Laws of Reflection

How light bounces off a smooth surface.

When a ray of light strikes a polished surface it bounces off in a predictable direction. The arriving ray is the incident ray, the departing one is the reflected ray, and the line drawn at right angles to the surface at the point of contact is the normal.

Angles are always measured from the normal, never from the surface itself. A rough surface scatters light in many directions because each tiny patch has its own normal, yet every single ray still obeys the same law.

• First law: the incident ray, reflected ray and normal lie in one plane.
• Second law: the angle of incidence equals the angle of reflection.
• Smooth surfaces give regular reflection; rough ones give diffuse reflection.

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