There have been multiple reports of blue light emanating from LENR reactors. I purposely won't mention names or specific examples. This is purely an exploration of the science.
For the sake of discussion, let's consider a situation where some element in a LENR cell emits photons from an ionized metal plasma under electrical or other stimulus.
Each element has characteristic strong emission line(s). For example Na (Sodium) is at 589 nm (5890 Angstroms). This is the typical yellow color of Sodium Vapor street lamps.
The blue part of the visible spectrum is roughly 420-480 nm. Refer to the list of metal vapor element/wavelengths at
We see only the following candidates, with peak wavelengths in nano meters:
Note that the emission wavelengths shown are for plasma-phase emission, not
merely thermal as would be seen in a chemical flame test.
Any of these could be present in the reactor. Calcium or Strontium may
be present as oxides (both are used for catalytic production of
Cherenkov radiation seems unlikely in this scenario, because the particles
causing it would have to be relativistic, slower than C but still very fast (really big energy required!)
The other possibility of course is the characteristic color of ionized air.
The typical blue color of an electric arc in air is primarily due to the emissions of ionized Nitrogen:
(Wiki) "Neutral nitrogen radiates primarily at one line in red part of the
spectrum. Ionized nitrogen radiates primarily as a set of lines in blue
part of the spectrum. The strongest signals are the 443.3, 444.7,
and 463.0 nm lines of singly ionized nitrogen"
I hope these comments will start a constructive discussion of the possible science behind various reports of visible blue light from LENR. Please leave politics and opinion out of the dialog.