Plasma "arc" or discharge lamps using hydrogen are notable for their high output in the ultraviolet, with comparatively little output in the visible and infrared. This is similar to the situation in a hydrogen flame. Arc lamps made with ordinary light-hydrogen (hydrogen-1) provide a very similar UV spectrum to deuterium, and have been used in UV spectroscopes. However, lamps using deuterium have a longer life span and an emissivity (intensity) at the far end of their UV range which is three to five times that of an ordinary hydrogen arc bulb, at the same temperature. Deuterium arc lamps, therefore, despite being several times more expensive, are considered a superior light source to light-hydrogen arc lamps, for the shortwave UV range.