These wavelength-indexed spectra always seem a bit weird... the blue is so cramped! When you plot them by frequency they feel just right. We say "ultraviolet

These wavelength-indexed spectra always seem a bit weird... the blue is so cramped! When you plot them by frequency they feel just right. We say "ultraviolet" and "infrared" for a reason; never "infraviolet" or "ultrared". It's like a piano that had the high notes to the left.