HIGH-INTENSITY DISCHARGE LAMP

Abstract

The present invention relates to a high-intensity discharge lamp (1) comprising a discharge vessel (2) enclosing a filling in a discharge chamber (3), and a pair of electrode rods (4, 5) being formed of a material which is free of thorium and protruding from opposite sides into the discharge chamber (3). The diameter ED of the electrode rods (4, 5) in the discharge chamber (3) N satisfies the formula (I), wherein W represents the value of the nominal lamp power in mW and Ed represents the value of the distance of the electrode rods (4, 5) in the discharge chamber (3) in mm, and wherein the nominal lamp power W is between 20 W and 50 W. With the above formula, high-intensity discharge lamps can be easily designed with different nominal powers and/or 10 electrode distances without time consuming experiments in order to achieve an optimum performance.

[00001]$\begin{array}{cc}\mathrm{ED}{\mathrm{ED}}_0=\sqrt{.Math..Math.W/\left[1+\frac{\mathrm{Ed}-3}{3.Math..Math.\mathrm{Ed}}\right]}.Math.m-10.Math.m,& \left(I\right)\end{array}$

Claims

1. High-intensity discharge lamp comprising a quartz glass discharge vessel enclosing a filling in a discharge chamber, and a pair of electrode rods of simple rod shape being formed of a material which is free of thorium and protruding from opposite sides into the discharge chamber, wherein the discharge chamber has an inner diameter between 2.0 mm and 2.8 mm and an outer diameter between 5.3 mm and 6.3 mm, and wherein a diameter ED of said electrode rods in the discharge chamber satisfies the formula: $\mathrm{ED}{\mathrm{ED}}_0=\sqrt{.Math..Math.W/\left[1+\frac{\mathrm{Ed}-3}{3.Math.\mathrm{Ed}}\right]}.Math..Math.m-10.Math..Math.m,$ W representing a value of the nominal lamp power in mW and Ed representing a value of a distance of the electrode rods in the discharge chamber in mm, and wherein the nominal lamp power W is between 20 W and 50 W.

2. The lamp according to claim 1, wherein the electrode rods are formed of a material which is free of any emitter.

3. The lamp according to claim 1, wherein the diameter ED of the electrode rods is between ED.sub.0 and ED.sub.0+40 m.

4. The lamp according to claim 1, wherein the distance of the electrode rods in the discharge chamber is between 2.0 and 4.0 mm.

5. The lamp according to claim 1, wherein the filling includes an emitter.

6. The lamp according to claim 5, wherein the filling includes thorium or a thorium composition or compound as the emitter.

7. The lamp according to claim 6, wherein the filling includes a salt of halides including at least 8% ThI.sub.4, preferably 10% ThI.sub.4.

8. The lamp according to claim 6, wherein the filling includes a composition of NaI/ScI.sub.3/ThI.sub.4.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0013] The proposed high-intensity discharge lamp is described in the following by way of examples in connection with the accompanying figure.

[0014] FIG. 1 shows a cross section of a HID lamp according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[0015] FIG. 1 shows a cross section of a mercury-free quartz glass HID lamp 1 according to an embodiment of the present invention. The lamp 1 comprises a quartz glass discharge vessel 2 enclosing a discharge chamber 3 containing a fill gas. The inner diameter of the discharge chamber 3 shown in this example can be between 2.0 mm and 2.8 mm, and the outer diameter can be between 5.3 mm and 6.3 mm. This results in a capacity of the discharge chamber 3 between 15 l and 30 l. Two electrode rods 4, 5 protrude into the discharge chamber 3 from opposite ends of the lamp 1. During manufacturing, the quartz glass of the discharge vessel 2 is pinched on both sides around the shafts of the electrodes to seal the fill gas in the discharge chamber 3. An electrical connection between the electrode rods 4, 5 and conductive leads 41, 51 to the outside is made by a molybdenum foil 40, 50 enclosed in the pinch or seal area. The electrode rods 4, 5 therefore extend a certain distance into the pinch.

