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.