Ultraviolet Lights To Read Watermarks

It was suggested that I could read watermarks with an ultraviolet light, which I note was not the case, according to a search of this database (Stamp collection essentials and others) - was also advised that there were two settings pson some UV lamps(two types of UV?) where one would work. Can you shed any light (no pun intended) on this subject?
It was also mentioned that the UV light was useful for 'tagged' stamps.
Same question.

Thanks
Art

I don't recommend using UV light for detecting watermarks -- it doesn't always work well (my opinion). It's much easier to simply use watermark fluid and a small black tray.

To detect tagging on US stamps, you will need to use a shortwave UV light (~254nm, preferably filtered). The consumer grade black lights you get at the malls or party supply stores are too broad-spectrum to use for this purpose.

Different countries use different taggants, which means the excitation frequency will not necessarily be the same. For US and Canadian stamps, use short-wavelength UV. On most US stamps, the taggant will glow green or red. There are a handful of exceptions.

Yes, I tried it with (probably) a uv light with the same characteristics you mention.
Thank you for the info on taggants as well. Can you tell me who sells the short wavelength UV lights? Or what type of store?
Art

Art, try this thread
https://goscf.com/t/26540

Outstanding.
Thanks much.
Art