[0016] The electrodes rods 4, 5 are made from tungsten and manufactured to be essentially free of thorium and protrude into the discharge chamber 3. The tips of the electrode rods 4, 5 are separated from each other by a certain distance. This electrode distance may be in the range of between 2.0 and 4.0 mm dependent on the type of the lamp, e.g. satisfying D3 or D4 specifications. In the present example, the electrode rods 4, 5 of the lamp 1 are realized in form of simple rods of uniform thickness from base to tip. The thickness or diameter ED of these electrode rods 4, 5 is selected to be ED.sub.0 in accordance with the formula

[00003]$\mathrm{ED}{\mathrm{ED}}_0=\sqrt{.Math..Math.W/\left[1+\frac{\mathrm{Ed}-3}{3.Math.\mathrm{Ed}}\right]}.Math..Math.m-10.Math..Math.m,$

[0017] For sake of clarity, the figure shows only the parts that are pertinent to the invention. Not shown is the base and the ballast that is required for the lamp for control of the current or power of the lamp. Since these and other additional components will be known to a person skilled in the art, they will not be explained in any detail here. When the lamp is switched on, the ballast's igniter rapidly applies an ignition voltage at several thousand volts across the electrode rods 4, 5 to initiate a discharge arc. The temperature in the discharge chamber increases rapidly, and the metal salts evaporate. While the arc of high luminous intensity is gradually established, the ballast regulates the power down to the operational level (nominal power), for example 35 W for a D4 lamp.

[0018] In a first example, the proposed high-intensity discharge lamp is designed for a nominal power of 35 W and has a volume of the discharge chamber of 27 l and a electrode distance of 3.7 mm (optical separation: 4.2 mm). The diameter of the electrode rods is 320 m which satisfies the above formula. The rate of the total salt fill in the filling of the lamp in this example is 300 g. The filling is a composition of NaI/ScI.sub.3/ThI.sub.4 with or without InI or ZnI.sub.2. The filling may also contain other substances dependent on the desired effects.

[0019] In a second example a high-intensity discharge lamp with a nominal lamp power of 25 W is provided with a volume of the discharge chamber of 20 l and an electrode distance of 3.5 mm. In this case the diameter of the electrode rods is chosen to be 290 m which also satisfies the above formula. The total salt fill in this example is 200 g. The filling is a composition of NaI/ScI.sub.3/ThI.sub.4 with or without InI or ZnI.sub.2. The filling may also contain other substances dependent on the desired effects.

[0020] In a third example, the high-intensity discharge lamp has a nominal power of 27 W, a volume of the discharge chamber of 21 l and an electrode distance of 2.6 mm. The diameter of the electrode rods is 300 m which also satisfies the above formula. The total salt fill in this case is 250 g. The filling is a composition of NaI/ScI.sub.3/ThI.sub.4 with or without InI or ZnI.sub.2. The filling may also contain other substances dependent on the desired effects.

[0021] All of the above examples result in a high-intensity discharge lamp having a high-intensity output over a long life time of the lamp and at the same time low EMI and no commutation problems. The electrode diameter necessary for such a performance can be easily calculated with the above formula according the present invention, thereby avoiding any time consuming experiments and tests in order to find the electrode diameter for optimal performance.

[0022] While the invention has been illustrated and described in detail in the drawings and foregoing 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 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. Any reference signs in the claims should not be construed as limiting the scope of the invention.

LIST OF REFERENCE SIGNS

[0023] 1 HID lamp

[0024] 2 discharge vessel

[0025] 3 discharge chamber

[0026] 4 electrode rod

[0027] 5 electrode rod

[0028] 40 molybdenum foil

[0029] 41 conductive lead

[0030] 50 molybdenum foil

[0031] 51 conductive lead

[0032] ED diameter of electrode rods

[0033] Ed distance of electrode rods in the discharge chamber