US 2899584 A
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Aug. 11, 1959 W. VERWEY SODIUM-VAPOUR DISCHARGE TUBE Filed Jan. 11, 1956 sobo- K INVENTOR WESEL VERWY AGENT United States Patent SODIUM-VAPOUR DISCHARGE TUBE Wessel Verwey, Eindhoven, Netherlands, assignor, by
mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application January 11, 1956, Serial No. 558,556
Claims priority, application Netherlands January 24, 1955 2 Claims. (Cl. 313-112) The invention relates to sodium-vapour discharge tubes having a rare gas-filling consisting of neon and a small amount of some other gas or gases.
It is common practice to add a small amount, for
example 0.7 percent by volume, of argon in order to decrease the ignition voltage of the lamp.
The addition of argon suifers from the disadvantage that this gas disappears in a comparatively short period of time (due to the phenomenon known to those versed in the art as clean-up), as a result, the ignition voltage will no longer be decreased to the required extent so that the lamp can no longer be put into operation.
As is well known, a decrease of the ignition voltage of a lamp can be achieved by the addition to the main gas of an auxiliary gas the ionisation voltage of which is less than the excitation voltage of the metastable energy level of the main gas.
Consequently, with neon as the main gas, use may be made of auxiliary gases other than argon in order to decrease the ignition voltage.
When xenon is used, it is found that this gas is cleaned up at a much lower rate than argon, which results in a wider choice of the composition of the glass of the discharge vessel.
However, the addition of xenon has the limitation that the number of lumen-hours at the beginning of the life of the lamp, the proportions of the lamp being constant, is less than when argon is used as the auxiliary gas.
According to the invention, the addition consists of 0.1% to 0.3% of xenon and 1% to 4% of helium, both percentages being expressed in a percentage by volume of the neon, and the inner wall of the discharge vessel consists of borate glass which substantially does not discolour during life.
By the use of this composition of the gas-filling the disadvantages described are avoided, whilst the choice of the borate glass which does not discolour, which choice is made possible by the composition of the gasfilling, provides a sodium-vapour discharge tube having light transmission properties superior to those of a tube containing an argon addition.
As examples of borate glasses which do not change colour we may mention glasses which contain 20-30% B 0 2030% A1 0 30-60% CaO+BaO The invention will be described in detail with reference to the accompanying drawing in which:
Fig. 1 is a graph showing the lumen output of a lamp according to the invention as a function of life; and
Fig. 2 is a view in section of a lamp according to the invention.
In Fig. 1 curve a shows the behaviour of a conventional sodium lamp of approximately 85 watts. This lamp, shown in Fig. 2, has a gas-filling consisting of neon and approximately 0.7% argon at an overall pressure of approximately 15 mms. of mercury at room temperature.
The U-shaped discharge tube 1 is arranged in a Dewar flask 2 with double walls and has an internal diameter of approximately 11.5 mms. the distance between the activated electrodes 3 is approximately 610 mms., measured along the axis of the tube. The lamp ignites at approximately 400 volts.
This lamp starts with a light output of approximately 7000 international lumens; after 1500 hours of operation, the lamp output is approximately 5300 lumens, the number of lumen-hours is approximately 8.5 10 during the first 1500 hours of operation.
The curve b shows the behaviour of a sodium lamp which is similarly proportioned, but in which instead of 0.7% of argon 0.2% of xenon has been added. This lamp starts at approximately 5600 lumens. The number of lumen-hours during the first 1500 hours of operation is approximately 8.0x 10 that is to say less than in the lamp provided with an argon addition.
Finally, the curve 0 shows the behaviour of a sodium lamp according to the invention, which is equally proportioned but in which instead of 0.7% of argon a mixture of approximately 0.2% of xenon and 3% of helium has been added.
The light output starts with approximately 6700 lumens. The number of lumen-hours during the first 1500 hours of operation is approximately 9.4 10
The discharge vessel of the lamps b and c which contain xenon is made of lime glass which is internally coated with a layer of borate glass of the composition 22% B203 10% CaO 22% A1203 40% BaO 6% K20 With glass of this composition no addition of argon can be used, since the argon is substantially cleaned up after a few hundred hours of operation. For this reason, the lamp according to curve a is provided with a discharge vessel which is made, as is usual, of lime glass which is internally coated with a layer of the composition 9% SiO,, 51% B 0 N330 10% CaO 15% A1 0 This glass composition has the property that the argon gas is not cleaned up or at least is cleaned up at a lower rate than in the first-mentioned glass; the transparency, however, is poorer than in the first-mentioned glass owing to discoloration.
What is claimed is:
1. A sodium vapor lamp comprising a light-transmissible envelope having an inner wall consisting of a borate glass containing about 20% to 30% B 0 about 20% to 30% A1 0 and about 30% to 60% CaO and BaO, spaced electrodes positioned within said envelope, and a filling within said envelope consisting of a mixture of sodium and neon containing about 0.1 to 0.3% of xenon and about 1 to 4% helium.
2. A sodium vapor lamp as claimed in claim 1 in which the borate glass has approximately the following composition:
22% B 0 10% CaO 22% A1 0 40% BaO 6% K 0 (References on following page) References Cited in the file of this patent 2,103,052 2,135,284 UNITED STATES PATENTS 2,152,999 1,736,642 Beaud y *Nov. 19, 1929 2,161,824 2,090,098 'Berger et a1 Aug. 17, 1937 5 2,177,895 2,103,039 Pirani at; al. Dec. 21, 1937 2,228,327
Wiegand Dec. 21, 1937 Found Nov. 1, 1938 Milner f" Apr. 4, 1939 Krefft et a1 June 13, 1939 Lecorguil lier Oct. 31, 1939 Spanner Jan. 14, 1941