Differences Between a Regular Fluorescent and Germicidal UV Lamp 

The differences between a regular fluorescent lighting lamp and a germicidal UV lamp are outlined below. The most noticeable difference is that the germicidal UV lamp does not contain the white phosphor coating on the inside of the glass envelope of the lamp. This phosphor coating is what actually produces the visible light in the regular fluorescent lamp. We’ll start by explaining how the UV radiation of a germicidal UV lamp is produced. When a voltage (typically, steady state) is applied across the lamp, an ionizing effect of the surrounding low pressure mercury (Hg) vapour gas mixture (including the Penning gases) in the vicinity of the filaments at one end of the lamp causes a breakdown of the ionization potential of the gas establishing an arc discharge along the path length of the lamp to the other end where the second filament lies. The arc discharge emits germicidal ultraviolet (UV photon) radiation, typically in the wavelength region between 250-280nm (a subcategory of the UV-C spectrum) in addition to a small amount of 185 nm. In a regular fluorescent lamp, when the UV photons strike the phosphor coating on the inside surface of the lamp envelope they become converted to visible light. 

Other differences between these two lamp types are: 1) with the medium pressure UV lamp, involving the excitation to a metastable state of the noble or fill gases, an increase in Hg vapour gas pressure produces a higher power lamp plasma, 2) the material of the glass envelope of the UV lamp typically involves the use of quartz to allow for higher lamp wall operating temperatures. This also affects or determines the UV content of the emitted spectrum, 3) Hg amalgams can enhance the UV emission of a germicidal lamp (in many cases doubling or tripling the UVC output) which in turn increase its operating temperature to near 100°C. This results in a more stable operation of the lamp over a wider ambient temperature range, 4) clear coatings, which are proprietary to manufacturers of UV lamps, can be added on the inside of the quartz envelope to enhance UV maintenance of germicidal lamps and 5) special coatings (typically, BaO) can be added to the filaments of the UV lamps to reduce sputtering and improve their robustness and quality and increase their reliability. 

by Bill Himaras

Aug 4th, 2021