||Siemens Brothers of Preston, England was perhaps the most scientifically oriented producer of mercury lamps. The physics laboratory was responsible for many breakthroughs in discharge technology, and so frequent were the improvements to their lamps that its rare to find any two the same. Dozens of electrode geometries and chemistries were evaluated, along with the addition of colour-enhancing elements to the discharge and physical assembly techniques.
Siemens is also the only known company to have offered these unique coloured MA lamps, intended for floodlighting applications. Yellow, Green and Blue glass envelopes were developed to transmit only those peaks in the mercury lamp spectrum, and a long arc neon lamp was offered for red lighting. Their use was probably very rare by virtue of the fact that they do not appear in any of the company's catalogues and these are the only known examples.
The electrodes take the form of large diameter open tungsten coils in line with the arc - Siemens being the first company to recognise the benefits of the hollow anode ring design to extend electrode life. The main electrode consists of an oxide-coated tungsten coil mounted at the centre of the anode ring. A very large auxiliary electrode resistor is necessary in this design and it is sleeved in a glass tube and mounted near the cap. Finally, it should be noted that Siemens Bros. worked independently of German Siemens, all ties between the two companies had been severed with the second world war. Siemens Bros. merged with Royal Ediswan to form Sieswan, which was amalgamated with Ekco and Metrovick to form AEI many years later and it ultimately ended up as part of the Thorn Lighting Group.