EP1307898A2

EP1307898A2 - Flash lamp and flash lamp structure

Info

Publication number: EP1307898A2
Application number: EP01974152A
Authority: EP
Inventors: Ingo DÜNISCH
Original assignee: PerkinElmer Optoelectronics GmbH and Co KG
Current assignee: Excelitas Technologies GmbH and Co KG
Priority date: 2000-08-11
Filing date: 2001-08-09
Publication date: 2003-05-07
Also published as: WO2002015213B1; US6867547B2; JP2004507039A; WO2002015213A2; DE10039383A1; CN1470065A; WO2002015213A3; US20040032218A1

Abstract

The invention relates to a flash lamp (10) comprising a glass gas-filled discharge tube (10) and, on each end, a power electrode (14, 15) that is sealed by means of a glass solder. The flash lamp has a glass, which comprises one or more of the following UV transmission values Tw: at 180 nm: Tw > 5 %, preferably > 9 %; at 200 nm: Tw > 30 %, preferably > 45 %; at 254 nm: Tw > 60 %, preferably > 80 %. The inside diameter (11) of the discharge tube can be larger than 1.2 times the value of the diameter of the plasma channel. The starting electrode (16) can be a part of the reflector (30-33) or can be electrically connected to the same. The flash capacitor (42) can be rated for a charging voltage of greater than 370 volts, preferably greater than 400 volts.

Description

Flash lamp and flash lamp construction

The invention relates to a flash lamp and a flash lamp structure. In particular, it concerns flash lamps for applications in the UV range (wavelength <450 nm).

FIG. 5A shows a general structure of a flash lamp 50. It has a closed glass body 53 in which a gas, for example xenon, is at a certain filling pressure. The tubular body 53 has electrodes 51 at both ends. For thermal resistance, these electrodes are made of tungsten, at least in the area within the tube. The DC voltage of a flash capacitor is applied to the electrodes, conventionally approx. 300 to 350 volts. This voltage alone is not enough to cause a discharge. Rather, this only arises when a further ignition voltage (1000 volts AC or more) is capacitively applied via an ignition electrode 52, which then triggers the start of the discharge, the discharge continuing even when the ignition voltage is again applied to the ignition electrode 52 has subsided. The electrodes 51 are melted into the glass body 53 via glass sleeves 54. 5B shows in cross section a flash lamp 50 in connection with a reflector 55 in a known construction. The reflector can be a parabolic reflector, which essentially directs the light emitted all around by the flash lamp in one direction. The flash lamp 50 can rest on the reflector 55. The reflector can be a sheet metal, which is used as an ignition electrode and is accordingly included in the electrical sound system and is held in an insulated manner.

Known flash lamps have various problems, particularly with regard to UV applications:

Glasses commonly used have poor UV transmission. This means that although UV light is certainly generated within the flash lamp 50, it is already absorbed within the glass so that it does not reach the outside. Conventional flash lamps are made in particular from tempered borosilicate glass because this allows a particularly economical melting technique for the electrodes. Such a tempered glass with a thickness of 0.5 mm is, however, no longer sufficiently transparent for wavelengths of 320 nm and shorter, so that it is unsuitable for UV applications.

There are certain glasses with improved UV transmission. Quartz glasses have a high melting point and therefore require a complex manufacturing process that is justified only for flash lamps with high flash energy (> 100 Ws). However, it cannot be used for flash lamps for UV Low flash energy (<100 Ws) applications are used as this would not be economical.

Another problem with known flash lamps is that of glass wall blackening. During a discharge, the electrodes in the flash tube evaporate to a certain extent. The metal vapor is deposited on the inner walls of the glass tube 53. This further affects the permeability of the vitreous body, particularly for UV light. 5B, it has been shown that there is a certain accumulation of the precipitate of the evaporated tungsten material in the region of the contact of the reflector 55 with the glass tube 53. Here too, however, a flat distribution of the precipitation is observed over the inner circumference of the glass tube.

