EP0393449B1 - Fluorescent lamp - Google Patents

Abstract

The fluorescent lamp consists of a discharge space outwardly limited by a glass tube and of discharge electrodes as well as of an elongated inner element that limits inwardly the discharge space. The entire inner wall of the glass tube and the outer wall of the inner element are covered with a layer of fluorescent material and inside of the inner element, at least along a part of its entire length, an electrically conductive material is placed that is connected with a discharge electrode. In order to improve the lamp efficiency and also to reduce the cost of manufacture of such a lamp, the lamp according to the invention is so designed that the inner element is a support for the capacitor elements which are placed in the inner space of the inner element. The capacitor elements extend at least along a part of the entire length of the inner element. An electrical potential emitting from the said capacitor elements acts perpendicular against the known discharge current of the lamp. The said capacitor elements are connected through wires with a high frequency generator and other electronic ballast whereby the inner space of the inner element is open to atmospheric pressure, however, this inner space of the inner element is sealed gas-proof against the discharge space of the lamp.

Description

The invention relates to a fluorescent lamp according to the preamble of the main claim.

Such fluorescent lamps are known from DE-A-11 99 882. According to DE-A-27 25 412 and US-A-36 09 436, as well as according to US-A-20 01 501, GB-A-518 204 and DE-A 28 35 574, it is also known in the interior of fluorescent lamps to additionally arrange straight or U-shaped discharge tubes and to equip them with a plurality of discharge electrodes. According to DE-A-27 25 412 it is also known to provide the outer wall of the discharge tube with a phosphor layer over half of its circumference and its entire length. The lamps according to these publications are small, have a threaded connection base, and the discharge takes place in the inner discharge tube and in the lamp bulb. The electrical discharge in the discharge spaces initially generates UV radiation, which is converted into visible light in the phosphor layer. However, the UV radiation that is generated in the inner discharge tube is only involved to a small extent in the generation of visible light, which is emitted into the surroundings by the surface of the lamp bulb. For this reason, the luminous efficacy or the efficiency of such lamps is relatively low. The electrical energy that is required for the discharge in the inner discharge tube alone is approximately 50% of the total energy consumption, and in the end these 50% account for only approx. 10% of the total luminous efficiency of the lamp. Another disadvantage of the previously known lamps is the homogeneity of the light distribution on the surface of the lamp, which is difficult to obtain. Furthermore, the large number of discharge electrodes required for lamps of this type is a further economic disadvantage. In addition, a complicated and therefore expensive electrical circuit is required to control the electrodes.

The prior art also includes lamps which are known in the literature under the name "compact lamps". From the technical-scientific treatise of the OSRAM Society, 1986, volume 12, pages 383 to 393, it is known that these "compact lamps" are equipped with built-in ballasts and with a threaded base and are operated at higher frequencies of the lamp current. The advantages of compact lamps compared to those in the above. Small lamps made of fonts are the even smaller dimensions, the improved lamp efficiency and the reduced flickering of light. Despite the advantages of these "compact lamps", they are expensive and their light output is still relatively low. As for the fluorescent lamp mentioned at the outset according to DE-A-11 99 882, which is assumed here, this is also a discharge lamp, an inner element serving as an electrically conductive component mainly as an auxiliary ignition electrode and at the same time the so-called recombination surface of the discharge space enlarged.

The invention is therefore based on the object of further improving the efficiency of such fluorescent lamps, with the proviso that the manufacturing costs of such lamps can be further reduced.

This object is achieved with a fluorescent lamp of the type mentioned according to the invention by the features stated in the characterizing part of the main claim. Advantageous further developments and practical embodiments result from the subclaims.

In contrast to all the other lamps mentioned above, the principle of operation of the lamp designed in this way is based on two electrical fields, and - and this is essential to the invention - the first field in a known manner between two Discharge electrodes in the discharge space, and wherein the second field extends from the interior of the inner element perpendicular to the first field.

