# Recognize several reflections of light on specular and diffuse surfaces

①Regular reflection and specular reflection (regular reflection, specular reflection) The reflection generated on a smooth interface is called specular reflection, also known as regular reflection. As shown in Figure 1, an incident ray will generate a reflected ray, and the relationship between them is as follows: the incident ray, the reflected ray, and the interface normal passing through the incident point are all in the same plane; the angle between the incident ray and the normal is the same The angle between the emitted ray and the normal is equal and is on either side of the normal.

The ratio of the energy of the reflected light to the incident light, in addition to other factors, mainly depends on the ratio of the refractive indices of the two media and the angle of incidence (the angle between the incident light and the normal line of the point interface). The closer the incident angle is to 90°, the closer the energy ratio of the reflected light is to 100%.

②Spread reflection When light is incident on a diffused aluminum plate, a brushed metal plate or a matte white paint coating from a certain direction, the reflected light is scattered in different directions, but the general direction is Consistently, as shown in Figure 1, the axis direction of the beam still obeys the law of reflection. This reflection of light is called scattered reflection.

③Diffuse reflection When light is incident on a rough surface or a surface coated with a matte coating from a certain direction, the light is dispersed in many directions. There is no regular reflection on the macroscopic level, and the reflection of this light is called diffuse reflection. If reflection obeys Lambert’s cosine law:

That is, the light intensity Iθ in any direction is proportional to the cosine of the angle θ formed by the light intensity I0 in the normal direction of the reflective surface, and has nothing to do with the incident direction of the light. This kind of light reflection is called isotropic diffuse reflection. In this case, the brightness of the reflected light is the same when viewed from all directions of the reflective surface.

④ Mixed reflection When the light is incident on the enamel or the highly glossy paint layer from a certain direction, both regular reflection and diffuse reflection are combined, which is called mixed reflection. The luminous intensity of this kind of reflection in the direction of directional reflection is much larger than that in other directions, and it has the maximum brightness. There are also a certain amount of reflected light in other directions, and its brightness distribution is not uniform.