Colors

Colors are very important for those who work in the textile industry. Managing the consistency of colors in products is a serious matter. What exactly are these colors? What lies beneath the surface of something appearing to be red or blue?

The way the human eye perceives colors is a complicated mechanism, which takes place in the cerebral cortex and the nervous system. Put in a simple way, eyes transmit light to the brain through the optic nerves and the brain analyzes the image. The interesting fact here is that all people perceive the same image differently since the construction their brain and eyes are different with their own distinctive DNA structure. So it is important to understand that each person perceives a color a bit differently, although there is just one color in front of him or her.

What are the principle colors? Sunlight or artificial light is composed of various waves. Classified by the length of each wave, it is composed of electromagnetic wave, infrared ray, visible light, ultraviolet ray, x-ray, and gamma ray. The electromagnetic wave is used for radio, radar, and microwave oven. The wavelength that human eyes can perceive is from 390 nm (nanometers) to 700 nm and it is called visible light.

Human eyes cannot perceive waves with lengths shorter than 390 nm because these waves have very low energy. Waves with lengths beyond 700 nm are invisible because human eyes cannot transmit these. The amount of energy in waves increases as the wavelength shortens. The ultraviolet rays can seriously damage the human body. X-rays can penetrate certain parts of the body and gamma rays can easily penetrate all parts. Gamma rays can disturb the molecular structure of the human body with its high energy. When we look at the sun, more than a billion neutrinos penetrate the body in a second. Fortunately, neutrinos are not harmful because their energy is extremely low.

When a ray of visible light is transmitted through the spectrum, it is divided into seven colors with different wavelength. So when sunlight hits our eyes, optic nerves perceive the wavelength of each color and signal the brain. The shortest wave in visible light is purple and the longest is red. The human eye cannot see the waves beyond these, ultraviolet and infrared.

Visible light waves hit the cornea about 600 billion times each second. Since the velocity of light is 300,000,000cm per second, the wavelength of visible light is be 500 nm.

The frequency for red and purple rays is approximately 460 trillion per second and 760 trillion per second, respectively. Each color has a specific wavelength and frequency. With these exact values of waves called natural frequency, visually impaired would be able to actually feel each color.

Why do human eyes can see only visible light? Each object has different preferred frequency and wavelength of light waves. These take on different colors. Most natural elements on Earth do not absorb visible light. But waves such as gamma rays are absorbed by all elements, including air. Therefore, gamma rays vanish in the air. How fortunate it is! If human eyes could perceive gamma rays or objects on Earth received these rays, all materials would appear black.

A ray of sunlight is mostly visible light. Stars with high temperature radiate mainly ultraviolet rays. Stars with low temperature radiate infrared rays. A black hole radiates x-rays, which allow scientists to detect and confirm their existence.

What does mean for an object to have a specific color? Every object has a specific range of visible light that it can absorb. This determines the object’s color. The color of an object that we see is the complementary color of light that it absorbs. The composition of the reflected light is seen. For an example, a red tomato absorbs the waves near 500 nm that come under green and blue areas of visible light. So it appears red, the complementary color of green and blue. Simply, reflecting blue and green makes a red tomato.

The primary colors are Red, Green and Blue. With these three colors, every other color in nature can be created. The picture on television screen is composed by the three primary colors. It is made of several thousands of very tiny dots in red, green, and blue.

The color of most plants are green because photosynthesis requires red color. The plant’s chlorophylls absorb red waves of sunlight and reflect other colors.

Certain objects reflect sunlight entirely. In this case, the color appears white. On the other hand, objects look black if they absorb all rays of sunlight. If a certain object appears blacker, it has higher rate of absorption. The most blackish object is the black velvet. Velvet reflects only few percentage of visible light due to its piles. However, smooth surface of a black object makes it appear less black by reflecting some colors. A black object with rough surface would not reflect much light and would appear more blackish. The degree of whiteness or blackness is not a matter of color but the percentage of reflection. The brightest white object in the nature is clean snow. But even snow reflects the only 75% visible light.

The reason why the sky looks blue is that the air scatters blue waves invisible light. This is the same reason why ocean is blue. Looking up at the sky from the moon appears black since it has no atmosphere. In Mars, it is red since the planet has a thin atmosphere. Venus has bright blue sky since its atmosphere is 90 times that of Earth. Even on a rainy day, the average temperature of the surface is 480℃.

Chroma measures the purity of color. Chroma value would be high if the level of the absorbed colors is low in the reflected color ray. For instance, pure red should not have blue ray in it. If red is mixed with bluish green, it would appear gray with the purity of red lowered. Color with high chroma looks brighter and color with low chroma looks duller.

Lightness is the index of light level received by the eyes. It is measured from 0 to 10. Lightness of white is 10 and that of black is 0. With hue and chroma fixed, high value in lightness makes the color appear lighter and low value in lightness makes it appear darker.

The reason that dyes show a specific color is due to the chromophoric group in its molecular structure. The chromophore absorbs the specific waves of the spectrum and reflects others. It is connected with the unsaturated double bond of the chromophore and the absorption of the photon. The typical chromophorics are Azo, Azoxy, Nitroso and Quinoid. And auxochrome makes dyes brighter or aids its bondingwith fibers. Sometimes, colors could be changed by auxochrome. Well-known auxochromes are Amine, Alkoxy, Hydroxyl, Sulfone.