JPH04284348A - Electrode-less type low pressure discharge lamp - Google Patents

Abstract

PURPOSE:To provide an electrode-less type of low pressure discharge lamp with improved starting characteristic by constantly emitting initial electrons which trigger the discharge. CONSTITUTION:In an electrode-less low pressure discharge lamp comprising a light emitting tube 1 filled with discharge gas, and external electrodes 3 and 4 disposed outside the light emitting tube, high frequency power applied to the external electrodes to excite the discharge gas and emit light, an exoelectron emitting substance 6 exposed to a discharge space to emit electrons caused by exciting energy below that of a work function in the dark is disposed in the light emitting tube.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrodeless low-pressure discharge lamp with improved starting characteristics in darkness.

0002

2. Description of the Related Art In general, various types of discharge lamps cannot be smoothly ionized unless there are initial electrons that trigger discharge at the time of starting, making starting impossible or difficult. Initial electrons that trigger discharge include thermoelectrons, photoelectrons, electrons emitted by high electric fields, and natural cosmic rays.

However, if a discharge lamp is placed in a dark atmosphere where no light from the outside can reach, there will be no photoelectrons and only cosmic rays will be produced, making it difficult to start. Furthermore, when a lamp is used in a completely shielded housing or casing, natural cosmic rays often cannot reach it, and initial electrons cannot be expected.

When starting with thermionic electrons, an electrode that emits thermionic electrons is required inside the arc tube, and a material that easily emits thermionic electrons is coated and heated to supply thermionic electrons. Therefore, the electrode structure and lamp structure become complicated.

Conventionally, in order to improve the starting characteristics of low-pressure discharge lamps, the internal electrodes were provided with a radioactive isotope (RI) such as 63Ni or 147Pm, or the internal electrodes were coated with CaO to block external light. Proposals have been made to release initial electrons by irradiation.

However, when a radioactive isotope is provided, specialized care is required when handling it, and it also needs to be sealed in the electrode in the form of a sealed radiation source, making the structure complex and causing damage to the electrode. It takes time and effort to manufacture and is expensive. On the other hand, CaO does not emit electrons without external light, so it does not function well in complete darkness, resulting in poor reliability. Furthermore, these measures apply to types in which electrodes are provided inside the arc tube, such as hot cathode or cold cathode low-pressure discharge lamps.

[0007]

[Problems to be Solved by the Invention] However, recently, in backlights of display devices, electrodes are not provided inside the arc tube, but are provided outside the arc tube, and high-frequency power is supplied to this external electrode to discharge the discharge gas inside the arc tube. There is a trend toward adoption of external electrode type lamps that emit light through ionization and excitation, that is, electrodeless lamps. Such an electrodeless low-pressure discharge lamp has advantages such as a simple structure and easy manufacture because no electrodes are required within the arc tube.

However, such an electrodeless low pressure discharge lamp does not have good starting characteristics in the dark because there is no metal such as an electrode that emits electrons in the discharge space. That is,
In the case of lamps with internal electrodes, even if starting is difficult, conductive metals such as electrodes and lead wires are exposed inside the arc tube, so when metal lattice defects disappear, there are only a few However, in the case of electrodeless low-pressure discharge lamps, conductive metals such as electrodes and lead wires are not exposed within the arc tube, so the metal lattice defects mentioned above disappear. We cannot even expect electrons due to For this reason, there is a problem in that the starting characteristics are worse than lamps with internal electrodes.

In particular, in the case of a xenon discharge lamp, in which a discharge gas consisting mainly of xenon is filled in the arc tube without mercury, the ionization properties of xenon are poor, making it difficult to discharge, resulting in a high starting voltage. , there is a strong tendency for it to take a long time to start.

The present invention was made based on the above circumstances, and its purpose is to provide an electrodeless low-pressure discharge lamp whose starting characteristics are improved by constantly emitting initial electrons that trigger discharge. This is what I am trying to do.

[0011]

[Means for Solving the Problems] The present invention includes a discharge gas sealed in an arc tube, an external electrode provided outside the arc tube, and a high frequency power applied to the external electrode to excite the discharge gas. In an electrodeless low-pressure discharge lamp that emits light using ),
For example, it is characterized by the provision of aluminum oxide or magnesium oxide.

0012

[Operation] According to the present invention, the E
Because xo electron-emitting materials emit electrons even in the dark,
It can create a trigger for electrical discharge and improve starting performance.

[0013]

Embodiment The present invention will be explained below based on a first embodiment shown in FIG.

FIG. 1 shows an electrodeless fluorescent lamp used as a backlight of a liquid crystal display device, and 1 is an arc tube bulb. The arc tube 1 of this embodiment has a straight tube shape, and is a glass tube having an outer diameter of 9.5 mm, an inner diameter of 8.0 mm, and a total length of, for example, 270 mm.

