Many of us rarely think much of lighting outside of the need to turn on a lamp in order to read a book or avoid smashing a shin on the coffee table at three in the morning. Ever since we became able to harness the power of electricity and produce light at the flick of a switch, lighting has for most people become something we rarely think about, take for granted, and assume has little use beyond providing a means of keeping the dark at bay. In truth, visible light is only a small part of the radiation that makes up the electromagnetic spectrum, and non-visible forms of light make up a significant and important part of our daily lives even though most of us aren’t aware of it. 

The electromagnetic spectrum is made up of both visible and non-visible forms of energy including radio waves, visible light, microwaves, and x-rays for examples. All of this energy is categorized according to the wavelength at which it radiates. The wavelength at which electromagnetic energy radiates determines whether it is visible or not. We tend to call the visible forms of electromagnetic energy “light” and consider it differently because we can see it, although in truth, all the energy of the electromagnetic spectrum behaves similarly. All of it can be reflected or absorbed, and all of it can affect the objects it contacts in some way depending upon wavelength and the composition of the materials in question. 

Although the visible wavelengths of the light spectrum are by far the most commonly used, other non-visible wavelengths are equally useful. Electromagnetic energy above and below the wavelengths of visible light is in particular useful for a huge variety of practical applications. These wavelengths include infrared light energy, ultraviolet, and x-rays. Each wavelength interacts with materials differently due to its wavelength and how certain materials react at those wavelengths. This allows us to tailor the electromagnetic energy to particular applications in order to achieve a desired effect. Below we will detail some different applications that utilize the ultraviolet end of the electromagnetic spectrum.  

Ultraviolet radiation is just above the wavelengths of visible light with a range of 400 nm (nanometers) to 10 Nm. Ultraviolet is a highly energetic form of electromagnetic radiation and as such can have a significant impact on molecular structures and chemical compounds depending on the particular wavelength of the UV being used. Generally, UV above 315Nm (UVA) is considered less energetic and has little biological effect while UV below 315 (UVB-UVC) is considered more energetic and can cause serious damage to biological tissues such as sunburn and cancers. Contact with some UV wavelengths can cause materials to fluoresce and emit visible radiation as with a typical black light (UVA), while other wavelengths can alter chemical compositions or molecular structures, similar to how you get sunburn from too much exposure to UV in sunlight (UVB-UVC).

Non Destructive Testing:

With NDT, UV radiation is used to illuminate materials and reveal details that ordinarily would be difficult or impossible to see under normal visible light without causing any damage to the object being tested. Dyes, pastes, liquids and other penetrants containing compounds that glow under UV light are applied to materials, the excess removed, and a strong UV light shined on object. The fluorescent materials saturate and impregnate cracks, flaws and imperfections in the surfaces of the materials, which then become visible as cracks or irregularities in the surface as the fluorescent penetrant remaining within the imperfections reacts with the UV light. This is a very common and effective inspection method used in a wide variety of applications including aircraft and aerospace testing and maintenance, industrial machining and manufacturing, semi-conductor development and manufacturing, and the automotive industry just to name a few. Non destructive testing using UV penetrants is highly effective and well suited to electronically automated testing systems, allowing the use of computer aided machinery that can visually scan and inspect materials very quickly.

Health and Sanitation:

UV light of certain wavelengths can alter the chemical and molecular properties of some biological materials. In bacteria and pathogens, UV radiation can disable the ability to reproduce, thus rendering dangerous bacteria harmless or a virus unable to spread. UV radiation is commonly used in dental and surgical applications to sterilize equipment. More involved processes utilizing UV radiation include exposing biological tissues to be used in medical procedures to UV radiation in order to ensure no contamination. Blood and solid tissues are commonly treated with UV radiation to remove pathogens, and UV exposure is currently the only 100% effective method for treating blood.

UV light is also used in the control of rodents and other pests. The urine of rodents glows when exposed to UV light, whether the urine is older and dry or fresh. UV light can reveal the presence of rodents in the absence of visible feces and reveal whether sensitive items such as foodstuffs and containers have been contaminated. Similarly, UV light can also be used to reveal pet urine as well when working with real estate sales and rentals. Prospective buyers and renters can apply a strong source of UV light to reveal whether or not a location has been contaminated by either cat or dog urine, and sellers and management companies can use UV to determine if a property requires treatment to remove urine contamination.

Authenticity Testing:

Currency, artwork, antiques, and other similar items carry high value and as such are prime targets for forgery and fraud. For currency, issuing agencies include watermarks and identifiers that normally are invisible, but glow a specific color when exposed to UV radiation. UV light can also reveal differences between the inks and pigments used on a paper and the signatures it contains, often revealing an attempt at forgery. ID cards, bank and credit cards, checks and more all often contain hidden symbols or markings that only appear under UV light to indicate authenticity.

Art work can be inspected with UV light to reveal differences in the paints used, the type of paper or canvas used, and even if there are images underlying the main subject. All of these can be indicators of inconsistencies which suggest fraud or forgery. UV light can also reveal whether a piece of art has been retouched or restored and to what extent this has been done. Likewise, under UV light antiques can show where different materials have been used to repair or alter a piece as well as reveal whether paints and coatings are modern or original.