Finally, the known reflector constructions according to FIG. 5B have the disadvantage that multiple reflections occur between flash lamp 50 and reflector 55, which on the one hand reduces the light yield due to repeated absorption and on the other hand the thermal load, in particular also because of the uneven distribution of the incidence of light over the circumference elevated.

The object of the invention is to provide a flash lamp which can be easily manufactured and which is particularly suitable for UV applications.

The invention encompasses several aspects which can be used on their own, but also particularly advantageously in combination. In detail: A. A flash lamp is specified which emits radiation power predominantly in the UV range (wavelengths <450 nm) and whose energy per flash is less than 100 Ws, preferably less than 50 Ws.

B. A low-melting glass with good UV permeability is used for the body of the flash lamp in connection with a melting technique based on glass solder for the electrodes.

C. An inner diameter of the glass tube is chosen which is larger than the arc diameter during the discharge. This dimensioning is preferably carried out in conjunction with a one-sided, line-shaped trigger electrode.

D. The trigger electrode is formed by the fold of a reflector, the fold being an elongated fold which can run in the longitudinal direction of the glass tube and can be attached to it.

E. The highest possible xenon filling pressure is used.

Q. A comparatively high charging voltage is used.

By using one or the combination of several of the above feature groups A. to F., a good UV yield of an economically producible flash lamp is achieved. You can then reach areas of UV light yield that allow certain characteristics, in particular to influence the spectrum in particular by choosing the glass wall thickness. Contrary to the primary goal of making a glass wall as thin as possible in order to obtain the lowest possible absorption, the wall thickness can be chosen thicker or the glass material more freely in order to obtain certain properties of the flash lamp.

Particularly advantageous combinations are pairings of the above characteristics B., C. and D. (B. and C, B. and D., C. and D.), or all three groups of characteristics together (B., C. and D.) , the resulting flash lamps, if necessary in conjunction with one or both of the feature groups E. and F. Characteristic group A. can be produced.

Individual embodiments of the invention are described below with reference to the drawings. Show it:

1 is a flash lamp according to the invention,

2 dimensions and definitions for a flash lamp,

3 shows an overall structure of the flash lamp and reflector according to the invention,

Fig. 4 shows a circuit for a flash lamp, and

Fig. 5 known embodiments. In general, the invention resides in the creation of a flash lamp which emits more than 30%, preferably more than 50%, more preferably more than 70% of its radiation power in the UV range (wavelengths <450 nm) and its energy per flash is less than 100 Ws , preferably less than 50 Ws, more preferably less than 20 Ws. The energy per flash can be over 1 or 2 Ws. This creates flash lamps that are suitable for disinfecting objects in the home.

The flash lamp can be constructed as shown in FIG. 1. Fig. 1 shows a flash lamp 10 schematically in longitudinal section. 11 denotes the glass body of the flash lamp. It is preferably elongated and round cylindrical. At the longitudinal ends of the flash lamp are electrodes 14 and 15, which can be melted into the glass body 11 in a manner to be described later. The electrodes 14, 15 have anode 14a and cathode 15a. An ignition electrode 16 is provided outside the interior 12 of the flash lamp. It can be a conventional construction or a construction according to the invention to be described later. The ignition electrode preferably extends in the longitudinal direction of the flash lamp. In particular, it preferably covers the focal length of the flash lamp (the area between the electrode plates 15a, 14a).

The glass of the tubular body 11 has good UV permeability. It can be described as follows:

It has a low content of polyvalent ions, especially iron. The content is below 30%, preferably below 10% of the value of Glasses used for conventional flash lamps (photo flash lamps). The same can apply to the oxides of aluminum and more generally of alkali and alkaline earth metals.

With regard to UV transmission, the glass can be described as follows on the basis of its transmission values Tw at certain wavelengths: at 180 nm Tw is greater than 5%, preferably greater than 9%, at 200 nm Tw is greater than 30%, preferably greater than 45%, at 254 nm (mercury line) Tw is greater than 60%, preferably greater than 80%. A glass that meets the above transmission value specifications is the 8337B glass from Schott, which according to.

Manufacturer's specification has a transmission value of 10% at 180 nm, a transmission value of 50% at 200 nm and a transmission value of 90% at 254 nm. The information on Tw in this description and in the claims are to be understood as material constants in the sense that they refer to glasses with a thickness of 0.5 mm. Actually built flash lamps can have different transmission values depending on their glass wall thickness, in particular lower ones for thicker glasses and higher ones for thinner glasses.

The glass used meets one or more of the above-mentioned conditions with regard to UV transmission or material composition. The associated more difficult processability can be compensated for by melting the electrodes 14 and 15 or electrode assemblies 14, 14a, 14b and 15, 15a and 15b onto the glass body 11 using glass solder 13a, 13b. The electrodes 14 and 15 preferably have or consist of tungsten. The elongated, piercing the vitreous 11 Pins 14, 15 can be surrounded by glass solder 13a, 13b in the region of the passage through the glass body 11 (not shown). The glass solder is in turn fused to the glass body 11, which is composed or has properties as described above. In addition, a sealing ring (not shown) can also be provided between glass solder 13a, 13b and glass body 11, which likewise consists of glass. The electrodes 14 and / or 15 can, as shown in FIG. 1, also be provided lying in a glass plate 14b, 15b. The glass plate can be attached to the glass body 11 by means of glass solder 13. With a suitable diameter of the glass plate 14b, 15b, the fastening can take place on the cylindrical circumference of the glass tube 11, as shown.

The anode 14a may be a simple continuation of the tungsten wire (other than shown). The cathode 15a can have a sleeve over the tungsten wire, which has tungsten and / or nickel and / or niobium and / or tantalum and / or titanium.

The glass solder 13 has a very low temperature response in terms of its hardness. In particular, it is several 10 ° C. below that of the glass of the glass body 11, which in turn has a low melting point (in particular, for example, in terms of softening point, transformation point). The corresponding temperatures of the glass solder can be at least 60 or 80 ° C lower than those of the glass of the body 11. The glass solder also has a coefficient of thermal expansion which is closer to that of the tungsten wire than to that of the glass of the body 11. The same applies to the temperature response of the coefficient of thermal expansion, in particular in the range between room temperature, processing temperature and operating temperature. By matching the thermal expansion coefficients of glass solder 13 and metal pins 14, 15, the transition between metal and glass is comparatively insensitive to cracks and leaks, which can occur in particular as a result of alternating stresses due to changing temperatures during the life of a lamp or initially during its manufacture. The connection between glass solder 13 and glass body 11 is particularly intimate due to the similarity of material and is therefore also satisfactory. The low-temperature processing of the glass solder allows an operation that is gentle on the glass of the body 11, which also has a low melting point.

2 shows preferred dimensioning features which, alone or in conjunction with the above features, lead to particularly good flash lamps. 2A shows a flash lamp 11 in cross section. 12 is the interior of the flash lamp. 13a symbolizes the glass solder, 14a the end face of the electrode. Di is the inside diameter of the cylindrical glass tube. Dlb symbolizes the diameter of the arc, which results when the arc is between the electrodes 14 and 15. Since the arc is not necessarily spatially delimited, the radius at which the emission intensity has dropped to half the maximum value can be taken as a measure of the arc diameter. This is indicated in Fig. 2B. The emission intensity I is plotted there over the radius r. In the example it is assumed that the maximum intensity Imax is at radius r = 0 (i.e. in the center of the tube). Where it has decayed to half the maximum value Imax / 2, the arc radius (half the arc diameter, Dlb / 2) is set by definition. A dimensioning rule for the inner diameter Di and the arc diameter Dlb has proven to be advantageous if Di is greater than Dlb, if in particular Di> 1.2 Dlb applies, or further preferably Di> 1.4 Dlb. Such a dimensioning rule prevents the hot plasma from contacting the inner glass wall, so that the thermal load on the glass of the body 11 is reduced. This is particularly advantageous if the glass is a low-melting glass as mentioned above.

A further advantage results if the ignition (triggered by electrode 16) takes place along a sharply delimited line on the inner wall of the glass. The latter does not mean that the electrode should lie on the inner wall of the glass. Rather, care must be taken to ensure that the electrical field coupled in by the trigger electrode 16 can be traced back to a point that is as punctiform as possible (in the cross section of FIG. 2A), so that the fed-in trigger E field runs at least in the radial direction at least in the vicinity of the trigger electrode , This cannot be achieved by a configuration according to FIG. 5B. A configuration according to FIG. 2A is advantageous, which indicates a linear trigger electrode 16 on the outside of the body 11. Another embodiment will be described later with reference to FIGS. 3A and 3B.

The linear design of the trigger electrode has the advantage that the material of the electrodes evaporated during the arc is deposited in a spatially limited manner in the vicinity of the trigger electrode 16 (linear blackening on the inner wall of the glass over the life of the flash lamp). In conjunction with the diameter dimensioning mentioned above, there is the advantage that the material that has been deposited is less likely to be detached by the arc and redistributed in the interior.

The trigger electrode is preferably designed in such a way that it has no appreciable extension in the sectional view in the circumferential direction or in the tangential direction of the flash lamp, provided that it is not spaced from the flash tube. This can be done using a conventional wire or as described below.

3A and B show a flash lamp in which the trigger electrode or ignition electrode is formed by part of a reflector plate. FIG. 3A shows an embodiment in which the trigger electrode is formed by a web 31 which is attached to the reflector 30. At least the web 31 is made of metallic material or metallized. The reflector 30 itself can be metallic or non-metallic. The web 31 would then have to be included in the wiring of the flash lamp as an ignition electrode 16 and wired accordingly.

3B shows a further embodiment. Here, the reflector 32 is designed as a folded sheet. The fold 33 in the reflector plate 32 is elongated and preferably extends along the longitudinal direction of the flash lamp 10, preferably it lies against the body 11 of the flash lamp 10 (in the installed state). The reflector 32 would then in turn be connected to the Include flash lamp and wire appropriately. Possibly. it must be kept isolated.

The shape of the reflector 32 can be axisymmetric in the section of FIG. 3B. The reflector can have two concave halves, preferably symmetrical and abutting on the fold 33. The cross-sectional shape can be that of a “W”, the shapes being rounded in the middle apart from the fold 33. The inside angle α at the fold can be 120 ° or less, preferably 90 ° or less, more preferably 60 ° or less. The reflector halves can be shaped with regard to the desired scattering or bundling properties of the overall structure.

The design of the reflector described with reference to FIG. 3B also makes it possible to avoid multiple reflections. Because light emitted to the rear (in FIG. 3B below) is not thrown back onto the glass body 11 of the flash lamp 10, but rather transversely away from it and then to the front, which is indicated in FIG. 3B by a few beam paths 34a, b, c is. As a result, the special thermal stress on the rear wall of the tube 11 is largely avoided. This leads to a reduction in asymmetrical thermal expansions and to a reduction in the heating of the flash tube, especially in the area in which evaporated material due to the selected ignition electrode structure is reflected on the inside. The reduced temperatures lead to a lower tendency of the material once chipped off to evaporate again and to precipitate elsewhere. In addition, the light yield is improved by avoiding multiple reflections, since UV radiation is particularly strongly absorbed in the glass of the tube 11. With only one back reflection (originally out, then back in and finally out again), the absorption coefficient of the glass would be effective three times, so that the corresponding light would be lost in terms of yield on the one hand and would contribute to the undesired warming up of the glass on the other hand.

A reflector, as has been described with reference to FIGS. 3A and B, is regarded as an independent and, if appropriate, separately usable part of the invention.

Fig. 4 shows a flash lamp structure. It has a flash lamp 10, which can have the features described above. A capacitor 42 is used

Consumption of electrical energy that is primarily intended to feed the flash process. The energy can be taken, for example, from a possibly transformed and rectified AC voltage, which then charges the capacitor 42 via the connections 41. Energy can also be supplied from a battery. A suitable higher DC voltage for charging the capacitor would then be generated via a chopper and coil / transformer and applied to the terminals 41. The capacitor 42 is preferably an electrolytic capacitor.

Its connections are connected to the connections 14 and 15 of the flash lamp 10, so that the capacitor voltage is present at their connections. Another small capacitor 43 is used to generate the ignition voltage. It is also loaded. By actuating switch 45, it is short-circuited. The resulting change in current or voltage in the primary coil 42a of a transformer 44 has alternating voltage components which are transformed up by a suitably dimensioned transformer 44. Its secondary coil 44b is connected to the ignition electrode 16 (for example according to FIG. 3) of the flash lamp.

Thus, the switch 45 is used to trigger the flash. It can be an electrically, electronically or manually operated switch. The ignition voltage is only required to trigger the flash. Accordingly, the capacitor 43 can also be dimensioned comparatively small. Once the flash lamp 10 has ignited (by applying the ignition voltage to the ignition electrode 16), the ohmic resistance of the flash lamp 10 drops significantly due to the plasma that is produced, so that the capacitor voltage from the flash capacitor 42 alone is sufficient to discharge the current hold. The discharge can subside by itself (capacitor 42 partially emptied) or can be actively interrupted by suitable circuit structures, not shown.

The flash capacitor is designed for a charging voltage / operating voltage of more than 370 volts, preferably more than 400 volts and less than 450 volts, preferably less than 430 volts. A comparatively high operating voltage causes a comparatively high discharge current, which, moreover, is disproportionately high due to the non-linearity of the plasma. This results in a comparatively hot plasma, which is particularly in the UV area radiates a lot of energy. According to the formula E = 0.5 CU (E = energy in the capacitor, C = capacitance, U = voltage), a smaller flash capacitor can also be selected with the same flash energy. Moreover, a comparatively "small" flash capacity 42 is also advantageous because the time constant t for the discharge (t = R * C42) then becomes small, so that the discharge duration is short, the temperature is high and thus the UV component is higher. The upper limit of the selectable voltage (and thus possibly indirectly the lower limit of the selectable capacity) form economic considerations with regard to the flash capacitor 42. Very high capacitor voltages require expensive capacitors, so that 450 or 430 volt charging voltage may seem sensible as the upper limit of the flash capacitor below 500 μF, more preferably below 300 μF.

A further possibility for increasing the UV yield is to increase the filling pressure in the flash lamp 10, in particular the xenon filling pressure. By increasing the filling pressure, the plasma channel becomes narrower during the flash without the peak current and thus the flash power and flash energy being significantly reduced. The narrowing of the plasma channel makes the plasma hotter, so that more energy is emitted in the ultraviolet range. However, a higher xenon filling pressure also increases the required ignition voltage at the ignition electrode 16. Since this cannot be raised as high as possible to avoid flashovers, the ignition conditions also place an upper limit on the xenon filling pressure. The xenon filling pressure can be above 0.5 bar, preferably above 1.5 bar, more preferably above 2 bar. If several of the features described above are combined, comparatively high UV yields can result. They can then be so high that absorption parameters of the glass of the body 11 of the flash lamp can finally be used to set certain properties of the flash lamp. For example, the thickness of the glass wall can finally be chosen to be thicker than it would have to be with regard to mechanical stability, also with regard to thermal stress, in order to obtain certain spectra or distributions.