The economic advantage of the fluorescent lamp according to the invention consists in the substantially greater luminous efficacy per unit of electrical energy supplied compared to the luminous efficacy of known fluorescent lamps. The achievable efficiency of the fluorescent lamp according to the invention is approximately twice as high as the efficiency of known fluorescent lamps which are operated at 50 Hz. Furthermore, according to the invention, the efficiency of the lamp is approximately 1.6 times greater than the efficiency of known so-called "compact lamps" which are operated at approximately 35 kHz. Another advantage is the homogeneous light distribution that results on the surface of the lamp bulb, and furthermore, the ballasts required for the two electrical fields are easy to manufacture and cheaper than the ballasts of known fluorescent lamps with comparable luminous efficacy, apart from that, represent the total manufacturing costs of the invention Fluorescent lamp are significantly reduced compared to those of known lamps.

The fluorescent lamp according to the invention is explained in more detail below with reference to the drawing of exemplary embodiments.

• Fig. 1 teilweise im Schnitt und Ansicht die erfindungsgemäße Leuchtstofflampe in Röhrenform;
• Fig. 2 einen vergrößerten Schnitt durch die Lampe längs Linie II-II in Fig. 1;
• Fig. 3 im Schnitt das eine Ende des Innenelementes der Leuchtstofflampe gemäß Fig. 1;
• Fig. 4 teilweise in Schnitt und Ansicht die Leuchtstofflampe in Kolbenform;
• Fig. 5 im Schnitt eine besondere Ausführungsform des Innenelementes;
• Fig. 6 die graphische Darstellung der Potentialgradienten in Abhängigkeit von der Lampenstromdichte;
• Fig. 7 die graphische Darstellung der Impulsspannung an der Kondensatorplatte in Abhängigkeit von der Zeit
• Fig. 8 die graphische Darstellung der Entladungsspannung in Abhängigkeit von der Zeit und
• Fig. 9 das Funktionsprinzip der erfindungsgemäßen Lampe.

It shows schematically

• Fig. 1 partially in section and view of the fluorescent lamp according to the invention in tubular form;
• Figure 2 is an enlarged section through the lamp along line II-II in Fig. 1.
• 3 shows in section the one end of the inner element of the fluorescent lamp according to FIG. 1;
• Fig. 4 partially in section and view of the fluorescent lamp in the form of a bulb;
• 5 shows in section a special embodiment of the inner element;
• 6 shows the graphical representation of the potential gradients as a function of the lamp current density;
• Fig. 7 shows the graphical representation of the pulse voltage on the capacitor plate as a function of time
• 8 shows the graphical representation of the discharge voltage as a function of time and
• Fig. 9 shows the principle of operation of the lamp according to the invention.

1 to 3 consists of a tubular lamp bulb 1 and a discharge space 3 delimited by the latter and by the inner element 2, the inner wall of the lamp bulb 1 being covered with a phosphor layer 4. The discharge space 3 is filled with mercury vapor and with an inert gas or with an inert gas mixture. In the region of the two inner ends of the lamp bulb 1, discharge electrodes 7, 8 are arranged on the inner element, as shown, in the discharge space 3, between which the electrical discharge takes place in the discharge space 3. The outer surface of the inner element 2 is also covered over the entire length with a phosphor layer 9 or covered with a UV radiation reflector. The inner element 2 is arranged concentrically to the longitudinal axis of the lamp bulb 1 so that its mouth 10 is connected gas-tight to the inner ends of the bulb 1 and in this way together with the Lamp bulb 1 are integrated into the base 5, 6. the inner element 2 consists of a glass tube like the lamp bulb 1.

