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Why Does Sunlight Fade Colors?

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It’s an undeniable fact that exposure to sunlight causes colors to fade, giving the material a dull appearance. While it’s easy to think that the sun burns away the colors causing them to lose their sheen, that’s hardly the case.

Sunlight causes colors to fade by initiating photodegradation, a process that causes irreversible changes to molecules and compounds that give a material its color. The changes cause the fabric to lose the ability to absorb and reflect visible light at a specific wavelength.

The rest of the article will explore a few topics related to this question in detail, including what comprises colors, the role of sunlight in fading colors, the mechanism of fading colors, and the composition of the sun’s energy.

Why does sunlight fade colors

What Comprises Color?

It isn’t easy to imagine a world without colors as they inject an element of beauty into our surroundings. But where do colors come from?

To answer this question, you need to understand how matter interacts with light. When you say something is colored, it means that the object reflects the light in specific wavelengths more strongly while absorbing the rest of it.

Each material gets its color from chromophores, regions in its molecular structure that absorb photons of visible light at defined wavelengths.

Since most objects can’t absorb all the photons, they reflect what they reflect the rest of the light energy. The wavelengths of the reflected photons determine the color the human eye can see.

The properties of an object determine which wavelengths are absorbed and reflected.

Why Does Sunlight Fade Colors?

While everything is made of atoms and electrons, the number of atoms and electron configuration gives each substance its unique characteristics.

How each substance behaves in the presence of light affects how it’s perceived by the human eye, i.e., its color.

When light interacts with an object, one or more of these actions take place:

  • Scattering and reflection. Reflective materials have a higher number of free electrons. Instead of absorbing light energy, the electrons vibrate and send out the light energy at the same frequency.
  • Absorption. In opaque materials, the electrons have almost the same vibrational frequency as the incoming light. As a result, the electrons absorb much of the incoming energy.
  • Transmission. If the light energy is way higher or much lower than the vibration frequency of the electrons of a material, the light passes unchanged. That’s why objects such as glass appear transparent to the human eye.
  • Refraction. If the light energy and the electron vibration frequency in a material match, the light penetrates deep into the material. It causes tiny vibrations that cause the electron to vibrate at the same frequency as the light source. That gives the light inside the material a bent look, as is the case of straw in a glass.

The light receptors in the human eye, coupled with the brain, translate the visible light into color. This Ted-Ed video explains how the human eye sees color:


How Does Sunlight Affect Colors?

As discussed above, the color of an object is simply the range of wavelength it reflects the most. When chromophore absorbs photons of light, it excites the electrons, causing them to enter a higher energy state.

In most cases, the electrons give off the extra energy as heat and return to their original state endlessly. However, during a high energy state, an excited molecule can undergo a chemical reaction. The reaction can break covalent bonds or cause two molecules to react irreversibly.

Sunlight provides a consistent supply of high-energy photons. Constant exposure to these photons leads to an avalanche of chemical reactions.

The chemical reactions damage the structure of the chromophores, effectively altering the material’s ability to emit light at specific wavelengths.

Red colors are more susceptible to fading because their molecules absorb shorter wavelengths, which are the higher energy light.

Red materials also absorb a lot of photons of ultraviolet light, which also have higher energy.

A high amount of available energy triggers more chemical reactions. In turn, this causes the chromophores to degrade faster. Consequently, red-colored materials tend to fade quickly. The UV wavelengths have more energy, which is why UV-B rays have been linked to skin cancer.

Sun’s Composition

While the sun is more than 150 million kilometers above the earth, it provides enough heat and light to sustain life. Sun’s energy arrives on earth as electromagnetic radiation. The radiation is transmitted in waves at different frequencies and wavelengths.

The electromagnetic spectrum describes the distribution of the seven types of radiation from the sun over a color spectrum.

The light spectrum is measured by the size of the wavelengths—the distance between two peaks—in nanometers.

Electromagnetic radiation is arranged in the order of decreasing wavelength and increasing frequency and energy:

  1. Radio waves (long wavelengths)
  2. Microwaves
  3. Infrared (IR)
  4. Visible light
  5. Ultraviolet light  
  6. X-rays
  7. Gamma-rays (small wavelength)

Sunlight contains three distinct spectral components—infrared radiation, ultraviolet rays, and visible light spectrum. Each of these components is distinguishable by their specific wavelength ranges:

  • Infrared radiation is invisible to the human eye. It starts at the edge of the visible spectrum. It has some of the longest wavelengths, ranging from 700 nm to 4045 nm. Infrared is associated with heat since hot objects emit such radiation.
  • The human eye is only sensitive to the visible light spectrum. The visible spectrum extends from 380 nm to 780 nm. Visible light progresses from blue to green to yellow to orange to red. Blue is the most energetic color, and the energy levels decrease systematically across the spectrum.
  • Ultraviolet rays are invisible to the human eye. They cover an invisible part of the electromagnetic spectrum, ranging from 100 to 400 nm and consist of three bands: UVA, UVB, and UVC.

Of the three spectral components of the sun’s energy, ultraviolet is the most significant factor in fading colors.

Why Does Sunlight Fade Colors?

Ultraviolet Radiation Rays

Ultraviolet, which comprises three bands, is the most damaging form of sun’s radiation. Each of the bands represents a different tier of wavelength size.

UV-A denotes the largest ultraviolet wavelengths and represents the bulk of UV rays reaching the earth. They range from 315 nm to 400 nm. These rays penetrate deep into the human skin, causing premature aging and wrinkle formation.

UV-B rays are the medium wavelengths of the UV spectrum and are particularly dangerous. UV-B rays cause sunburn and cause skin cancer. Fortunately, the atmosphere absorbs up to 98% of the carcinogenic UV-B rays, leaving only 2% to reach the earth.

UV-C rays have the smallest UV wavelengths, measuring 100 nm to 280 nm. Most of the UV-C rays don’t reach the earth as they are absorbed by the ozone layer and the earth’s atmosphere.

Together, UV-A and UV-B rays have the most damaging effects on colors, materials, and human skin. They comprise the integrity of dye pigments and other materials, causing them to fade and disintegrate.

The two UV rays also disrupt the integrity of the DNA in the human skin, increasing the risk of skin cancer.

Conclusion

Technically, sunlight comprises radiation energy, and frequent exposure of a material to this energy causes changes at the molecular level.

The radiation energy damages the structure of chromophores, the regions that give each material its color. UV rays are the most damaging form of rays from the sun. Once a chromophore is degraded, its ability to absorb and reflect colors is affected. If an object can no longer emit specific colors well, the colors start to fade.

Red materials are the most affected by fading because they tend to absorb a lot of UV rays, which contain a lot of energy.