As I understand it, the most efficient LEDs peak at around 395nm, but I think that some are available working down to a little over 200nm. In my particular case, I don't actually have a current interest in using the spectrometer down in the UV; my interests are in the the VIS-NIR region.....but, this instrument goes through a self-test on start-up which fails if the UV source is not good, but I don't know what wavelength that check is made at.
E