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Ultraviolet radiation indoors: What you don't know can hurt you.

If you never venture outside, never walk in open air, spend your entire existence between your office, home, car and supermarket - well, that is not fun. You might think that the upside of such a lifestyle is to never have to worry about sun damage. I'd have to disappoint you again. Indeed, you won't have to worry about sunburn and could worry less about skin cancer. However, being indoors does not protect you from the kind of UV damage that causes skin aging. There are two kinds of ultraviolet radiation that affect the skin: UVB and UVA. UVB (the one that causes sunburn) does not generally get indoors whereas UVA (the one that causes skin wrinkles) does so with relative ease. (See our article on ultraviolet radiation to better understand the relationship between UV rays and skin damage.).

Glass and UV protection

Most people believe that ordinary window glass blocks UV radiation, making any other UV protection unnecessary indoors. This is half-truth at best. Window glass blocks UVB but lets much of UVA through. The percentage of UVA that passes depends on the type of glass and the type of coating on the glass. Window glass falls into three major categories: ordinary (clear) glass, reflective glass (allows to see in one direction much better than in the opposite one), and tinted glass. While all these types of glass block UVB, their capacity to block UVA varies considerably. As architectural fashion keeps moving towards larger windows, the impact of these differences is continuing to grow.

Clear glass allows up to 75% of UVA to pass. Tinted and reflective glass absorbs more of the UVA but still allows about 25-50% to pass; they also have the shortcoming of blocking more of the visible light than clear glass. There is also the so-called Low-E (low-emissivity) glass, developed to minimize heating and cooling costs. As far as UV is concerned, regular Low-E (the ones w/o special anti-UV coating, etc.) behaves similarly to clear glass: most UVB is blocked, most UVA gets through.

The best protection comes from the types of glass specially geared towards blocking UV rays, such as laminated glass and UV-blocking coated glass. Both filter out from 95 to 99% of all UV light. Neither is common in residential or commercial structures. Laminated glass, made of two layers of glass with a plastic layer in between, is used in some public buildings, such as airports and museums; it is also used for automobile windshields. UV-blocking coated glass is also used largely in special circumstances. All in all, whenever indoors, don't assume protection from the windows against UVA unless you know that special glass in installed.

UV protection indoors

If your home and office have special windows with full spectrum UV protection (see above), you can consider yourself a lucky exception. Otherwise, if you want to minimize skin aging, you need to protect yourself from indoor UVA exposure.

If possible, use window blinds or shades during peak sun hours. Arrange workspace and sitting/recreation areas not to be too close to the windows. As a minimum, they should not be in direct sunlight. Indoor UVA intensity decreases as the distance from the window increases. If you have large windows, you may want to avoid spending too much time close to the windows, even if sun is not shining into the room directly. The above steps should reduce indoor UVA exposure to acceptably low levels. However, if you feel that the indoor areas where you spend a lot of time receive too much daylight, you may consider additional protective measures. This may include additional window blinds or shades, sufficient clothing and sunscreen. If you spend some of the time outdoors, you need a good, strong sunscreen anyway. Otherwise, a moderately robust sunscreen with good UVA protection applied to face and neck should suffice. Many popular moisturizers provide moderate sun protection as an extra feature. Such a moisturizer may be a good choice for indoor UV protection as long as it adequately covers UVA range.

UV protection in cars

In the modern world, people are spending ever greater portion of their time in cars. This trend is likely to continue unless rising fuel costs and/or global warming bring about major changes in our transportation habits.

In the majority of modern cars, the windshield is built of laminated glass that blocks all of UVB and the vast majority of UVA. However, the side and rear windows are usually made from non-laminated glass and let much of UVA through. Clear non-laminated car windows allow up to 60-70% of UVA to penetrate. Tinting reduces UVA penetration to about 15-30%, a much better but still significant level.

If your car has clear glass windows, you can add tinting at a qualified auto shop. However, make sure the facility can guarantee compliance with the federally mandated standard of 70 percent of minimum visible light transmittance through the windshield.

There are other factors influencing UVA exposure in the car: you position (the closer you are to a non-laminated window, the greater the exposure), direction of driving relative to the sun, time of day/year, etc. However, people rarely have much control over any of these. Therefore, you should still use sun protection measures while in the car, such as sunscreens, protective clothing, and so forth.

Fluorescent lighting

There are two common urban myths about fluorescent lighting and UV exposure. The first myth says that fluorescent lighting generates hazardous amounts of UV rays, rivaling direct outdoor sun exposure. The second one says that the first myth is complete nonsense and that fluorescent lighting generates no UV rays whatsoever.

The reality is a bit more complicated. Most fluorescent lamps work on the following principle. Inside the lamp, electrical discharge excites a gas (usually neon or mercury vapor in argon), which emits ultraviolet radiation. UV rays hit a special dye covering the bulb, which absorbs UV radiation and emits visible light. In this process, most of the UV radiation is absorbed (or otherwise blocked) by the fluorescent dye and/or the glass of the bulb. Yet, some does get through.

Fortunately, it seems that typical exposure to the UV light from commonly used types of fluorescent lamps is relatively small. According to the report by the UK Health Protection Agency, fluorescent lighting may add about 3% to the lifetime UV exposure. However, this estimate is imprecise and some lamps may be greater offenders than others.

If you spend a lot of time under intense fluorescent light, you could consider extra protection. One possible step is to ensure that fluorescent bulbs have plastic diffusers over them. Depending on the material used in the diffuser, UVA would be reduced by 17-99% and effective UVB by 19-100%.

Halogen lighting

Halogen lamps are incandescent lamps filled inert gas and a small amount of a halogen such as iodine. Halogen lamps operate at a higher temperature than regular incandescent lamps and emit a somewhat different spectrum of light, which includes some UV light. Furthermore, halogen lamps are often made of quartz because it is more resistant to intense heat. (Regular glass cannot withstand the heat generated by halogen lamps.) The problem is that quartz does not block UV radiation.

Manufacturers of halogen lamps are certainly aware of this issue and resolve it by using the so-called doped quartz (quarts with UV-blocking additives) or special heat-resistant glass, or by simply enclosing quartz bulb inside a regular glass bulb. As a result, most of UV light generated by common halogen lamps is blocked. The question is what percentage, if any, is not blocked and what are the variations among lamp models and/or manufacturers. Unfortunately I am not aware of such data being publicly available. My guess would be that UV risks of halogen lamps are relatively small but not necessarily negligible -- perhaps similar to those of fluorescent lamps. If you spend a lot of time under direct light of halogen lamps consider additional protective measures such as diffusers or switching to lamp designs that employ reflected light.


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