Figure 2-15. Regular reflection.

TM 9-258

d. The direction in which any single ray of light will

be reflected can be plotted by erecting a perpendicular or

normal at the point of impact and applying the law of

reflection (fig 2-16). Any rough surface can be regarded

as an almost infinite number of elementary plane

surfaces at each of which the law of reflection holds true.

e. Light is reflected by diffusion or by regular

reflection and diffusion from nearly every object which is

seen. Because the light falling on such an object is, in

part, scattered in all directions, the object is made visible,

generally, when viewed from any direction. Skin, fur, and

every dull surface reflect light in essentially a diffused

manner. The glossy finish of a new automobile or the

bright finish of a polished casting reflect light essentially

by regular reflection and partially by diffusion.

f. Surfaces of transparent mediums such as optical

interfaces also will reflect. The amount of incident light

reflected depends upon the angle of incidence. As the

angle of incidence increases, so does the amount of

reflected light. When light passes through a piece of

glass, reflection occurs at both surfaces as in figure 2-

17. Approximately 4 percent of the incident light is lost or

Figure 2-15. Regular reflection.

reflected at the first surface and another 4 percent of the

emergent light is lost by reflection at the second surface.

c. If a beam of light strikes a rough surface, such

Thus, both reflection and refraction (the bending of light)

as a sheet of unglazed paper or ground glass, the light is

occur at any optical interface. The importance to optical

not reflected regularly but is scattered in all directions (fig

systems is discussed in detail in paragraphs 4-1 through

2-16). This is called irregular reflection or diffusion.

Figure 2-17. Reflection at optical interfaces

Figure 2-16. Irregular or diffuse reflection.

2-12