US2272467A - Electric high pressure discharge lamp - Google Patents

Description

Feb. 10, 1942. KERN ETAL 2,272,467

ELECTRIC HIGH PRESSURE DISCHARGE LAMP Filed Sept. 7, 1939 'INVENTORS Jo sef' K e rn Hermann Kr-efft BY TTORNEY Patented Feb. 10, 1942 2,272,467 ELECTRIC HIGH PRESSURE DISCHARGE LAMP Jose! Kern and Herman KreiIt, Berlin-Schoneberg, Germany, assignors to General Electric Company, a corporation of New York Application September .7, 1939, Serial No. 293,850 In Germany September 10, 1938 2 Claims. (01. 17s 122) This invention relates to electric high pressure discharge lamps with discharge vessel of glass with high melting point, especially quartz glass, which contains solid thermionic electrodes, a rare gas filling and a small quantity of mercury and is so loaded that an operating vapor pressure of many atmosphere is produced.

The object of the invention is, to produce such a high pressure discharge lamp for power inputs of less than 200 watts, which can be operated by ordinary mains voltages and is well suited for general illuminating purposes. At the same time the lamp should not require a complicated cooling arrangement, a such as the known watercooled high pressure capillary lamps.

In solving this problem the invention is based on a new discovery. Hitherto it was always pointed out, that high pressure discharge lamps, especially those with are burning voltage approximating the mains voltage, are extremely sensitive to fluctuations in voltage, because for example in the event of a sudden increase in the supply voltag the current-limiting series resistance determining the discharge current intensity must alone. take upthe whole excess voltage. Consequently. a 5% increase in supply voltage on a series resistance taking up about 20% of the supply voltage results in a 25% excess voltage which causes an increase of 25% in the discharge current. It was the general opinion of those versed in the art, that in reality the conditions were even worse because the are burning voltage not only does not increase as the current intensity increases but even drops, which particularly favors the occurrence of excess current.

However, it is particularly important that the power input and th light radiation of a lamp for general illumination and many other purposes should remain constant as far as possible. Otherwise the unavoidable voltage fluctuations occurring in meshed network lead to intolerable fluctuations in light and' hence the lamps would show in a disadvantageous manner very diiierent lighting powers, according to the points at which the lamps are connected to the current network subject to drop in voltage.

Now it has been unexpectedly discovered that by no means all high pressure discharge lamps, as was generally imagined, have a dropping current voltage characteristic curve but on the contrary the characteristic curve dropping in the case of small arc powerevery centimeter of the length of the arc becomes less steep as the are power increases, then merges into a horizontal section and then into a gently rising section and finally, in th case of very high power input exceeding 300 watts per centimeter of the length of the arc, shows a very considerable rise.

In the new lamp this peak range of the specific power input of the arc is utilized in an advantageous manner for avoiding the above mentioned objections. A number of additional advantages are attained, for example the advantage that, thanks to the steep rise of the characteristic curve, the series resistance hitherto generally used can be made very much smaller and under certain circumstances may even be omitted in the operation of the lamp.

The using of the peak range of the specific power characteristic curve of the are means further, that the relatively small lamp power 01' 40 watts for example on an extremely short arc section is converted into radiation, that is the electrode spacing for a lamp of a certain power is chosen extremely small. in turn enables on' the other hand the spherical or approximately spherical vessel used in these lamps to be of very small dimensions, less than 15 millimeters and to be consequently much more resistant to pressure, to heat more quickly when the lamp is taken into service, to be produced cheaply from very little material and rendered safe in service.

The new high pressure discharge lamp, constructed according to the invention for mains voltage operation and small power inputs of less than 200 watts, is thus characterized in that when using an electrode spacing of less than 5 millimeters the inner surface of the spherical or approximately spherical discharge vessel is less than 1 square centimeter for every 25 watts power input of the lamp and, in the case of an operating pressure of more than 50 atmospheres for obtaining a considerably steeper current voltage characteristic curve, the specific power input of the arc exceeds 300 watts per centimeter of the arc length.

Experiments which have been carried out with such extremely small maximum pressure lamps have shown that, if the lamp is made carefully, the dreaded wall blackening is avoided to' a great extent and a. sufliciently long lif is attained. Presumably the evaporation and particularly the atomization of the electrodes is suppressed to an unexpectedly great extent by the exceptionally high operating vapor pressure.

