Osira Medium Pressure Mercury MA/V 150W
In 1932 Osram-GEC of England introduced the world's first high-efficiency hot cathode mercury vapour lamp for general lighting applications. It was rated 400 Watts and intended to replace 1000W incandescent lamps for streetlighting of main roads. By 1934 it was joined by the smaller 250W rating for secondary roads, and the market called for an even lower power lamp for small industrial lighting applications. That was, however, not so easy to develop, and this 150W rating was produced only very briefly during 1936-37.

As the power of a mercury lamp is reduced its efficacy also drops. This is partly due to energy losses at the electrodes, which are approximately constant irrespective of power and become more significant at lower wattages. The reduction in discharge current density also causes a drop in efficacy. Ideally current would be kept high and the power reduced by reducing arc voltage - but to avoid excessive losses in the control gear, arc voltage can only be reduced slightly. The result was that the 150W MA lamp was so inefficient that it was not a commercial success.

These drawbacks can be overcome when mercury vapour pressure is increased, which causes a helpful increase in arc voltage. However, a higher mercury vapour pressure calls for a hotter arc tube, and the early aluminosilicate glass used for MA lamps would soften at such high loading. A successful low power mercury lamp was not feasible until the introduction of the high pressure types using quartz arc tubes, which can withstand the necessary high temperatures and increased power loading. Shortly after that had been achieved in 1936, the MA 150W lamp was replaced by the considerably more efficient MB 125W.
Manufacturer: The General Electric Company of England
Lamp Power: 150 Watts
Lamp Current: 1.4 Amps
Lamp Voltage: 120 Volts
Cap Type: E27s Brass + Vitrite
Bulb Type: T-43 T-13½ in eighths/inch
Bulb Finish: Clear Soda-lime soft glass
Electrodes: C-8 Open Coil Thoria pellet emitter
Arc Length: 88 mm 3½ inches
Atmosphere: Inner: Hg | Ar (1 atm) Outer: Oxygen
Luminous Flux: 4,800 lm @ 100 hrs
Luminous Efficacy: 32.0 lm/W @ 100 hrs
Colour Temperature & CRI: CCT: 5400K CRI: Ra 6
Chromaticity Co-ordinates: CCx: 0.337 CCy: 0.421
Lifetime: 1500 hours
Warm-up & Re-strike Time: 6 minutes 10 minutes
Burning Position: Vertical ± 10°
Overall Length: 230±15 mm 10 inches
Light Centre Length: 144±10 mm 5¾ inches
Factory: Hammersmith England
Date of Manufacture: 1936-37 Date Code: 5C16
Original Value: £1 15s 0d (1937)
References: 1) Osram-GEC Catalogue 1937 p59
2) The Electric Discharge Lamp, A Survey of Development, J.N. Aldington, Engineering Supplement to the Siemens Magazine No.138, November 1936
3) Timeline of Mercury Lamp Developments, Simon Cornwell