Optics and colors are related through the phenomena of refraction, reflection and dispersion of light.
What is color?
Among the various phenomena related to light , we can say that refraction and diffuse reflection of light are largely responsible for our visual perception of objects.
We know that white light coming from the Sun or from a lamp is an electromagnetic wave composed of several other electromagnetic waves , which differ in their wavelength , but which are similar in terms of their propagation speed in a vacuum. Thus, each color is an electromagnetic wave .
Isaac Newton (1642 – 1727) did an experiment in which he made a beam of white light pass through a glass prism . When crossing this prism, this light was refracted, that is, it underwent deviations and was decomposed, so that seven colors could be observed: red, orange, yellow, green, blue, indigo and violet. This set of separate colors is called the spectrum of visible light, because when passing through an inverted prism, the colors come together again, resulting in visible white light.
Isaac Newton performing experiments with light
See the electromagnetic spectrum below and note that the range of visible light is very small, so most radiation is not visible to the human eye .
How do we perceive different colors?
As white light is a composite of all other colors, when we illuminate an object with it and see it, for example, as blue, it is because this object diffusely reflected blue light and absorbed all other light. Otherwise, if we see this object as white, it is because it diffusely reflected all colors. If it is seen as black, it is because the object has absorbed all the colors that fall on it.
Furthermore, we can only see objects that emit light , which are called primary sources of light , or objects that reflect the light they receive . The latter we call secondary sources . Light from secondary sources reaches our eyes, passes through the cornea and reaches the lens , which is the crystalline lens . This lens is thin and convergent and can deform, becoming more or less convergent , as it is connected to the ciliary muscles that contract. The image is formed inverted on the retina and, through the optic nerve, is forwarded to the center of vision , in the brain, where it is interpreted.
The visual receptors in our eyes are the rods and cones . Cones are responsible for color vision (the eye has about 7 million cones); and rods are responsible for night vision , since they are not sensitized by color variations and, therefore, contribute a lot to visual adaptation.
The lack of vitamin A in the body impairs the performance of the rods. This is because their sensitization occurs by the regeneration of a substance called rhodopsin. When the brightness increases too much, the rhodopsin disappears, and when it gets dark, this substance regenerates. If there is vitamin A deficiency , the regeneration of rhodopsin will be impaired, and the individual ends up developing a disease called night blindness.