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86 Ophthalmic Lenses

Fig. 8.2: Light wave

The “Principle of Optical Interference” explains that there are two types of
optical interference:
• Destructive Interference, and
• Constructive Interference.
Destructive interference occurs when the light waves are traveling out of
phase with each other. When this occurs the peak of the wave is lined up
with the trough of another wave and they virtually cancel each other out.

Fig. 8.3: Destructive interference

With constructive interference we have the opposite effect happening.
In this case the light waves are traveling in phase with each other so that
the peaks and troughs of one wave line up with the peaks and troughs of
another wave. They are now working together creating one larger wave.