Are there restrictions for the eyes?

Think about whether you can distinguish 1 million colors, recognize a single photon, look as far as the nearby galaxy. That was great enough!

Discover the unexpected limits of human eyes

Look around the room, what do you see? Colors, walls, windows . everything seems obvious and they are there. It's strange to wonder how we can use sight to perceive our surroundings. In fact, this process is the reflection of light particles - photons from objects on our eyeballs.

When light particles reach 126 million photosensitive cells on the retina, their energy is translated by the brain and we will sense the shape, color, and brightness of the object and this will Create the world seen around us.

Are there restrictions for the eyes?

What the eyes are doing is amazing! However, our sense of vision is obviously not without limitations. We can't see radio waves emitted from electronic devices, can't see millions of bacteria in the palm. With the advances of Physics and Biology, we can now test and know what are the limits for human's natural vision. 'There will be a threshold for what you can see, a level you can reach, and then you can't see anything,' said Michael Landy, professor of psychology and neurology. from New York University said.

Color

The first limit that people care about when it comes to thinking is color. How do we feel colors? Our eyes have two types of light receptors: cones and rods . Rodent receptors handle chromatic factors such as different states of gray. They are the main active receptors to create night vision when the light is weak.

In contrast, cone receptors operate with daylight and color perception. Here, you should note that colors and colors are two different concepts even though we often call them together as a 'color '. The colors are distinguished by the wavelength of light they reflect to the eye. As we have blue, yellow, red . And the shades are distinguished by the intensity of light as we have light green, dark green, shades of gray .

Conical and rod cells help us to perceive colors

When the pigment molecules on the retina absorb the energy of the photons, they generate an electrical impulse. That signal passes through the optic nerve to the brain, where color perception is created.

Because we have 3 types of cones with corresponding pigment molecules. Each type is sensitive to a photon wavelength and is named S, M, L with short, medium and long wavelengths. Short wavelength cones give us a sense of green reclining, in contrast to long-wavelength cone cells that turn red. Combining all three types of cells allows us to recognize all seven colors of the rainbow. ' All colors we see come from a mixture of many wavelengths of light,' Landy said.

However, that is only a small part.Seven colors of light that we feel are only in wavelengths from 280-720nm. Longer wavelength photons such as infrared, radio and shorter wavelengths like X-rays and ultraviolet rays are outside this spectrum. So that's why we can't see them.

Sunlight contains lots of ultraviolet rays but we cannot receive them

Not without special cases. Some people have a syndrome called Aphakia, they can see ultraviolet rays. Aphakia is a condition in which the lens of the eye may be deficient due to surgical or congenital effects. The missing part has UV blocking effect. When they are lost, they can see wavelengths of up to 300nm, and they sense them blue-white.

How many colors can we see?

As analyzed, a normal person has 3 types of cone receptor cells in the eye. Each cell can do the task of analyzing 100 different shades of color. Therefore, most researchers think that we can distinguish about 1 million different colors. However, color perception is a subjective factor and varies from person to person. An exact number is difficult to give.

'There won't be a specific number ,' said Kimberly Jameson, a researcher from the University of California, Irvine. 'This person's ability to distinguish colors may be only a small part of others'.
Jameson didn't say too much. She is working with people in 'tetrachromats' condition . They have a fourth conical cell, which gives them the ability to distinguish up to 100 million colors. In contrast, people with color blindness only have 2 cones and can only distinguish 10,000 colors.

How many photons do we need to see?

Cones usually need more light to work than rod cells. That's why when light is low, we no longer feel the colors as best as we can. In the ideal conditions of a laboratory, a small number of photons can also activate cones.

However, rod cells do better than that. In 1940, an experiment showed that even a single light photon could be enough to create awareness. 'Everyone can be aware of 1 photon,' said Brian Wandell, Stanford professor of psychology and electrical engineering.

Later in 1941, researchers at Columbia University conducted an experiment. They led volunteers into a dark room and monitored the adjustment of rod cells. It will take a few minutes for them to achieve sensitivity. That is why we have trouble with our eyes when suddenly the room at night has a power outage.

The researchers then flashed a blue light in front of the volunteer. They calculated that 54 photons were enough for the volunteers to discover the event. After compensating for the light absorption of the parts of the eye, the results show that 5 photons will activate 5 rods and cause awareness of the candidate's event.

Where is the smallest and the longest distance we can see?

This may surprise you. There is no limit to the smallest or the longest distance we can see. As long as that object is any size and distance that reflects photons into the retina, we can recognize them.

In common literature, for example, you can see a candle 48 kilometers away in the dark night like ink. In fact, the night is always filled with photons and there will be no dark night like ink.Light photons scatter in space and are lost on their distance to the eye so they make vision limited.

We can look beyond infinity

Examples of infinity of vision are very close. We have the ability to see stars about 28 trillion kilometers from the nearest us. All the stars stand alone in the night sky coming from our galaxy Milky Way. We can still see objects in the Andromeda galaxy, 2.5 million light-years from Earth. Photons have traveled over a very long distance and reached the retina. So magical!
How clear can we look?

Although we see the Andromeda galaxy, we cannot distinguish each individual star in it. The resolution limits of vision are mentioned in this case. It is the ability to distinguish details such as a point or a line they do not blur together. Therefore, you can also think about the resolution of eyesight as separate pixels that we distinguish.

Ability to distinguish isolated black and white points in the vision test

Several factors affect the resolution of the eye. For example, the number and distance between cones and rods on the retina. In theory, the researchers showed that we have 120 pixels on each retina arc.

In vision test at ophthalmology clinic. You will see smaller letters. The doctor will measure at any point you cannot distinguish white or black gaps. For example, you can no longer distinguish the letter F or the letter P. There are documents showing that the human eye has a resolution of about a 576 Megapixel camera. The resolution limit is the reason we cannot see the bacteria on our hands with the microphone size.

In short, nature has favored people with a bad vision. Despite its limitations. However, think about whether you can distinguish 1 million colors, recognize a single photon, look as far as the nearby galaxy. That was great enough!