![]() (Source: The published specifications of this product are not particularly remarkable, but they are useful in that they enable us to evaluate the usefulness of this technology for germicidal applications. One of their evaluation products is of particular interest, as it generates nearly “monochromatic” 222-nm UV-C radiation ( Figure 2). However, one company – Eden Park Illumination – has adapted the technology formerly used in plasma television displays to produce thin microplasma lamps intended for general illumination purposes. For example, a combination of krypton (Kr) and chlorine (Cl) gases forming a Kr-Cl excimer emits 222-nm radiation, while krypton and bromine emit 207-nm radiation.Ĭompanies such as Ushio and SterilRay manufacture excimer lamps and products for industrial and medical applications, but the lamps are typically comparable to fluorescent lamps in size and form factor (e.g., Figure 1). This does not stop us, however, from asking the question: what does it take to design a UV-C disinfection system using far-UV radiation? Excimer LampsĮxcimer lamps consist of diatomic molecules that form a plasma when an electrical current passes through them. Indeed, there are already companies advertising such products, although they do not appear to be commercially available as yet. Unlike mercury-vapor lamps and UV-C LEDs, there does not appear to be any significant photobiological risk (if their residual UV-C emissions-those outside the 207-nm and 222-nm narrowband emissions-are blocked), and so they could be deployed in direct view of room occupants while disinfecting both the air and contaminated surfaces with their radiation. This leads to the exciting thought that we may be able to design UV-C germicidal systems using far-UV excimer lamps. Excimer lamps have the same germicidal properties as mercury-vapor discharge lamps, but the shorter-wavelength radiation cannot penetrate deeply enough into the outermost cells of the eyes and skin to disrupt their DNA. Recent medical studies have indicated that, unlike 254-nm radiation, the 207-nm and 222-nm “far-UV” radiation emitted by excimer lamps is likely harmless (e.g., Buonanno et al. More recent germicidal light sources include UV-C light-emitting diodes and pulsed xenon discharge lamps, but there is a newcomer on the block that has gained considerable media attention: far-ultraviolet excimer lamps. Unlike UV-B radiation (280 nm to 315 nm), UV-C radiation is much less likely to cause long-term cellular damage leading to skin cancer. These medical conditions typically only last for a few days, but they can be quite painful. The photobiological risks of these germicidal lamps are well known: exposure to UV-C radiation can result in photokeratitis (“snow blindness”), photoconjunctivitis (“pink eye”), and erythema (sunburn). They emit monochromatic radiation mostly at 254 nm, a wavelength that is very effective in disrupting the DNA of viruses, bacteria, and other pathogens. These are most commonly low-pressure mercury-vapor discharge lamps, which are basically fluorescent lamps without a phosphor coating and fused quartz rather than borosilicate glass bulbs. Germicidal lamps emitting ultraviolet-C (UV-C) radiation have been in use since the 1930s (Wells and Wells 1936). ![]() Senior Scientist, SunTracker Technologies Ltd. ![]() The views expressed in articles published on FIRES do not necessarily reflect those of IES or represent endorsement by the IES.
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