الالوان - الضوء .. الفيزياء

Colors - Light .. Physics

Colors

The speed of light changes within a material medium (as well as in free space) according to the difference in its wavelength, and therefore the value of the refractive index varies according to the wavelength, as it increases in the event of a decrease.

As a result, when a narrow light beam penetrates a certain medium - a glass prism, for example - it is divided into components of different colors, the amount of its refraction gradually increases, starting from red light to violet light.

Despite the division of light into its colored components, mixing these components in specific proportions is sufficient to give white light again.

It is sufficient to mix three lights, including red, green and blue, which give the best combination.
And obtaining any color is done by mixing these three colors in an appropriate way. This is the principle of color photography and color television as well.
For example, yellow light is composed of mixing green light with red light.

It is known that matter absorbs the light waves that penetrate it in degrees that vary in value according to the wavelength itself, and that a colored body reflects a portion of the spectrum of light falling on it and absorbs what it selects from the remaining part of it. As for the color of the body as seen by the eye, it is determined by the wavelength of the light reflected on it. It is also known that a white body reflects all waves, while a black body absorbs them all. If we take a red carpet, for example, and illuminate it with green light, it will appear black to us because it absorbs this green light and does not reflect any part of it at all. It is worth noting here that mixing colored pigments, such as paints and coatings, is different from mixing colored lights. The color resulting from mixing lights is nothing but the sum of all the colors in them. As for the pigment in paints, it absorbs a portion of the spectrum and does not reflect its own color. A mixture of pigments can absorb (or subtract) all the waves appropriate to its composition. A specific color is obtained by mixing the following pigments: red, yellow, blue, and white.

Selecting the reflection contributes to generating the colors of dark objects.

(Above) White light is divided into its composite colors by a prism (Down) What results from mixing lights and mixing pigments.