How does voltage affect lamp performance?

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Most sunbeds marketed in the U.S. employ pre-heat choke ballasts rated for a given wattage at input voltage of 220V. This ballast is a simple transformer, so increasing input voltage will increase wattage (electrical consumption) and, to a certain extent, will increase irradiance (UV output) from the lamps while increasing the heat generated by the sunbed’s electrical system. The pre-heat choke ballast regulates current to the lamp, not voltage, so the lamp “sees” any voltage change to the ballast. Higher voltage to the lamp makes for more rapid consumption of emissive material on lamp coils = earlier lamp failure, and faster degradation of the UV-emitting phosphors inside the lamp = shorter lamp service life. Wolff System rates service life as that point where irradiance has declined 30% from initial levels.

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The discussion above does not apply the same way to an older sunbed employing rapid-start magnetic ballasts, nor does it apply to equipment with electronic ballasts. These ballast styles compensate for input voltage variances within a fairly wide range. Increasing voltage to a rapid-start system will increase heat without any benefit, and result in virtually no change in an electronic system.

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If a manufacturer recommends running a bed at 230V, how will increasing to 245V affect lamp performance? If the equipment manufacturer recommends running your bed at 230V, it’s because that is the way the bed was tested to arrive at the maximum timer interval, or time to reach four (4) MED of UV exposure. Increasing voltage beyond 230V then shortens the time to reach four (4) MED through increasing lamp output, which is adulteration of the product. In this example and assuming the original equipment maker (OEM) employs the familiar 220V choke ballast, the OEM has already decided to accept shorter lamp service life, shorter lamp physical life and increased heat to get the desired timer setting. Increasing input voltage further will add more heat, further reduce lamp life and usefulness; but with diminishing increases in UV output. The example below demonstrates the diminishing returns and escalating costs relative to input voltage:

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If a bed has a maximum session time of 12 minutes, at what point during the session will four (4) MED be delivered? Twelve minutes into the session – if the original testing that leads to the maximum timer setting is done correctly. An OEM typically performs testing for timer-setting with lamps aged a few hours, so after installing a new set of lamps, we advise shortening sessions maybe 10% for the first 50-100 hours to compensate for higher UV output. Output depreciates more rapidly during the first 50-100 hours, and then the rate of decline flattens.

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Why is it that some equipment delivers four (4) MED within 50% to 70% of maximum session time? What is the industry standard percentage of maximum session time for delivering four (4) MED? A sunbed delivering four (4) MED in half or 70% of the maximum session time shown on the bed label (and in the accompanying operations manual) is “defective” per FDA regulations, and per good manufacturing practices. The industry standard is to market and deliver sunbeds that are not defective. Possibly, the method of determining that a bed delivers four (4) MED in substantially less time than called for on the label needs review; or possibly, the bed has been fitted with sunlamps that are entirely too strong for the equipment design. In any event, exposing a tanner to a full-session UV dose equaling eight (8) MED (your “50%”) is irresponsible, and creates a potential liability for everyone in the supply chain resulting in the overlong tanning session, and can be damaging to the indoor tanning industry, as a whole.

Input voltage to Voltage Wattage/percent Lamp output Lamp service
160W choke ballast life (estimate)

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