3, the electrode 8 is integrated gas-tight at the mouth 10 and by means of lines 17 ′, 18 ′ leading to connections 17, 18 ′ with the network with the interposition of ballasts (see FIG. 9). The electrode 7 at the other end is integrated in the same way in the other base 5. In the interior 11 of the inner element 2, one or more elements 12 acting as a capacitor are arranged, which are connected by lines 15 and 16 to a voltage source, which is arranged in the longer base 6, but is not shown. The element (s) 12 (FIG. 3) are formed from a sheet, a sieve, a metal layer or the like. But they can also consist of fine metal chips or "aluminum wool" 13 or a grid 14 with which the interior of the inner element 2 is simply filled. These elements 12, which act as a capacitor, are part of a capacitor because they are in the charged state as electrically conductive plates when the lamp is in operation.

The electrically conductive plasma in the discharge space 3 forms the second electrical conductor of the capacitor, the wall of the inner element 2 forming the dielectric. Caused by the voltage source arranged in the base, an electric field oscillates in this capacitor. Current flows through the lines 17, 18 to the electrode 8, which at the same time also causes the lamp or discharge current between the electrodes 7 and 8.

The lamp bases 5, 6 are designed so that they fit into the known versions. The length of the lamp according to FIG. 1 can be, for example, 450 mm to 2370 mm and the diameter of the lamp bulb 1 can be, for example, 30 to 55 mm. The distance D between the inner wall of the lamp bulb 1 and the outer wall of the inner element 2 can be, for example, 5 to 13 mm.

4, 5, in which corresponding reference numerals are used, show a so-called compact lamp which is equipped with ballasts installed in the base 6 (high-frequency generator 20 filter choke 24) and is provided with a threaded base 19 and can thus be used in conventional incandescent lamp holders. The capacitor element 12 extends according to FIG. 4 over the entire length of the interior 11 of the inner element 2 and is preferably formed from a metal grid that is simply inserted into the glass tube during the manufacture of the inner element 2. A line 16 connects the element 12 to the voltage source, which is located in the base 6, but is not shown.

In the embodiment according to FIG. 5, only a discharge electrode 8 is provided on the inner element 2 at the mouth 10 and at the other end of the inner space a short capacitor element 12, from which a line 16 leads to the voltage source located in the base 6. The second pole of the voltage source 21 is connected to the electrode 8 via a line 23. The electrical circuit between the capacitor element 12 and the plasma in the discharge space 3 is closed by the wall of the inner element 2. The length of this lamp can be, for example, 150 mm to 250 mm and the outer diameter of the lamp bulb 1 can be, for example, 30 mm to 60 mm. In contrast to the discharge space 3, the interior 11 of the inner element 2 is not sealed off from the atmosphere (see in particular FIG. 3.5).

1 to 5 are located in the interior 11 of the inner element 2.

Depending on the lamp power required and the overall geometric and electrotechnical parameters of the lamps, a decision must be made as to whether only one capacitor element 12 (FIG. 5) or two separate capacitor elements 12 (FIG. 3) are to be provided. This depends on the frequency of the voltage that is applied to the capacitor elements 12 and also on the distance D between the inner element 2 and the lamp bulb 1. If the distance D is small, the frequency of the electrical voltage on the capacitor plates must be higher than for a larger distance D. The luminous efficacy of the fluorescent lamp is inversely proportional to the distance D between the inner element 2 and the lamp bulb 1, that is to say as the distance D increases the luminous efficacy of the lamp and vice versa. A second parameter that improves the efficiency of the lamp is the frequency of the voltage applied to the capacitor elements 12. A third important parameter for improving the efficiency of the lamp is the pulse duration of a so-called monopolar electrical pulse, which is fed to the capacitor elements mentioned. If the pulse duration is shorter, ie if the rise time of the pulse is shorter, the efficiency of the fluorescent lamp is greater.

1 is connected in a known manner to the usual mains voltage of 50 Hz. After ignition, the lamp current flows between the electrodes 7 and 8, and at the same time the voltage of the capacitor element 12 acts perpendicularly on the lamp current (see FIG. 9). This vertically oriented voltage increases the electrical resistance of the plasma located in the discharge space 3, the resistance of the plasma increasing proportionally with this vertically oriented voltage, mainly when the current density of the lamp current in the plasma is greater. This physical phenomenon controls the homogeneity of the electrical current in the entire discharge space 3. If, for example, the current density in a locally limited small space increases faster than in an adjacent space, the electrical resistance in the space increases with the rapidly increasing current density under the action of the perpendicular Voltage faster, which slowed the increase in current density (mA / mm²) in this limited space becomes. In the end, a homogeneous current density is achieved in the entire discharge space 3, which guarantees a homogeneous light distribution of the visible light on the surface of the lamp bulb 1.

6, and as mentioned above, the resistance of the plasma in the discharge space 3 is also dependent on the distance D. When the distance D between the inner wall of the piston 1 and the outer wall of the inner member 2 becomes smaller, the resistance of the plasma increases. The resistance of the plasma per centimeter of the discharge length can easily be calculated from the data in FIG. 6. The voltage (V / cm) of the lamp length, also called the potential gradient, is shown on the vertical axis in FIG. 6 and the current density (mA / mm²) of the lamp current on the horizontal axis. All data in Fig. 6 are measured without vertical tension. Each curve in FIG. 6 shows the dependence of the voltage on the current density at a different distance D. For curve I the distance is D = 13 mm, for curve II D = 10 mm, for curve III D = 8 mm and for Curve IV is D = 5 mm. A lamp with a distance D = 5 mm has the largest potential gradient, while a lamp with a distance D = 13 mm has the smallest potential gradient. The data in Fig. 6 change significantly when pulsating voltage with a short pulse duration is applied to the capacitor elements. It is advantageous if the vertical voltage consists of short-lasting pulses and if the frequency of the pulses is high. For this purpose, all known high-frequency generators can be used for the generation of the vertical voltage, wherein generators are most suitable which generate pulses whose rise time is in the range of nanoseconds (1.10⁻⁹ sec.). For example, a small high-frequency pulse generator according to DE-A-37 06 385 was arranged in base 6. The frequency of the monopolar pulses generated by this method can be set in a wide range. The polarity of the pulses is the same as that of the carrier half period of the mains voltage.

Fig. 7 shows schematically the curve of an oscillograph, which has a monopolar pulse P in every half period of a mains voltage of 50 Hz. The pulse voltage (V) is shown on the vertical axis and the time in milliseconds (ms) on the horizontal axis. These pulses P are applied to the capacitor elements 12. Fig. 8 shows schematically another graphical representation of the oscillation of the lamp voltage in the discharge space 3, which oscillates simultaneously with the pulse P under the effect of the pulse P between the voltage V₁ and V₂. A higher frequency of the pulses P than the frequency shown in FIG. 7 naturally produces a higher oscillation of the lamp voltage in the discharge space 3. The oscillating vertical voltage P on the capacitor plates produces an oscillation of the plasma in the discharge space 3, which is of the frequency of the discharge current which flows between the electrodes 7 and 8 is independent. Each known high-frequency generator 20, which is connected to the capacitor elements 12, leads to an oscillation of the plasma in the discharge space 3 and thus significantly improves the luminous efficacy of such lamps.

The attached table contains the luminous efficacy in lumens per watt (1m / W) for lamps with a distance D of 5 mm and D = 8 min with different electrical energy, which is introduced at 50 Hz through the electrodes 7, 8 into the discharge space and also the energy which is conducted at around 35 kHz through the capacitor elements into the lamp. According to column 2 of the table, the electrical energy at 50 Hz is 88% and the electrical energy at 35 kHz is 12%.

