Ultraviolet Radiation

Ultraviolet radiation is an electromagnetic radiation with wavelengths between 100~400nm. These rays are emitted from the sun and are not visible to our naked eye. Based on the effects, UV radiation is categorized into 3 ranges: UV-A, B and C.

UV-A covers wavelengths of 320-400nm, and is not absorbed by the ozone layer and is the least harmful UV ray. Most of the sun’s natural light is categorized into UV-A. It penetrates deep into the skin causing wrinkles and aging over time. People come in contact with UVAs when they are sun-tanning.

UV-B covers wavelengths of 280-320nm. There is more energy in UV-B than UV-A, and it is partially absorbed by the ozone layer. UVB is needed for the production of vitamin D. Vitamin D regulates calcium metabolism which is crucial in our nervous system, bone growth, immunity, cell development, insulin secretion and blood pressure. However too much UV-B exposure can lead to direct DNA damage, sunburn and skin cancer.

UV-A and UV-B can help treat skin conditions such as psoriasis and vitiligo, however they can destroy vitamin A in the skin. All 3 types of UV radiation can damage collagen fibers and thereby accelerate aging of the skin.

UV-C covers wavelengths of 100-280nm. This shortwave radiation is almost never observed in nature because the ozone layer absorbs UVC before it reaches the earth’s surface. UVC have the ability to kill bacteria in air, surface and water. In humans, UVC is absorbed in the outer dead layers of the epidermis. Unintentional overexposure to UVC causes skin redness and eye irritation, but does not cause skin cancer or cataracts.

Fluorescent lamps produce UV radiation by ionizing low-pressure mercury vapor. When phosphorescent coating is added to the lamps, UV-A, UV-B, UV-C and all visible light can be produced. The mercury amalgam allows the temperature of the lamps to rise and UV-C ray emission increases. The main mercury emission wavelength is in the UV-C range. Unshielded exposure of the skin or eyes to mercury arc lamps that do not have a phosphorescent coating is very harmful. Low pressure mercury lamps are used for disinfection. There are many practical UV lamps with continuous emission spectra such as xenon arc lamps, deuterium arc lamps, mercury-xenon arc lamps, metal-halide arc lamps, and tungsten-halogen incandescent lamps.

Ultraviolet light emitting diodes (LEDs) can be manufactured to emit light in the ultraviolet range. LED arrays are used for UV curing applications.