Take a shot at explaining how the wattage of a fluorescent lamp is determined. Does more wattage equal better tanning capability, or just more power consumption?

The wattage of a fluorescent low pressure lamp is determined by the lamp design and, more importantly, by the ballast. All of this is influenced by the input voltage to the ballast/lamp system. In simple terms, the ballast will determine the system wattage, so installing a 100W lamp in a higher wattage ballast (say 120W/1200mA) will result in approximately 120 watts of power consumption.

Wattage is primarily a measure of power consumption, not necessarily irradiance (output). Wattage is also a measure of heat. One watt = 3.412 BTUs. British Thermal Units are a heat value standard, and you see this term commonly used in air conditioning. Total wattage of your equipment at actual input voltage, including fans and other onboard electrical devices, tells you the BTUs of air conditioning required to deal with the heat load. This is something to keep in mind if you are "upgrading" a few smaller beds to larger beds with more lamps/wattage/BTUs... your HVAC guy should be consulted to be certain your air conditioning is adequately sized.

In our industry there is a move to higher wattage sunlamps versus the standards of 100W and 160W. The standard sunlamp envelope is F71/T12/Bi-Pin. In its 100W iteration, the internal environment of the lamp is tough; at 160W it is almost hostile. Increasing wattage further magnifies this effect, thus the shorter service life to be expected with increasing wattage due to amplified phosphor degradation and, to some extent, physical wear & tear. Increasing wattage will increase output of the lamps, but not in a linear sense. Increasing wattage (and heat) past optimal lamp design by 10% yields about 5% greater irradiance and 10% higher power use. Keep in mind that in each of these scenarios, the lamp is the same size, you're just demanding more out of it.

So the answer to the question is: All other things equal, increasing fluorescent sunlamp wattage results in increased output and power consumption. That is not to say that it is wise to put 100W lamps in 160W equipment...cathode and mount designs are very different for these two lamp styles, and this kind of misapplication will certainly disappoint you. Whether a sunlamp is a reflector or full-coat, the wattage does not change due to the reflector...radiant heat is directed differently by reflector lamps, but there is not more of it.

Since tanning equipment of any size (or wattage, or UV source) can only deliver a maximum session equaling a dose of 4 MEDs, there are reasons for higher wattage:

• Aesthetics / ergonomics - greater lamp irradiance allows for longer exposure distances so the unit can look the way the designer wants (or just be bigger)
  
• Economics 1 - greater irradiance allows for shorter maximum session times in like-sized equipment, thus higher tanner throughput and revenue at the salon
  
• Economics 2 - same size equipment and same exposure time allows for fewer lamps, reducing component count and cost for the producer and lower prices to the equipment buyer