A phosphor coating 2 is formed on the inner surface of the arc tube 1. This phosphor coating 2 uses, for example, a three-wavelength band emitting type phosphor that is a mixture of phosphors each having blue, green, and red light emitting regions. In the case of this embodiment, as shown in FIG. 1(c), a substance 6 that emits Exo electrons is mixed in the phosphor coating 2. This Exo electron emitting material layer 6 is made of a transparent metal oxide, such as alumina Al2O3,
It consists of magnesia MgO etc. In this embodiment, alumina powder is mixed with phosphor powder as the Exo electron emitting material layer 6, and a predetermined amount of mercury and a gas such as argon are applied to the inside of the arc tube 1. Enclosed with rare gas.

External electrodes 3 and 4 are formed on the outer surface of the arc tube 1 to face each other. These external electrodes 3 and 4 are formed, for example, by applying silver paste in a band shape along the axial direction of the arc tube.
is connected to a high frequency power source 5 such as a high frequency transistor inverter circuit. High frequency power supply 5 is 103 to 10
It is designed to emit high frequency power of 6 Hz, and for example, power of 1300 V at 50 kHz is applied to the arc tube 1.

The fluorescent mercury discharge lamp having such a structure has a frequency of 50 kHz,
By supplying high frequency power of 1300V, mercury atoms evaporated within the arc tube 1 are ionized and excited. Therefore, ultraviolet light is emitted from the mercury, and this ultraviolet light is converted into visible light by the phosphor coating 2 and emitted to the outside of the arc tube 1.

[0018] The fluorescent mercury discharge lamp having such a structure can be easily started even in the dark, and the starting time can be significantly shortened. That is, an Exo electron emitting material 6, such as alumina powder, mixed with a phosphor coating 2 is exposed inside the arc tube 1, and this Exo electron emitting material 6 can be exposed to a high electric field even in the dark at room temperature. It emits electrons without imparting any. Therefore, the Exo electrons trigger a discharge, and the discharge lamp can be quickly turned on even in the dark, even in a space where the surrounding area is shielded from cosmic rays.

In particular, since the Exo electron emitting material 6 is exposed to the discharge space, there is no member to block the Exo electrons, and the Exo electron emitting material 6 is exposed to the discharge space.
Electrons effectively function as a trigger for starting discharge, and since there are no metals such as internal electrodes or lead wires, reliable starting is possible even if electron emission cannot be expected due to the disappearance of metal lattice defects.

[0020] Such a lamp does not require the use of radioactive isotopes, making it easy to handle, and since no internal electrodes are required, the structure is simple and easy to manufacture, and it can be started without external light. Therefore, reliability is improved.

In the above embodiment, mercury vapor is used as the discharge gas, but the present invention is not limited to this, and the present invention is not limited to this, but instead of using mercury as the discharge gas, a gas mainly composed of xenon, such as xenon and argon, Alternatively, it may be an electrodeless xenon discharge lamp containing xenon and neon.

When a xenon discharge lamp with the structure shown in FIG. 1 was made and tested, the following results were found. A conventional xenon discharge lamp without mixing Exo electrons and a xenon discharge lamp with Exo electrons mixed in the phosphor coating 2 as shown in Fig. 1 were each kept in the dark for 24 hours. We measured the average time delay when turning on the light in the dark. As a result, while the conventional xenon discharge lamp had a time delay of 85 seconds, the lamp shown in Figure 1 had a time delay of 0.3 seconds and turned on instantly, proving the effectiveness of the present invention. It was done. Next, a second embodiment shown in FIG. 2 will be described.

In the case of the above-mentioned xenon discharge lamp, the phosphor coating 2 may not be formed on the inner surface of the arc tube 1, and in such a lamp, as shown in FIG.
The Exo electron emitting material coating 10 may be formed directly on the inner surface of the substrate. When the Exo electron emitting material coating 10 is formed of alumina, for example, a suspension is prepared by mixing fine particles of alumina and nitrified cotton with butyl acetate, and this suspension is applied to the inner surface of the arc tube 1. It can be formed by firing this to form a ceramic.

Note that another method is to immerse the arc tube 1 in an organic compound aluminum solution, for example, an alkoxide aluminum solution,
It is also possible to pull this up, dry it, and then sinter it to form an alumina film on the inner surface. In the case of such a structure, when the average time delay was measured in the dark as described above, the time delay was 0.001 seconds, and it was found that the light turned on instantly. Next, a third embodiment shown in FIG. 3 will be described.

