describes light that has a wavelength which is after the violet (= light purple ) end of the range of colours that can be seen by humans . Light of this type causes the skin to become darker in the sun .
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例句
1. It's called ultraviolet rays. 它被叫做紫外线。 2. The sun's ultraviolet rays are responsible for both tanning and burning. 阳光中的紫外线是皮肤晒黑和灼伤的根源。