Guide To Ultraviolet Light

Ultraviolet(UV) light is defined as radiation lying in the ultraviolet range which has wavelengths shorter than visible light but longer than x-rays. UV light is identified by ranges classified as UVA, UVB and UVC. The sun is our largest source of UV light, and although UV light can be dangerous, very effective uses of UV light have been found in industries such as health care, water treatment, and inspection. This document will focus on the definitions, effects, and applications of UV radiation.

Definitions:

UVA: also known as longwave UV or blacklight, is closestto the visible spectrum: wavelength range: 400nm-320nm

UVB: also known as shortwave UV: wavelength range: 320-280nm

UVC: the least common of the UV’s. Most of UVC is absorbed by the atmosphere. Wavelength: below 280nm.

Phosphorescence: Phosphorescence is the continued emission of visible light after a source of radiation is removed and may last anywhere from a few seconds to a few years depending on the materials ability to hold energy.

Fluorescence: Fluorescence is the action of emitting visible light during exposure to UV radiation

Health Effects and Medical Applications of Ultra Violet Light

UVA can be used to diagnose medical conditions such as ringworm. The ringworm fungus fluoresces whether it is on a person or an object. Small amounts of UVB exposure are beneficial to people and is essential for the bodies production of Vitamin D and because of its powerful germicidal effects, UVC can be used for the treatment of skin disorders.

Several medical uses for UV involve the eyes. The white portion and crystalline lens of the eye have natural white fluorescence, so UV light is used to detect lens opacities such as cataracts. Corneal foreign bodies, abrasions, and lesions can be located quickly by dropping fluorescent dye into the eye and examining it with a UV light. UV light is also gaining ground as a healing mechanism. Some research shows UV light can be used to stimulate the immune system and various enzyme systems. has also been used as an effective treatment for botulism, pneumonia, acute gangrenous appendicitis, and peritonitis.

UVB exposure induces the production of vitamin D. Vitamin D helps with the absorption of calcium and helps prevent some types of cancers. Vitamin D fortified foods and incidental UVB exposure is usually adequate for vitamin D needed, but fortified foods and vitamin supplements are preferred over UVB exposure. Despite its positive effects when used properly, prolonged exposure to the UV in the B range has been linked to skin cancer. Most carcinomas, the most common type of skin cancer (also know as nonmelanoma skin cancer), are linked to prolonged exposure and are easily treated if detected in time and are rarely fatal. The more malignant version of skin cancer is melanoma and appears to have a link to brief, high intensity exposure to UV and the later development (10-20 years) of the melanoma. There may be other factors involved, such as personal lifestyle or environmental conditions, but there are twice as many deaths due to melanoma in Florida and Texas as there are in Wisconsin and Montana. This could be due to the duration and intensity of UV exposure in southern states. Another effect of long term UV exposure is the premature aging of the skin. UVA, UVB, and UVC all contribute to this effect. Just as UV radiation from the sun can damage skin, tanning beds, thought to be safe by some, damage cell DNA and cause permanent damage to the skin.

Something most people do not think about is the UV that is absorbed by the eyes and over time or in high doses will cause damage in a variety of ways. The cornea, which absorbs UV light, is particularly susceptible to damage. A temporary clouding of the cornea, commonly called “snow blindness” is one such condition. Chronic doses of UV have been tentatively linked to the formation of cataracts. Below are tips that will help alleviate risks from UV exposure.

Safety Tips Regarding Exposure to UV and Skin Cancer

Sun exposure at any age can cause skin cancer. Take appropriate precautions in the sun if you spend a lot of time outdoors, burn easily, or have any of the following:

  • Numerous, irregular, or large moles
  • Freckles
  • Fair skin
  • Blond, red, or light brown hair

Self Examination: It is important to perform monthly examinations. Skin cancer detected early can almost always be cured. The most important warning sign is a spot on the skin that changes size, shape, or color during a period of one month or 1 to 2 years.

Skin cancers usually take the following forms:

  • Pale, wax-like, pearly nodules
  • Red, scaly, sharply outlined patches
  • Sores that don’t heal
  • Small, mole-like growth -this is melanoma, the most serious type of skin cancer

If you see such unusual skin changes, see a health care professional for diagnosis and treatment.

