Good Things Ultraviolet Rays

Ultraviolet light is dangerous but also useful for various applications.

Ultraviolet light is infamous as a common cause of skin cancer. Despite its foul reputation, UV has a number of beneficial applications. Though exposure to a lot of ultraviolet light is harmful, a little exposure to sunlight is important for synthesis of vitamin D. UV light is also used in scientific research, medicine and industry.

Vitamin D

When ultraviolet light strikes some of the cells in your skin, it alters a molecule called 7-dehydrocholesterol, producing another molecule called cholecalciferol or vitamin D. Your liver and kidneys use vitamin D to make calcitriol, which binds to receptors in some cells to promote synthesis of a protein that helps you take up calcium from the food you eat. Basically, calcitriol works together with parathyroid hormone to regulate the amount of calcium in your bloodstream. Insufficient vitamin D can lead to diseases like rickets, so though the UV rays in sunlight can cause skin cancer, a limited amount of sunlight exposure is a good thing.

Spectroscopy

DNA strongly absorbs UV light with a wavelength of 260 nanometers, while some amino acids found in most proteins strongly absorb UV at 280 nm. Biology labs use these properties to help quantify the concentration of DNA in a sample and determine its purity; a pure sample of DNA will have a much higher ratio of absorbance at 260 nm to absorbance at 280 nm than an impure sample. UV light is also important for a variety of other scientific techniques. Biologists often use a method called UV circular dichroism, for example, to help them study proteins in solutions.

Sterilization

UV light is damaging to many kinds of microbes; bacteria and protozoan parasites are especially vulnerable. UV light can be used for disinfection in water treatment or in health-care settings, although it must be designed so that humans are not exposed. Germicidal UV acts primarily by damaging microbial DNA; bacteria have various mechanisms to repair DNA damage, so the dose must be sufficient to overwhelm their DNA damage repair capabilities.

UV Curing

The same property that makes UV light dangerous to your DNA also makes it useful for curing certain kinds of adhesives. The chemicals in these materials contain weak bonds that break when they absorb the UV light, starting a polymerization process that yields the finished coating or adhesive. Black light with UV rays in the 315 to 400 nm wavelength range is usually used for this kind of application.

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