1945 GE-Mazda A-H4

The development of modern high-pressure mercury lamps began in Europe in the early 1930s resulted in the commercial introduction of the first hard-glass atmospheric lamp by GEC (England) in 1932 and of the superior quartz superatmospheric variant by Philips (the Netherlands) in 1935. The latter technology was applied primarily to lower-wattage mercury lamps due to its higher efficacy compared to that hard-glass lamps below 250 W. It is only in 1938 that mercury lamps with quartz burners were introduced in the USA by GE, in the form of the 85 W H3 and the 100 W H4. While the first type was intended as a source of visible and ultraviolet radiation for lab applications, the second type, shown here, was aimed at general lighting purposes.

At that time the smallest hard-glass mercury lamp available in North America was the 250 W H2 with a light output equivalent to that of 500 W incandescent lamps. The introduction of the smaller H4 targeted applications catered for by 200 W tungsten filament lamps, and more particularly street and industrial lighting, areas where color quality is not of prime importance. Since mercury lamps requires a current-limiting ballast for its operation, the H4 was made with a special admedium (E29) end cap in order to avoid its accidental use in incandescent lamp sockets. Discharge lamp control gears were a relatively new lighting component at that time, and the risk of lamp mismatch was not negligible.

The burner used in the present A-H4 has a design typical of very early quartz mercury lamps, featuring electrodes attached to the quartz vessel via graded-glass seals that form gas-tight feedthroughs. The main electrodes are made of a tungsten rod sheathed with a tungsten coil which holds a sliver of thorium metal whose purpose is to optimize electron emission. A third auxiliary electrode, located sideways and connected to one of the main electrodes via a wire-wound ceramic resistor, ensures a reliable discharge ignition at low voltages. The quartz burner is held into place by two metal cups, shaped to limit heat losses behind the main electrodes, thus preventing mercury condensation there. This ensures that the lamp operates at its 8 bar design pressure, critical to the realization of an efficacy of 33 lm/W, about 80 % higher than that of 200 W incandescent lamps.



This 100 W mercury lamp proved very popular and initiated a long lineage of discharge lamps that dominated street and road lighting applications well into the 1970s. Interestingly, its mercury burner was also used in the S4 sunlight source, introduced around the same period as the H4. The main difference between the two lamps lies in the shape and glass nature of the outer bulb. The design of the A-H4 shown here was improved in the early 1950s with a mechanically pinched quartz burner provided with molybdenum foil seals, and with starting electrode fed via a small carbon resistor. During that decade several variants of the 100 W mercury lamp emerged in order to cater to various specific applications. The original tubular A-H4 was then assigned to general and black-light lighting and its design saw little changes in the following decades. While general and street lighting lamps benefited from the introduction of the oxide electrode in 1958, the A-H4 remained produced with its original thorium electrodes, which capped its service life to 6 kh at 50 % failure while that of other mercury lamps reached four times that duration. GE eventually phased out its tubular 100 W mercury lamp in 1990.