Tips on How Ultraviolet Specialty Fluorescent and Germicidal Low-Pressure Gas Discharge Lamps Work

Many custom designed fluorescent and germicidal lamps are considered special.  Beneath the thin layer of phosphor on fluorescent lamps, there are no appreciable differences in the anatomy of these two types of lamps. The basis of operation is the excitation of mercury atoms and the extraction and use of the ultraviolet photons. 

When the lamp starts, mercury atoms are excited by collisions with electrons which are “boiled” off coated tungsten coils (electrodes) at the ends of the lamp. Since the lamp contains a trace of mercury vapor along with a rare gas (either pure or as a mixture), the emitted electrons collide with mercury atoms exciting them. The excited atoms will eventually emit photons. The colliding electrons energies must be “tuned” by adjusting the gas composition and/or pressure to assure just enough energy to do the job but not so much as to ionize the Mercury. The amount of mercury vapor must also be controlled since either too much or too little will result in a loss of visible light or UV output.

In both fluorescent and germicidal lamps, the ultraviolet radiation emitted by the excited mercury atom does all the work. In fluorescent lamps and type “L” germicidal lamps (made with quartz that blocks 185nm) it is the 254nm photon that is critical.  For the purposes of ozone production and/or TOC reduction, the emission of the 185nm photon comes into play. The 185nm wavelength is a very energetic line produced by all low-pressure mercury lamps, but “blocked” by the doped quartz germicidal “L” glass or the phosphor coated soda lime glass body of the fluorescent lamp.  Making the germicidal lamp body out of pure “VH” glass will allow the 185nm radiation to reach outside of the lamp.

The “specialness” of low-pressure gas discharge lamps is largely in the gas pressure and gas composition to achieve the desired specialty lamp performance characteristics (lamp diameter, operating current, temperature, desired power level, uv/light output, color, etc.)  Gas pressures vary depending on lamp diameter; lower gas pressures for large diameter lamps and higher gas pressure for smaller diameter lamps. Gas composition also varies for changes in diameter and power level.

For two lamps of exactly the same design and operating current differing only in length, it is the longer of the two lamps that would be the most efficient.  Since the power lost at the ends is dependant only on current and electrode design, longer lamps have less power loss at the ends. Overall lamp geometry (length, diameter, even bent lamps) affects lamp starting and operating voltage.

Specialty low-pressure gas discharge lamps can be designed to meet a variety of visible light and non-visible UV applications.  Performance criteria requirements are determined by using a combination of lamp material, lamp processing schedules and design parameters to result in the “special” lamp for that unique application.

LightSources and our affiliated companies represent the leading high-tech designers and manufacturers in the lamp industry today.  Our products are used world-wide in a multitude of applications and industries such as our UV germicidal lamps that offer patent-protected, OEM-oriented solutions.  Please contact us to learn more about our extensive selection of lamps.