Electrical gas-discharge lamp with discharge-coupled active antenna

Abstract

The present invention relates to an electrical gas-discharge lamp comprising an inner bulb (1) arranged within an outer bulb (2), said inner bulb (1) being filled with a discharge gas and comprising a first electrode (3) and an opposing second electrode (4) having a distance from the first electrode (3) which allows ignition of a gas-discharge by applying an ignition voltage between the electrodes (3, 4). At least one through hole (11) is formed in the feedthrough to the electrically conductive lead (5) to the first electrode (3). An electrically conductive member (10) extents within a space formed between the inner (1) and the outer bulb (2) from a position close to the through hole (11) to a distance from the second electrode (4) which is smaller than the distance between the two electrodes (3,4). When applying the ignition voltage between the electrodes (3,4) an electrically conducting path (12) forms through the through hole (11) between the electrically conductive member (10) and the electrically conductive lead (5) by ionization of the gas in the outer bulb (2). With this transient conductive path the coating (10) forms an active antenna effectively lowering the ignition voltage. The fabrication of the proposed lamp with reduced ignition voltage requires only few additional fabrication steps compared to a lamp without such an ignition aid.

Claims

1. An electrical gas-discharge lamp comprising: an inner bulb and an outer bulb, the inner bulb being arranged within the outer bulb, said inner bulb being filled with a discharge gas and comprising a first electrode and an opposing second electrode having a distance from the first electrode which allows ignition of a gas discharge in the inner bulb by applying an ignition voltage between the electrodes, said first electrode being electrically contacted by a first electrically conductive lead, which extends in a first electrically insulating feedthrough on a first side of the inner bulb through the outer bulb, said second electrode being electrically contacted by a second electrically conductive lead extending in a second electrically insulating feedthrough on a second side of the inner bulb through the outer bulb, and said outer bulb being filled with a second gas, at least one through hole is formed in the first feedthrough to the first electrically conductive lead and an electrically conductive member extends within a space formed between the inner and the outer bulb at least from a position close to the through hole to a distance from the second electrode which is smaller than the distance between the two electrodes, said position of the electrically conductive member close to the through hole being such that, prior to ignition of the lamp, the electrically conductive member is not electrically connected to said first electrically conductive lead, and such that an electrically conducting path forms through the through hole between the electrically conductive member and the first electrically conductive lead by ionization of the second gas when applying said ignition voltage between the electrodes.

2. The electrical gas-discharge lamp according to claim 1, wherein at least the first electrically conductive lead comprises a section being formed of a metal foil, wherein said through hole extends to the metal foil.

3. The electrical gas-discharge lamp according to claim 1, wherein the electrically conductive member extends from the position close to the through hole to the second feedthrough.

4. The electrical gas-discharge lamp according to claim 1, wherein the electrically conductive member is formed of a coating or partial coating on the inner bulb.

5. The electrical gas-discharge lamp according to claim 1, wherein the electrically conductive member is formed of a stripe-shaped coating on the inner bulb.

6. The electrical gas-discharge lamp according to claim 1, wherein the electrically conductive member is formed of a material which is optically transparent in the visible wavelength range.

7. The electrical gas-discharge lamp according to claim 1, wherein the inner bulb contains metal halides in addition to the discharge gas.

8. The electrical gas-discharge lamp according to claim 1, wherein the pressure of the second gas in the outer bulb is lower than atmospheric pressure.

9. The electrical gas-discharge lamp according to claim 1, wherein the inner bulb is formed of quartz glass.

10. The electrical gas-discharge lamp according to claim 1, wherein the pressure of the discharge gas in the inner bulb is selected to form a high-pressure discharge lamp.

11. The electrical gas-discharge lamp according to claim 1, designed to be used as an automotive HID lamp.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The proposed electrical gas-discharge lamp is described in the following by way of examples in connection with the accompanying figures. The figures show:

(2) FIG. 1 a schematic cross-sectional view of a HID lamp of the prior art;

(3) FIG. 2 a schematic cross-sectional view of an exemplary embodiment of the proposed gas-discharge lamp;

(4) FIG. 3 a schematic view on the gas-discharge lamp of FIG. 2 perpendicular to the view of FIG. 2;

(5) FIG. 4 a schematic cross-sectional view of a further embodiment of the proposed gas-discharge lamp;

(6) FIG. 5 a schematic cross-sectional view of a further embodiment of the proposed gas-discharge lamp; and

