Practical Applications of Ultraviolet Light|
Article- December 2011 By Larson Electronics.com
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For most people, ultraviolet light represents a curiosity, something they used at parties and to light up velvet posters back in their teenage years. While the everyday uses for ultraviolet light are fairly limited, the special properties of UV light lend themselves well to a huge variety of practical commercial and industrial applications. Since UV light has a shorter wavelength than visible light, it appears invisible to human beings. In most cases, UV is only visible to us` because of the way it can cause many materials to fluoresce, or, emit visible light when exposed to ultraviolet radiation. It is in part this ability to cause certain materials to emit visible light that makes UV so useful in practical commercial and industrial applications.
UV light is produced naturally by the sun and most people are well aware of some of its potential effects. If you’ve ever had sunburn, then you are acquainted with the biological effects of ultraviolet radiation. Sunburn is only one of many ways however, that UV can provide a notable interaction with materials, and not exactly one of the more useful at that. Although UV is part of the electromagnetic spectrum and therefore technically “light”, because of its place within the electromagnetic spectrum, known as wavelength, ultraviolet light energy is not visible, but still interacts with any chemicals, compounds, and organic materials it contacts according to their specific properties. With visible light, the objects it contacts absorb certain parts of the visible electromagnetic spectrum while reflecting others. This is in large part why we perceive different materials as having different colors. Slight variations in structural, molecular, and chemical properties of a material cause variation in the absorption and reflection of different electromagnetic wavelengths, and thus the light that is reflected from an object and reaches our eye is a reflection of those variations, hence coloring.
Visible light is normally what we consider “white” light. White light is made up of several wavelengths within the electromagnetic spectrum, with specific parts of this range representing colors of light. We can see this whenever we notice a rainbow forming. The water droplets in the atmosphere act as prisms, and break down the visible light from the sun into its various specific wavelengths, resulting in the distinct colors of the rainbow. Similarly, we perceive colors because objects absorb some of these wavelengths more readily than others, while reflecting the rest. Objects do not inherently posses color, but appear a certain color because they reflect that part of the electromagnetic spectrum representing that specific color the most. For example, an apple when exposed to sunlight readily absorbs much of the electromagnetic radiation it receives, yet readily reflects the wavelength representing red light. Thus, we perceive the apple as being red in color.
Since ultraviolet light radiates over a part of the electromagnetic spectrum below that of visible light, it is invisible to us regardless of what it comes into contact with. However, this does not mean UV does not interact with materials, only that we cannot visually perceive this part of the electromagnetic spectrum. In many ways, UV radiation interacts with materials the same way visible light does in that it can be absorbed and reflected, however, it also has some specific differences, which is where we find UV radiation to be the most useful. For instance; since UV radiation causes some compounds to emit electromagnetic radiation in the visible range, commonly known as fluorescence, we can use UV light to identify chemicals and compounds according to how they fluoresce when exposed to UV radiation. Just like with the visible light spectrum, different wavelengths of UV will react differently with different molecular structures, causing some to fluoresce a certain color, which can tell us what a material is made of or what its properties are. We can also use fluorescence to create identifiers that are normally invisible under visible light, but become visible under UV of a certain wavelength.
In the case of fluorescence, real world applications include things like using specific materials in paper money to create hidden watermarks which make it easier to identify counterfeit currency, or creating hidden symbols on drivers licenses and identification cards to help prevent the creation of fraudulent identification. Other applications include using UV light to inspect artwork and antiques for signs of alteration or outright fakery. Since it is often difficult or impossible to utilize the same exact materials once available many years ago when such artwork was first created, those looking to create copies must use modern materials which will react differently with UV light than the originals. Some entertainment industries use UV reactive stamps to mark participants in order to manage crowds, and in the military, hidden UV light reactive identification on uniforms, equipment, and signage provides an effective covert form of communication and identification.
In other cases more practical for industrial and commercial applications, UV radiation of certain wavelengths can cause changes in molecular structures, similar to what occurs when you get sunburn. This process allows manufacturers to use UV radiation to increase the cure rate for certain adhesives and ensure a high quality bond between materials. In other applications, dyes and markers which fluoresce under UV light can be introduced into systems containing liquids and vapors to identify leaks or defects where fluids could escape. Machining and manufacturing benefits from UV light by using computer aided machine visioning that can inspect surfaces at an almost microscopic level under UV light to reveal surface imperfections and hairline cracks and fractures that could later cause failure of the finished part. In the aerospace and aircraft industries, UV light is used in conjunction with markers and dyes to reveal minute cracks and fractures in wings and fuselage caused by metal fatigue.
In still other applications such as the medical field, the ability of UV light to affect the molecular structure of materials is used. UV light of certain wavelengths can cause many bacteria to become unable to reproduce, or outright destroys bacteria on contact, making UV radiation effective for sterilization of surfaces and equipment. In the utilities industries, UV radiation is used to treat effluent and waste products before release, effectively rendering bacteria and pathogens the waste may contain harmless and unable to reproduce.
These are just a few of the ways UV light is used in practical applications. Although invisible to the human eye, UV light still provides a wide range of benefits as a useful part of the electromagnetic spectrum. Along with infrared, visible and Xray radiation, UV light has real world applications that go far beyond novelty and entertainment.