The Celtic Glow Worms were named that because:
We've planted this "glow" bit very deeply in our cheeks, and for the purposes of the FORKNI-L/FKFIC-L War universe, found that all of us, and all of the regular (fictional) staff at the Fiendish Glow have a peculiar sort of bioluminescence that is undetected by most humans (not sure about the vamps, yet!) and by most surveillance equipment.
Our glows are detectable by our special high-tech surveillance equipment (the stuff not generally available to the general public -- we use this equipment for recording anything from sensitive private meetings to social affairs) and also by those of us who have had direct or indirect contact with the Faer Folk on the astral plane. Celtic Glow Worms whose glows have been established in War fiction have the following-colored glows: