JPH04349336A - Negative glow discharge lamp - Google Patents

Abstract

PURPOSE: To maximize the energy transfer efficiency by providing a light transmitting envelope and an electrode means, and making filling material contain gas, the base of which is metal having low ionization potential. CONSTITUTION: A vacuum type lamp envelope 10 formed of light transmitting material such as glass or the like surrounds a discharge space 12, and the space 12 is adapted to emit ultraviolet radiation by excitation and contains filling material provided for reducing power needed for promoting electron emission. This filling material contains cesium-mercury mixture and noble gas, one of noble gas is neon, mercury is adapted to radiate ultraviolet rays by excitation, and cesium makes a tungsten anode adhere to be used for reducing work function. Further, a cathode 16 and an anode 18 are provided in the space 12, thereby accelerating the emitted electrons. Thus, the energy transfer efficiency can be maximized as much as possible and the energy conversion efficiency can be improved.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates generally to negative glow discharge lamps, and more particularly to negative glow discharge lamps in which the fill material contains, for example, mercury and noble gases, as well as the power required to stimulate electron emission. metal-based gases, such as cesium, which increase the overall efficiency of the lamp by reducing
The invention relates to a lamp that also contains metal-based gas (hereinafter simply referred to as metal-based gas).

0002

BACKGROUND OF THE INVENTION Most mercury negative glow lamps use electrode structures made from tungsten. No. 4,450,380; 4,518,897; 4,516,057;
Nos. 450, 380, 4, 413, and 204 are standard examples of previously disclosed mercury negative glow discharge lamps. An electrode structure with a thermionic cathode and a bare anode emits electrons, which in turn initiates the process of visible light production. The work function of a standard tungsten anode is approximately 4.55 electron volts and is defined as the potential energy barrier that electrons must overcome during emission. This potential energy barrier requires that sufficient energy be provided for proper electron emission, resulting in inefficient energy transfer.

0003

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a mercury negative glow discharge lamp in which the resulting energy transfer efficiency is maximized as much as possible. Another object of the invention is to provide a discharge lamp in which the power required to drive the electron emission process is reduced. Yet another object of the invention is to provide a discharge lamp in which the work function potential energy barrier of the tungsten anode is reduced.

[0004] In order to achieve the above and other objects, features and advantages of the present invention, a light transmissive envelope, a fluorescent layer on the inner surface of the envelope and electrode means for effecting electron emission are provided. To provide a negative glow discharge lamp. The improvement according to the invention consists in the provision of a filler material, in particular a filler material containing a metal-based gas, preferably cesium, covering the tungsten anode of the electrode means and reducing the work function associated therewith. include. The metal-based gas is selected to have a low ionization potential. In the lamp of the present invention, the impurity cesium reduces the potential energy barrier of the tungsten anode by about 50%.
It is characterized by having a much higher energy conversion efficiency than its pure mercury lamp counterpart on the basis of the fact that

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a negative glow discharge lamp according to the invention. A vacuum type lamp envelope 10 made of a light-transmitting material such as glass serves as a discharge space 12.
is surrounding. The discharge space 12 contains a filling material that upon excitation emits ultraviolet radiation and also serves to reduce the power required to stimulate electron emission. The fill material includes a cesium-mercury mixture as well as a noble gas. One of these noble gases is neon. The mercury is used to emit ultraviolet radiation upon excitation and the cesium is used to deposit the tungsten anode and reduce its potential energy barrier or work function.

The inner surface of the lamp envelope 10 has a phosphorescent layer 14 which emits visible light by absorption of ultraviolet radiation. FIG. 1 shows an evacuated outer glass envelope 11 where an infrared reflective material is deposited to increase the cold spot temperature of the lamp.
is also illustrated. Also included within the discharge space 12 of the lamp envelope 10 are a cathode 16 and an anode 18 .

Generally, the function of the cathode 16 is to emit electrons, and the function of the anode is to accelerate the electrons emitted by the cathode 16. cathode 1
6 and anode 18 are both made of tungsten and cathode 16 is coated and wrapped with radioactive material to aid in electron emission and anode 18 is left bare.

A support conductor 20 provides an electrical connection to a single power source through the envelope 10 in the airtight seal. In operation, a voltage is applied to the thermionic cathode 16 through conductor 20 to provide a readily available source of electrons.

The work function of a pure tungsten anode is approximately 4.55 eV. Work function is defined as the amount of energy required for an electron to cross a potential energy barrier. For a discharge current of 2.0 amperage, the wasted power loss is about 9.0 watts, which is significant for a lamp operating at a power of about 30 watts. According to the present invention, a metal-based gas such as cesium is introduced as an impurity in the tungsten to reduce the work function and therefore the total power required to drive electron emission.

