I recently purchased a spectrometer from Science Surplus, and have calibrated it using known stable DPSS wavelengths (473, 532, 561, 589 and 593.5). With the spectrometer's default diffraction grating, I can get a range of a bit over 200nm. While the DPSS approach has worked great so far, I'm looking to re-calibrate my spectrometer to cover the 400 to 600 nm range.
This means that I really need to locate a calibration light source, of some sort, in the very low 400s (or even in the high 300s). Can anyone brainstorm a creative calibration light source that would fit the bill? (my bill, by the way, is something I hope to keep to under $30). The light source doesn't need to provide anything other than the low 400 spectral line. I can use a 473, 532, and 561/589/593.5 for the rest.