Hmmm again. I recently bought some UV LEDs on eBay for about US $0.50 each. Supposed to be 385nm wavelength. When I tried one, it produced a faint visible glow - whiteish blue if I recall correctly, but it definitely could make UV-sensitive materials fluoresce (like the security bands in US paper currency). Have I been duped or has there been a recent breakthrough that makes these kind of UV LEDs cheap? It also seems to me that I've seen tiny "blacklight" pens for several years now which are intended to check for valid currency. These seem to be using LEDs. Am I wrong? The output of these devices definitely is not bright blue light. Sean On Mon, Jan 14, 2013 at 9:58 PM, RussellMc wrote: >> Hmmm, I always assumed that the "blue light" device used to cure >> dental adhesive was actually a UV source which just happened to "spill >> over" into the visible spectrum and produce a small amount of visible >> light. > > No. That would have been a logical conclusion based on what we know > about sun-tanning etc, but the dental and similar LEDs are typically > "Royal Blue" with relatively little energy in the near UV region and > essentially no deep UV. > > UV LEDs producing even a few mW of power have until recently cost > hundreds of dollars. > Nichia now have some UV LEDs at a range of wavelengths in their latest > catalog. Samples on request. POA :-(. > > Manufacturers such as Cree offer Blue, Dental Blue and Royal Blue LEDs > with wavelength decreasing - ie Royal Blue is closer to UV than Dental > Blue is. > > The attached graph shows spectral distributions for the Cree XT-E warm > White & Royal Blue LEDs. > Compare the shapes of the blue components. > > > Russell McMahon > > Interest only: Graph saved at JPG60 (low res) and with Irfanview RIOT > bandwidth limiting plugin. > > JPG70 39kB > JPG60 34 kB > JPG60 + 20kB RIOT limit 20 kB. > > Additional noise visible on RIOT limited image but superb result for > the file size. > > > > Russell McMahon > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .