High pressure tanning equipment got its name from the tanning lamp technology used. All true high pressure tanning systems utilize short-3 inch quartz lamps filled with mercury vapor that produce very high ultraviolet radiation (UVR) intensity levels. The pressure of the mercury vapor gas inside the tanning lamp is higher than that of a long tube lamp found in traditional tanning beds, thus the name "high-pressure" tanning was coined.
Low pressure tanning equipment got its name in much the same way. The difference is that the lamps used in low pressure tanning beds (identified by long tubes that run the full length of the tanning bed) have a negative atmospheric pressure or "vacuum". These are examples of low pressure tanning beds because they contain long tube style bulbs.
Both types of tanning beds can be highly effective at producing a tan but in recent years there has been some confusion between salon owners and tanners when it comes to high pressure. Some salon operators advertise having a high pressure bed when technically speaking, they do not. Others define high and low pressure beds by the amount of UVA and UVB the lamps put out. Based on this thinking, the higher the UVA, the more "high pressure" it is. This concept would allow long tube lamps that have a high UVA output to be classified as a high pressure and the small quartz lamps that output high UVB levels to become classified as low pressure. Again, this is not the case and it never has been. Simply put, a tanning bed that uses any number of long tube lamps is not a true high pressure bed. High and low pressure is defined by the lamp type used and never by the UVA/UVB output of that lamp.