||During the early 1890s some particularly novel forms of incandescent lamps appeared, as manufacturers tried to circumvent the Edison patents. One of these was the Novak lamp invented by John Waring in 1893, whose design differs from the Edison patent, as its name would appear to imply, by virtue of the fact its bulb contains no vacuum.
Novak lamps employed Perkins filaments of rectangular bamboo, treated by the Weston process to achieve a more uniform section. These were inserted into small tubes of platinum formed from the lead wires. Note the shiny metallic appearance of the deposited carbon joint in the close-up photo of one of the mounted filament tails. The exhuast sequence consisted of evacuating the lamps with a simple mechanical pump and admitting bromine vapour, a second pump-fill cycle, and finally pumping to 1/600th of an atmosphere - leaving about 1500 microns of bromine.
It was claimed that the presence of bromine improved lumen maintenance over life by ensuring that carbon deposited on the bulb had a pale greenish colour instead of the usual black. In fact a halogen cycle was not operating, instead the bromine is believed to have acted as a getter.
Novak lamps were made at the premises of Waring's former employer, the Perkins Electric Lamp Company, which had been closed down by Edison litigation in 1892. It was made only very briefly because the courts deemed the pressure of bromine to be so small that it was in effect a vacuum lamp and thus violated Edison's patent. However the Edison patent itself expired in 1894, and Waring escaped closure. After this time production switched to vacuum lamps.