Low pressure mercury vapor discharge lamps are commonly used to generate ultraviolet radiation and used to irradiate a fluid to kill potentially harmful organisms contained in the fluid. Often, relatively high doses of ultraviolet radiation are required. The necessary relatively high doses of ultraviolet radiation typically require the use of multiple germicidal lamps. The use of multiple germicidal lamps increases expenses, as well as maintenance. Therefore, it is desirable to use fewer higher output germicidal lamps. However, producing a high output germicidal lamp is not without difficulties. During operation of a low pressure mercury vapor discharge lamp, the vapor pressure of the mercury greatly affects lamp operation. A predetermined vapor pressure is desirable for efficient operation of the lamp. However, under heavy loads used to produce a high output, mercury vapor pressure may increase reducing the efficiency and operation of the lamp. Amalgam has often been used to control the mercury vapor pressure within the lamp, permitting the lamp to operate more efficiently. However, the higher temperatures occurring at high loading of the lamp often cause the amalgam to melt. If the amalgam melts, it will move out of position and could make contact with an electrode and cause possible shorting or ineffective operation of the lamp.
A germicidal lamp using an amalgam is disclosed in Patent Cooperation Treaty international application No. PCT/DE96/00647 having a publication number of WO96/31902 and published Oct. 10, 1996, entitled “Low Pressure Mercury Vapor Discharge Lamp”. Therein disclosed is a low pressure mercury vapor discharge lamp having an amalgam placed along the inner wall between the electrodes. The lamp tube is in mechanical contact with a cooler on the outside of the lamp adjacent the location of the amalgam. While this lamp structure is helpful in keeping the amalgam cool and therefore permitting higher loading of the lamp to improve output, the amalgam could still melt causing the amalgam to move out of position. This is particularly problematic in applications where the lamp is held vertically rather than horizontally, which could result in the amalgam falling downward onto one of the electrodes.
Therefore, there is a need for a low pressure mercury vapor discharge germicidal lamp for producing a high output of ultraviolet radiation that reduces the possibility of an amalgam melting or moving out of a desired location during high loading.