skylight devices or a wide range of diffused light are often used as supplementary light. Main light: it is the dominant light in the lighting, and the terms "keynote light" or "modeling light" are correct, because the main light really determines the "keynote" of the scene (high-key or low-key), and its position will produce the modeling outline formed by highlights and shadows. Relatively speaking, if you choose a softer and more harmonious light source as the supplementary light, you will often choose a more "harsh" light as the main light. Parabolic reflector, small silver reflective umbrella, and lights that produce flickering highlights can all be selected as the main light. Ratio: the confusion of the concept of light ratio comes from the numbers that explain the light ratio. It is important to remember that the main light is only used to illuminate the highlight or bright part of the subject, but it cannot illuminate the shadow part of the subject. It should also be remembered that if the fill light is located above the camera axis, it can illuminate everything that the lens can see, namely highlights and shadows. The light ratio expressed by numbers refers to the ratio of the total amount of light shining on the highlight to the amount of light in the shadow. The highlight part can receive the total effect caused by the main light and the supplementary light at the same time, and the shadow part can only receive the supplementary light effect. If we can understand inverse square law, it is not difficult to control the correct light ratio. If a specific light source is away from the subject 10 foot, the subject will receive the light of 100 foot. Candlelight lighting, so when the distance is 20 feet, what is the light intensity of the subject? If you think that the distance is twice, that is, the brightness is half -50 feet/candle, then you may want to review inverse square law, because you are wrong! Inverse square law pointed out that all light follows to a certain extent, and the reduction of light energy is natural, which is based on the change of the square of distance. ———————————————————— Square refers to the multiplication of a number itself. For example, if the light is one foot away from the subject, the calculation method of the subject's luminosity is: one times one equals one, then the reciprocal is one-third, or one is divided by one, then the subject's luminosity is X (expressed in photometric units). Move the lamp back two feet, use the formula, two times two equals four, find its reciprocal, divide by four, and the illumination of the subject is only 1/4X. Move the light back three feet, three times three equals nine-that is, the light reception is only 1/9X. Returning to the problem discussed earlier, applying inverse square law's formula-multiplying the distance by itself and then finding its reciprocal-it can be determined that at 10 feet, the subject receives1100 light from the light source, while at 20 feet, the subject only accepts1/from the light source. That is to say, when the distance is doubled, the amount of light received by the subject is only the original 1/4.