What is light folding? What is triangular light?

The superposition of light says that the professional point is the interference of light. Two light waves meet. Just like water waves, some of them increase in amplitude and some decrease in amplitude. . . . That is, the bright spots and dark spots in the interference experiment.

Triangular light is a light distribution method. Also known as three-point lighting method, it is the basic lighting level in figure photography lighting. That is to say, the light levels of main light, auxiliary light and profile light are connected together to form a triangle. It is the three basic lights in the lighting of objects and people. Side light, also known as backlight, is often used as decorative light and isolation light (even if the main body of the picture is separated from the northern background). Three-point lighting is the basic lighting method for shooting portraits, but it is not the only method. The main light forms a 45-degree angle with the camera (that is, the positive side light), which can be used on both sides. The auxiliary light is near the camera, and the side light basically faces the direction of the lens, slightly higher. Rembrandt only corrected the side light, which is the light effect often shown in Rembrandt's paintings, but Rembrandt's paintings rarely use strong backlight.