MD Water-Cooled Super Pressure Mercury

Mercury Vapour lamps operating at super high pressure and with water-cooled quartz arc tubes are classified as the MD style. Mercury vapour pressure is typically in the region of 50-200 atmospheres and the discharge dissipates more than 100 watts per centimetre of arc length.

The reason for the development of the MD lamp was to create a source of extremely high surface intensity with high colour temperature. It found a multitude of technical and laboratory applications and less frequently could be found in photographic projection apparatus and television studio illumination.

To create such high brilliancy from the arc an extremely high power loading is necessary, and there is no known arc tube material capable of withstanding such conditions without auxiliary cooling. To prevent even the quartz bulb from instantaneous destruction, the arc tube can only be lighted inside a water jacket which causes chilled water to flow over the arc tube surface at extremely high velocity. The flow rate must be suitably high to prevent boiling of the water in contact with the arc tube, which would otherwise lead to an explosion from the great amount of steam produced in the chamber - followed of course by explosion of the arc tube itself!

The general failure mechanism of MD lamps is devitrification of the quartz arc tube. Either it becomes so opaque that the intensity falls off and the lamp becomes useless for its application, or it will become sufficiently weakened that it cannot contain the pressure and will explode. Despite the immensely high pressure within the arc tube the explosion is not particularly violent in view of the very small tube volume. Typical service life is of the order of fifty hours or so.



MD/H arc tube with water jacket



SP500 arc tube mounted in reflector housing



H-6 Super pressure water-cooled arc tube



Mercury Capillary with curved & coated tube
c. 2000