Abstract
Spectral energy distributions of several radiation sources for ultraviolet region are briefly discussed. In practice, as the standard of spectral energy, the Krafft's standard lamp seems to be the most useful source at present. With the appearance of the photomultiplier as a high sensitive detector, the ribbon filament tungsten lamp would become useful source emitting continuious spectrarn in U. V. region.
As for the qualtz enveloped low pressure mercury discharge lamp, caution is necessary for its weak fluorescence in same cases. The high wattage Xe-arc lamp is the strongest source emitting continuious spectrum in U. V. region. The hot cathode hydrogen discharge lamp can be easily stabilized in its radiation intensity with application of vacuum tubes, so that it is a quite suitable source for measuring absorption transmission etc.
