Measurement of the Ultraviolet Output of an Underwater Monochromatic (254 nm) Low Pressure–Mercury Ultraviolet Lamp

Abstract

The International Ultraviolet Association (IUVA) recommended a method to measure the ultraviolet (UV) output of monochromatic (254 nm) UV lamps. In that method, the lamp is operated in open air and it is not applicable to the underwater UV lamp because temperature influences the UV output of a UV lamp. In this work, a method to measure the UV output of a UV lamp inside a quartz sleeve that is fully immersed in water was established. First, the quartz sleeve was set to be partially immersed in water and the UV output was determined by the IUVA method for a lamp in open air. Second, the measured value was modified by the ratio of the measured relative UV outputs in the cases that the lamp and quartz sleeve was fully and partially immersed in water. The measurement outcome was the UV emission from the quartz sleeve, which is the concern in UV application, rather than that from the lamp. When applying the measurement method, it is key to control the water level to be lower than a threshold. A formula to calculate the threshold of the water level was derived.