The Practical Side of Ultraviolet Light |
Chances are your only real familiarity with ultraviolet light has been with the classic two foot long tubes sold in novelty stores that lit up your old Jimi Hendrix poster back in 1981. Although the most common, these simple fluorescent tubes represent only a tiny fraction of the real practical uses that UV light provides. In the most basic of terms, UV light is light emitted just above the range at which human eyes are able to perceive light. Some objects become “fluorescent” or more accurately, fluoresce, because when exposed to UV light they tend to very readily absorb light in this range of the light spectrum, then immediately re-radiate that same light, only at a spectrum that is then visible to the naked eye. Although the light emitted in the ultraviolet spectrum is for practical intents all the same color, the light radiated by different objects exposed to the same UV light appears as different colors because the different properties of different materials tends to cause them to re-radiate UV light at different wavelengths. This is why your old Jimi Hendrix poster had all those cool greens, reds and blues when you flicked on the old black light.
Similarly, different material textures can also have an effect on how an object radiates the UV energy it absorbs. A smooth piece of aluminum for instance may not appear to fluoresce much at all, but break that same piece of aluminum in half and the rough and jagged edges will show a much different appearance as the UV light is no longer being re-radiated evenly and the rough edges tend to break up the uniformity of the radiated UV light. A practical example of this would be an inspector checking an aircraft’s fuselage for damage. By applying a fluorescent chemical to improve detection and passing a UV light over the aircraft’s aluminum surface, hairline cracks that were previously invisible to the naked eye are revealed, signaling a possible structural safety problem that could have easily gone unnoticed.
UV light is a natural part of the light spectrum and is emitted by the sun on a constant basis. The sun emits UV along the entire UV spectrum, but only part of this light makes it to earth, which is lucky for us since things would be a bit uncomfortable if the full force of the sun’s UV radiation were to reach us. Imagine a barbeque with you as the main course.
UV-A: UV light used in commercial applications such as the aforementioned aircraft inspection is generally produced in the 400nm-315nm range and is known as UV-A. This is the longest of the UV wavelengths as well as the safest UV range has it holds the least energy. This is the one that lights up our old posters, the ones we threw away once we grew up, or not. We’re not here to judge, just talk UV light, so everyone can relax.
UV-B: The next UV range is the 315nm-280nm portion of the light spectrum, known as UV-B. More than likely, you are more familiar with this one than you realize as it’s the part of the UV spectrum largely responsible for all those nasty sunburns. Although a very aggressive form of UV, this part of the UV spectrum remains quite useful in commercial applications.
UV-C: The last of the UV range is made up of the 280nm-100nm range and is known as UV-C. This end of the UV spectrum is generally only encountered with artificial sources as the earth’s atmosphere tends to completely absorb it before it can penetrate to the surface. UV light in this range is quite powerful and dangerous, yet still has practical uses in commercial and industrial applications.
Most commercial and practical industrial uses of UV light take advantage of the way objects fluoresce when exposed to it. In commercial settings these applications are quite varied. As well as our previous safety inspector example, UV light is used to inspect antiques and valuables for condition and authenticity. Consider that before 1950, paper was made simply by purifying and compressing wood fibers. After 1950, paper manufacturers began adding special chemicals that react with UV light, causing their paper products to appear whiter. Thus, if a would be seller of antique books wishes to authenticate a particularly old volume, one of the ways this would be done would be to expose it to UV light. If the pages fluoresce beyond what is expected of “clean” paper, the book is likely a reproduction and not an original.
Similarly, banks and law enforcement agencies make use of UV in much the same way. Certain paper money is impregnated with materials that fluoresce a specific color when exposed to UV light, giving banks and police investigators an easy way to quickly determine a real bill from a counterfeit. UV light is also useful in law enforcement as certain organic materials will readily fluoresce although they are invisible to the naked eye. Blood, semen, urine and other bodily fluids will readily fluoresce when treated with a compound such as luminol and then exposed to UV radiation if even small trace amounts are left behind, giving investigators an effective way to locate and identify evidence that once was undetectable.
UV light also holds a great deal of usefulness in military applications as well. Identification papers, object and personnel markers and even some covert operations equipment make use of UV light to provide fast, accurate and easy verifications. Combined with a portable source of UV light like a Larson Electronics UV LED Pistol Grip Spotlight, fluorescent dyes, markers and materials can be used to identify friendly forces from long distances, mark locations and objects for later covert reference and even as a covert light source for certain types of specialized night vision devices.
To be certain, the above is only demonstrative of a tiny fraction of the practical uses associated with UV light. UV light can be used to sterilize foods and chemicals, purify water, speed up the curing process of adhesives, assist in medical procedures, test and identify manufactured goods and hundreds more uses it would take volumes to list and explain. Suffice it to say, UV light is more than just a cool novelty, it’s an effective tool that has led to improvements we benefit from every day of our lives.