• Optics
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  • Princ. of Geometrical Optics
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  • Colors

Color is a property of light related to its frequency. The human eye is able to see only a specific range of all possible frequencies of light, this range is known as the visible spectrum.


Illustration of a prism, an optical instrument that is able to disassemble white light into its different colors (frequencies) through the refraction phenomenon.

Light, for its colors, is categorized as:

Monochromatic Light
It is the light of a single color, i.e., frequency.
Polychromatic Light
The light made of two or more colors (frequencies).
Primary Colors
They are: red, green and blue. They are considered primary because it is the combination of these three colors, of all others, which can produce the widest range of composite colors.
Complementary Colors
They are two colors that when combined give white. So that our eye has the sensation of white, it is not necessary to mix all the colors of the spectrum. Examples: yellow and blue; red and bluish green; green and purple.

The white light emitted by the sun or a light bulb consists of a multitude of monochromatic colors, which can be divided into seven main colors:


Objects Colors

The color of an opaque object depends on: a) color (frequency) of the light that it reflects diffusely to the observer's eye and b) color (frequency) of the light incident on it.

White Body
It is one that reflects all the light beams.
Black Body
It is one that absorbs all the light beams.
Colored Body
It is one that absorbs all colors except one. For example, an object is considered to be red when the red color is reflected and all other colors are absorbed. However, consider a red object illuminated by a blue light (frequency in the blue range). In this case, the red object appears to be black, because there is no red light to be reflected by it.

Color Filters

The color of transparent objects (filters) depends on the color of the light they transmit. The green glass (transparent) absorbs all colors but green, which is transmitted. For making objects with different colors, pigments are used, which are small grains that, according to their nature, absorb a certain color of light. Therefore, pigments subtract a composed incident light, a certain color. An object sends to our eyes the colors that their pigments cannot absorb. With this, we can "subtract" the color of an object.

The Subtractive Process of Colored Lights
It is related to the removal of part of the light falling on an object, which in turn depends on the pigments that are deposited in the body.


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