Fluorescent lamp

A fluorescent lamp constituted by joining a pair of shells of glass that at least one of the shells is molded. A recess is formed on a portion of the jointing surface of the shells so as to become circular when the shells are overlapped each other. An exhaust tube and lead-in wires of electrode stem are hermetically fixed in the recess by adhering or by welding. An anode getter plate is arranged independently from an electric circuit including an electrode filament.

BACKGROUND OF THE INVENTION 
The present invention relates to a fluorescent lamp which is constituted by 
joining a pair of shells of glass that at least one of the shells is 
molded and more particularly to a fluorescent lamp in which an exhaust 
tube and lead-in wires of stem mounted thereon are hermetically fixed in a 
recess previously formed on the shells by adhering or by welding. 
DESCRIPTION OF THE PRIOR ART 
The demands of state of the art indicators requires that each one have a 
self-contained light surce. The bases for this requirement are that the 
indicator be clearly visible, that various colors be utilized to 
facilitate the differentiation of one indicator from other existing 
indicators, and that the indicator be aesthetically pleasing. 
However, since the conventional indicating device which self-contains a 
light source is circular or cylindrical in its configuration, in order to 
uniformly illuminate an indicating surface made by synthetic resin or the 
like, a certain distance is necessary between the light source and the 
indicating surface and a diffusion plate must be inserted into a middle 
portion between the light source and the indicating surface. Because of 
this spacing requirement, the indicating device will necessarily be larger 
in size. In addition, since the diffusion plate interrupts the light, the 
brightness of the illumination of the indicating surface is reduced. 
Although no such problem will arise in a large-sized indicating device, 
the problem is of considerable difficulty in a small-sized indicator. 
In the conventional fluorescent lamp there is known a structure which 
comprises an exhaust tube disposed in a cutway portion on the periphery of 
one of the receptacles, electrode filaments mounted on and arranged to 
lead-in wires to put a partition provided inside of the receptacle between 
the filaments, the other receptacle rested on the receptacle, and glass 
adhesive having low melting point jammed between the peripheral and center 
circular jointing surfaces of the receptacles so as to seal and fix the 
receptacles by heat. In this structure, the manufacturing step is 
relatively reduced since the exhaust tube is previously provided in the 
cutway portion of one of the receptacles and the electrode filaments and 
the lead-in wires are jointed when the receptacles are jointed. However, 
the electrode filaments are not avoidable from wrong affections occurring 
from heating temperature when jointing the receptacles and further are 
difficult to arrange at a normal position and can easily cause their 
deformations. Accordingly, in order to solve these defects the structure 
becomes complicated in the manufacturing process becomes more expensive. 
In a fluorescent lamp of such a structure, a large amount of glass adhesive 
having low melting point (solder glass) is necessary as a soldering agent 
in order to solder the lead-in wires put between the receptacles. 
In order to mass-produce such a discharge lamp, there has been proposed a 
method which solders a thin film made by screen-printing the glass 
adhesive having low melting point (solder glass), as a method which is 
better in yield rate and work efficiency. However, when the lead-in wires 
are inserted between the soldering surfaces of the receptacles of glass 
the use of the screen-print is difficult because of the necessity of 
increasing the thickness of the glass adhesive having low melting point 
(solder glass) used as a soldering agent and care must be taken to make 
the joint air-tight near the lead-in wires. 
In the other conventional fluorescent lamp, the structure comprises a pair 
of ring receptacles of glass formed in generally circular shape in 
section, a portion for inserting an electrode formed in short cylindrical 
shape on a portion of the receptacles and adapted to enclose therein 
lead-in wires supporting an electrode filament, glass adhesive having low 
melting point for adhering and fixing inner and outer peripheries of the 
receptacles, an exhaust tube formed in the same manner as the portion for 
inserting electrode and adapted to be enclosed after exhausting, and a 
partition provided to intercept the discharge passage between the 
electrode filaments. 
In this structure, since the portion for inserting electrode and the 
portion for mounting the exhaust tube on one of the receptacles are 
previously formed on one receptacle, and since the other receptacle is 
joined with the one receptacle after enclosing the electrode filaments, 
the number of production steps is increased therefore the manufacturing 
process becomes complicated and the cost becomes higher. In addition, 
damage to the portion for enclosing the electrode and the electrode 
filaments occurring from the heating temperature when jointing the 
receptacles. 
