The IEC Spectrum Lamp Power Supply & Stand is specially designed for use in the classroom. It is powered from 220/240V.AC. 50/60Hz mains and is fitted with a removable mains cable. Spectrum tubes are not included. Spectrum tubes are special long thin discharge lamps (sometimes called Geissler tubes or Capillary tubes) which, during manufacture, are filled with certain specific gases. When electric current is passed through the gas, the discharge glows and a certain set of known wavelengths of light is emitted and is used for optical experiments. The voltage required to force the gas to conduct electric current is very high (several thousand volts) but, once conduction begins, a much lower voltage is required to maintain the current flow. The power supply provides these conditions. A gas discharge tube has a low light output.