When and how was visible light discovered

Visible light

Only a very small area of ​​the electromagnetic spectrum is visible to the human eye. All the colors of the rainbow belong to it.

In the seventeenth century, the English physicist Isaac Newton let sunlight fall on a prism. On a screen he could see the colors of the rainbow. His conclusion: white light is composed of all colors.

Red light has a wavelength of about 750 billionths of a meter (750 nanometers); Violet corresponds to about 400 nanometers. The rest of the colors are in between. Visible light is given off by atoms when the outermost electrons change their orbit around the nucleus and lose energy in the process.

Why do we see light of all things?

It is nowhere near that the Earth's atmosphere allows all radiation from the sun to pass through. But this is the case for the range of visible light: the atmosphere is permeable, especially in that section of the spectrum in which the sun radiates almost half of its energy.

But not only the atmosphere, but also water is transparent to visible light. This is the only reason why light can reach the retina through our eyes, which are largely made up of water. According to the theory of evolution, one can now assume that our eyes have adapted to these “light windows” of the atmosphere and water over the course of millions of years in order to be receptive to the radiation that is most abundant.

How is a rainbow created?

Rainbow

Raindrops can break down sunlight into its colorful components. Because at the boundary between two translucent materials such as air and water, rays of light are refracted, i.e. the ray of light makes a kink. How much the light changes direction depends on its color: red rays are not deflected as much as blue rays.

When it rains and the sun shines at the same time, light falls on the raindrops. Rays of light enter the drops, are reflected on the inside and exit again. Because the colors contained in the white sunlight are refracted to different degrees when entering and exiting the drops, they are deflected differently and the result is a colored rainbow.