In the above conventional lamp also since the exhaust tube and the 
electrode portion are fixed independently on the periphery of the 
receptacles, it is not suitable for mass-production and further it has a 
defect that the position of the disposed electrode filaments is uncertain. 
In the fluorescent lamp as mentioned above, it has been known that a 
blackening phenomenon occurs near the electrode during use. It is stated 
as the cause that the electrode is gradually damaged or broken down by ion 
bombardment when starting the fluorescent lamp whereby the lamp wall 
becomes black by sputtering of the electrode itself and the oxide of the 
electrode material, and a power loss occurs from the voltage drop 
presented at the electrode. 
In order to prevent the blackening phenomenon, it is effective to prevent 
the sputtering of the oxide of the electrode material as possible and to 
catch and adsorb the sputtering material before it reaches the lamp wall 
and to minimize the voltage drop at the electrode. 
An electrode part generally used in such a lamp is composed of a preheated 
electrode to which is applied an oxide of an alkali earth metal which 
serves as a layer of electron emission material directly on the electrode 
filament supported on a stem through the intermediary of inner lead-in 
wires. In this case an auxiliary electrode is supported on the lead-in 
wires and at the peripheral side of the electrode filament so as to make 
the start of discharge easy and is disposed to not disturb the discharge 
passage between the electrodes. In the electrode part of such a structure, 
it has a defect in that a spot is easily caused locally near the electrode 
thereby to have a bad influence upon the life time of the lamp. 
As an improvement of the above conventional electrode, there has been 
proposed an electrode structure in which the electrode is adapted to keep 
warm by means of a cylindrical screen. This is so intended that the 
cylindrical screen reduces a chance of occurrence of local electrode spot 
and catches the sputter emitting from the electron emission material 
applied to the electrode filament thereby to prevent advance of the 
blackening in the discharge lamp. However, in this structure, because the 
heat capacity is large, greater time is required to start discharge. 
Further, in a case of a small-sized discharge lamp, it has defects that 
because the voltage drop becomes larger the dark portions at both sides of 
the discharge lamp attract attention and that the lamp becomes black in 
reflecting the color tone of the screen. 
OBJECT OF THE INVENTION 
It is an object of the invention to provide a fluorescent lamp which is 
suitable for various applications necessitating a small surface source of 
light. 
It is another object of the invention to provide a flat fluorescent lamp in 
which an exhaust tube and lead-in wire of a stem are hermetically fixed by 
adhering or by soldering in a recess previously provided on shells. 
It is a further object of the invention to provide a fluorescent lamp 
having an electrode structure which is adapted to prevent reduction of 
luminous flux resulting from blackening near the electrode. 
The above and other objects and features of the invention will be 
understood more fully hereinafter from a consideration of the following 
description taken in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a fluorescent lamp having flat side 
surfaces. Glass shells 1 and 2 forming the side surfaces are made by 
molding, as shown in FIG. 1. Upon molding of the shells 1 and 2 on a 
longitudinal end of the shells a generally circular recess 13 is formed to 
make a circle when overlapping the jointing surfaces 14 of the shells to 
meet each other. 
Fluorescent material 9 is applied and stained on inner surfaces of the 
shells 1 and 2. Reference numeral 8 is a supporting wire for supporting an 
electrode filament 4. The supporting wire 8 is provided on a stem 3. 
The electrode filament 4 is made from, for example, tungsten. The surface 
of the electrode filament 4 is covered by alkali earth metals used as an 
electron emission material. In the recess 13 provided on the jointing 
surface of the shells 1 and 2 are fitted outer lead-in wires 6 and 6 and 
an exhaust tube 7 as shown in FIG. 1 and they are adhered or soldered 
integrally with each other by means of glass adhesive 11 having low 
melting point applied between the jointing surfaces of the shells 1 and 2. 
With the adhering or soldering, the recess 13 of the shells, the outer 
lead-in wires and the exhaust tube are tightly fixed and thus the inside 
of the shells is sealed in an air-tight condition. 
A body 15 formed by joining the shells 1 and 2 removes impure gas to 
outside through the exhaust tube 7 and thereafter encloses the least 
amount of mercury vapor 10 and inert gas 12 which are necessary for 
discharge. After completion of these works the exhaust tube is tipped off. 
The outer lead-in wires 6 and 6 extending to the outside are electrically 
connected with base pins (not shown) by soldering or the like. In the 
above description though each part relates to those placed in the left 
hand portion of the lamp in FIG. 1, it should be understood that the same 
parts are arranged opposite to the described parts in the right hand 
portion of the lamp in FIG. 1. 
