Comments About the Article ``On the Similarities of Low-Temperature Plasma Discharges''

The Comments present some information that is valuable in our opinion, but absent in the article ``On the Similarities of Low-Temperature Plasma Discharges'' (Y. Fu, and J. P. Verboncoeur, IEEE Transactions on Plasma Science, Vol. 47, No. 5, PP. 1994-2003, May 2019). The cited article considers the validity of the similarity laws for low-temperature plasma discharges in different discharge regimes and describes recent experimental and numerical studies, including the scaling of gas breakdowns and steady-state discharges. It is stated that the motivations of this article also include increasing the fundamental understanding of basic plasma sciences. This article is rather informative. However, the authors did not consider the very important and widely used example of discharges - low pressure discharge light sources (mercury fluorescent lamps, sodium lamps of low pressure etc.). It is known that for such discharges there are particular similarity laws. Besides, in the cited article, there is no description of real similarity law application to plasma diagnostics. There is also no satisfactory explanation for the physical reasons of the similarity laws occurrence. So, the focus of attention of the Comments is to fill in the lack of this information for readers.