Siemens MAT/V "Dual" Mercury Blended

The MAT lamp is a rather rare and most unusual looking light source, which represents the first known example of a tungsten filament being used to ballast an electric discharge with the two elements being enclosed in the same outer bulb. It was invented in 1935 by Dr. J.N. Aldington and W.H. Lemarechal of the British Siemens company, and was first marketed on September 2nd of that year.

The filament performs the triple role of ballasting the discharge, providing instant light at switch-on, and increasing the colour rendering properties. It was a popular light source in industrial installations until the 1940s, when it was superseded by the MBT type quartz mercury lamps.

One difficulty of employing a resistive ballast for a mercury lamp is the fact that the arc voltage changes considerably as the lamp runs up. Initially when the volt drop across the discharge tube is only about 15 volts, the current flowing through the resistance is very high, and in the case of a filament ballast this causes severe over-heating leading to a reduction in life. MAT lamps counteract this weakness by changing the filament resistance as the discharge tube runs up. At first the entire filament length is used, then after a few minutes once the discharge tube voltage has risen, a bi-metallic switch cuts out part of the coil. This construction made MAT lamps rather expensive, and was dispensed with in the later self-ballasted mercury lamps.

The electrodes in this lamp are of a particularly early design. They consist of a tungsten coiled-coil which pre-dates the use of normal oxide emissive coatings. Instead a pellet of radioactive thorium oxide is contained within the coil.
Manufacturer: Siemens Electric Lamps & Supplies Ltd.
Lamp Power: 300 Watts
Lamp Current: 1.30 Amps
Lamp Voltage: 250 Volts
Cap Type: E40s/45 Brass + vitrite
Bulb Type: GS-80 GS-25 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Electrodes: Coiled-coil tungsten Thoria pellet
Arc Length: 86.9 mm 3.42 inches
Atmosphere: Hg | Ar (1 atm) Outer: Nitrogen
Luminous Flux: 6,300 lm (@ 100hrs) 5,100 lm (@ 2,000hrs)
Luminous Efficacy: 21.0 lm/W (@ 100hrs) 17.0 lm/W (@ 2,000hrs)
Colour Temperature & CRI: CCT: CRI:
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 2,000 hours (to 50% survival)
Warm-up & Re-strike time: 5 minutes 10 minutes
Burning Position: Vertical cap up
Overall Length: 380 ± 20 mm 15 inches
Light Centre Length: D:150mm    F:245mm D: 6 inches    F: 95/8 inches
Factory: Strand Road, Preston England
Date of Manufacture: February 1942 Date Code 24
Original / Present Value: £3 0s 0d (1945) £105.90 (2011)
References: 1) Siemens-Ediswan Lamp Catalogue, UK, 1945, p.35
2) Aldington, J.N.,Electric Lamps & Kindred Devices, Siemens Engineering Bulletin, December 1948
3) Light & Lighting magazine, Oct. 1935, p.348