(7) FIG. 6 a measurement diagram showing the reduction of the ignition voltage achieved with the proposed gas-discharge lamp.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) FIG. 1 shows a schematic side view of an exemplary embodiment of a HID lamp of the prior art, as known e.g. from WO2008/007283 A2. The discharge lamp is formed of an inner bulb 1 arranged within an outer bulb 2. Both bulbs are made of a quartz glass material optically transparent in the visible wavelength region. The inner bulb 1 comprises two electrodes 3, 4 which are arranged at a distance from one another to allow ignition of a gas-discharge by applying an ignition voltage between the electrodes 3, 4. The inner bulb 1 together with the electrodes 3, 4 and the outer bulb 2 are gas-tightly sealed. The electrodes 3, 4 are electrically contacted by corresponding electrically conductive leads 5, 6 which extend through appropriate feedthroughs 7, 8 to the outside of the outer bulb 2. The electrically conductive leads 5, 6 comprise a section formed of a molybdenum foil 9 as known in the art. The inner bulb 1 is filled with a high-pressure inert discharge gas and with metal halides, the outer bulb 2 with a second gas. In order to lower the ignition voltage, an active antenna is arranged in the space between the inner bulb 1 and the outer bulb 2. The antenna is formed of an electrically conductive, optically transparent coating 10 on the outer surface of the inner bulb 1 and extends from the first feedthrough 7 to the second feedthrough 8 as indicated in the figure. A through hole 11 is formed in the first feedthrough 7 to the molybdenum foil 9 of the electrically conductive lead 5. This through hole 11 is filled with the electrically conductive material of the coating 10 to achieve a direct electrical connection between the coating 10 and the lead 5, thus forming an active antenna for lowering the ignition voltage of the lamp.

(9) FIG. 2 shows a cross-sectional view of an exemplary first embodiment of the proposed gas-discharge lamp. The proposed gas-discharge lamp has a similar construction as that of FIG. 1. Therefore, the corresponding identical elements, i.e. bulbs, electrodes, leads and feedthroughs, are not newly described. In contrast to the lamp of FIG. 1, the through hole 11 in the proposed lamp is not filled with a coating but filled with the second gas of the outer bulb. In this embodiment, the antenna is formed of only a partial electrically conductive coating 10 which forms a stripe on the outer surface of the inner bulb 1 and extends from the through hole 11 to the second feedthrough 8 of the lamp. Therefore, prior to ignition of the lamp, the electrically conductive coating 10 is not electrically connected to the electrical conductive lead 5 of the lamp but forms only a passive antenna. When applying the ignition pulse to the lamp, an electrical connection between the coating 10 and the molybdenum foil 9 of the first electrically conductive lead 5 is temporarily generated by ionization of the second gas, i.e. by generation of a small discharge 12 in the through hole 11. This discharge 12 is only schematically indicated in FIG. 2. With his transient electrical connection, the originally passive antenna behaves like an active antenna and effectively lowers the ignition voltage of the lamp.

(10) The through hole 11 may be formed by laser machining as is already known in the art of such lamps and has only a small diameter of e.g. 100 m. As can be seen from FIG. 2, the distance between the electrically conductive coating 10 forming the antenna and the second electrode 4 is lower than the distance between the two electrodes 3, 4.

(11) FIG. 3 shows a view onto the lamp of FIG. 2 perpendicular to the side view of FIG. 2. In this figure, the exemplary geometrical form of the antenna coating 10, i.e. the stripe-shaped form, can be recognized. This figure also shows the molybdenum foils 9 from another view.

(12) The coating 10 forming the antenna must not in any case extend until the second electrode 4 or second feedthrough 8. Such an embodiment is schematically shown in the cross-sectional view of FIG. 4. Since the antenna in this embodiment has a higher distance to the second electrode 4, the ignition voltage is only lowered to a smaller degree than in the case of FIGS. 2 and 3. Nevertheless, the ignition voltage is still lowered compared to a construction without such an antenna.

(13) FIG. 5 shows an embodiment of the proposed discharge lamp, in which the inner bulb 1 is completely coated with an optically transparent, conductive coating 10 forming the antenna of the discharge-lamp. Such a complete coating 10 can be applied in a very simple manner by only dipping the inner bulb 1 into a corresponding coating solution during fabrication.

(14) A lamp as shown in FIGS. 2 and 3 has been fabricated by printing an antenna stripe with a width of about 1 mm with a high temperature-resistant, electrically conductive paint on the outer surface of the inner bulb 1. The lowering of the ignition voltage was measured with such a lamp. The lowering of the ignition voltage is shown in comparison with reference lamps in the probability plots of FIG. 6. For the reference lamps, 25 W lamps from D5 production with DBD and small passive antenna, the ignition voltages vary between 15 and 17.5 kV. If a through hole is added to enhance the DBD, the variation is between 12 kV and 16.5 kV. That is, there is a clear reduction of the mean, but unfortunately not as much of the maximum ignition voltage by this measure. When using a HID lamp according to FIGS. 2 and 3, the ignition voltage is only between 11 kV and 13 kV, which is a dramatic improvement compared with the reference lamps.

(15) While the invention has been illustrated and described in detail in the drawings and forgoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The terms first and second in the claims and description are only used to differentiate the corresponding elements from one another and can also be interchanged. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The features of claims 1 to 8 can be freely combined which each other. Any reference signs in the claims should not be construed as limiting the scope of the invention.

LIST OF REFERENCE SIGNS

(16) 1 inner bulb 2 outer bulb 3 first electrode 4 second electrode 5 first electrically conductive lead 6 second electrically conductive lead 7 first feedthrough 8 second feedthrough 9 molybdenum foil 10 electrically conductive coating 11 through hole 12 discharge