“On a sunny day, upwards of 100 million times more photons are available to the eye than on a cloudy, moonless night. Photons aren’t just less numerous in darkness, but they also hit the eye in a less reliable way. This means the information that photoreceptors collect will vary over time, as will the quality of the image.”
“In darkness, trying to detect the sparse scattering of randomly arriving photons is too difficult for the eyes of most daytime animals. But for night creatures, it’s just a matter of adaptation. One of these adaptations is size.
“Take the tarsier, whose eyeballs are each as big as its brain, giving it the biggest eyes compared to head size of all mammals. If humans had the same brain to eye ratio, our eyes would be the size of grapefruits. The tarsier’s enlarged orbs haven’t evolved to make it cuter, however, but to gather as much light as possible.”
Learn more about eyes in these videos:
• Animals with night vision
• How do animal eyes see the world?
• Why do cats have vertical pupils?
• Why do goats have rectangular pupils?
• The case of the green-eyed squid