A special feature in the structure of the fluorescent lamp according to the 
invention exists in the mounting portion of the stem which is mounted on 
the glass shells 1 and 2. In the conventional lamp, the stem installing 
the electrode filament is disposed by fusion on one of the divided 
receptacles. Otherwise only the exhaust tube is disposed with fusion and 
the other portion overlaps the divided receptacles when forming the body 
of receptacle or is enclosed after inserting the lead-in wires between the 
receptacles. Accordingly, the lamp is complicated in its manufacturing 
processes and is high in cost. Further, since the lamp necessitates heat 
upon adhesion of the receptacles, damage to the electrode due to the high 
temperatures cannot be avoided. 
In order to solve the above defects, the present invention is away from the 
conventional concept relating to the stem seal and is so constituted that 
the shells are hermetically fixed by the exhaust tube and lead-in wires 
supported on the stem. That is, in the conventional concept of the stem 
seal, it is a practical wisdom that the air-tight enclosing is performed 
at the flare portion or at the button portion in a case of the flare stem 
or the button stem. In the lamp of the present invention, the sealing is 
performed by the exhaust tube and lead-in wires supported by the stem. 
With such a construction of the invention the recess 13 on the body 15 
becomes smaller and the surface source of light is obtained in a very thin 
and flat condition by only boring a frame in a thin plate. Special care 
also is not necessary in spacing the light source and the indicating 
surface since the indicating pattern, such as letters, figures or the like 
is formed or mounted directly or indirectly on the thin and flat 
indicating surface. It further is capable of obtaining the desired 
indication easily without disposing an additional member, for example, a 
diffusion plate. The flat configuration of the lamp of the present 
invention is easily produced in the molding thereof, because of the small 
size of recess 13. Accordingly, it is desirable in the production of the 
lamp to select a method for sealing the stem which inserts tightly the 
lead wires 6 and the exhaust tube 7 into small recess 13 previously formed 
on the portion of the glass shells and which adheres or solders them. 
Although the screen printing process cannot be used to seal the recess 13, 
the air-tight adhesion near the latter may be performed by applying a 
desired glass adhesive having low melting point (solder glass). 
In the conventional structure, the receptacle body is not formed directly 
by joining a pair of molded glass receptacles together as in the present 
invention. Accordingly, when the stem is enclosed in the glass receptacles 
the opening is required to be larger than the size of the electrode 
affixed to the stem. The large opening is not desirable for the thin and 
small-sized discharge lamp. 
Consequently, if the receptacle body is formed by joining together the 
molded glass shells as in the present invention since the stem can be easy 
enclosed in the shells by fixing the exhaust tube together with the 
lead-in wires in the small recess in a tight fitting condition the 
structure of the thin and small-sized discharge lamp may be greatly 
simplified. 
With the structure of the invention as mentioned above, as compared with 
the conventional surface source of light adapted to obtain a uniform 
illumination by adjustment of the distance between the light source and 
the indicating surface or by use of the diffusion plate, because the light 
source itself is a thin, flat and uniform surface source of light the 
whole lamp may be produced in a small-sized, thin and flat configuration 
if the surface source of light is formed integrally with the indicating 
surface. Accordingly, the indication can be obtained in the very striking 
and clear condition. 
In the invention the luminous color may be changed by pre-selecting the 
fluorescent material and therefore a colorful indication can be attained 
by the combination of the indicating pattern and the luminous color. 
In the present invention, the indication is made on both the sides of the 
body of the lamp. However, a very light indication can be obtained by only 
one side of the lamp where reflective material such as aluminium, titanium 
oxide or the like is applied or vacuum-evaporated on the other side of the 
lamp. 
In the present invention, pre-staining of the fluorescent material is not 
necessary since the staining can be performed at the same time the shells 
are enclosed. Further, since ornamental patterns are easily formed on the 
surfaces of the shells, the lamp can be used as an indoor instrument, that 
is, an interior decoration in cooperation with the color effect. 
In the fluorescent lamp according to the invention as mentioned above, a 
superior lamp can be provided by having an arrangement which is adapted to 
remove a blackening phenomenon caused near the electrode. Referring to 
FIG. 2, there is shown the structure of the stem 3, lead wires 8 and 8 
made from a conductive metal, such as nickel support an electrode filament 
4 of tungsten. An anode getter plate 16 is mounted on a supporting bar 17 
independently of any electric circuit including that of the electrode 
filament 4 and is disposed directly opposite electrode filament 4 so as to 
interrupt a direction of electron emission from the electrode filament 4. 
