The human eye is one of evolution's greatest achievements. It can see tiny dust specks and huge mountains, near or far, in full colour. Backed by the processing power of our brains, it can also pick out movement and help us identify the people we love just by their faces.
One of the eye's best tricks is so good, you don't notice it. When you step from the brightly-lit outdoors into a dimly-lit building, the light level drops massively, but your eyes adjust almost immediately. That's because they have evolved to work even when there isn't much light around.
But other species are even better in dim light. Try reading a newspaper in the gloom of twilight, and the black letters will merge with the white background into a smoky greyness that your eyes cannot decipher. However, hand the paper to a cat and it would be fine, or at least it would if it knew how to read.
But even cats, despite their habit of hunting at night, are far from the most light-sensitive animals around. .
To compare how much light animals need to see by, we'll be using lux - the amount of light per square metre. Human eyes work well in bright sunlight, when the illumination can be well over 10,000 lux. We can also see, albeit dimly, in just 1 lux, which is about what you get on a dark night.
Cats have also changed the makeup of their retinas. There are two types of light-sensitive cells there. Cones are colour-sensitive but only work in bright light, while rods only do black-and-white but work in dim light. Humans have lots of cones, giving us rich colour vision in the day, but cats are big on rods. They have 25 rods to each cone, compared to four rods to each cone in humans.
Tarsiers are tree-dwelling primates from South East Asia. They have probably the largest eyes, relative to their body size, of any mammal. A tarsier's body, excluding the tail, is about 9-16 cm. Meanwhile its eyes are 1.5-1.8 cm across, and occupy almost the entire head.
This carpenter bee from the Western Ghats of southern India goes one better. It can even fly on moonless nights, when light intensities are even lower. "They can fly in starlight, on cloudy starlit nights and even when there is a lot of wind.
American cockroach American cockroach
We can't directly compare cockroaches to the other animals, because their vision has been measured in a different way. But it is clear that their eyes are extraordinarily sensitive.less than one photon per second
One of the eye's best tricks is so good, you don't notice it. When you step from the brightly-lit outdoors into a dimly-lit building, the light level drops massively, but your eyes adjust almost immediately. That's because they have evolved to work even when there isn't much light around.
But other species are even better in dim light. Try reading a newspaper in the gloom of twilight, and the black letters will merge with the white background into a smoky greyness that your eyes cannot decipher. However, hand the paper to a cat and it would be fine, or at least it would if it knew how to read.
But even cats, despite their habit of hunting at night, are far from the most light-sensitive animals around. .
To compare how much light animals need to see by, we'll be using lux - the amount of light per square metre. Human eyes work well in bright sunlight, when the illumination can be well over 10,000 lux. We can also see, albeit dimly, in just 1 lux, which is about what you get on a dark night.
Tarsiers are tree-dwelling primates from South East Asia. They have probably the largest eyes, relative to their body size, of any mammal. A tarsier's body, excluding the tail, is about 9-16 cm. Meanwhile its eyes are 1.5-1.8 cm across, and occupy almost the entire head.
We can't directly compare cockroaches to the other animals, because their vision has been measured in a different way. But it is clear that their eyes are extraordinarily sensitive.less than one photon per second
We can't directly compare cockroaches to the other animals, because their vision has been measured in a different way. But it is clear that their eyes are extraordinarily sensitive.
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