Defining High Pressure
Q: What is a high-pressure sunlamp?
A: High-pressure sunlamps commonly are seen as added facials at the head end of tanning bed canopies. Popular in numerous tanning bed styles, facial lamps recently have become more prevalent in stand-up tanning booths.
High-pressure lamps are inches in length versus feet for low-pressure lamps. The tube most often is a quartz blend versus glass for low pressure. The pressure within the tube is more than one atmosphere, and the heavier quartz tube is needed to withstand the thermal and emissive energy while containing the pressurized environment. The compactness of the high-pressure lamp makes it easier for equipment manufacturers to design effective delivery optics.
High-pressure also is an arc discharge source. An arc struck across the lamp’s length vaporizes a small amount of mercury resulting in ultraviolet emissions. Output from early high-pressure products was derived essentially from the arc discharge itself. Figure 1 shows the spectral output of these early high-pressure lamps. Almost all of the output was UVA, which is effective for pigment darkening but has little effect at generating new pigment. Some UVB is present, and a small amount of UVC. The filter or filters between the lamp and the tanner block undesirable UVC. These filters always must be kept in place and in good repair.
Conventional UV phosphors, such as those used in low-pressure lamps, are not suitable for the rugged environment of a high-pressure lamp. In order to change the output character to modify high-pressure output as is done in low pressure, materials must be added to the arc stream. Metal halides (metallic salts) have been added to some high-pressure lamp types to accomplish this objective. Like the mercury, these halides are incorporated into the arc stream, with resulting changes in UV emissions. Figure 2 shows the spectral output of a typical high-pressure lamp employing metal halides.
The modern high-pressure technology results in more total output and more UVB than earlier types. This means there is somewhat more pigment-generating efficiency without sacrificing pigment darkening. Both high-pressure styles still are in service in the United States, though metalhalide styles are becoming more prevalent. High-pressure lamps are contained in fixtures with one or more lenses and filters which, and this bears repeating, should always be in place and in good repair. This arrangement provides for two things: 1) containing hot lamp shards in the event of a rupture failure, and 2) filtering undesirable wavelengths emitted by the lamp.
For any questions or comments about this topic, or if you have a specific lamp question you would like answered, please e-mail sales@wolffsys.com or call (800) 959-6533.