On a surface of the getter plate 16 is applied a getter material 18 
consisting of, for example, alloy of aluminium, zirconium or the like. In 
this case, the getter material made by the SAEZ Company is effective. 
The electrode filament 4 is usually covered by a layer 5 of alkali earth 
metal used as an electron emissive material. The elctrode filament 4 is 
supported on a stem 3 by lead-in wires 8 and 8. The stem 3 supports outer 
lead-in wires 6 and 6 and an exhaust tube 7 passing therethrough. 
As an example, the getter plate of the present invention may be 
manufactured by applying fine powders such as zirconium, aluminium or the 
like as a getter material 18 on a surface of a base plate of iron, nickel 
or the like, 
Some structural features of the invention are (1) that getter plate 16 that 
is supported by the supporting bar 17 independently of any electric 
circuit including that of the electrode filament 4; (2) that the anode 
getter plate 16 that is arranged at a position so as to prevent passage of 
electron emissive material from one electrode to the other electrode part, 
and (3) that a getter function is performed by the getter plate itself. 
In the structure of the invention, it is necessary to determine a width 
dimension of the getter plate 16 so as to have an area corresponding to 
about three to five times the projected area of the electrode filament 4. 
By having such a width dimension, even if the getter plate 16 is arranged 
in a position such that it covers electrode filament 4 as shown in FIG. 2, 
since the area of the getter plate 16 is at most three to five times that 
of the projected area of the electrode filament 4 the electron discharge 
is permitted to go around the periphery of the getter plate 16 and the 
flow is not adversely affected by the getter plate 16. 
In relation to an electrode filament, the spot has a somewhat large extent 
and the temperature of the spot is lower when a getter plate 16 is 
provided. If the getter plate were not provided the spot would be 
localized and the temperature thereof would be much higher. 
Furthermore, a getter plate 16 serves to reduce the voltage drop at the 
electrode filament, which is one problem on the design of the discharge 
lamp having a lower pressure gas such as fluorescent lamp and thereby the 
dark portion near the electrode becomes smaller. Accordingly, since the 
uniform illumination is obtained at each portion of the longitudinal 
direction of the lamp and the shade and color of the anode getter plate 
itself are not reflected to the outside, the good discharge can be 
obtained. It has been known that the above phenomenon of the electrode 
filament voltage drop results from negative space charge appearing around 
the electrode filament and may be reduced as the electrode filament 
dimension is increased to correspond to the energy which must give to 
overcome the resistant force of the space charge. In the present invention 
the cause of blackening is removed by forming the getter material 18 
integrally on the getter plate 16 and thereby the blackening phenomenon 
can be prevented. 
According to the present invention, the temperature of the getter plate 16 
rises immediately after start of the discharge and therefore the impure 
gas produced by the electrode and the other portions of the lamp can be 
fully adsorbed on the surface of the getter plate. Consequently, since the 
blackening of the tube wall is remarkably reduced in the discharge lamp 
the high flux of light can be maintained until the end of the life time. 
With the invention, the electric power required for the lamp can be reduced 
by about 5% due to the utilization of the getter plate 16. Further, since 
the size of the electrode filament spot is increased somewhat and the 
temperature of the lamp is considerably lower than that found in a lamp 
which does not have a getter plate 16. The life time of the lamp can be 
extended considerably. 
According to the invention, the dark area normally produced by a voltage 
drop near the electrode is not present and a uniform illuminating light 
can be obtained. The design and placement of the getter plate 16 is such 
that it operates effectively as a getter without producing a shadow 
visible outside the lamp. 
As mentioned above, with the invention, it can provide a fluorescent lamp 
which is small-sized and which has a long life time. The lamp according to 
the invention is suitable for a very wide range of applications, such as 
an indicating light for indicating room name, room number, direction guide 
or the like in house, hotel or the like, an indicating light for informing 
counter or the like, an indicating light for automatic vending machine, 
instrument or the like, an all-night light, a comfortable illumination 
lamp, a light source for liquid crystal indicator, a panel for automobile, 
a room lamp, a reading lamp, other illumination which necessitates a 
small-sized surface source of light or the like. 
While the invention has shown and described certain present preferred 
embodiments it is to be distinctly understood that the invention is not 
limited thereto but may be otherwise variously embodied within the scope 
of the following claims.