Manfacturer: British Thompson-Houston
The lamp shown here is a very early mercury vapor lamp. It is a tubular 400 watt mercury vapor lamp with a large, medium pressure arc tube. Unlike todays' mercury lamps that use smaller quartz arc tubes, the arc tubes used in early lamps are actually made of aluminosilcate hard glass. Although the basic technology for mercury vapor was first invented as a low pressure tube (called the Cooper-Hewitt tube) back in 1901, commerically available mercury lamps using medium to high pressure arc tubes did not come out until 1933, and were developed by GE in the USA and BTH in England. The US version was called the 400 watt H-1 Mercury Lamp, soon followed by the 250 watt H-2 Mercury lamp, which came in two versions, one with a medium base and no outer bulb (see photo of H-2 mercury on this page), and a T-16 mogul based lamp physically similar to the H-1 but a few inches shorter. The British versions, like the one shown here, were called MA lamps, which refers to medium pressure mercury technology. The US and British ones are very similar (save for the E-39s and E-40s bases) and use the same basic technology. I previously thought the US and British versions were incompatible because I have heard of them running on different voltages, but they turn out to actually be compatible because both types have a nominal starting voltage at 240 volts and a nominal operating voltage at 130 volts.
While the medium pressure mercury lamp was proven to be more efficent and longer lasting than the high wattage incandescents they were designed to replace, they had some drawbacks. Due to the lower internal arc tube pressure than later quartz lamps, the arc is not as constricted, thus if one is operated horizitonally, the arc would bow up severely, eventually blowing out the arc tube and outer bulb. For this reason, H-1 and MA lamps were made to only operate in vertically base up or base down, never horiziontal. This lamp shown here has the MA/V ordering code, the /V suffix refers to vertical operation. However, it was later made possible to operate these lamps horizontally by use of electromagnetic coils outside of the lamp in line with the arc tube, which controls the bowing of the arc tube. Some early mercury streetlight lumianires (such as the Form 109) came equipped with an electromagnetic coil as an option since they were introduced at a time when the medium pressure mercury lamp was still in heavy use. Mercury vapor lamps with 400 watt quartz arc tubes (the lower wattage quartz lamps came out earlier, however) were introduced in 1948, and eventually became the standard in the 1950s. The medium pressure mercury lamp continued in production at least through the late 1950s. Today, the old medium pressure H-1, H-2, and MA lamps are highly sought by light bulb (especially HID) and streetlight collectors, and can easily sell for good $$$ on eBay, especially in NOS condition. Enjoy the additonal photos shown below!
Lamp: MA Mercury Vapor
Wattage: 400 watt
Starting Voltage: 240/250 volts
Operating Voltage: 120/150 volts (on 240/250 volt curcuits)
Ballast Type: Unknown
Color Temperature: Unknown
CRI: Unknown
Light Output: 18000 Lumens (intial)
Bulb: T-16 Hard Glass (T-51 in international units)
Finish: Clear
Base: E-40s Brass Mogul Base (E-40s GES in internationa units)
Class: -
Filament: -
Lamp Life: 2,000 hours
Manf. Date: May 1943
Country of
Orgin: England
