H6 Water-Cooled Super Pressure 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 the mercury evaporates. The reservoirs are necessary to prevent the seals from overheating and potentially cracking.

In the G-E lamps, the arc tube is designed to be replaceable on its own, and can be detached from the holder which places it within the water jacket. Thus both ends of the lamp are in contact with the water and some electrolysis does take place, to an extent depending on the conductivity of the water, and there is always a current leakage across the outside of the lamp. In closed water cooling systems contamination of the water quickly occurs, resulting in greater leakage current and the arc then becomes unsteady. Corrosion of the cooling system can also be a problem. The GE solution was to use a velocity tube in the water jacket having a very small clearance around the arc tube, so that the cross-sectional area of the water is high and its electrical resistance is increased. The generally superior European solution was to design lamps having one end insulated.

Manufacturer:	General Electric Co. of U.S.A.
Lamp Power:	1000 Watts
Lamp Current:	1.4 Amps (2.6 Amps during starting)
Lamp Voltage:	840 Volts (1200 Volts during starting)
Cap:	3/16 inch brass sleeves
Bulb Finish:	Clear
Bulb Type:	T-6	(T-2 in American units)
Overall Length:	3 3/16 inches	(81 mm)
Lighted Length:	1 inch	(25 mm)
Electrodes:	Thoriated Tungsten Wire
Atmosphere:	Argon (1/25 atm. when cold, 80 atm. in operation)
Luminous Flux:	65,000 lm (at 100 hours)
Luminous Efficacy:	65 lm/W (at 100 hours)
Max Brightness, cd/cm2	195,000 cd/in2	(30,200 cd/cm2)
Run-up Time:	2 seconds (with 2 second hot-restrike delay)
Rated Life:	50 hours
Factory:	Cuyahoga Factory, NELA Park	U.S.A.
Date of Manufacture:	July 1960
Original / Present Value:	Not Known


References:	1) Weitz, C.E., GE-Mazda Lamps - Characteristics & App. lications (Bulletin LD-1) , General Electric U.S.A., 1939.
	2) Bourne, H.K., Discharge Lamps for Photography & Projection, Chapman & Hall, London, 1948.