Wilkey, my lamp emits at wavelength 254nm - well into the short wave range. Like I said, however, it's a cheap lamp and it might well be firing off some long wave stuff as well.
Like this one:
http://cgi.ebay.com/L85-Short-Wave-UV-Lamp...1QQcmdZViewItem
I do know that some "invisible" markers on stamps and banknotes are designed to only be detectable under short wave as this kind of light is not as likely to be encountered from lamps bought in the usual light bulb stores. The Cuban seals apparently are not if folks are getting them to glow under the more common long wave lights.
Whatever the nature of the markers, I'm just glad that the seals are made with the phosphorescent markers so that we have another tool to help find the forgeries.
Your point about the usage of these lamps in philately is well taken. In fact, I got my lamp from CP member Centurycigar, who is a dealer of stamps (and coins, I think.) He tried both lamps he had in stock, long and short wave and reported that it was the long wave, and the long wave only that made the seal fluoresce.
Your comments have caused me to go back and reexamine my understanding about this subject. As a start, I pulled up information on Ciba Uvitex-OB, a workhorse brightener that I have used and that is a good example. This compound absorbs strongly between 335nm and 405nm with 20% relative intensity down as far as 305nm. It emits strongly between 405nm and 485nm. 245nm is way down into the deep UV part of the spectrum and I doubt that something like a Uvitex OB would respond visibly to that wavelength. However, this is not an ink grade brightener.
The fact that the image did not fluoresce under 395nm suggests that it was not responsive to deep blue. However, near-UV is just a bit further down at 360-365nm. Shortwave is down below 275nm so there is a big gap where things seem to light up. Without knowing the actual wavelength output by my lamp, I can't feel really confident that I know for sure what is going on.
Wilkey
Well I got to say, I appreciate all the information! For a simple guy like myself, I'm confused as hell. Maybe I'll just smoke NCs. :laugh: