GB2032681A - A fluorescent lamp - Google Patents

Abstract

In a fluorescent lamp suitable for use as an indicator lamp having an envelope 18 formed by two flat glass shells 1 and 2 joined together by glassy adhesive applied to jointing surfaces 14, and an electrode structure comprising a stem 3 to which are fixed lead-in wires 6 supporting an electrode filament 4 and an exhaust tube 7, the exhaust tube 7 and wires 6 are hermetically sealed in a recess 13 formed in the jointing surface 14 whereby the stem 3 is supported within the envelope. The lead-in wires 6 extend into and are soldered to hollow pins 16 of a connector body 15 having a slot 17 in which jointing flanges of the shells are fixed. An anode getter plate 21 may be independently supported from the stem 3 and positioned so as to block the direct line of sight between the filaments at opposite ends of the envelope. <IMAGE>

Description

SPECIFICATION A fluorescent lamp THIS INVENTION relates to a fluorescent lamp which is suitable for use as an indicator lamp.

Modern indicators tend to be of the kind which have a self-contained light source. This is because such indicators give a clearly visible indication, are visually attractive and readily permit different colours to be used to distinguish one indicator from another in a group of indicators.

However, since known indicators of this kind generally comprise a light source which is circular or cylindrical in configuration, uniform illumination of an indicator plate made of synthetic resin or the like requires that the indicator plate be spaced from the light source and that a diffuser plate be interposed between the light source and indicator plate.

This increases the size of the indicator and makes it difficult to provide compact, small size indicators.

A known fluorescent lamp for use as the light source of an indicator comprises an envelope made by joining a pair of glass receptacles, one of which is provided with a peripheral recess receiving an exhaust tube through which air is exhausted from the assembled lamp envelope. Electrode filaments are so supported in the one receptacle, by respective pairs of lead-in wires that they are separated by a central partition provided in the receptacles. The other receptacle is bonded to the one receptacle by the application of a layer of glassy adhesive (solder glass), having a low melting point, to the circular peripheral and central partition jointing surfaces of the receptacles which are then sealed together by heat.

Manufacture of this known lamp is facilitated by the pre-assembly of the exhaust tube in the peripheral recess of the one glass receptacle and the fact that the lead-in wires are sealed in position automatically when the two receptacles are joined together. However, the electrode filaments can be degraded by heat during the joining of the glass receptacles, are difficult to position and easily deformed in this structure. In order to solve these defects in the known structure the manufacturing processes become more complicated and costly.

In the known fluorescent lamp structure a large bulk of glassy adhesive having a low melting point (solder glass) is necessary as a soldering agent in order to seal the lead-in wires passing between the receptacles.

In order to mass-produce such a discharge lamp, it has been suggested that an improved yield and efficiency could be provided by a method in which the glassy adhesive is screen-printed as a thin film on the jointing surfaces of the receptacles. However, the insertion of lead-in-wires between the jointing surfaces of the glass receptacles means that the use of screen-printing is difficult because of the required thickness of the layer of glassy adhesive and care must be taken to ensure sealing around the lead-in wires.

In another known fluorescent lamp structure the lamp envelope comprises a pair of ringlike glass receptacles having a generally circular cross-sectional shape.

A Short cylindrical portion is provided on the receptacles for introducing an electrode structure comprising lead-in wires supporting an electrode filament. An exhaust tube is formed in the same manner as the cylindrical portion for introducing the electrode structure and is adapted to be closed after exhausting of the lamp envelope. A partition is provided in the receptacles to intercept the discharge path between the electrode filaments.

Since in this known lamp portions for introducing the electrode structure and the exhaust tube are provided on one receptacle to which the other receptacle is joined after introduction of the electrode filaments, the number of production steps is increased, thereby complicating the manufacturing process and increasing the cost. In addition the structure is susceptible to damage to the electrode-introducing portion and the electrode filaments due to the heating temperature when joining the receptacles.

This second kind of known lamp is also unsuitable for mass-production, since the exhaust tube and the electrode structure are fixed independently on the periphery of the receptacles and further the position of the disposed electrode filaments is uncertain.

In the known fluorescent lamps, it is observed that blackening of the glass envelope occurs near the electrode during use. The cause is believed to be that the electrode is gradually damaged or broken down by ion bombardment when starting the fluorescent lamp, whereby the glass envelope of the lamp becomes blackened by sputtering of the electrode itself and the oxide coating of the cathode and power loss occurs from the voltage drop presented at the anode.

In order to prevent the blackening phenomenon, it is necessary to prevent the sputtering of the oxide coating of the cathode as much as possible and to catch and absorb the sputtering material before it reaches the glass wall of the lamp and to minimize the voltage drop of the anode.

An electrode structure generally used in such a lamp is constituted by a heated cathode formed by a layer of an oxide of alkali earth metals applied as electron emission material directly on a cathode 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 at the peripheral side of the cathode filament so as to make the start of discharge easy and is disposed so as not to disturb the discharge path between the cathodes. In such a structure, a spot is easily caused locally near the electrode thereby adversely affecting the life time of the lamp.

There has been proposed an improved cathode structure in which the cathode is kept warm by means of a cylindrical screen. The cylindrical screen reduces a chance of a local cathode spot occurring and catches any sputter from the electron emission material of the cathode filament thereby retarding blackening of the lamp. However, in this structure, because the heat capacity is large, the lamp takes a long time to start. Further, in the case of a small-sized lamp, because the voltage drop becomes larger the dark portions at both sides of the discharge lamp attract attention and the lamp becomes black in reflecting the color tone of the screen.

According to the invention, in one aspect thereof, there is provided a fluorescent lamp comprising an envelope formed by a pair of shells which are jointed together and at least one of which is moulded, a stem for supporting an electrode filament in the envelope, lead-in wires fixed to the stem and connected to the filament, and an exhaust tube fixed to the stem, in which lamp a recess is formed in a jointing surface of the shells so as to form a passage when the shells are brought together, and the exhaust tube and lead-in wires are hermetically fixed in the said passage and support the stem within the lamp envelope.

In another aspect, the invention provides a fluorescent lamp having an electrode structure which comprises a support stem, lead-in wires fixed to the stem, an electrode filament supported on the lead-in wires, and an anode getter plate provided independently of the electric circuit of the electrode filament, the anode getter plate being arranged between the electrode filament and another electrode filament of the lamp so as to raise the temperature at which a getter function is fully attained and to block the direct line of sight between the electrode filaments, and being spaced from the electrode filament so as to function to reduce anode voltage drop and obtain uniform illumination from the lamp.

In order that the invention may be readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view, partially cut away and exploded, showing an embodiment of a small-sized fluorescent lamp according to the invention; and Figure 2 is a perspective view showing an improved electrode structure used in the fluorescent lamp of Fig. 1.

Fig. 1 shows a flat, substantially rectangular fluorescent lamp comprising an envelope 18, having plane major surfaces and formed from two shallow dish-shaped moulded glass shells 1 and 2 and joined together at jointing surfaces 14. During moulding the jointing surface 14 of at least one of the shells 1 and 2 is provided with a substantially semi-cylindrical recess 1 3 which forms a passage when the jointing surfaces 14 of the shells are brought together. Fluorescent material is applied to and stained on inner surfaces of the shells 1 and 2.

An electrode structure of the lamp comprises a stem 3 from which extend supporting wires 8, formed by the ends of lead-in wires 6, for supporting an electrode filament 4 which is made, for example, from tungsten.

The surface of the filament 4 is coated with alkali earth metals which serve as an electron emission material. The lead-in wires 6 and an exhaust tube 7 extending from the stem 3 are fitted in the recess 1 3. The shells 1 and 2 are joined together to form the lamp envelope 1 8 by means of glassy adhesive 11 having a low melting point applied between the jointing surfaces 14 of the shells. Upon joining of the shells, the lead-in wires 6 and the exhaust tube are hermetically sealed in the recess 1 3 and support the stem 3 within the envelope 18.

After joining of the shells 1 and 2, air is removed from the inside of the envelope 1 8 through the exhaust tube 7. A small amount of mercury 10 and inert gas 12, sufficient for operation of the lamp, are then introduced into the envelope, whereafter the exhaust tube 7 is tipped off.

Electrical connection to the electrode structure is established via the lead-in wires 6 which extend through an external electrically insulating connector body 1 5 into respective hollow pins 1 6 in which they are soldered at 1 6. The connector body 1 5 is made of synthetic resin, such as polyacetal resin, urea resin or the like, or of ceramic. The connector body 1 5 has a rectangular cross-section slot 1 7 in which the jointing flanges of the completed envelope 1 8 are received and secured for example by adhesive.

Although only one electrode structure is shown in detail in Fig. 1, the other electrode structure is similarly constructed.

In known lamps, the stem 3 carrying the electrode filament is fused to one of the receptacles from which the lamp envelope is formed. Otherwise only the exhaust tube is previously fused to the receptacle and the stem overlaps the divided receptacles when forming the envelope or is enclosed after inserting the lead-in wires between the mczp- tacles. Accordingly, manufacture of the lamp is complicated and high in cost. Further, since the lamp necessitates heating upon joining of the receptacles there is no avoiding a detremental effect on the electrode due to the heat.

In the lamp embodying the present invention, the shells are hermetically sealed at the exhaust tube and lead-in wires fixed to the stem. That is, in a conventional stem seal, the sealing is performed at the flare portion or button portion of a flare stem or button stem.

In a lamp embodying the invention, the sealing is performed at the exhaust tube and leadin wires fixed to the stem and accordingly the recesses 1 3 can be smaller and more easily reached.

Using a lamp embodying the invention a compact indicator can be provided in a very thin or flat condition simply by mounting the lamp in a frame cut in a thin plate. There is no need for spacing of an indicator surface from the light source since the indicating pattern, such as letters, figures or the like may be formed or mounted directly or indirectly on the exposed flat major surface of the lamp.

Similarly, no diffuser plate is needed.

Since the flat shells with their recesses 1 3 are easily moulded, the yield rate in the moulding of the shells is good. Accordingly, in the production of the lamp it is appropriate to adopt the method of sealing in which the lead-in wires 6 and exhaust tube 7 are tightly fitted in a small recess 1 3 previously formed in the glass shells and the shells are joined by glassy adhesive. Although screen printing cannot be performed in the recesses 13, the necessary air-tight sealing at the recesses can be achieved by application of a desired glassy adhesive having a low melting point (solder glass).

In the known structure, the lamp envelope is not formed directly by joining a pair of moulded glass shells. Accordingly, when the electrode mount is introduced into the glass receptacle the opening in the receptacle is necessarily larger than the size of the electrode on the mount. Such a large opening is not desirable for a thin, small-sized discharge lamp.

If the lamp envelope is formed by joining flat moulded glass shells, as in the invention, the electrode mount can be easily enclosed in the shells by fitting the exhaust tube and the lead-in tightly in the small recesss in the jointing surface of the shell, and the structure of the lamp may be considerably simplified.

Unlike the known indicators which uniform illumination is obtained by adjustment of the distance between a light source and an indicating surface or by use of the diffusion plate, a light source embodying the invention itself is a thin, flat and uniform surface source of light so that the whole indicator may be produced in a small-sized, thin and flat configuration if the surface source of light if formed integrally with the indicating surface.

Accordingly, the indication can be obtained in a very striking and clear condition.

In the invention the luminous colour may be changed by selecting the fluorescent material of the fluorescent lamp and therefore a colourful indication can be attained by the combination of the indicator pattern and the luminous colour.

A lamp embodying the invention may provide illumination from both major surfaces of the lamp envelope. However, a very bright illumination can be obtained from one major surface only if reflective material such as aluminium, titanium oxide or the like is applied or vacuum-deposited on the other major surface of the lamp envelope.

With the lamp of the invention, pre-staining of the fluorescent material is not necessary since the staining can be performed at the same time as its application to the shells.

Further, since it is easy to form an ornamental pattern on the major surfaces of the shells, the lamp can take effect as an indoor instrument, that is an interior decoration in cooperation with the colour effect.

The above described fluorescent lamp according to the invention may be provided with an arrangement which is adapted to avoid a blackening near the electrode and which will now be described.

Referring to Fig. 2, there is shown an electrode structure in which end portions 8 of lead-in wires 6 made from nickel support an electrode filament 4 of tungsten. An anode getter plate 20 is mounted on a supporting bar 23 independently from an electric circuit including the electrode filament 4 and is arranged in a position such as to interrupt a direction of electron emission from the electrode filament 4. The surface of the anode getter plate 20 is coated with a getter material 21 consisting of, for example, an aluminium alloy, 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 22 of alkali earth metals used as an electron emission material. The electrode filament 4 is supported on a stem 3 through which pass the lead-in wires 6. The stem 3 also supports an exhaust tube 7.

