US Regulations for Tanning Beds
In the United States, the maximum exposure time in most tanning beds is 20 minutes but varies from bed to bed. This is calculated by the manufacturer according to the amount of time needed to produce 4 MEDs (minimal erythemal doses). This is essentially 4 times the amount of UV that is required to produce a reddening on unexposed skin. A person would start with a much shorter session time and work their way to the maximum exposure time in about 4 weeks. Every tanning bed is required to have a "Recommended Exposure Schedule" on both the front of the tanning bed and in the owners manual. It must also list the original lamp that was certified for that particular tanning bed, and salon owners must replace the lamps with either the exact same lamp, or a lamp that is certified by the lamp manufacturer to be legally equivalent. Lamp replacement and salon compliance is regulated by the individual state in the USA, whereas the manufacturing and sale of new equipment is regulated by the federal government.
Since many factors can change the performance of any given individual lamp, the FDA requires that every tanning bed model is certified separately, and lamps themselves do not have MED ratings. Lamps do have typical TE (or Time Exposure) ratings, but these are not used for certifying beds. Session times on beds can range from 5 minutes to 45 minutes, depending on many factors.
Tanning beds are used for somewhat different reasons in the US than in Europe. In the US, tanning is more seasonal, where most users begin in January and stop or slow down by June. It is most often used as a way to jump start the tanning process, so that once the summer begins, they can go to the beach or enjoy other outdoor activities and already have a significant base tan built up. This is also why tanning lotions and bronzers are more commonly used in the US.
Europeans may enjoy tanning seasonally, but less so than Americans. This is due to many areas in Europe having significantly fewer days of sunshine than the USA, so Europeans are more likely to use a tanning bed all year long, for both the cosmetic and mood altering benefits. European tanning beds generally use a different type of lamp as well, with UVB ratings in the 1% to 3% range (using US measuring methods) whereas most tanning beds sold in the US use 4.2% to 6.5% UVB ratings, and aftermarket lamps with up to 8.5% or higher being popular. Of course, these lamps have less UVA and will produce a sunburn quicker, but many Americans seem to like them because a short session produces a "reddening", or instant gratification. These lamps actually produce a slower deep tan (but a faster base tan) that fades faster, but are simply marketed as "hotter", although technically they have about the same amount of UV but with different ratios of UVA and UVB.
While the primary reason for both Americans and Europeans to use a tanning bed is cosmetic, there are many other reasons why they are used. It is common for people to tan simply because it makes them feel good. Also, most tanning beds generate a large amount of heat, including infrared, which has deep penetrating action that can relieve minor muscle aches.
The tan produced by a tanning bed is not as deep as a tan produced in the sun. This is due to the fact that tanning beds have higher overall levels of UV than the sun on a typical day, so the exposure times are shorter than the average session spent in the sun to achieve the same amount of tan. This can cause someone with a dark indoor tan to go outside and get a bad sunburn quickly because the deeper levels of their skin have not been exposed previously, and have no natural protection above what white skin would have. It is strongly recommended that a person does NOT tan indoor and outdoors on the same day, due to the likely chance that they will get overexposed. Because overexposure actually destroys melanin, getting a sunburn will result in LESS tanning. The popular wisdom that you "need to burn to tan" or that a sunburn will turn into a tan is simply wrong, and greatly increases your chances for skin cancer later in life.