FIG. 3 illustrates an s-shaped isotherm curve for electron emission in a device using a cesium film for the tungsten electrode. The graph illustrates current density for various electrode temperatures. The isotherm is defined as the bath temperature for a pure cesium system. The straight lines shown represent different cesium surface coverages on the tungsten electrode and therefore have different work functions. The typical operating temperature of the anode of a mercury negative glow discharge lamp is in the range of 900-1000 DEG K., illustrated as the shaded area in FIG. 3 and designated by the reference numeral 28. The lamp operates within this temperature range so as not to disturb the mercury emission function of the lamp.

A standard cesium bath temperature of 341°K (68°C
) is shown as an s-shaped isotherm curve with reference numeral 30. This curve is (2 as the work function is shown)
．． 2 electron volts) and the line of cesium surface coverage marked with reference number 32 and the allowable electrode operating temperature range 2
8 and intersect at point 34. This is 341°K
It shows that for a cesium bath temperature of , the work function of the tungsten anode would be reduced (by the introduction of cesium) from the pure tungsten work function of 4.55 eV to 2.2 eV. At a 2.0 amp discharge current similar to that used in the example above,
．． An energy savings of 7 watts was achieved, which is 5 watts of power that would have been wasted without the introduction of cesium.
It is 0% or more. The procedure used to determine how much cesium to incorporate into a mercury-based fill material is outlined below.

This concept of using adsorbed cesium in a tungsten anode to reduce the work function requires that cesium gas be present in the fill material. Cesium-mercury type negative glow discharge lamps have reduced efficiency compared to mercury negative glow discharge lamps when one considers only the fill material radiation which simply increases the light output of the lamp and ignores the reduction in work function. This is due to the cesium resonance line excitation of additional energy channels (with wavelengths of 852 nm and 894 nm) which does not increase the total light output of the lamp. Therefore, a balance should be achieved such that enough cesium is introduced to reduce the work function of the anode, but not enough to adversely affect the total light output from the lamp.

A computer simulation study was carried out to study the behavior of the light output of a cesium-mercury negative glow discharge lamp at various cesium vapor pressures, ignoring the energy gain due to work function reduction. These studies revealed optical efficiency losses due to cesium radiation. The objective of the study is to find the maximum possible cesium vapor pressure where the light efficiency is not greater than 3.0%, ignoring work function gain, and less than the light efficiency of a mercury negative glow discharge lamp operated under similar conditions. Met. The results are illustrated in FIGS. 4 and 5.

FIG. 4 is a graph illustrating the percent reduction in light efficiency for a mercury negative glow discharge lamp with varying cesium vapor pressure. FIG. 5 illustrates similar percentage reductions for varying cesium cold spot temperatures corresponding to the various isotherms of FIG. The parameters used are a mercury vapor pressure of 4 x 10-3 Torr and a discharge current of 2.0A.

Choosing an allowable light efficiency reduction of approximately 3.0%, the corresponding cesium vapor pressure is 2×10 − , as can be seen at point 36 in FIG.
It is in the range of 4 to 3 x 10-4 Torr. This point 36 marks the intersection between the decrease in the efficiency curve and the 3.0% decrease in the efficiency horizon.

Knowing the cesium vapor pressure and the mercury vapor pressure, the required fill weight for the cesium-mercury system can be determined. Using the above results, a suitable range for cesium vapor pressure is between 2.times.10@-4 and 3.times.10@-4 Torr. The standard range for mercury vapor pressure is 4×
It ranges from 10-3 to 9 x 10-3 Torr. The results for various cesium amalgams show that in order to obtain the correct cesium and mercury vapor pressures, as illustrated in FIG. It is shown that the use of a preferred amalgam consisting of 55 weight percent cesium provides the desired results.

In addition to the preferred amalgam consisting of cesium and mercury, the weight of cesium and mercury is essentially 4
It can vary between 0 percent and 60 percent. For example, an amalgam may be comprised of 60 weight percent cesium and 40 weight percent mercury. At the other end of the spectrum, the amalgam may consist of 40 weight percent cesium and 60 weight percent mercury. Furthermore, instead of cesium, sodium can be used as a fill material in combination with mercury and noble gases. Similar weight percentages are also applicable for the use of sodium in place of cesium.

In the context of the method of manufacturing a lamp according to the invention, FIG. Please refer.

Specifically, FIG. 2 illustrates the use of an A-23 incandescent lamp envelope 10 coated internally with a fluorescent compound 14. Cesium-mercury pellets 40 having a predetermined mercury to cesium ratio are placed in a large diameter exhaust pipe 42. Electrode mount assembly 44 is 0.02
It consists of a multi-pin wafer-like stem member 46 to which is attached a lead-in wire 20 made of inch (approximately 0.051 cm) diameter nickel wire. Electrodes are clamped to the ends of each pair of lead-in wires in turn. A triple coil tungsten exciter numbered 41 is used with one coiled electrode deposited with a radioactive deposit serving as cathode 16. The other electrode is left bare and serves as the anode 18.

The lamp is then evacuated and heated in an oven to a temperature of about 400°C. The cathode is approximately 1
Activation is performed sequentially in a sealed vacuum by heating to 250°C. The cesium-mercury amalgam in pellet form is then rapidly heated using an RF electromagnetic field 50 to transform it into a liquid state. A burst of neon gas (approximately 300 torr) is then used to force the amalgam into the lamp envelope. The lamp is sequentially filled with 2-3 torr of neon gas and tip-off of the lamp is performed. Finally, the lamp is placed in an evacuated outer envelope 11 that reflects infrared radiation.

As mentioned above, in a preferred embodiment of the invention, cesium gas is used in the fill material of the negative glow discharge lamp. This increases lamp efficiency compared to mercury negative glow discharge lamps. In the present invention, the energy loss due to power-wasting electrons is approximately 5
It can be reduced by 0%.

[Brief explanation of the drawing]

FIG. 1 is a schematic illustration of a negative glow discharge lamp according to the invention.

2 is a schematic diagram illustrating intermediate steps in the manufacture of the lamp, in particular those related to its filling; FIG.

FIG. 3 is a graphical diagram illustrating current density curves for various electrode temperatures and listing the corresponding work function of a cesium-deposited tungsten electrode.

FIG. 4 is a graph illustrating lamp efficiency reduction with respect to cesium radiation losses for various cesium vapor pressures.

FIG. 5 is a graph illustrating lamp efficiency reduction with respect to cesium radiation losses for various cesium cold spot temperatures.

FIG. 6 is a graphical diagram illustrating a cesium-mercury weight ratio curve with corresponding vapor pressure and cold spot temperature.

[Explanation of symbols]

The main names indicated by each reference number in the figure are as follows. 10 Envelope 11 Outer envelope 12 Discharge space 14 Fluorescent layer 16 Cathode 18 Anode 20 Lead-in wire

Claims (19)

[Claims] 1. A negative glow discharge lamp having a light-transparent envelope, a fluorescent layer on the inner surface of the envelope, and electrode means for effecting electron emission, wherein the filling material has a work function of the electrode means. Negative glow discharge lamp characterized in that it contains a metal-based gas with a low ionization potential to reduce the ionization potential. 2. The negative glow discharge lamp of claim 1 including an evacuated outer glass envelope coated to increase the cold spot temperature of the lamp. 3. The negative glow discharge lamp of claim 1, wherein said fill material includes a noble gas. 4. The negative glow discharge lamp of claim 3, wherein said noble gas comprises neon. 5. The negative glow discharge lamp of claim 1, wherein said electrode means includes an anode made of tungsten for providing electron acceleration. 6. The negative glow discharge lamp of claim 5, wherein said metal-based gas includes cesium which is absorbed by the tungsten anode and reduces its work function. 7. The negative glow discharge lamp of claim 5, wherein said metal-based gas includes sodium which is absorbed by the tungsten anode and reduces its work function. 8. The negative glow discharge lamp of claim 1, wherein said fill material is comprised of 40% to 60% by weight cesium and the balance by weight mercury. 9. The negative glow discharge lamp of claim 1, wherein said fill material is comprised of 40% to 60% by weight sodium and the balance by weight mercury. 10. A light-transmissive envelope, electrode means disposed within the envelope and comprising an anode and a cathode and for effecting electron emission between the anode and the cathode; a filler material introduced into the vessel, the filler material reducing the work function of the anode and increasing the efficiency of the lamp over metal-based gasless lamps. A negative glow discharge lamp characterized in that it contains a predetermined amount of a metal-based gas and mercury and a noble gas adapted to be absorbed in the lamp. 11. The negative glow discharge lamp of claim 10, wherein said metal-based gas comprises cesium. 12. The negative glow discharge lamp of claim 10, wherein said metal-based gas comprises sodium. 13. The negative glow discharge lamp of claim 10, wherein said metal-based gas is comprised of about 40% to 60% by weight cesium and the balance by weight mercury. 14. The negative glow discharge lamp of claim 10, wherein said metal-based gas is comprised of 40% to 60% by weight sodium and the balance by weight mercury. 15. A glow discharge lamp with improved efficiency, carried out by reducing the work function of the anode by introducing a metal-based gas into the lamp envelope for absorption at the anode. The construction method includes providing an amalgam of mercury and a metal-based gas, heating the amalgam, introducing the amalgam in a liquid state into an envelope, further filling the envelope with a noble gas, and tipping off the envelope. a method of constructing a glow discharge lamp, the metal-based gas being absorbed by the anode to reduce the work function of the anode and thereby increase the efficiency of the lamp. 16. The method of claim 15, wherein said cathode is activated in a sealed vacuum by heating. 17. The method of claim 16, wherein activation of the cathode is by heating to a temperature of about 1250°C. 18. The method of claim 15, wherein said amalgam is formed from cesium-mercury pellets that are rapidly heated to a liquid state using an RF magnetic field. 19. A method of constructing a glow discharge lamp according to claim 18, comprising introducing a burst of neon gas to force the amalgam into the lamp envelope.