Mazda MD/H 1000W/40/1.4 Water Cooled Mercury

It is often desirable to increase the brightness of mercury lamps, however in ordinary arc tubes the quartz is destroyed above about 50W/cm. Forced air cooling is not satisfactory as it simply makes the mercury condense on the tube wall from where it is nearly impossible to vaporise. The MD water-cooled style was created to overcome these problems.

A quartz arc tube 6mm diameter with 2mm wall thickness has a tungsten electrode sealed into each end using only one intermediate glass. Special conical end chambers surround the electrodes, and these are almost completely filled with mercury. The electrode tips protrude approx. 0.5mm ahead of the reservoirs, and during operation the discharge is saturated, i.e. only a small amount of mercury evaporates. The reservoirs are necessary to prevent the seals from overheating and potentially cracking. One end has a brass cap, while the other is cemented into an ebonite housing with a rubber washer to effect the water seal.

The water jacket consists of two concentric quartz tubes, the coolant entering via the inner so-called velocity tube which accelerates the water so fast that it cannot boil and diffuse the image of the arc. At the rate of 3.5 litres per minute it returns around the outside of this tube and travels back towards the water union cap, exiting via eight small holes. Despite such extreme cooling the arc tube only lasts some 50 hours and fails as a result of quartz devitrification. Operating pressure is approx. 75 atmospheres and owing to the high power dissipation, the warm-up and restrike times are almost instant. These lamps used to find applications in photography and television studio lighting. The radiated heat is low due to water absorbing wavelengths >1400nm.

Manufacturer:	The British Thomson-Houston Co. Ltd.
Lamp Power:	1000 Watts
Lamp Current:	1.35 Amps (2.6 Amps during starting)
Lamp Voltage:	840±70 Volts
Cap:	Special screw terminals
Bulb Finish:	Clear
Bulb Type:	T-28
Overall Length:
Light Centre Length:
Electrodes:	Solid Tungsten Wires (25mm arc gap)
Atmosphere:	Argon
Luminous Flux, lm:	62,500 lumens (0 hrs)
Luminous Efficacy, lm/W:	62.5 lm/W (0 hrs)
Max Brightness, cd/cm2	30,000 (0 hrs)	22,500 (25 hrs)	15,000 (50 hrs)
Initial H.C.P.:	7,000 candle power	(30,000 stilb)
Rated Life:	50 hours
Factory:	Leicester	England
Date of Manufacture:	May 1947
Original / Present Value:	Not Known


References:	1) Bourne, H.K., Discharge Lamps for Photography & Projection, Chapman & Hall, London, 1948.
	2) Electric Lamp Manufacturer's Association - Internal Agreed Data for Group IX lamps, circa 1951.