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Infrared vs Ultraviolet: A Complete Comparison

Infrared and ultraviolet light represent unique forms of radiation that exist just outside the visible spectrum. This guide will examine the key differences between infrared and UV – from the history of their discovery to their applications and hazards. You‘ll learn exactly how these invisible rays compare in terms of origin, energy, wavelength, frequency, uses, and health effects. Read on for a comprehensive overview of infrared vs ultraviolet radiation.

The Discovery of Infrared and Ultraviolet

Our understanding of infrared and ultraviolet light began in the early 19th century with two breakthrough discoveries:

In 1800, British astronomer Sir William Herschel performed an experiment measuring temperatures of different colors created by a prism. He noticed the temperature continued rising beyond the red end of the visible spectrum. Herschel concluded this must represent a new type of invisible radiation, which he termed "infrared."

Just one year later in 1801, German physicist Johann Wilhelm Ritter investigated the opposite end of the spectrum. Using silver chloride paper, he found light beyond violet had the greatest chemical effect. Ritter named these rays "ultra-violet" or "chemical rays."

So while infrared and ultraviolet were identified within 12 months of each other, their unique properties made them the subject of ongoing scientific fascination and inquiry.

William Herschel’s pioneering work with infrared was pivotal to the field of astronomy. It enabled more advanced analysis of stars and galaxies by detecting infrared emissions invisible to the human eye.

Johann Ritter’s discovery of ultraviolet meanwhile revealed new possibilities for chemical analysis and manipulation. Once the chemical effects of ultraviolet were understood, applications like water purification and curing inks became achievable.

Electromagnetic Properties: Wavelength, Frequency, Energy

Infrared and ultraviolet represent neighboring bands of radiation along the electromagnetic spectrum:

Electromagnetic spectrum

Electromagnetic Spectrum

Electromagnetic waves are characterized by their wavelength, frequency, and energy:

  • Wavelength – The distance between successive wave peaks. Determines the energy level of the radiation.
  • Frequency – How often the wave pattern repeats per second. Measured in hertz (Hz).
  • Energy – Related to the wavelength and frequency. Shorter wavelengths and higher frequencies correspond to higher energy waves.

The wavelengths and frequencies of infrared and ultraviolet differ significantly:

Radiation Wavelength Range Frequency Range
Infrared 700 nm – 1 mm 300 GHz – 400 THz
Ultraviolet 10 nm – 400 nm 30 PHz – 800 THz

Wavelength and Frequency Ranges

So in general, infrared has longer wavelengths and lower frequencies than ultraviolet light. This means ultraviolet radiation has higher energy than infrared.

The shorter wavelengths of ultraviolet allow it to penetrate materials and interact with electron orbitals, which infrared’s longer wavelengths cannot achieve. This accounts for many of ultraviolet‘s unique chemical effects.

Nature and Applications of Infrared

Infrared radiation is emitted by molecules and atoms as they undergo rotational-vibrational transitions. This occurs naturally in processes where the components of materials vibrate and rotate, releasing infrared light.

The primary natural source of infrared radiation is heat. Any object above absolute zero emits some level of infrared light. The hotter an object becomes, the more infrared waves it generates. For example, red-hot stovetops can reach over 1000°F and release intense infrared radiation. This allows infrared cameras to visualize hot spots based on infrared emissions.

Hot stove emitting infrared radiation

A Hot Stove Emits High Levels of Infrared Radiation

Infrared light is commonly divided into three sub-regions:

  • Near-infrared – Closest to visible light, primarily used for fiber optic telecommunications.
  • Mid-infrared – Used for applications like thermal imaging, spectroscopy, and missile tracking.
  • Far-infrared – Borders on microwaves, absorbed by gases like carbon dioxide.

Some of the most common uses and applications of infrared radiation include:

  • Night vision goggles – Enhance vision in low light conditions by detecting infrared.
  • Tracking and imaging – Infrared cameras identify heat signatures of people, animals, and objects.
  • Remote controls – Use infrared LEDs to wirelessly send control signals.
  • Heating and cooking – Infrared waves excite molecules and efficiently heat interior of ovens.
  • Meteorology – Measure clouds, humidity, and other weather data by interacting with infrared radiation.
  • Astronomy – Allows observing galaxies, stars, and phenomena emitting infrared light.