Typical dimensions and data of a flash lamp can be:

Inner diameter Di between 3 and 6.5 mm, typically between 4.5 and 5.5 mm,

Focal length (distance between the electrodes 14a and 15a) between 15 and 25 mm, typically 18 to 22 mm,

Glass wall thickness 0.2 to 0.8 mm, typically 0.4 to 0.6 mm,

Xenon filling pressure 0.5 to 5.5 bar, typically 1.5 to 4.5 bar,

• Flash capacitor capacitance 100 to 300 μF, preferably 150 to 250 μF,

• Energy per flash between 5 and 17 Ws, preferably between 10 and 15 Ws.

Claims

EXPECTATIONS

1. flash lamp (10) with a gas-filled discharge tube (11) made of glass and at each end each a power electrode (14, 15), characterized in that a glass is used which has a thickness of 0.5 mm one or more of the following transmission values Tw: at 180 nm: Tw> 5%, preferably > 9% at 200 nm: Tw> 30%, preferably > 45% at 254 nm: Tw> 60%, preferably > 80%.

2. Flash lamp according to claim 1, characterized in that at least one power electrode (14, 15) is also connected by means of glass solder (13a, 13b) to the discharge tube, the glass solder having a softening point and / or a transformation point which is at least 60 ° C is below that of the glass of the discharge tube (11).

3. flash lamp (10), preferably according to one of the preceding claims, with a discharge tube (11), power electrodes (14, 15), one

Ignition electrode (16) and a reflector (30-33), characterized in that the ignition electrode (16) is part of the reflector (30-33) or is electrically connected to it.

4. flash lamp (10) according to claim 3, characterized in that the ignition electrode (16) is formed by a fold (33) in the reflector plate (32).

5. flash lamp according to claim 3 or 4, characterized in that the reflector has two halves abutting on the fold (33).

6. flash lamp (10) according to one or more of claims 3 to 5, characterized in that the fold (33) extends in the longitudinal direction of the flash lamp (10).

7. flash lamp (10), preferably according to one or more of the preceding claims, with a discharge tube (10), power electrodes (14, 15) at the ends of the tube (10) and an ignition electrode (16), characterized in that the inside diameter of the discharge tube

(11) is larger than 1.2 times the diameter of the plasma channel.

8. flash lamp (10) according to claim 7, characterized in that the inner diameter of the discharge tube (11) is larger than 1.4 times the diameter of the plasma channel.

9. flash lamp (10) according to claim or 8, characterized in that the ignition electrode (16) has no significant extension in the circumferential or tangential direction of the discharge tube (11).

10. flash lamp (10), preferably according to one of the preceding claims, with a discharge tube (11) and a xenon gas filling, characterized in that the xenon filling pressure is greater than 0.5 bar, preferably greater than 1.5 bar.

5

11. flash lamp (10) according to claim 10, characterized in that the filling pressure is below 4.5 bar.

12. flash lamp assembly with a flash lamp (10), preferably according to one of the preceding claims, and a flash capacitor (42) connected thereto, characterized in that the flash capacitor (42) is designed for a charging voltage above 370 volts, preferably above 400 volts.

5 13. Flash lamp assembly according to claim 12, characterized in that the flash capacitor (42) is designed for a charging voltage below 450 volts, preferably below 430 volts.

14. flash lamp assembly according to claim 12 or 13, characterized in that the capacitance of the flash capacitor (42) is below 300μF.

15. flash lamp (10) with a discharge tube (11) made of glass, characterized in that the wall thickness is thicker than a value which would be chosen with regard to mechanical and thermal stability. 5

16. flash lamp (10) according to claim 15, characterized in that the wall thickness is selected so that there is a certain absorption behavior at a certain wavelength or in a certain wavelength range.

17. flash lamp, preferably according to one of the preceding claims, the radiation power predominantly in the UV range (wavelengths

<450 nm, preferably <350 nm).

18 flash lamp, preferably according to one of the preceding claims, whose energy per flash is less than 100 Ws, preferably less than 50 Ws, more preferably less than 20 Ws.