Ultraviolet rays are invisible to most humans. The lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. Humans also lack color receptor adaptations for ultraviolet rays. Nevertheless, the photoreceptors of the retina are sensitive to near-UV, and people lacking a lens (a condition known as aphakia) perceive near-UV as whitish-blue or whitish-violet. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm.Near-UV radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.
紫外线是大多数人看不见的。人眼的晶状体会阻挡300-400 nm波长范围内的大部分辐射；较短的波长被角膜阻挡。人类还缺乏针对紫外线的颜色受体适应性。然而，光感受器的的视网膜是近紫外光敏感，缺乏一个镜头（被称为条件的人无晶体眼）认为近紫外发白的蓝色或白色，紫色。在某些情况下，儿童和年轻人可以看到低至约310 nm波长的紫外线。昆虫，某些哺乳动物和鸟类可以看到近紫外线辐射。小型鸟类具有紫外线的第四种颜色接收器。这使鸟类具有“真正的”紫外线视力
