Low-Pressure Lamps

The low-pressure lamp, or fluorescent lamp, is a gas-discharge lamp that operates on a principle very different from that of the high-pressure mercury lamp. Its gas pressure is much lower and is not contained in a clear layer--the phosphors--on the inside.

As in other gas-discharge lamps, a discharge takes place when a stream of electrons strikes the molecules of mercury vapor. These become "excited" or acquire an excess of energy that is subsequently emitted as ultraviolet radiation with a wavelength of 254 nm. This UVC radiation then encounters the phosphor layer on the inside of the glass tube that converts it to radiation of longer wavelengths.

The specific composition of the output is governed by the qualities of the specific phosphors used. There is, as a result, a wide range of possible lamp output. One of these is the UV fluorescent lamp, designed to emit optimum amounts of ultraviolet radiation of the ideal wavelengths.

Tanning lamps generate UV light in a similar way as light is produced by standard fluorescent lamps commonly used in general lighting. The major difference between these two lamp types lies in the phosphors used. The fundamental mechanism to produce light radiation is called the photo-luminescence process. The main components responsible for producing UV radiation in a sunlamp are the electrodes, the gas filling, the phosphor and the trace amount of mercury, which all are sealed inside the lamp.

There are two basic steps from the point of plugging in the lamp to the emission of radiation. First, the electrical energy received by the lamp is transformed into short-wave radiation (UVC) during the discharge process. Second, the phosphors inside the lamp come into play and transform the short-wave radiation into a continuous spectrum of longer wavelength (UVB, UVA, etc., depending on the phosphor).

When the voltage is applied via the electrodes, particles called "electrons" are charged and move in a stream from one electrode to the other through the gas-filled tube.

On their way through the tube, these "loaded" particles (the electrons) hit the mercury atoms of the gas inside the lamp and create a higher energy level. The electrons peak at this higher energy level only for a very short time and then fall back to their original level. During their relapse, the electrons release the stored energy in the form of radiation at a certain wavelength. In the case of mercury vapor, low-pressure discharge is produced at a wavelength of 254 nm.

This UVC radiation hits the phosphor layer on the inside of the glass tube that changes the character of the radiation. The energy is physically transformed from the shorter wavelength into rays of longer wavelengths, including UVB, UVA, visible light and infrared rays, depending on the phosphors used. Although UVC is "produced" inside the tube, no UVC actually is emitted through the tube.

Finally, the transformed radiation passes through the glass of the lamp that can act as a filter and cause additional modification of the emission spectrum.

Prerequisites For Producing An Emission Spectrum

The available number of loaded particles (the electrons) are of extreme importance. It is the electrons that interact with the mercury atoms and which are responsible for continuously producing the primary radiation to excite the phosphor layer.

This electrical discharge must be stabilized immediately after ignition of the lamp. An inductive working ballast generally is used to produce such stabilized conditions for the lamp's operation.

The phosphor used in the lamp has perhaps the most significant effect on lamp output. It absorbs the short-wave energy and then transforms it into longer wave radiation. The phosphor's efficiency at converting the radiation contributed to the level of the final output. As a rule, it can be established that lamps with good operating phosphors emit about 20 percent to 25 percent of their electrical input as UV radiation.

Creating Different Tanning Lamps

The different types of tanning lamps, or, the different radiation spectra of lamps, are determined by the phosphors used and by the UV-transmission properties of the lamp glass.

The phosphor determines the main spectral properties of the emitted radiation. Even though the short-wave radiation hitting the phosphor layer is always the same, the different types of phosphor used produce different emission spectra, thus creating different lamps.

Lamp characteristics, such as "maximum radiant flux" or the "band-width" of the spectrum, are closely determined by the phosphor type used. Therefore, it is essential to pinpoint a suitable phosphor type for tanning purposes. The emission has to fulfill the spectral prerequisites for good tanning efficiency or the lamp will not provide a satisfactory output performance.

This is one of the reasons that only a few manufacturers are able to offer lamps with distinctly different properties--for example, lamps for fast tanning or lamps for the gentle tanning of sensitive-skinned people.