So infrared’s properties relating to heat and molecular excitation make it ideal for thermal imaging, spectroscopy, communications, and more.

Hazards and Precautions

The primary hazard associated with infrared radiation is eye damage from high-frequency near-infrared sources. However, most everyday infrared exposure is low energy and does not pose risks.

It’s recommended to avoid staring directly at intense IR emitters like industrial radiant heaters. Welders and glass blowers also sometimes use special IR-filtering goggles to protect from glare. But in general, infrared radiation is considered safe for humans at common environmental levels.

Nature and Effects of Ultraviolet

Unlike infrared, ultraviolet radiation carries sufficient photon energy to ionize atoms. This means it can remove tightly bound electrons from atoms, creating ions.

Ionization alters the chemical properties of materials. It degrades plastics and causes biological damage. These effects make ultraviolet useful for applications like disinfection, but also create hazards for living tissue.

Sun emitting ultraviolet radiation

The Sun Outputs Ultraviolet Radiation

As with infrared, ultraviolet is categorized into wavelength ranges:

  • UVA – Longest UV wavelengths. Able to penetrate skin deeply.
  • UVB – Medium wavelengths. Primarily responsible for sunburn and direct DNA damage.
  • UVC – Shortest UV wavelengths. Absorbed by the ozone layer before reaching Earth.

Due to its high energy, ultraviolet radiation can induce a number of chemical reactions and biological effects. It is used in applications such as:

  • Fluorescence – Materials absorb UV photons and re-emit visible light, causing them to glow. The basis for fluorescent and black lights.
  • Analytic chemistry – The UV absorption of a substance helps identify its composition.
  • Air/water purification – Ultraviolet destroys the DNA of bacteria and viruses, disinfecting surfaces, water supplies, or the air.
  • Curing and polymerization – UV energy quickly dries and sets inks, adhesives, and protective coatings.
  • Medical therapy – Carefully controlled ultraviolet exposure treats skin conditions like psoriasis and eczema.

Overexposure to ultraviolet radiation also poses significant health risks:

  • Skin damage – UVB causes sunburns, premature skin aging, wrinkles, and cancer. UVA penetrates skin deeply and contributes to melanoma.
  • Eye damage – Corneal damage, cataracts, and macular degeneration.
  • Weakened immune system – Reduced ability to fight infections and cellular abnormalities.

Precautions are essential when working with UV sources. Direct exposure must be avoided and skin protected with clothing and broad spectrum sunscreen. UV-filtering glasses also help defend the eyes.

Key Differences Between Infrared and Ultraviolet

To summarize the main ways infrared and ultraviolet radiation differ:

  • Origin – Infrared is emitted by heat and molecular vibrations. Ultraviolet is generated by ionization.
  • Wavelength – Infrared has longer wavelengths (700 nm – 1 mm) compared to ultraviolet (10 – 400 nm).
  • Frequency – Infrared exhibits lower frequencies (300 GHz – 400 THz) than ultraviolet (30 PHz – 800 THz).
  • Energy – Ultraviolet light contains more energy per photon than infrared.
  • Applications – Infrared is widely used for thermal imaging and heating. Ultraviolet commonly enables chemical analysis and reactions.
  • Hazards – Both can damage eyes. Ultraviolet especially damages skin and the immune system.

In summary, while infrared and ultraviolet occupy adjacent bands in the electromagnetic spectrum, their distinct properties make each uniquely useful and hazardous in different ways. Infrared’s long wavelengths interact with molecular vibrations, enabling thermal imaging and heating applications. Ultraviolet’s short, energetic waves induce chemical changes, powering disinfection, chemical analysis, and phototherapy. Understanding the physics behind these invisible rays allows us to safely apply their capabilities in technology and medicine.


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