Why does a high speed rotating fan see every blade clearly when it is lit at night?

The cool of summer sometimes makes their work less efficient, if there is an electric fan or air conditioner on the side to cool down the environment we are in, it is also very good, many people have found a fan that rotates at high speed, why can you see clearly at each blade of the light at night? That's because our eyes have to see through the reflected light of the object into the eye, and the light produced by the electric light is not continuous, so we see the leaves very clearly in the light at night. Let's find out why.

First of all, we know that all the objects we see with our eyes are a process that enters our eyes through the reflection of light, without a light source, it is difficult for us to see an object clearly, and it is difficult to see its blades clearly when the fan rotates rapidly during the day, that is because under the continuous irradiation of sunlight, the frequency that our eyes see is not the same as the frequency of the blade rotation, so it is difficult for us to see the rotating blade clearly, and we can only see a circular trajectory. So the light source at night is the energy-saving lamp above our heads, this kind of light we can't see with our eyes is an intermittent light source, if we shoot this light with a high-speed camera, we can see that it is intermittent bright light, but our eyes can't feel it. <>

It is the factor of the light source that causes the electric fan blades we see in the daylight to present a face, and the light source generated at night is not continuous because of the alternating current frequency, and the rotating blades can be clearly seen when we see the light hitting the blades with similar frequencies at night, which is why we see the blades at night, not only at night, but also during the day when we can use the powerful camera to take pictures instantaneously and clearly see the blades. <>

Therefore, our eyes sometimes "deceive" ourselves, and we must treat the interesting scientific events around us with a scientific attitude, so that our lives will not be boring.

Visual persistence is a property of the human eye that is a response to the phenomenon of retinal light retention in the eye. The human retina is sensitive to light to be able to see objects. However, when the light of an object reaches the human retina, it forms an image and is input into the human brain by the optic nerve, making the person feel the appearance of the object.

This feeling does not suddenly disappear as the object is removed, but remains for a certain period of time, which is the phenomenon of visual retention. This phenomenon is due to the fact that retinal photosensitive imaging and optic nerve transmission take a certain amount of time, and it is also the result of long-term human evolution. <>

Studies have shown that this phenomenon of visual persistence lasts for seconds. It is this effect that allows people to see not only the blades of the fan, but also the blades of the propellers of the aircraft, and sometimes the propellers of the aircraft seem to stop or even turn upside down. But to see this phenomenon, the speed of the object must be suitable for the reaction characteristics of the human eye and the human brain, and it is not good to be fast or slow.

This phenomenon has been studied for almost 300 years. This phenomenon was first proposed by Pete Mark Rogett, a professor at the University of London, who described it in his 1824 study "The Visual Persistence of Moving Objects". Later, many scientists studied this phenomenon and it was quite controversial.

In an article by William Benjamin Carpenter in 1868, he argued that the motion effect in the so-called "optical toy" was caused by the residual image on the retina, and that this hallucinatory effect was due to "spirit" rather than "retinal phenomenon".

The high-speed rotating fan can see clearly at the light at night, and every blade is clearly visible, which is physically called the strobe phenomenon. That is, the frequency of the general light is 50Hz, and when the frequency of the fan rotation is a multiple of 50, there will be a strobe phenomenon, that is, the phenomenon that the fan blades seem to stop moving. This is because the fan blades are in the same position at the moment the light is illuminated, while the fan blades are in the same position when the light is not on.

If it is illuminated with a DC light, this phenomenon will not occur.

Because the speed of the fan is not as fast as the speed of light, the light of the light passes through the gap between the fan blades very quickly, much faster than the speed of the fan, so people can see each fan blade.

Because of the frequency of alternating current used in our lights, the light source generated is not continuous.

The light under the light is very clear, when the fan blades are rotating, although it is rotating at high speed, but it can be seen clearly through the refraction of light.

The fan is generally three-bladed, and when the light is turned on at night, the three-leaf entity will be reflected by the light on the wall, and it will be clearly displayed.

Because the lights are constantly refreshed and don't shine all the time like the sun. As a result, every blade can be seen clearly.

This is a typical phenomenon of my eyes "deceiving" me, which is scientifically known as "visual stopping", which is a phenomenon of visual delay.