Small spherical high pressure discharge lamps with an internal diameter of about 15 millimeters, an operating vapor pressure exceeding 10 atmospheres and a power input exceeding to be easily This short arc length watts per centimeter have been proposed for the production of low power lamps, but it has not been recognized that very great andentirely unexpected advantages are derived if the pressure and power values indicated are very considerably exceeded and at the same time the arc and the lamp vessel are confined to extremely small dimensions. These advantages outweigh by far the supposed disadvantage of the presence or exccptionally high operating vapor pressures which were hitherto used only for lamps of an entirely diilerent type and only for the production of maximum illuminating densities.

An embodiment of the invention is illustrated by way of example in the only figure of the accompanying drawing which shows in natural size a high pressure lamp enclosed in an enveloping vessel with socket for a power input of 50 watts.

The spherical discharging vessel I of quartz glass has an internal diameter of only about 6.5 millimeters, that is an internal surface area of about 1.3 square centimeter, so that the specific watt load of the inner surface is about 31 watts per square centimeter, that is considerably more than 25 watts.

The electrodes 2 are arranged at a mutual distance of about 2 millimeters and consist of small hollow tungsten bodies provided with apertures and containing a small quantity of thorium oxid or zirconium oxide. tion of the glowing electrodes may be dispensed with. The electrode bodies 2, as shown in the drawing, are mounted on the wall of the "vessel, so that a favorable cooling of the electrodes is attained owing to the heat being conducted off by the thick walled quartz glass vessel. The current leads 3 of the electrodes 2 are fused with the aid of molybdenum bands 4 into the diametrically opposite, outwardly projecting supports 5 which are fixed on the holding wires 1 by means of carrier straps 6. These holding wires 1 are electrically connected at one end to the socket contacts 8 of the enveloping vessel 9 and at the other end to the electrodes 2 by the wires I0.

For facilitating the ignition the discharging vessel I has a filling of rare gas, such as argon, at a pressure or 20 millimeters. For obtaining a. rapid heating of the discharging vessel a fundamental gas filling of considerably higher pressure, for example a pressure of 400 millimeters,

may, however, be used.

Moreover, the discharging vessel I contains a certain amount of mercury II, the quantity of which is so measured that, when the lamp is in service, an undersaturated vapor atmosphere at a pressure of about 130 atmospheres occurs.

The enveloping vessel 9 has a nitrogen fiilling at a pressure of about 300 millimeters. If a par- If desired a separate activaticularly intensive cooling of the discharging vessel I appears necessary, the enveloping vessel may also contain a gas of high heat conductivity, such as hydrogen.

The enveloping vessel I is preferably made to diffuse light so as to avoid dazzling. Luminous substances may also be provided or luminous glass used for additionally utilizing the considerable ultraviolet radiation of the lamp. Owing to the extremely high specific power input of the arc the high pressure lamp according to the invention has a very high red content, which renders the lamps particularly suitable for general illumination.

We claim:

1. An improved lamp which is capable of operating without series ballast and comprising the combination of a translucent substantially spherical vessel of high melting point material and of internal diameter less than 15 millimeters, spaced solid electrodes in said vessel and less than 5 millimeters apart, mercury in the vessel in such amount as to be completely vaporized at an operating pressure on the order of one hundred and thirty atmospheres, and a power source connected to the lamp, said source having a potential of such value that energy is supplied in excess of 25 watts for each square centimeter of internal surface area of the vessel and also in excess of 300 watts for each centimeter of the length of the discharge between the electrodes, whereby the lamp operates with an internal pressure in excess of 50 atmospheres and exhibits a sharply rising current-voltage characteristic.

2. An improved lamp which is capable of operating without series ballast and comprising the combination of a spherical quartz vessel of internal diameter of about 6.5 millimeters, said vessel containing a fixed gas and mercury in such amount as to be completely vaporized at an op erating pressure on the order of one hundred and thirty atmospheres, solid electrodes projecting inwardly from the wall of the vessel at diametrically opposite points thereof and having their extremities about 2 millimeters apart, and a power source connected to the lamp, said source having a potential of such value that energy is supplied in excess of 25 watts for each square centimeter of surface area of the vessel and also in excess of 300 watts for each centimeter of the length of the discharge between the electrodes, whereby the lamp operates with an inter nal pressure in excess of 50 atmospheres and exhitbits a sharply rising current-voltage character- 1s 1c.

JOSEF KERN. HERMANN KREFF'I.

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