GB2076218A - Discharge lamps - Google Patents

Abstract

A low pressure discharge lamp includes two electrode groups 1a, 2a and 1b, 2b each comprising respectively a cathode 1 and an anode 2, wherein the anodes 2 and cathodes 1 are connected to the cathode 4 and anode 5, respectively, of respective first and second semiconductor rectifier 3a and 3b, the discharge being effected alternately between opposed electrodes as shown at 10 and 11. The discharge lamp apparatus is a small multi-purpose, high-efficiency apparatus which provides a large luminescence output. The lamp may, for example, have a high U-V output for sterilization, and the envelope may have an exterior or interior coating of luminescent material, e.g. in stripes or dots, to provide an additional or alternative lighting function. The lamp may be mounted in an outer envelope, Fig. 5 (not shown), and may include reflective surfaces, or it may be mounted in a housing, Fig. 6 (not shown) which divides it into two parts having different functions. In one arrangement the cathode emissive material is barium strontium calcium beryllate (BaSrCa)BeO2. Starting of the lamp may be aided by use of the circuits of Figs. 2 and 3 (not shown). <IMAGE>

Description

SPECIFICATION A discharge lamp apparatus The present invention relates to a discharge lamp apparatus and more particularly, but not exclusively, to a small multi-purpose highefficiency discharge lamp apparatus which provides a large luminescence output.

Varieties of discharge lamp apparatuses are commercially available for civil and industrial applications, and they naturally differ from each other in performance, structure, shape and dimensions depending upon the use to which they are put. The lamp apparatus is so designed, manufactured, selected and used that the advantages thereof are derived and the disadvantages thereof are minimized.

For industrial applications, the lamp apparatus is generally used in connection with commercial production and processing of commodities, and therefore good economics is also required for the use of the lamp apparatus which is regarded as part of the production facilities used.

If a certain lamp apparatus exhibits an excellent degree of performance in a specific application, it may not be very recommendable from the viewpoint of economics. For example, discharge lamps for sterilizer apparatus are commercially available which emit rays in the range between 2,000 to 3,000 A having a good sterilization efficacy. Typical lamps for this application have power consumption of a few scores of watts. There are some with power consumption of 200 watts or so, which require a lamp length as much as 2 meters. This dictates the use of several lamp apparatuses in practical industrial applications resulting in a large combination of equipment.More particularly, if rapid sterilization is intended using large doses of 2,000-3000 A rays at power consumption of KW, a combination of five lamp apparatuses are required, which certainly is a disadvantage associated with the apparatus of the prior art in terms of economics.

There is a good market for the sterilizer lamp, and recently it seems, advanced studies for improvement and development thereof have been pursued. But it cannot be said yet that a discharge lamp apparatus ideally suited to industrial applications has been provided.

According to the present invention there is provided a discharge lamp apparatus comprising a bulb in which: two electrode groups comprising an anode and a cathode, are placed, the anode and cathode of a first group being connected to the cathode and anode, respectively, of a first semiconductor rectifier, and the anode and cathode of a second group being connected to the cathode and anode, respectively, of a second semiconductor rectifier; and at least mercury is provided, as a discharge medium, in an amount required to provide a pressure of 1 mmHg or less during discharge luminescence, the apparatus being such that the discharge is effected, when the lamp is in use, alternately between the anode of the first group and the cathode of the second group and between the anode of the second group and the cathode of the first group through the discharge medium contained in the bulb.

One embodiment of the present invention provides a small high-performance discharge lamp apparatus having a relatively simple shape and structure.

It may also provide a low-pressure mercury discharge lamp apparatus suitable for industrial applications.

For a better understanding of the present invention and to show how it may be put into effect reference will now be made by way of example to the accompanying drawings in which: Figure lis an explanatory drawing of a lowpressure mercury discharge lamp apparatus including fundamental features of the present invention; Figure 2 is an explanatory drawing of a high-tension superposition circuit that can be added to the transformer of the apparatus; Figure 3 is an explanatory drawing of part of another discharge lamp apparatus including fundamental features of the present invention; Figure 4 is an explanatory drawing showing the design of electrodes involved; Figure 5 is an explanatory drawing of part of still another discharge lamp apparatus including fundamental features of the present invention; and Figure 6 is an explanatory drawing of part of still another discharge lamp apparatus including fundamental features of the present invention.

