In human eyes, retinal cells recognize photons, which are energy particles of light coming from the outside. In particular, there are several types of retinal cells in the eye.
In retinal cells, rod cells are sensitive to a small amount of light, which allows people to identify objects in the dark.
And there are cone cells that recognize Red, Green, and Blue wavelengths in light, respectively.
The signal of light recognized by the retinal cells is transmitted to the brain, which recognizes the color and shape of the object in the brain.
There are also retinal cells (ipRGCs) involved in the regulation of the circadian rhythm. The ipRGCs are very responsive to specific wavelengths (blue light), and the transmitted signal to brain plays important roles to control the rhythm via hormone changes including being alert during daytime and sleeping during nighttime.
These retinal cells are a type of nerve cell that starts visual cognition and can act as a camera film.
Human retinal cells have been able to recognize each wavelength from natural sunlight for over four million years and have played an important role in the maintenance of human circadian rhythm.
Therefore, the wavelength of light and the amount of light exposed to retinal cells will be very important for modern people who spend most of their time indoors.
And the photons, energy particles of light, have a great influence on all kinds of animals and plants on the earth.