In this embodiment, a phosphor coating 2 and an Exo electron emitting substance coating 10 are continuously formed on the inner surface of an arc tube 1. In this case, the phosphor coating 2 is formed on the inner surface of the linear portion of the arc tube 1 so as to effectively contribute to light emission, whereas the Exo electron emitting material coating 10 is located at the end of the arc tube 1. Preferably, the electrode is formed so as to be exposed to the discharge space. Furthermore, a fourth embodiment shown in FIG. 4 will be described.

In this embodiment, Ex
o A coating 10 of an electron-emitting substance is formed, and a phosphor coating 2 is superimposed on the inner surface of this coating 10. In this case, the phosphor coating 2 is not formed at the end of the arc tube 1, and the Exo electron emitting material coating 10 is directly exposed to the discharge space.

In the case of these third and fourth structures,
When the average time delay was measured in the same darkness as above, the time delay was 0.003 seconds, and it has been confirmed that the lights turn on instantly.

In the case of a lamp provided with an internal electrode, the Exo electron emitting material exposed to the discharge space is covered with the scattered electrode material, leading to a decline in the function and lifespan of the Exo electron emitting material. In the case of electrode lamps, such problems do not occur.

In other words, in the case of an internal electrode type fluorescent lamp in which an Exo electron emitting material made of Al2 O3 is provided on the inner surface of the bulb near the internal electrode and exposed to the discharge space in order to start the discharge quickly, in the initial stage of lighting. At this stage, the average lighting delay time was 0.01 seconds, and the average lighting delay time after 2000 hours of lighting was measured to be 0.05 seconds. On the other hand, the external electrode type lamp of the present invention shown in FIG. The average lighting delay time is 0.003 seconds, and the average lighting delay time after 2000 hours of lighting is 0.0.
07 seconds was measured.

Therefore, compared to a lamp provided with internal electrodes, in the case of an electrodeless lamp such as the one of the present invention, the Exo electron coating is not covered by the scattered electrode material, so that the Exo electron emitting material is Less functional decline. Note that the Exo electron emitting material layer is made of alumina Al2O3
In addition to magnesia and MgO, zinc oxide ZnO and lead oxide P
It is possible to carry out even if it is bO. The cross-sectional shape of the arc tube may be circular, elliptical, or oval, and the outer appearance of the arc tube may be bent into a U-shape, W-shape, ring shape, or the like.

Furthermore, the external electrodes 3 and 4 are not limited to those that directly contact the outer surface of the arc tube 1, but a pair of external electrodes may be provided apart from the arc tube, and the arc tube is placed in the high frequency electric field between these external electrodes. It may also be made to emit light.

As already mentioned, when a discharge gas consisting mainly of xenon is filled in the arc tube, that is, a xenon discharge lamp, the ionization characteristics of xenon are poor, so it is difficult to discharge, the starting voltage becomes high, and it is difficult to start. It tends to be time consuming. Therefore, the present invention is even more effective when applied to such xenon discharge lamps.

[0033]

As explained above, according to the present invention, the Exo electron emitting material provided in the arc tube emits electrons even in the dark, so it is possible to create a trigger for discharge and improve starting performance. In particular, since it is an external electrode type in which there are no electrodes or lead wires that act as conductors inside the arc tube, even if electron emission cannot be expected due to the disappearance of metal lattice defects in these electrodes or lead wires, the Exo electron emitting material directly Since electrons are emitted into the discharge space, starting is possible even without external light, improving reliability.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of the present invention, (a) is a cross-sectional view of an electrodeless fluorescent lamp, (b) is a cross-sectional view of an electrodeless fluorescent lamp;
A cross-sectional view taken along line A, and (c) an enlarged cross-sectional view of portion C in the figure (a).

FIG. 2 is a sectional view of an electrodeless xenon discharge lamp showing a second embodiment of the present invention.

FIG. 3 is a sectional view of an electrodeless fluorescent lamp showing a third embodiment of the present invention.

FIG. 4 is a sectional view of an electrodeless fluorescent lamp showing a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Arc tube, 2... Fluorescent coating, 3, 4... External electrode, 5
...High frequency power supply, 6, 10...Exo electron emitting material.

Claims (2)

[Claims] 1. An electrodeless device in which a discharge gas is sealed in an arc tube, an external electrode is provided outside the arc tube, and high frequency power is applied to the external electrode to excite the discharge gas and cause it to emit light. 1. An electrodeless low-pressure discharge lamp, characterized in that an electron emitting material is provided which is exposed in the arc tube and emits electrons in darkness with stimulation energy below the work function. 2. The cold cathode discharge lamp according to claim 1, wherein the electron emitting material is aluminum oxide or magnesium oxide.