Referring to Fig. 1, which is a drawing useful in explaining a low-pressure mercury discharge lamp apparatus including fundamental features of the present invention, reference numerals 1a, 2a and 3a are a directheated cathode, an anode and a semiconductor rectifier, respectively, belonging to a first group of the electrodes, and 1 b, 2b and 3b are a direct-heated cathode, an anode and a semiconductor rectifier, respectively belonging to a second group of the electrodes. The anode and cathode of each group are connected to the cathode 4 and anode 5 of the semiconductor rectifier. The anodes 2a, 2b and cathodes 1 a, 1 b are sealed in the ends 6a and 6b of the bulb 6. The bulb 6 contains a slight amount of mercury or mercury and argon. Reference numeral 7 is a choke coil for restraining flow of the current.Reference nu meral 8 is a transformer containing secondary windings 8a, 8b and 8c. The secondary windings 8a and 8b function as power supplies for the direct-heated cathodes 1 a and 1 b, respec tively. The secondary winding 8c is connected to the anodes 2a and 2b of the first and second groups, respectively, for luminous discharge purposes. The primary winding 8d of the transformer 8 is connected with a commercial 100 or 200 VAC source 9.

The required discharge is effected in the lamp apparatus as follows: The current flows in the direction of arrows 10 during the first half cycle and in the direction of arrows 11 in the next half cycle of the alternating current. The discharge is maintained by repetition of this flow of current.

The direction of current is opposite to the direction of the flow of electrons.

Thus, the discharge is effected alternately between the anode of the first group and the cathode of the second group and between the anode of the second group and the cathode of the first group through the same discharge medium.

The fundamental advantages of the discharge lamp apparatus described herein are: (1) Usually the anode and cathode are manufactured based upon different design ideas. According to the present embodiment, the anode and cathode can be designed solely upon a design idea of anode and cathode, respectively, leading to the provision of a high-current, low-pressure mercury discharge lamp apparatus, for example. Further, the design of electrode with long life time or low firing voltage is facilitated.

(2) The metal vapor discharge lamp with a long arc designed as a conventional DC type tends to undergo biased presence of the metallic ions towards the cathode, resulting in uneven luminescence. The present embodiment eliminates such a defect of the apparatus of the prior art.

These advantages of the apparatus of the present embodiment can be understood more clearly from the examples given below.

A bulb having an internal diameter of 10 mm. and an arc length of 300 mm. was made of ozoneless quartz, in which an amount of mercury that would provide a vapor pressure of 6 x 10-3 mmHg during discharge was sealed together with 0.3 mmHg of argon gas. The discharge lamp apparatus attained was of the low-pressure type with the power consumption of approximately 200 W at the voltage of about 59 V and the current of 4 A.

The cathode was designed to provide the best possible emission of electrons by use of a tungsten filament coated with barium strontium calcium beryllate, (BaSrCa)BeO2. The anode was designed sufficiently durable and resistant to the impulse of large electron flow by use of a tungsten rod. Thus, the discharge lamp apparatus of the present embodiment features a reduced length of about 1/6 that of the conventional type and a substantially increased unitraviolet radiation.

It is known that an increased amperage used in the low-pressure mercury discharge lamp causes an increase of ultraviolet radiation, but none of the conventional design ideas has succeeded in the development of a small, long-life low-pressure mercury dis charge lamp apparatus. This is evident from the fact that all the commercially available fluorescent, low-pressure mercury and steril izer lamps have the amperage of less than 2 A.

A comparison of the low-pressure mercury discharge lamp apparatus of the present em bodiment with a conventional 200 W sterilizer lamp in the dosage from a 1-cm arc length at 2,537 A reveals that the apparatus of the present embodiment provides scores times as much emission intensity as that of the conventional lamp and is superior in economics in industrial applications almost beyond comparison.

As can be understood from the example described above, further advantages of the low-pressure mercury discharge lamp appa ratus of the present embodiment include: (3) A small, long-life apparatus capable of operating at scores of amperes can easily be obtained.

(4) A powerful discharge lamp apparatus for ozone production can be obtained by use of a bulb made of quartz glass that allows good permeation of rays at 1,849 .

(5) A powerful discharge lamp apparatus free of ozone production can be obtained by use of a bulb made of ozoneless quartz glass or hard sterilizer lamp glass.

Quartz glass, ozoneless quartz glass and sterilizer lamp glass are all commercially available, and the spectral transmittance characteristics therof are known from a number of technical papers and documents. In addition to the materials mentioned above, light-transmitting ceramics such as polycrystalline alumina, trade named "Lucalox", may be used for the bulb.

The mercury vapor pressure during discharge luminescence may be controlled by the amount of mercury sealed in the bulb in the process of manufacturing the discharge lamp; or by maintaining a mercury reservoir that may be attached with the bulb at a predeter- mined temperature. The hot cathode involved may be of the indirectly heated type. These are all known from the literature.

A fluorescent lamp apparatus providing intense luminescence may be used, with its bulb coated internally or externally with a fluorescent material.

The low-pressure mercury discharge lamp apparatus described above is not so good at starting characteristics as the conventional apparatus, but this disadvantage can be eliminated by use of a conventional technique. The novel apparatus requires a high voltage of 600-800 V at startup. The transformer 8 can be designed to meet the power, current and voltage requirements for normal operation, to the secondary winding 8c of which is added a high-tension superposition circuit illlustrated in Fig. 2. The added circuit is so structured that its switch SW, should be closed only at startup of the apparatus. The startup of the discharge lamp apparatus may be effected, for example, by a trigger electrode attached in close proximity to the external surface of the bulb, as in the case of the conventional flash discharge lamp.When such a trigger electrode means was used with the apparatus described above, it was found that the trigger voltage required was 5 to 10 KV. A conventional startup technique can be used.

Referring to Fig. 2, reference numeral 12 represents a transformer for high voltage generation, 1 3 a capacitor, 1 4 a power supply, 1 5 a resistance and 28 a high-tension gap.

In Fig. 3 is illustrated another part of another discharge lamp apparatus including fundamental features of the present invention, wherein the anode and cathode are placed close to each other so that, when the temperature of the anode increases during discharge luminescence, the cathode is sufficiently heated by radiation of heat from the anode to emit thermions therefrom.

Referring to Fig. 3, reference numerals 1 spa, 1 7a, 1 8a and 1 9a represent a DC supply, a first switch, a second switch and a resistance, respectively, of a first group, and 1 sub, 1 7b, 1 8b and 1 9b represent the corresponding elements of a second group. At startup of the apparatus with the first switch closed and the second switch open, the DC discharge is allowed between the anode and cathode of each group, followed by opening the first switch and closing the second switch when the cathode is sufficiently heated. The discharge is maintained during discharge luminescence the same way as shown in Fig. 1.

The example shown in Fig. 3 exhibits the following advantages: (6) Despite the use of the trigger voltage at startup in connection with the added hightension superpostion circuit, the voltage requirement is relatively on the low side.

(7) The electrodes and the portions of the bulb in which they are sealed are fabricated in simple structure, thus the design and manufacture thereof are facilitated.

Fig. 4 is an explanatory drawing showing the design of the electrodes suitable for the example shown in Fig. 3. Referring to Fig. 4, the anode 2a consists of a tungsten wire coiled closely in a hollow cylindrical form, in which the cathode la is placed. In the end 20 of the bulb 6 in which one end of each electrode is sealed are buried a pair of metal foils 21 as intermediate conductor. If the bulb is so designed that the distance t between the cathode la and the anode 2a is about 1 mm and that the discharge medium contains several mmHg of argon gas, the voltage from the DC supply 1 spa can be no more than a few scores of volts. It is a matter of course that the required DC can be obtained from rectified commercial AC.

It is believed that embodiments of the present invention can be understood well from the foregoing descriptions, but additional various designs of the apparatus are possible in combination with other conventional techniques. For example, if the bulb is so designed that the low-pressure mercury vapor provides a presure of 1 mmHg or less during discharge luminescence and the lamp is lit at 2 A or more, the resulting emission intensity at 2,537 A amounts to several times that of the conventional mercury lamp having the similar pressure of 1 mmHg or less during the luminescence. Thus, in designing a low-pressure mercury lamp apparatus, the selection of mercury vapour with its pressure of 1 mmHg or less as the discharge medium immediately brings about practical advantages of the apparatus. Argon gas may be added in a trace amount as required.

Two additional applications of the present invention will now be described with reference to Figs. 5 and 6.

In Fig. 5, the bulb 6 is placed in an outer bulb 23 supported by a supporter 22. The outer bulb 23 has on either end a base 24 with lead-pins 25 attached. The lead-pins 25 are electrically connected with the anode and cathode in the bulb 6.

In the illustrated example, the discharge lamp apparatus is of the so-called "double bulb" type, and the bulb 6 is usually called an "inner bulb" in contrast to the outer bulb 23.

The conventional "double bulb" type discharge lamp apparatus is well known in the field of high-pressure fluorescent mercury lighting lamp and low-pressure sodium lamp equipment. Some of the techniques used in such conventional equipment can be applied to the discharge lamp apparatus of Fig. 5: (8) The outer bulb can be coated internally or externally in whole or or in part with a fluorescent material so that this apparatus may be employed as a fluorescent lamp apparatus.

(9) Part of the outer bulb can be designed as a reflector which functions to intensify the radiation of light in a desired direction in order to improve the effectiveness of the light generated.

(10) The surface of the inner or outer bulb can be coated with a fluorescent material in stripes or in dots so that the apparatus may be used for decoration purposes or for multiple purposes. Sonme fluorescent materials are commercially available that provide green, orange and other luminescence.

Fig. 6 illustrates another example of the apparatus in which shades 26a and 26b are attached over the bulb 6 to the bases 24 fixed on both ends of the bulb 6. Fig. SA is a side view, with the shades shown in section, of part of the apparatus seen from a direction perpendicular to the longitudinal direction of the bulb 6. Fig. 6B is an end view of the part of the apparatus seen from the end of the bulb 6 to which the shade 26b is attached via a supporter 27.

In this example, the bulb 6 is composed of an ozoneless quartz portion 6a connected via a graded seam Sc with an ordinary quartz portion 6b. The apparatus shown in this example has a number of multi-purpose applications.

(11) This apparatus is effective for both sterilization and deodoration by means of ozone. If a fluorescent material is applied to the shade 26a, it combines the lighting function as well.

(12) With the shades 26a and 26b designed as reflectors effective for ultraviolet or visible rays, and with only the ozoneless quartz tube 6a coated with a fluorescent material, this appartus is good for both lighting and deodoration purposes. If, in contrast, the quartz tube 6b is coated with a fluorescent material, this apparatus is effective for sterilization and lighting. Thus, various multi-purpose applications can be attained.

(13) In attaining multi-purpose applications of the apparatus as described above in (12), various contrivances can be made whereby, for example, the whole bulb 6 may be made of one material, and the shades 26a, 26b may be designed to possess a function to interrupt rays emitted in a particular direction, and further any suitable fluorescent material may be applied on any particular portion of the shade and/or the bulb, depending upon the use to which the apparatus is put.

As described in the foregoing, the present invention may provide some completely novel discharge lamp apparatuses useful not only for industrial applications but also for civil applications in which a discharge medium of a type different from that for industrial purposes is used. The performance, structure, shape and dimensions of the apparatus may be modified depending upon the intended application thereof.

It is to be noted that in some embodiments of the invention the pressure of the discharge medium may be greater than 1 mmHg during discharge luminescence, and also the discharge medium need not contain mercury.

Claims (11)

1. A discharge lamp apparatus comprising a bulb in which: two electrode groups, each group comprising an anode and a cathode, are placed, the anode and cathode of a first group being connected to the cathode and anode, respectively, of a first semiconductor rectifier, and the anode and cathode of a second group being connected to the cathode and anode, respectively, of a second semiconductor rectifier; and at least mercury is provided, as a discharge medium, in an amount required to provide a pressure of 1 mmHg or less during discharge luminescence, the apparatus being such that the discharge is effected, when the lamp is in use, alternately between the anode of the first group and the cathode of the second group and between the anode of the second group and the cathode of the first group through the discharge medium contained in the bulb.

2. A discharge lamp apparatus as defined in claim 1, in which the anode of the first group is also connected to the positive terminal of a first direct current supply and the cathode of the first group is also connected to the negative terminal of the first direct current supply, the anode of the second group being also connected to the positive terminal of a second direct current supply and the cathode of the second group being also connected to the negative terminal of the second direct current supply.

3. A discharge lamp apparatus as defined in claim 1 or 2, wherein said bulb is an inner bulb enclosed in an outer bulb, thus forming a double bulb structure.

4. A discharge lamp apparatus as defined in any preceding claim, wherein a mercury reservoir is added to said bulb containing the electrode groups.

5. A discharge lamp apparatus as defined in any preceding claim, wherein the or at least one bulb is coated in whole or in part with a fluorescent material on the internal or external surface.

6. A discharge lamp apparatus as defined in any preceding claim, wherein said bulb containing the electrode groups is made of a material selected from the group consisting of quartz glass, ozoneless quartz glass, hard sterilizer lamp glass, light-transmitting ceramic, or a combination of a plurality thereof.

7. A discharge lamp apparatus as defined in claim 3, or any of claims 4 to 6 appended directly or indirectly to claim 3, wherein a portion of the outer bulb is adapted to function as a reflector.

8. A discharge lamp apparatus as defined in claim 3, or any one of claims 3 to 7 appended directly or indirectly to claim 3, - wherein the inner or outer bulb is provided on the surface with a fluorescent material in stripes or in dots.

9. A discharge lamp apparatus as defined in any preceding claim, wherein a trigger electrode is provided in close proximity to the external surface of said bulb containing the electrode groups.

10. A discharge lamp apparatus as defined in any preceding claim, wherein a high-tension superposition circuit is aded to the circuit including the anode and cathode between which discharge is to be effected, to aid starting of the discharge lamp apparatus.

11. A discharge lamp apparatus substantially according to any of the embodiments hereinbefore described with reference to the accompanying drawings.