红外线下每个人看起来都青面獠牙

Like humans, most animals rely on visible light for seeing, and plants rely on it for photosynthesis. In addition to the light that's visible to us, the sun also radiates ultraviolet and infrared light.
和人类一样，大多数的动物需要依赖可见光才能看见东西，而植物则需要光来进行光合作用。除了可见光，太阳的辐射还包含紫外线和红外线。

Snakes have infrared sensors, and bees can see some ultraviolet light, but they're among the few exceptions to the rule. Why are we earth dwellers so attuned to visible light, instead of some other segment of the spectrum?
蛇可以感知红外线，蜜蜂可以看到部分紫外线，但是它们都属于极个别的情况。为什么地球生物的眼睛都对可见光如此情有独钟却对其他光线“视而不见”呢？

Why Don't We See Ultraviolet Or Infrared?
为什么我们看不见紫外线和红外线？

The traditional answer to this question was that most of the sun's radiation is visible light, so our eyes evolved to see those wavelengths. However, the sun also gives off a whole lot of infrared radiation. What would it be like if our eyes evolved to see infrared light?
一般对这一问题的回答是：大多数的太阳光都是可见光，所以我们的眼睛在进化过程中已经形成了选择性偏好。然而，太阳的不可见光辐射也不在少数，要是我们眼睛能够进化成可见其他光线会是什么景象？

If we could see infrared, the sky would appear dark, and grass and trees very bright. Our veins would shine darkly through our skin, and warm blooded creatures would be very easy to spot. That would be a great advantage not only for predators on the prowl, but also escaping prey.
如果我们能看见红外线，天空会看起来颜色暗淡，而绿草和树木则会非常明亮。我们的血管会在皮肤之下闪着暗暗的光，温血动物会非常醒目。无论对于捕猎者还是猎物来说，这都会成为一项极大优势。

Visible Light
可见光

No one knows for sure why animals and plants on earth evolved to perceive visible light, rather than infrared. One theory is that maybe there's no biochemical reaction that would allow us to translate infrared light into a visual image we can perceive, as we do with visible light. Or, maybe evolution just hasn't found it yet.
没有人能够解释为什么地球生物在进化过程中形成了对可见光的青睐。有理论称，大概是因为不存在能够使我们将不可见光可视化的生物化学反应，或者，可能还没进化到那个阶段吧。