Different UV Wavelengths for Different Lighting Jobs|
Article- February 2013 By Larson Electronics.com
Larson Electronics Ultraviolet LED Light Emitter
Ultraviolet light, also known as “black light”, has some unique properties that make it ideal for specialized applications. Although all light is part of the electromagnetic spectrum, light within different parts of this spectrum can cause different reactions when it strikes different organic and non organic materials. In the case of light within the ultraviolet range of the electromagnetic spectrum (10 nm to 400 nm), the light energy is invisible, but when it strikes certain materials, it can be absorbed by the material and the absorbed energy then emitted by the material as visible light. This is known as fluorescence, and it is the process that makes black light so effective in certain applications.
UV light is broken down into three basic types.
UVA -long wave which encompasses light produced by the commonly seen blacklight in stores and spreads across the 320 to 400 nm range of the light spectrum.
UVB -mid-wave spreads across the 280-315nm 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 200-280 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 ultraviolet wavelengths. This wavelength is readily absorbed by a wide variety of materials and is usually considered the safest of the ultraviolet ranges. It’ll make your whites glow like crazy, but it takes prolonged exposure to have significant effect on organic and non organic materials. However, the damage from UVA can be more serious due to its long wavelength which allows it to penetrate deeper into skin tissues. The variety of applications where UVA is effective are widely varied and in some cases rather surprising. Because of its ability to cause different materials to fluoresce and how irregularities in an objects surfaces can alter how the material radiates fluorescence, it can be used to reveal details in objects that would otherwise be invisible to the naked eye.
UVB is a mid range wavelength of the ultraviolet spectrum and has the potential to damage both organic and inorganic materials. This wavelength of UV radiation is shorter, so it does not penetrate into organic tissue such as skin as deeply as UVA, however, 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.
UVC is the shortest of the UV wavelengths and is readily blocked by oxygen and ozone. As a result, almost all UVC produced by the sun is blocked by the earths atmosphere and never reaches the earths surface. Due to its shorter wavelength and thus higher intensity, UVC has a significant effect on organic tissues. At the viral and bacteriological level, UVC light actually causes damage to the DNA of such organisms and renders them incapable of the processes of metabolism and cell division. In essence, UVC is an effective anti-microbial agent because it causes the organisms to starve as well as be unable to reproduce.
Given the effects mentioned, for the astute it is clear that UV light has a lot of potential for use in practical applications. The following are few such applications along with a description of the wavelength and type of UV radiation normally associated with them.
Non Destructive Testing-
Non destructive testing denotes a process whereby items are evaluated and assessed without causing any alterations of changes in the items being tested that would otherwise interfere with the items integrity or operation. These types of applications are widely varied and represent everything from inspecting machined items for defects to inspecting valuable artwork for authenticity. In the case of industrial NDT such as with manufacturing or aerospace assembly operations, operators may take a finished product or wing surface for example and coat it with a dye that reacts under UV light, causing it to fluoresce. The operator applies the dye, removes the excess, and then inspects the item under UVA illumination. The dye will accumulate in any cracks or surface irregularities that are normally invisible to the naked eye, and when exposed to UV light will glow, rendering the defect easily visible.
Detection, Covert Applications-
When inspecting artwork for authenticity, the operator will apply UVA light to a piece and inspect for any differences in pigments, the color and intensity of any fluorescence, and in some cases fluorescence alone is enough to indicate forgery. Different paints and dyes will fluoresce differently. If a piece shows wide variations in fluorescence, it is possible that a painting has been created using an original yet otherwise non valuable piece of artwork in an effort to fool collectors. Likewise, depending upon the age of a piece, many older pigments will not fluoresce at all, so if fluorescence is detected, forgery is again revealed.
UVA is also used to inspect currency for markers placed into paper bills by the federal mint to help prevent counterfeiting. In covert applications such as those used by the military or law enforcement, special UV identifiers can be used to indicate valid clearances for personnel, reveal hidden markers, and otherwise use UVA to act as a normally invisible way to mark and identify subjects and objects.
Health and Food Industry-
UVC as mentioned has excellent anti-microbial properties and as a result is widely used in the health and food industries where control of contaminants is critical. With its ability to destroy the reproductive abilities and metabolism of microbes, exposure to UVC radiation provides a very effective and efficient means of sterilization. Hospitals and clincs use UVC to sterilize equipment, purify air, and ensure rooms are free of viral and bacterial contaminants. Germicidal UV lamps are used in the food industry to provide control of molds and bacteria in processing rooms, conveyor lines, and is even applied directly to foods to provide increased shelf life without causing any change in the foods themselves.
Although most people are familiar with UV light as it relates to the old black light posters of the 70’s and 80’s or suntanning, the practical aspects are not so well known. In practical applications UV light has shown an effectiveness that goes far beyond the typical luminary qualities of lighting, and provides far reaching and widely varied benefits. With new lighting technologies such as LED now able to also produce UV light even more efficiently and bacterial resistance to traditional controls always a problem, it is for certain that UV lighting will continue to play a large and growing role in industry.