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Team Wolff frequently gets asked these two related questions: Do sunlamps depreciate over time or just with use? Do they have a “shelf life”?
First, let’s talk about how a low-pressure sunlamp works. During manufacturing, the interior of the glass tube gets a thin phosphor coating, and it is filled with small amounts of inert gas and mercury. When power is supplied to the lamp, emissive material (a chemical coating) sputters from the cathodes at each end inside the lamp. These emissions assist in the ignition of an electric arc between the cathodes. This electric arc vaporizes the mercury, contributing its properties to the arc stream. The phosphors are “excited” by the ultraviolet energy of the mercury, causing them to fluoresce (glow).
As you can see, a sunlamp is composed of glass, metals, gas and phosphors. When Wolff System defines sunlamp performance depreciation, we are referring to the known characteristics of the phosphor within the sealed glass tube that makes up the lamp.
When a lamp is started and operated in a tanning system, the depreciation process begins. As the lamp continues to operate, the phosphor will weaken and the lamp will produce less UV output. This is a natural result of the interaction between the phosphor material and the electric arc from one end of the lamp to the other, plus a phosphor-weakening factor is present in the form of heat. This natural decline in output (from the degradation of the phosphor’s efficacy) leads us to the service life ratings we publish: service life equals that point when UV output has declined 30 percent from when the lamp was new.
Once the lamp is turned off, the depreciation process is halted until the next time the lamp is started. There is nothing organic in a lamp that will fail or “spoil” over time, such as with bread or milk. Our service life ratings speak to lamp-on hours, not elapsed time. In some applications, it may take ten years to collect 1,000 hours on a lamp; a sunbed in a busy salon may do that in a few months. Burn a lamp for one hour then turn it off, bury it in a time capsule and unearth it 100 years later – it still has only one hour of use and it is the same as when it was put away.
Likewise, tanning lamps sitting in inventory have no shelf life, because the components and materials used in the manufacturing process do not expire, age or deteriorate. The production date codes simply identify when the lamp was produced and is only used as a reference by the manufacturer, to comply with FDA regulations, and as a component of quality control processes.
Also, it doesn’t matter if the lamps are stored in a vertical or horizontal position. If stored vertically, you want to be sure that they are propped up securely to avoid being knocked over. Salon operators also ask if lamps can be stored in a cold garage. This poses no problem; however, it may take the cold lamps a few minutes to adjust to the ambient temperature change in the salon enabling them to fully light in the tanning unit. Once the lamps adjust, they will work just fine.
Michael Stepp joined Wolff System as President in 1998, bringing years of lighting industry experience with GTE Sylvania, Osram Sylvania and Philips. Married for 38 years, he has a daughter and granddaughter.
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