US3339100A - Fluorescent electric discharge lamp having the phosphor particles admixed with indium powder particles - Google Patents

Description

Aug. 29, 1967 R MENELLY 3,339,190

FLUORESCENT ELECTRIC DISCHARGE LAMP HAVING THE PHOSPHOR PARTICLES ADMIXED WITH INDIUM POWDER PARTICLES Filed NOV. 27, 1963 FIG, 2 RICHARD A. MENELLY INVENTOR ATTORNEY United States Patent C) 3,339,100 FLUORESCENT ELECTRIC DISCHARGE LAMP HAVING TI-IE PHOSPHOR PARTICLES AD- MIXED WITH INDIUM POWDER PARTICLES Richard A. Menelly, Danvers, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Nov. 27, 1963, Ser. No. 326,573 2 Claims. (Cl. 313-109) This invention relates to fluorescent lamps utilizing an amalgam as a source of mercury vapor. Such amalgams are used in lamps for operation at high ambient temperatures, so that the mercury vapor pressure will not rise to a value giving a serious loss in efiiciency. The efliciency is generally best at about 36 0, whereas lamps may have to operate under conditions in which even the ambient temperature is well above that value.

Indium is a very eflective metal to use with mercury in an amalgam for such purposes, and the invention is particularly useful with it. The use of an indium amalgam in fluorescent lamps is shown in my copending United States patent application Ser. No. 220,714, filed Aug. 31, 1962. The relationship between the amounts of indium and mercury in the lamp is explained in said application.

I have now discovered that by mixing fine indium particles with the suspension used in coating the lamp with phosphor, a coating of phosphor and indium is obtained over the inside surface of the lamp envelope, the indium being mixed uniformly with the phosphor in the coating. This provides more rapid re-absorption of mercury into the indium when the lamp is extinguished, easier starting, uniform brightness along the length of the tube, and a shorter period of coming to full brightness. A reduction from 12 minutes to 5 minutes is obtained in the latter respect. The easier starting is from the increased conductivity along the envelope wall.

In addition, the lamp of my present invention gives a 2% to 4% improvement in lumen maintenance at the usual 100-hour operation point at which fluorescent lamps are rated.

Instead of mixing the indium with the phosphor, a coating of indium can be applied first and then the phosphor layer over it. In either case, the indium is used in the form of a suspension, and is distributed along the length of the lamp and around its inner surface.

Other objects, advantages and features of the invention will be apparent from the following specification, taken in connection with the accompanying drawing, in which:

FIG. 1 shows a fluorescent lamp in which an indium layer is under the fluorescent layer.

FIG. 2 is a larger view of an end of the lamp, showing the layers in more detail; and

FIG. 3 is a lamp in which the indium is mixed with the phosphor in the fluorescent layer.

In FIG. 1 and FIG. 2, a glass tube 1, sealed at its ends, has the usual electrodes 2 at each end, supported on leadin wires 3, 4, which are sealed through the glass envelope 1 and connected to the contact prongs 5, 6 extending in the usual manner from the customary bases 7.

A coating 8 of indium is on the inner surface of the tube 1, and a coating 9 of phosphor over that.

The lamp contains a filling of inert gas such as argon at a low pressure, for example, 2 millimeters, although various other fillings can be used, for example, one of 85% argon and helium. A small quantity of mercury is present in the lamp. The amount of mercury should be sufiicient to produce the desired vapor pressure, or vapor density, but is preferably present well in excess of that amount, and in sufiicient quantity to insure enough mercury is present throughout lamp life, despite the amount of mercury lost or cleaned up by combination with various parts of the lamp.

3,339,100 Patented Aug. 29, 1967 A lamp bulb 1 may be coated with the coating 8 by applying a suspension of indium in a clear vehicle by floating, spraying or Welling-up. After application of the coating 8 the bulb is heated in a lehr at a temperature of between 520 C. and 580 C., preferably about 550 C., and after cooling is coated with a fluorescent suspension of phosphor in the usual manner. It is then heated in a lehr in the same temperature a second time. In each case the heating should be long enough to insure that all the binder used in coating is removed by vaporization or oxidation. If the suspensions used for the indium and for the phosphor have diflerent binders, for example, if one has nitrocellulose and the other ethylcellulose the two coatings may be made consecutively, without the intermediate step of heating in a lehr and both can be heated together afterward.

In one suitable example of a suspension for the indium, purified indium powder fine enough to pass through a 325 mesh screen is added to a l2-second viscosity ethylcellulose vehicle specific gravity 0.860, and dispersed by rolling. The specific gravity is checked, until a value of 0.870 is attained and the proportion of indium in the suspension is 10 milligrams per cc. About 13 /2 cc. of this suspension is necessary to coat a standard ISO-watt T12 tube, that is a glass tube about 72 inches long and 1 /2 inches in diameter. The amount of indium present in the tube is thus controlled by the coating. In finishing the manufacture of the lamp the amount of mercury can be put into the bulb in a controlled amount in the usual manner.

Instead of using separate indium and phosphor suspension, it is generally more convenient to make a single suspension containing both materials.

This is the preferred embodiment, shown in FIG. 3, in which the coatings 8 and 9 are replaced by a single fluorescent layer 10, which contains indium particles dispersed uniformly among the phosphor particles.

One example of a suspension suitable for applying such a coating is the following:

300 grams of phosphor 4.05 grams of indium 250 cc. of 12-second ethylcellulose 3.42 grams of Armeen CD, a dispersing agent This suspension is adjusted to a specific gravity of 15- second viscosity by adding a suitable solvent for the ethylcellulose such as amyl acetate or xylol, and to proper specific gravity to obtain proper density of coating on the bulb. This coating is applied to the bulb, dried and heated in a lehr to between about 520 C. and 580 C., preferably about 550 C. in the usual manner. The resulting coating will have the indium dispersed through it uniformly throughout the length of the coating. Although particular examples of the invention have been described above, various modifications can be made without extending the scope of the invention. For example, other means may be used to disperse the indium broadly over the bulb wall, for example vacuum or chemical deposition.

What I claim is:

1. A fluorescent electric discharge lamp having a coating of phosphor particles admixed with indium powder particles on the inside surface of its envelope, the indium particles being disposed uniformly through the coating and therefore the length of the coating.

2. The method of coating an electric discharge lamp, which comprises: applying a suspension of indium powder and phosphor powder in a lacquer, then heating to a temperature sulficient to remove the lacquer but not suflicient to remove the indium and phosphor.

(References on following page) I 3 .4 References Cited 3,007,071 10/1961 Lompe 313178 UNITED 3,152,278 10/1964 Dzlergwa 313-109 X JAMES w. LAWRENCE,Primary Examiner.

V c Wmg et-a. 10/1958 Ishler et a1. 117 33.5 5 DAVID GALVIN Emmmer- 9/1959 Jones 11733.5 R. JUDD, Assistant Examiner.

Claims (1)

1. A FLUORESCENT ELECTRIC DISCHARGE LAMP HAVING A COATING OF PHOSPHOR PARTICLES ADMIXED WITH INDIUM POWDER PARTICLES ON THE INSIDE SURFACE OF ITS ENVELOPE, THE INDIUM PARTICLES BEING DISPOSED UNIFORMLY THROUGH THE COATING AND THEREFORE THE LENGTH OF THE COATING.

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