Lamp output also may be altered by the degree to which the lamp glass allows or inhibits the passage of ultraviolet light. Generally, radiation in the short wave range up to about 330 nm is more affected by the glass. It is possible, for example, to control the UVB/UVA ratio to some extent by using different glass types that have different UV-transmission ratings. In such cases, the glass acts as a filter. Most manufacturers typically apply only one type of glass in their entire tanning lamp program. However, the choice of glass can have a remarkable influence on the UV output of a lamp.

RUVA Lamps

More than a decade ago, a new type of lamp was introduced for indoor tanning. Rather than relying on external reflectors to prevent any light from being lost from the rear of the lamps, these so-called reflector or RUVA lamps each have an internal reflective coating that typically covers a 220-degree area of the inside of the lamp. This focuses all output through the front end of the lamp. While the orientation of their output is different, standard and reflector lamps do not differ in their technical efficiency at producing UV rays. In fact, the same type of phosphor usually is used in both reflector and standard lamps, so the output of both types have similar spectral properties.

Why then introduce reflector lamps to the tanning market? The answer is simple: RUVA lamps provide a more intense UV output, thereby reducing the required exposure times.

Each individual lamp, with its built-in reflector, assures that the UV rays developed inside of the lamp reach the skin directly virtually without any loss. Since external reflectors of the type normally mounted in tanning units are then not necessary, reflector tanning beds make it possible for lamps to be mounted closer together. In return, this means more output without needing more space, resulting in a higher intensity of tanning rays.

Furthermore, the absence of external reflectors simplifies the handling and cleaning of RUVA tanning beds and saves a great deal of maintenance.

But with more lamps, more heat is produced. For this reason, manufacturers of tanning beds with closely mounted reflector lamps must have an appropriate cooling system in the unit in order to guarantee optimal working conditions. Otherwise, either the output or the useful life of the lamps will be decreased.

The UVB/UVA ratio, often called the UVB percentage, also becomes important when discussing reflector lamps. Remember that the UVB ratio only indicates the levels of UVA and UVB relative to one another and not the absolute output of either. If an enhancement of the UVA output takes place, the amount of UVB produced increases by the same factor. Compared to tanning units with standard sunlamps at a given ratio then, RUVA units with reflector lamps of the same UVB ratio will produce higher absolute levels of UVB.

Because skin reddening, or erythema, is produced primarily by exposure to UVB, the erythemal threshold dose could be theoretically reached more quickly with RUVA equipment, so the exposure time must be reduced to compensate. In terms of exposure time then, reflector lamps of a given UVB ratio generally are comparable to standard lamps with a higher UVB percentage. This is due to the higher overall output of the RUVA lamps, resulting in the same level of UVB, even though the percentage is less.

Today's lamp manufacturers produce such a wide variety of products that to classify them would be difficult. However, some general guidelines regarding the output of reflector lamps would be useful.

Early reflector lamps emitted a narrow spectrum, primarily concentrated in the UVA range, hence the "UVA" in RUVA. While the high UVA output darkened existing pigment grains in the skin, the extremely low UVB produced did little to stimulate the production of additional melanin. For example, a RUVA lamp with a UVB percentage of 0.1 percent does not emit enough UVB to stimulate melanin production. For the level of UVB to be high enough at this ratio, prohibitively high levels of UVA would be produced. Recently, RUVA lamps emitting more UVB have been introduced.

A UVB percentage of about 0.7 percent can result in acceptable immediate tanning, but also gently induces pigment formation, making this reflector lamp suitable for tanning light, sensitive skin.

A slightly higher UVB/UVA ratio, in the neighborhood of 1.3 percent, for example, is a fairly standard RUVA lamp and works well for normal skin that tans readily without burning.

Reflector lamps also are available with still higher UVB ratios. A ratio of 2 percent at emission levels present in RUVA lamps will be very effective in tanning, but is not recommended for use on sensitive skin.

This short summary shows that the range offered on reflector lamps corresponds to that of standard tanning lamps. The decision to use standard vs. reflector lamps really depends upon the type of tanning unit used, the exposure times wanted and personal preference. However, equipment must be specifically designed to use reflector lamps and they should not be installed in a unit that is not so made, nor should standard lamps be used in a unit made for RUVA lamps.