The best way to protect yourself from UV exposure is to limit exposure. Since that is not always an option, the next step is to cover up. Wear tightly woven clothing that blocks out light. Wear a wide brimmed hat, not a baseball hat. The wide brim will protect the neck, ears, eyes, forehead,nose, and scalp. Apply sun screen with an SPF (sun protection factor) of at least 15 which blocks 93 percent of UV rays. Lastly, wear sunglasses that block 99 to 100 percent of UVA and UVB radiation. Even standard clear polycarbonate safety glasses block 95-99 percent of UV. If you have questions, check the glasses specifications for the specific UV rating. Wearing clear or shaded lenses that have a UV rating on them are suggested for people of any age including children.

UV Applications

UVC at 253.7nm wavelength will kill germs such as bacteria, viruses, mold, fungi and spores that transmit infection, cause allergies, or trigger asthma attacks. UVC destroys the DNA of the microbial contaminants rendering them sterile. Since they can no longer reproduce they disappear from the indoor environment over time. Germicidal UVC has been used in hospitals, clinics, and laboratories for over 60 years. More recently, germicidal UVC is being used to clean HVAC systems to eliminate allergens and the other microbes listed above. Germicidal UVC is also used for of water purification. It has the same effect on microbes in water as it does on microbes in the air or on a surface. The advantages of UVC water purification are that it does not introduce any chemicals to the water, it produces no bi-products, nor does it alter the taste, pH, or other properties of the water. Also, it is not harmful to plumbing and septic systems.

  • UV use in Government, Criminology, and Mineralogy
    Substances that fluoresce are useful in varying applications. Several countries, including the US, have been using fluorescent “tagged” stamps in automatic mail sorting. In applications of criminology, invisible stains from various bodily fluids will fluoresce. In additions, some accelerants can be detected with UVA when performing arson investigations. In mineralogy, gems, such as diamonds and rubies fluoresce, which can aid in detection of precious gems, as well as enhancing their beauty. The deep, rich red color of rubies is partly due to fluorescing caused by the small amounts of UVA in natural and artificial light.
  • UV in Rodent and Leak Detection
    One of the more common uses for UV inspection can be detecting rodent infestation. Amino acids found in urine glow when exposed to UV light, which aids in rodent detection. Rats and mice leave evidence of their travels everywhere they go. Here are some helpful tips for rodent inspection: Rodent urine can be discerned from pet urine because rodent urine will glow bluish-white when fresh and yellowish-white when old. Pet urine glows an amber color. Additionally, rodent hair can also be detected as it will also glow bluish white. Rodent urine is typically deposited in a line of droplets, with the largest drops being first and tapering off to smaller droplets: Some mice and rats drag their tails behind them leaving a smeared line: In heavily contaminated areas, urine deposits may be in the form of large patches surrounded by smaller droplets of varying size: Rodents like to move along walls, so they may leave urine trails and grease stains from their body that may also fluoresce. UV light inspections have limitations, therefore, it should not be the sole source of identifying the presence of rodents. There should be visual confirmation of hair, dropping, or nesting material with a standard flashlight as well. Also, since UV light is weak, it is best used in dark areas. Keep in mind that low wattage UV lights may require being closer to the inspection area.

    UV light is also useful in leak detection. Many dyes used in leak detection will phosphoresce, aiding in visual identification of the leak. For more information on dye tracing and detection, see Guide to Dye Tracers.

Commonly Asked Questions

Q. Is there an OSHA standard regarding UV exposure?

A.No. The OSHA standard regarding radiation exposure covers ionizing (29 CFR 1910.1096) and non-ionizing radiation (29 CFR 1910.97). The ionizing radiation standard covers alpha, beta, gamma, x-rays, neutrons, high-speed electrons and protons and other subatomic particles. It does not include sound waves or radio waves, or visible, infrared, or ultraviolet light. The non-ionizing standard covers the radio frequency region, including microwaves.

Q. Can UV light be used for automotive inspection?

A. Yes. Using UVA (longwave) light, you can identify leaks by different, easily distinguishable fluorescent colors. This applies to engine oil leaks, air conditioning, differential, bearing, and brake system leaks. Techniques for automotive leak detection can be found here: http://www.uvp.com/pdf/a-102.pdf.

Please Note: The information contained in this publication is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the cited regulation or consult with an attorney.