While traveling and training salon operators, I often get questions about why the UV output of lamps being used in a 15-minute bed register on a meter about the same as another lamp model installed in a 20-minute bed. Another question is, “Why does the current batch of lamps meter differently than the previous batch.” I’ll explain.
Before tanning system manufacturers market their equipment, it must be tested with sophisticated spectroradiometry devices to determine the maximum exposure schedule in accordance with the regulations from FDA’s Center for Devices and Radiological Health. The maximum exposure time is that period which allows a tanner to receive four (4) MEDs (Minimum Erythemal Dose). Regardless of the number of lamps in the unit, the character of the original lamps installed, or the unit’s design, four MEDs is the maximum exposure.
If you are using a hand-held meter to monitor your sunbeds, it’s an excellent tool for tracking the output maintenance of a given set of lamps in a given bed. When you try to compare one set of bed/lamp data with another, you are actually looking at results from many variables other than lamps, such as bed geometry, lamp density, distance from lamps to tanner, acrylic solarization, etc. When comparing one group of lamps to another, there can be a slight variance or shift in the spectral output. Your meter has a small window from which to read the wavelengths. It’s basically taking a “snapshot” of the UV spectrum – not reading the entire spectrum. This is why you only want to track the lamps in a given tanning unit.
Remember also, that commercial sunlamps emit almost all of their UV energy in the UVA region. Maybe 96 percent of the energy is UVA, while four percent is UVB. To produce a lamp for shorter exposure times (a “hotter” lamp), lamp makers generally add more UVB-generating phosphor. If all other things are equal, to make a lamp with a 25 percent shorter exposure (20 minutes vs 15 minutes = 25%), the UVB emission needs to change by only a small amount. The result might only be that the “hotter” lamp delivers 95 percent UVA and five percent UVB. Since most of the energy from both of these lamp styles is UVA, your UV meter will give you very similar readings. After all, it is designed to detect total UV. There are other devices that actually “weigh” the erythemal effectiveness of the output tested, which would tell you something about maximum exposure times.
The spectral character of different lamps can affect the readings drawn from any radiometer. This is another reason to avoid comparisons between different lamps and beds or from one group of lamps to another. Without changing the effectiveness, one lamp might emit higher levels of irradiance at wavelengths not well-detected, while another lamp emits wavelengths most easily detected by the radiometer.
If you have sunlamp questions, please send an email to sales@wolffsys.com or call 800.959.6533.
