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To human eyes, the world at night is a formless canvas of grey.
人眼看见的夜间世界是个隐约的灰色帆布。
Many nocturnal animals, on the other hand, experience a rich and varied world bursting with details, shapes, and colors.
另一方面，许多夜行动物体验有着丰富细节、形状、颜色，多姿多彩的世界。
What is it, then, that separates moths from men?
人与飞蛾的差异是什么呢？
Moths and many other nocturnal animals see at night because their eyes are adapted to compensate for the lack of light.
飞蛾和其他许多夜行动物夜里能看得见，是因为它们的眼睛已经适应，弥补了光线的不足。
All eyes, whether nocturnal or not, depend on photoreceptors in the retina to detect light particles, known as photons.
无论是否是夜行的动物，所有的眼睛都靠视网膜的受光体，来侦测光的粒子，称为光子。
Photoreceptors then report information about these photons to other cells in the retina and brain.
受光体把光子的信息传给视网膜的其他细胞和大脑。
The brain sifts through that information and uses it to build up an image of the environment the eye perceives.
大脑筛选信息，用来建立眼睛感知的环境形象。
The brighter the light is, the more photons hit the eye.
光越亮，就有越多的光子进入眼睛。
On a sunny day, upwards of 100 million times more photons are available to the eye than on a cloudy, moonless night.
在阳光明媚的日子，眼睛接收到的光子是无月阴夜的数亿倍。
Photons aren't just less numerous in darkness, but they also hit the eye in a less reliable way.
在黑暗中，不只光子的数量少很多，光子进入眼睛的方式也不可靠。
This means the information that photoreceptors collect will vary over time, as will the quality of the image.
这意味着受光体接收的信息会随时间而变化，改变图像的质量。
In darkness, trying to detect the sparse scattering of randomly arriving photons
在黑暗中，试图侦测稀疏、随机抵达的散射光子，
is too difficult for the eyes of most daytime animals.
对于大部分的白天动物而言，太困难了。
But for night creatures, it's just a matter of adaptation.
但对于夜间生物而言，只是个适应的问题。
One of these adaptations is size.
其中之一的适应机制是眼睛的大小。
Take the tarsier, whose eyeballs are each as big as its brain,
以眼镜猴为例，眼球和脑一般大，
giving it the biggest eyes compared to head size of all mammals.
它的眼头比例是所有哺乳动物中最大的。
If humans had the same brain to eye ratio, our eyes would be the size of grapefruits.
如果人类有同样的脑眼比例，我们的眼睛将会大如葡萄柚。
The tarsier's enlarged orbs haven't evolved to make it cuter, however, but to gather as much light as possible.
眼镜猴演化的大眼球，不是为使它变得可爱，而是要尽可能地多收集光子。
Bigger eyes can have larger openings, called pupils, and larger lenses,
大的眼睛有更大的开口，也就是瞳孔，和更大的镜头，
allowing for more light to be focused on the receptors.
允许更多的光聚焦在受光体上。
While tarsiers scan the nocturnal scene with their enormous peepers, cats use gleaming eyes to do the same.
眼镜猴以巨大的眼睛扫描夜景，而猫用的是闪闪发亮的眼睛。
Cats' eyes get their shine from a structure called the tapetum lucidum that sits behind the photoreceptors.
猫眼的亮光来自照膜这个结构，位于受光体的后方。
This structure is made from layers of mirror-like cells containing crystals
这个结构由层层含有像镜子模样、晶体结构的细胞所组成，
that send incoming light bouncing back towards the photoreceptors and out of the eye.
把射入光反弹给受光体，然后从眼睛出去。
This results in an eerie glow, and it also gives the photoreceptors a second chance to detect photons.
如此产生了诡异的亮光，并给受光体二次侦测光子的机会。
In fact, this system has inspired the artificial cats' eyes we use on our roads.
事实上，猫眼启发我们设计出嵌在马路上的反光人工猫眼。
Toads, on the other hand, have adapted to take it slow.
另一方面，蟾蜍适应了放慢的节奏。
They can form an image even when just a single photon hits each photoreceptor per second.
它们能看见成形的图像，即使其受光体每秒只收到一粒光子。
They accomplish this with photoreceptors that are more than 25 times slower than human ones.
它们利用比人类慢25倍以上的受光体来完成这一过程。
This means toads can collect photons for up to four seconds,
意味着它收集光子的间隔长达4秒，
allowing them to gather many more than our eyes do at each visual time interval.
使得眼睛能在每个间隔4秒的视觉时间里比人收集更多的光子。
The downside is that this causes toads to react very slowly
缺点是使得蟾蜍反应迟缓，
because they're only receiving an updated image every four seconds.
因为每四秒才更新一次图像。
Fortunately, they're accustomed to targeting sluggish prey.
还好它们习惯猎食动作缓慢的猎物。
Meanwhile, the night is also buzzing with insects, such as hawk moths,
同时，夜间嗡嗡飞着的昆虫，如鹰蛾，
which can see their favorite flowers in color, even on a starlit night.
能看到喜爱的花朵色彩，即使在只有星光照明的夜空。
They achieve this by a surprising move -- getting rid of details in their visual perception.
它们通过异乎寻常的演化：省略细节的受光体。
Information from neighboring photoreceptors is grouped in their brains,
邻近的受光体所接收的信息在脑里组合成群，
so the photon catch of each group is higher compared to individual receptors.
因此每个群组捕获的光子较个别受光体的更多。
However, grouping photoreceptors loses details in the image,
然而，群组的受光体损失了图像的细节，
as fine details require a fine grid of photoreceptors, each detecting photons from one small point in space.
因为更多的细节需要更细密的受光体网络，网络的每一点都要有受光体。
The trick is to balance the need for photons with the loss of detail to still find their flowers.
关键是要平衡细节与光子数目，让它仍能找到花朵。
Whether eyes are slow, enormous, shiny, or coarse,
无论眼睛是缓慢的、巨大的、有光的，或粗糙的，
it's the combination of these biological adaptations that gives nocturnal animals their unique visual powers.
这些生物适应的组合给予夜行动物独特的视觉能力。
Imagine what it might be like to witness through their eyes the world that wakes up when the Sun goes down.
想象一下通过它们的眼睛看到太阳下山后的苏醒世界是什么样子。