As an example, the getter plate may be made by applying fine powder such as sirconium, aluminium or the like as a getter material 21 on a surface of a base plate of iron, nickel or the like.

The anode getter plate 20 is supported by the supporting bar 23 independently without connecting to the electric circuit including the electric filament 4, the anode getter plate 20 is arranged so as to prevent direct emission from the electron emission material of one electrode to the other electrode, and a getter function is performed by the anode getter plate itself.

In the electrode structure of the invention, it is necessary to determine the width dimension of the anode getter plate 20 so that the plate has an area corresponding to about three to five times the diameter (projected width) of the electrode filament 4. The electron discharge is thus forced to go around the periphery of the anode getter plate 20, whilst not being subject to the bad influence thereof.

The provision of anode getter plate 20 means that any cathode spot has a somewhat large extent and the temperature of the spot is low. If the anode getter plate is not provided, however, the spot localises and the temperature is high.

Further the plate 20 can reduce the anode voltage drop which is one problem in the design of a discharge lamp having a low pressure gas such as fluorescent lamp, and thereby the dark portion near the electrode becomes smaller. Accordingly, since uniform illumination is obtained throughout the length of the lamp and the shade and colour of the anode getter plate itself are not reflected to the outside, the good discharge can be obtained. It has been known that the anode voltage drop is due to negative space charge appearing around the anode and is reduced as the anode dimension is increased to correspond to the energy which must give to overcome the resisting force of the space charge. In the present lamp the cause of blackening is removed by forming the getter material 21 integrally on the anode getter plate 20 and thereby the blackening phenomenon can be prevented.

The temperature of the anode getter plate 20 rises immediately after start of the discharge and therefrom any impurity gas occurring from the electrode and elsewhere can be fully absorbed on the surface of the getter plate. Consequently, since the blackening of the tube wall is considerably reduced the high flux of light from the lamp can be maintained till to the end of its life.

Use of anode getter plate 20 may reduce the electric power required for the lamp can by about 5%. Further, since the size of the cathode spot is extended a little and the temperature is much lower than that with a lamp having no anode getter plate 20, the life can be extended.

No dark portion is derived from the anode voltage drop near the electrode and a uniform illuminating light can be obtained. It also has an effect that the anode getter plate 20 operates effectively only as the anode and the getter without appearing as a shadow to the outside.

The invention thus can provide a fluorescent lamp which is small-sized and which has a long life. A lamp embodying the invention is suitable for very wide range of applications, such as an indicator light for indicating room name, room number, direction guide or the like in houses, hotels or the like, an indicator light for an information counter or the like, an indicator light for automatic vending machines, instruments or the like, an all-night light, a comfortable illumination lamp, a light source for liquid crystal indicators, a panel light for automobiles, a room lamp, and a reading lamp.

Claims (7)

1. A fluorescent lamp comprising an envelope formed by a pair of shells which are jointed together and at least one of which is moulded, a stem for supporting an electrode filament in the envelope, lead-in wires fixed to the stem and connected to the filament, and an exhaust tube fixed to the stem, in which lamp a recess is formed in a jointing surface of the shells so as to form a passage when the shells are brought together, and the exhaust tube and lead-in wires are hermetically fixed in the said passage and support the stem within the lamp envelope.

2. A lamp according to claim 1, comprising an electrically insulating connector body having a slot for receiving jointing flanges of the shells to which the connector body is fixed, the connector body carrying a pair of hollow contact pins through which the lead-in wires extend and to which the lead-in wires are electrically connected.

3. A lamp according to claim 1 or 2, wherein the shells are of a shallow dish shape with flat major surfaces.

4. A fluorescent lamp having an electrode structure which comprises a support stem, lead-in wires fixed to the stem, an electrode filament supported on the lead-in wires, and an anode getter plate provided independently of the electric circuit of the electrode filament, the anode getter plate being arranged between the electrode filament and another electrode filament of the lamp so as to raise the temperature at which a getter function is fully attained and to block the direct line of sight between the electrode filaments, and being spaced from the electrode filament so as to function to reduce anode voltage drop and obtain uniform illumination from the lamp.

5. A fluorescent lamp according to claim 4, wherein the anode getter plate has a width corresponding to about three to five times the projected width of the electrode filament.

6. A fluorescent lamp substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

7. Any novel feature or combination of features herein described.