In the case of both light and water, a wave is either strengthened or weakened (the interference phenomenon) when it encounters another wave. If two waves with identical waveform and movement come into contact and their crests are superposed (in phase), the crests heights will double. Similarly, superposing each of the troughs creates a trough with twice the depth of the original. When two waves of the same amplitude but 180° phase difference are superposed, the crests of one wave coincide with of the troughs of the other neutralizing the highs and lows and creating a zero amplitude. In the case of light waves, if one crest overlaps another, you will see brighter light. The reverse is true with darker light, which occurs when one trough coincides with a crest.