Siemens MAT/V "Dual" Mercury Blended

The MAT lamp is a very rare and most unusual looking light source, which represents the first known example of a tungsten filament being used to ballast an electric discharge, the two elements being enclosed in the same outer bulb. It was invented in 1935 by Dr. J.N. Aldington of Siemens Electric Lamps & Supplies in Preston, England, and was first marketed on September 2nd of that year.

The filament performed the dual role of ballasting the discharge, and increasing the red ratio of emitted light. It was a popular light source in industrial installations before the development of phosphor-coated lamps, which increased the red ratio by a more efficient mechanism. In order to cause the arc tube to run-up suitably quickly, a higher current is required for the first few minutes. A normal inductive ballast will take care of this automatically, but a resistive tungsten filament is not suitable. At ignition, only half the filament is used and this permits higher current flow to warm up the arc tube quickly. After a few minutes, the closing of the contacts of a bi-metal switch near the lamp cap brings the rest of the filament into circuit, ensuring that both the arc and filament are then driven at a safe operating current. This specialised construction made MAT lamps very expensive, and before long they were totally superseded by cheaper MBT quartz mercury products.

MAT Mercury-blended lamps were manufactured solely by Siemens Bros. of Preston - however that company later became amalgamated into AEI and this very late design of MAT lamp was made at AEI's Leicester lamp works according to that factory's design, after all discharge lamp production had been centralised in Leicester.
Manufacturer: Associated Electrical Industries Ltd.
Lamp Power: 300 Watts
Lamp Current: 1.30 Amps
Lamp Voltage: 230 Volts
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Finish: Clear Soda-lime glass
Bulb Type: GS-85 GS-27 in eighths/inch
Overall Length: 285 ± 15 mm 111/4 inches
Light Centre Length (Arc): 160 mm 61/4 inches
Light Centre Length (Coil): 255 mm 10 inches
Electrodes: C-6 Open Coil Thoria pellet emitter
Atmosphere: Inner: Hg | Ar (1 atm) Outer: Nitrogen
Luminous Flux: 6,300 lm (@ 100hrs) 5,400 lm (@ 2,000hrs)
Luminous Efficacy: 21.0 lm/W (@ 100hrs)
Colour Temperature & CRI: CCT: CRI:
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Vertical cap up
Rated Lifetime: 3,000 hours (to 50% survival)
Warm-up & Re-strike Time: 5 minutes 10 minutes
Factory: Leicester England
Date of Manufacture: Circa 1955
Original & Present Value: £3 0s 0d (1959) £62.95 (2015)
References: 1) AEI-Mazda Lamp Catalogue, UK, 1959, Section A9
2) Aldington, J.N.,Electric Lamps & Kindred Devices, Siemens Engineering Bulletin, December 1948
3) Light & Lighting magazine, Oct. 1935, p.348