A dielectric barrier discharge based low pressure narrow band far UV-C 222 nm excimer lamp and its efficiency analysis

Far UV-C light at wavelength 222 nm is gaining popularity nowadays due to its properties that it cannot penetrate even the outer dead skin of humans and the tear layer of the eyes. This wavelength has been proven to be much safer for human health. In this paper, a dielectric barrier discharge (DBD) based Far UV-C excimer lamp with a very narrow and intense spectrum peaking at a wavelength of 222 nm has been reported. Optimization of high voltage electrodes has been carried out to minimize the lamp heating without using any external cooling. The discharge produced in this configuration is diffused discharge at a low pressure of 140 mbar. Generally, at low pressure, a very wide band of spectra having full-width half maxima (FWHM) of 8-15 nm is obtained. In this case, due to the confined gas gap and bi-polar pulse power arrangements, the spectra obtained are very narrow, having an FWHM of 1.7 nm. Applied voltage, frequency and gas pressure are optimized to get high electrical-to-optical conversion efficiency of the lamp. The measured radiated intensity at the applied input electrical power of 31 W from the optimized lamp is ∼2.5 mW cm−2, which results in the electrical to optical conversion efficiency as high as 12.5%. The bacterial efficiency of the developed lamp is also examined on pathogenic gram-positive (S. aureus) and gram-negative (E. coli) bacteria. Complete inactivation of S. aureus and E. coli has been achieved at a UV dose of 3 mJ/cm2 and 12 mJ cm-2, respectively. Morphological studies of treated bacteria have also been performed to correlate the results.