1 with a distance of D = 5 mm is then 157 1m / W and with a distance of D = 8 mm 128 1m / W. The data in columns 3 and 4 of the table indicate the efficiency of the lamp under other energy conditions.
The example according to the column in the table illustrates the luminous efficacy of a lamp without a high-frequency generator, only a voltage of 50 Hz being applied to the capacitor elements 12. The light output with such a simple electrical circuit of the lamp in FIG. 1 is 93 lumens per watt.
The data in the table make it clear that expensive high-frequency generators are saved because the electrical energy of the high frequency is only slightly involved in the total electrical energy. With a lamp power of 30 W, for example, only about 8 W of the electrical energy at 35 kHz and about 22 W at 50 Hz are involved. Such a lamp shines with approximately 4,600 lumens. The light output of the compact lamp according to FIG. 4 is approximately 1.6 times greater than the light output of the known compact lamp of this type. A high-frequency generator 20, which has a frequency of approximately 35 kHz, can be used for the compact lamp according to FIG. Even greater economy can be achieved if the compact lamp according to FIG. 4 is operated with a small high-frequency pulse generator according to DE-A 37 06 385. The manufacturing costs of the compact lamp according to FIG. 4 are considerably lower than the known compact lamps which emit a comparable amount of light.
In the basic illustration according to FIG. 9, the capacitor element 12 is connected via line 16 to the high-frequency generator 20, which in turn is connected via lines 16 ', 23 to the voltage source 21 and the discharge electrode 8 and thus to the plasma in the discharge space 3.

If only one capacitor element 12 is provided according to FIG. 5, line 16 leads to high-frequency generator 20 according to FIG. 9, and if an additional capacitor element 12 is present according to FIG. 3, this is connected to high-frequency generator 20 via line 15.

Claims (6)

1. A fluorescent lamp comprising a discharge chamber (3) sealed by a lamp bulb (1) against the atmosphere and containing discharge electrodes (7, 8) as well as an elongated inner element (2) inwardly confining the discharge chamber (3), with the entire inner wall of the lamp bulb (1) and the outer wall of the inner element (2) being covered by a fluorescent coating (4) and with electrically conductive material (13, 14) being provided within the inner element (2) at least across a part of the total length thereof, which material is electrically connected to a discahrge electrode,
characterized in that
the inner element (2) is in the form of a support for at least one capacitor element (12) disposed in the inner chamber (11) thereof and extending across at least a part of the total length thereof and orienting an electric voltage vertical to the discharge distance, which capacitor element (12), through a conduit (16), is connected to a high frequency-generator (20) and to adapters, with the capacitor consisting of the afore-mentioned material (13, 14) forming the first conductor, of the wall of the inner element (2) forming the dielectric, and the plasma in the discharge chamber (3) forming the second conductor, and with the inner chamber (11) open toward the atmosphere being sealed, in gas-tight manner, against the discharge chamber (3).

2. A fluorescent lamp according to claim 1,
characterized in that
disposed, in gas-tight manner, on either end of the outer wall of the inner element (2), in the vicinity of the opening (10), are the discharge electrodes (7, 8) which, through conduits (17′,18′23), are in communication with voltage sources and adapters.

3. A fluorescent lamp according to claim 1,
characterized in that
disposed, in gas-tight manner, on one end of the outer wall of the inner element (2), in the vicinity of the opening (10), is a discharge electrode (8) and disposed on the other end of the inner wall of the inner element (2) is a capacitor element (12) which, through a conduit (16), is in communication with the high-frequency generator (20) (Fig. 5).

4. A fluorescent lamp according to any one of claims 1 to 3,
characterized in that
the inner chamber (11) of the inner element (2), at least across a part of its total length thereof, is filled with an electrically conductive material (13) such as aluminum wool, forming the capacitor element (12), finely divided metal chips and metal powder and, through a conduit (16), is connected to a voltage source and to adapters (Fig. 1).

5. A fluorescent lamp according to any one of claims 1 to 3,
characterized in that
disposed on the inner wall of the inner element (2), at least across a part of the total length thereof, is a grid (14) forming the capacitor element (12), which grid, through a conduit (16), is in communication with a voltage source and with adapters (Fig. 1).

6. A fluorescent lamp according to any one of claims 1 to 5,
characterized in that
the electrical conduits (15,16,17′,18′,23) are disposed in the inner chamber (11) of the inner element (2).

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