||The high pressure mercury lamp is a very convenient light source in the laboratory. Not only is it a useful ultraviolet and line-emission spectrum reference, it also has a number of projection applications in particular where monochrome images are being projected.
BTH Mazda developed this 125W high pressure mercury lamp specifically to deliver maximum performance in laboratory applications. It has a quartz arc tube loaded at 42W/cm of arc length and operates at a pressure of 8-10 atmospheres. The principal application this lamp was created for was as a source of short wave ultraviolet in spectral photometers.
Its most notable feature is that there is a diaphragm pierced by a small hole at each end of the arc tube just ahead of the electrodes, and these serve two purposes. Firstly should the arc root position change on the electrode, the main arc will still be constrained in the point between the two diaphragms thus flicker is greatly reduced and the arc does not swirl around. Secondly, much of the material sputtered and evaporated from the electrodes does not travel through into the centre of the arc tube. Nearly all of the blackening takes place in the end chambers thus the light output from the central arc region is almost unchanged during lamp life.
The lamp is hand made throughout, with very long molybdenum foil seals terminating in a cold region inside the bakelite base to prolong service life. Both end chambers are coated with platinum paint to conserve heat. The lamp can be operated on DC, but it is essential that the cap contact adjacent to the long seal is made the positive terminal.