Types of UV Light for Different Applications|
Article - June 7, 2017 By LarsonElectronics.com
Types of UV Light for Different Applications
Ultraviolet (UV) radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself. He called them "oxidizing rays" to emphasize chemical reactivity and to distinguish them from "heat rays", discovered the previous year at the other end of the visible spectrum. In 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known that the most effective wavelengths were around 250 nm and, in 1960, the effect of ultraviolet radiation on DNA was established.
UV Wavelengths and Where They are Used
UV light is broken down into three basic types:
UVA: A long wave which encompasses light produced by the commonly seen black-light in stores and spreads across the 320 to 400 nm range of the light spectrum.
UVB: Mid-wave spreads across the 280 to 315 nm range and is damaging to some synthetic materials such as plastics and organic tissues like skin cells, causing the common sunburn for instance.
UVC: Shortwave spreads across the 200 to 280 nm range and is commonly known for its germ killing properties and is used as a germicidal control in the health and food industries.
For most industrial and commercial applications UVA is the most useful and thus commonly utilized of the UV wavelengths. The variety of applications where UVA is effective are widely varied. Because of its ability to cause different materials to fluoresce and how irregularities in an objects surface an alter how the material radiates fluorescence, it can be used to show details in objects that would otherwise be invisible to the naked eye.
UVB radiation features a shorter wavelength and holds the potential to damage both organic and inorganic materials. It does not penetrate into organic tissue, such as skin, as deeply as UVA light but, since its effects are more topical and fast acting, it is considered the most damaging to skin. UVB is the wavelength most responsible for sunburn and the fading of fabrics or oxidizing of plastics that are routinely exposed to sunlight. On the other hand, a number of skin diseases, such as psoriasis, lichen planus and atopic dermatitis, are treated with the use of UVB lamps.
UVC is the shortest of the UV wavelengths and is readily blocked by oxygen and ozone. As a result, almost all UVC light produced by the sun is blocked by the earths atmosphere and never reaches the earths surface. Due to its higher intensity, UVC has a large effect on organic tissues. Ultraviolet germicidal irradiation is a disinfection method that uses UVC light to kill or inactivate microorganisms and is considered to be the most effective way to do so.
Ultraviolet Photography (320+ nm):
Photographic film responds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350 nm. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. Photography with wavelengths shorter than 350 nm requires special quartz lenses which do not absorb the radiation. Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filter can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. This type of photography use UV light on the UVA, UVB and UVC end of the spectrum and is useful for medical, scientific and forensic investigations, in applications as wide spread as detecting bruising of the skin, alterations of documents, or restoration work on paintings.
Health and Sanitation (240-280 nm):
Lights using the UVC wavelength can be used to alter the chemical and molecular properties of some biological materials. In bacteria and pathogens, UV radiation can disable the ability to reproduce, rendering dangerous bacteria harmless or a virus unable to spread. UV radiation is also commonly used in dental and surgical applications to sterilize equipment. Another use is 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 food, have been contaminated.
Fluorescent Dye Uses (320-400 nm):
The fluorescent dyes used to detect certain things use the most common of the wavelengths, UVA. Colorless fluorescent dyes that emit blue light under UV are added as optical brighteners to paper and fabrics. The blue light emitted by these agents counteracts yellow tints that may be present, and causes the colors and whites to appear whiter or more brightly colored. UV fluorescent dyes that glow in the primary colors are used in paints, papers and textiles either to enhance color under daylight illumination, or to provide special effects when lit with UV lamps. Black-light paints that contain dyes that glow under UV are used in a number of art and aesthetic applications. To help prevent counterfeiting of currency, or forgery of important documents such as driver's licenses and passports, the paper may include a UV watermark or fluorescent multicolor fibers that are visible under ultraviolet light.
Non Destructive Testing (365 nm):
With NDT, UVA radiation is used to illuminate materials and reveal details that would usually be difficult or impossible to see under normal visible light without causing any damage to the object being tested. Dyes, pastes, liquids and other penetrates containing compounds that glow under UV light are applied to materials, the excess removed, and a strong UV light shined on an 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 penetrative remaining within the imperfections reacts with the UV lights. 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.
Most knowledge of UV light starts and stops with the black-light we see at parties and different clubs. The truth of the matter is, there are so many more practical uses for these UV lights that have proven to be beneficial in a large amount of different applications. With new technology, coming to surface, it is certain that UV lighting will continue to play a large and growing role in industry.