VHO Lamps

Besides standard, professional and reflector lamps, there also are VHO or "Very High Output" lamps for tanning. Standard and professional lamps differ from one another mainly by spectrum--in general, professional lamps show a higher UVB percentage--and reflector lamps, which have a reflector built into the lamp itself, enable the rays to be focused and therefore more intense.

VHO lamps feature a significantly higher power consumption generally between 140 watts to 160 watts for the same size lamp. These lamps have two distinct quality features that clearly standout.

First, electrically the VHO has an actual power consumption of 160 watt for the 6-foot lamp and 140 watts for the 5-foot lamp. Second, the VHO has an additional physical feature built inside the lamp: longer electrodes with a cooling zone at each lamp end. These cooling zones permit the VHO lamps their exceptional qualities. Be aware that VHO lamps do not produce any output within the range of the cooling zones, therefore the ends of the lamps seem dark. However, these dark zones have nothing in common with the blackening of the ends (electrode area) that may occur in conventional fluorescent lamps after several operating hours. The dark zones of the VHO lamp, rather, guarantee the proper operation of the lamp.

Proper cooling is extremely important with VHO lamps. Compared to conventional tanning lamps, there is a 60 percent higher thermal strain along the glass because of the increased power consumption. Without a sufficiently dimensioned cooling zone, the VHO lamp would become too hot during operation, resulting in a reduction in the electrical discharge that is responsible for generating the output. Therefore, the cooling zone ensures the optimum electrical discharge.

New VHO lamps, especially after shipment, are not ready for use immediately after installation. A burn-in phase is needed for the lamp to reach its thermal balance. This is when the gases within the lamp have dispersed entirely throughout, thereby creating an even output along the whole length of the lamp. If the VHO lamp were operated in a unit without any cooling, a thermal balance would be reached after 15 to 30 minutes; however, a burn-in phase of two to three hours is quite usual for operation in a normally functioning unit.

It is important that the ends of VHO lamps are cooled properly. In order to maximize the output of the lamps, the cooling air stream should be led over the lamp in a way that the cooling zones receive optimal cooling.

High-Pressure Lamps

The high-pressure lamp is filled with mercury vapor and emits a spectrum that can be made ideal for tanning purposes. Compared to low-pressure lamps, high levels of radiation in the UVA range are produced, resulting in a strong immediate tanning effect.

Apart from the UVA, other rays also are found in the emitted radiation, mainly UVC, UVB, visible light and infrared radiation. The undesirable radiation, however, is removed by the use of filters. The appropriate filter should be fitted by the manufacturer of the tanning apparatus. Extreme accuracy is practiced in the production of these lamps.

Very high radiation intensities can be achieved using high-pressure mercury lamps. The high-pressure lamp is particularly suitable for use in combination with reflectors, where the lamp can be efficiently employed for radiating both large and small areas.

The development of high-pressure tanning in the late '70s was partly a response to the customer's desire for a fast, efficient method of tanning indoors. Although quite popular in Europe for several years, high-pressure tanning has come into its own in the U.S. market in the past five years. Although more expensive than many low-pressure units, manufacturers and distributors are educating salon owners about the advantages and profitability of such systems as a viable tanning option.

Using UVA certainly can stimulate melanin and produce a cosmetic tan. However, UVA sometimes has been mistakenly labeled as the "safe UVA ray." The use of high-pressure (or any type of indoor tanning equipment) should not be advertised as a "safe" or "safer" alternative. The FDA guidelines on indoor tanning forbids such claims.

Compared to low-pressure lamps, the application of high-pressure lamps requires a higher standard of care. This is largely caused by two factors:

1. High-pressure lamps emit a broad spectrum of radiation which covers a wavelength range starting with the short-wave UV range (generally even below 250 nm) up to the Infrared Light Range.
2. In addition, these rays are produced in high intensities, depending on the power output.

It is, therefore, subject to FDA regulations that govern the application and the trade of high-pressure sunlamps. This is in contrast to Europe, where such lamps may be sold and installed with few restrictions. This is particularly true for regulations regarding the replacement of such lamps. According to regulations, the user only may replace high-pressure lamps if the lamps show a UVC-UVB ratio of more than three.